Learning IoT
The sole purpose of this repository is to store notes and code helping me learn things related to Internet of Things, but also basic electronics.
Contents
Microcontroller Unit (MCU)
Is a very small computer system self contained on an integrated circuit (IC). They normally don't have any external data storage available so everything has to be able to be stored in memory (or perhaps sent off somewhere to be stored elsewhere).
Is what actually runs our code. It looks like a small black box and has a number of small metal pins around it. The pins are connected to tracers that are like wires connecting components on the board.
Analog-to-digital conversion (ADC)
Microcontrollers convert analog values (continuous) that arrive on inputs (pins) into to digital values (descrete) to be processed.
ARM (Advanced RISC Machines/Acorn RISC Machines)
ARM holding is the company behind Arm based chips do not manufacture chips but instread they design parts of the chip and they license these designs to hardware manufactures that use them in their products (sometimes enhancing them). In contrast Intel both design chips and manufacture them.
Arm has a number of families of chip designs. For example there is the Cortex-M family which are mostly used in microcontrollers.
Cortex-M0 is designed for low cost/power usage. Cortex-M4 is a middle ground more features/performance than M0 but less expensive then M7.
Cortex-M7 is higher cost but has more features and better performance. Some additional information about Arm version can be found here.
Universal Synchronous and Asynchronous Receiver-Transmitter (USART)
Is a serial communication protocol which as the name suggests can be used sync (using clocks) or async(using start/stop bits).
Device 1 Device 2
+----------+ +----------+
| TX|-----------|RX |
| RX|-----------|TX |
| GND|-----+-----|GND |
+----------+ | +----------+
|
-----
---
-
The sender and reicever must agree on a data transfer rate, which is called the baud rate which is number of bits transferred per second. Simplex mode is when data is transferred in one direction only. Half-duplex is when data is transferred in both directions but not at the same time. Full-duplex is when data can be transferred simultainously in both directions at the same time.
The wire protocol:
+-----------+-------------+---------------+-------------+
|1 start bit|5-9 data bits|0-1 parity bits|1-2 stop bits|
+-----------+-------------+---------------+-------------+
Controller Area Network (CAN)
TODO:
Real Time Operating Systems (RTOS)
TODO:
Serial communication
Is the process of transmitting one bit of data at a time. Thing of this as being one wire and the bits flow through it. Only requires one wire which is one reason at it is used often in microcontroller system design.
Would require only two wires:
+---------+ b0 b1 b2 b3 b4 b5 b6 b7 +---------+
| OUT|-----------------------------|IN |
| | p1 p2 p3 p4 p5 p6 p7 p8 | |
| CLK|-----------------------------|CLK |
+---------+ +---------+
p = puls of the clock
So this would send one bit per plus of the clock.
Parallel communication
Is the process of transmitting multiple bits of data at one time. Think of this as muliple wires connected to the other side and multiple bits can be set and transmitted at once. Since it requires more wires it can be more expensive to implement. Crosstalk is an issue and it is susceptible to clock skew.
+---------+ +---------+
| OUT0|-------------b0--------------|IN0 |
| OUT1|-------------b1--------------|IN1 |
| OUT2|-------------b2--------------|IN2 |
| OUT3|-------------b3--------------|IN3 |
| OUT4|-------------b4--------------|IN4 |
| OUT5|-------------b5--------------|IN5 |
| OUT6|-------------b6--------------|IN6 |
| OUT7|-------------b7--------------|IN7 |
| p1 |
| CLK|-----------------------------|CLK |
+---------+ +---------+
p = puls of the clock
So this would send 8 bit per plus of the clock.
Synchronous transmission
It's called synchronous because the sender and reciever are synchronized. They both have a clock which use the same rate.
A clock in this case is something that changes between two values, like high/low or something like that. The sender might send only when the clock is high for example. This is not much of a problem if both sender and reciever share the same clock, if they are part of the same circuit for example, but if they are not it might be difficult as they need someway of sharing the clock.
Fast transmission (when is has been sent). May have to wait until data can be sent.
Examples are SPI, and I²C.
Asynchronous transmission
This type of communication is not synced, but instead it uses a start bit and and stop bit
start bit stop bit
↓ [ data ] ↓
+--------+ 0 11101001 1 +--------+
| Sender | -----------------> |Reciever|
+--------+ +--------+
The extra processing of the start/stop bit can affect performance making asynchronous slower. Is cheap and easy to implement (no clock sharing). Can transmit whenever it is ready (does not have to wait for the clock).
Clock
Is a signal that repeats/oscillates between high and low states:
high 1 | | | | | |
| | | | | |
low 0---- ---- ---- ---- ...
So it starts out at zero, changes to 1 for the same amount of time and then repeats like this. The clock tell us when the receiver should read from the data line. We might say that it should receive when the clock is high but notice that the line can be hight for a certain period of time. Instead we say that it should read when transitioning from low to high, and this point is called an edge:
high 1 | | | | | |
| | | | | |
low 0---- ---- ---- ---- ...
^ ^
raising edge +-- fallin edge
(from low (from high
to high) to low)
This is a single point instead of a region.
So lets say we want to send 5 (101). First we have to let the receiver know that we are going to send by setting a wire to high which is sometimes called slave select (SS_bar). After this is done we can send bits to the receiver:
Sender Receiver
-
|
|
CLK --* > CLK
101 SOUT --1-------------> RIN 1
So above when the first raising edge is encountered, remember that the sender and receiver share the same clock line so the receiver also knows when this happens. When this happens SOUT will become high for the binary digit 1 to be sent. This can then be read by the reciever from RIN above and placed into a buffer. The next time there is a raising edge encountered (clock tick) another bit will be placed in SOUT:
Sender Receiver
---- -
| | |
| | |
CLK ---- ---* > CLK
10 SOUT --------0-------> RIN 10
And so on:
Sender Receiver
---- ----
| | | |
| | | |
CLK ---- ---- ---* > CLK
10 SOUT --------------1-> RIN 101
I'm not 100% sure about the above but that is my understanding so far. I'm still waiting for a real device to try this out and verify.
Serial Peripheral Interface (SPI)
Is a synchronous serial communication spec developed by Motorola (1980s) and used for communicating between microcontrollers and small peripheral devices. Note that this is a defacto standard but there is no official standard for this protocol.
+-----------------+ +-----------------+
| SPI SCLK|-------+-->|SCLK SPI |
| Controller COPI|------+--->|COPI Peripheral|
| CIPO|<----+-----|CIPO |
| SS_bar|---------->|SS_bar |
+-----------------+ ||| +-----------------+
^ |||
| ||| +-----------------+
| ||+-->|SCLK SPI |
| |+--->|COPI Peripheral|
| +-----|CIPO |
+-------------->|SS_bar |
+-----------------+
SCLK = SPI Clock
CIPO = Controller Input Peripheral Output
COPI = Controller Output Peripheral Input
SS = Slave Select (to select among mulitiple connected slaves like above)
- Full Duplex
- Synchronous (it uses the clock to sync)
- 4+ wires (with multiple slaves there will be more than 4 wires)
- 25 Mbps
- No ack
- Low power consumption
- 20 cm distances
Universal Asynchonous Receiver/Transmitter (UART)
UART is not a communications protocol like SPI and I2C but instead a physical component/circuit in a microcontroller or a standalone integrated circuit. It is main purpose is to send and receive serial data.
An UART can look something like the following:
Data bus +------------+ +------------+ Data bus
---->|D0 P|S | | P|S D0|---->
---->|D1 A|E | | A|E D1|---->
---->|D2 R|R | | R|R D2|---->
---->|D3 A|I RX|<----------|TX A|A D3|---->
---->|D4 L|A TX|---------->|RX L|L D4|---->
---->|D5 L|L | | L| D5|---->
---->|D6 E| | | E| D6|---->
---->|D7 L| | | L| D7|---->
| | | | | |
-|R/W | | | | R/W|
-|CLK | | | | CLK|
-|INT | | | | INT|
+------------+ +------------+
An packet on the serial wire (TX->RX) will looks something like this:
+-+ +-+-+-+-+-+ +--+ +--+
|S| | | | | | | |P | |ST|
+-+ +-+-+-+-+-+ +--+ +--+
Start Data Parity Stop
The transimission line (TX) is usually held at a high voltage when not trasmitting. To start sending the trasmitting UART will pull the TX line from high to low for one clock cycle. When the receiving (RX) UART see this it will begin reading the bits in the dataframe at the frequency of the baud rate. Notice that the sender will get the data to be sent from the data bus, and likewise the reciever will place the received data on the data bus.
So there are only two wires which is a nice property. And there is not clock signal required between two UARTs. There is also parity checking which is good for reliable communication. One thing to note is that the data being sent can be a maxium of 9 bits. The is not way to support multiple peripherals.
Inter Integrated Circuit (I²C)
Only requires two pins.
+------------------+ +-----------------+
| Controller SCL|-----------|SCL Peripheral |
| SDA|-----------|SDA |
+------------------+ +-----------------+
SCL = Serial Clock Line for the clock signal
SDA = Serial Data line for sending and recieving data
So we have the usage of a clock so this is a synchronous protocol like SPI.
Data is transported in messages which have a specific format and an address is used to identify the destination peripheral:
+-+-+-+-+-+-+-+ +---+ +---+ +-+-+-+-+-+-+-+-+
| | | | | | | | |R/W| |ACK| | | | | | | | | |
+-+-+-+-+-+-+-+ +---+ +---+ +-+-+-+-+-+-+-+-+
Address Frame Data Frame
(7 or 10 bits) (8 bits)
Communication starts by the SDA (the data line) switches form high voltage to low. This is done before the SCL also switches from high to low.
At the end the sending the SDA will switch from low voltage level to high
after the SCL line switches from low to high.
In SPI we had a peripheral select wire (SS) which selected the peripheral we want to talk to. Instread in I2C each peripheral has an address. This is contained in the address frame which is always first frame after the start bit has been set. The controller send this message frame onto the SDA which all peripherals connected will see. Each peripheral will compare this to their address and do nothing if the address does not match. If the addresses match that peripheral sends a low voltage ACK bit back to the controller.
The READ/WRITE bit indicates if the controller wants to send or recieve data from the peripheral. If it wants to send then this bit is low (0) and if it wants to read it will be a high voltage.
Current
Is the flow of free electrons
Concuctors
Take a conductor like a coppar wire which is good at allowing a current to flow through it. Now, coppar is made up on coppar atoms which like all atoms contain protons, neutrons, and electrons:
Cu
Protons: 29
Neutrons: 35
Electrons: 29
Shell 1: 2 electrons
Shell 2: 8 electrons
Shell 3: 18 electrons
Shell 4: 1 electrons (free electron)
A coppar wire without any current flowing will have electrons randomly moving from atom to atom but this is not in any perticular direction. If an electron moves away from its atom that would leave the atom slightly positively charged and that would attract an electron. How does the electron leave the atom, this is a little unclear to me. One thing I've read is that it is actually the atom that overlap the volume of other atoms and exchange the free atom. So there does not need to be any energy to cause the electron to move. But I've also read that this could be influence of room-temprature heat energy.
So we have the sea of electrons that are moving around randomly. Now, if we connect a cell that contains one end with negative electrons and the otherside with atoms what are positivly charged ( would attract electrons) the electrons will move towards the positiv end.
The conduction band is the band above the valence band.
-----------------------
Conduction band
-----------------------
Band gap
-----------------------
Valance band
-----------------------
...
----------------------- Electron shell n-1
For electrons to be able to move to an outer shell energy needs to be applied. For conductors the conduction band and the valance band/band gap/conduction band overlap allowing the free electrons to move in this space. But for insulators there is a clear band gap and energy is required for this to happen (that is if there are free electrons in the valance shell), if we are thinking of atoms where no energy is applied to it.
Bond: When an atom bonds with another they can share electrons in their valence shell, this type of bond is called covalent bond.
Take two silicon atoms for example, they would share a pair of electrons:
* * * = electron in valance shell
** = paired electrons
* Si ** Si *
* *
Many silicon atoms that are bonded like this will allow for each Si atom to be connected though sharing four electrons:
This is something that can be seen in silicon where each silicon atom is connected to four other silicon atoms.
If a conductor (metal) is heated it becomes less conductive. So metals conduct electricity better at colder temperatures.
Band theory
Energy
^
| +--------------+
| | Conduction |
| +--------------+ | |
| | Conduction | +--------------+
| +--------------+ | |
| Conduction | +--------------+
|--------------|
|--------------| +--------------+ +--------------+
| Valancy | | Valancy | | Valancy |
+--------------+ +--------------+ +--------------+
Conductors Semiconductors Insulators
Notice that for conductors the conduction band and the valancy band overlap which is why the conduct so well. For semiconductors there is a gap between these two bands so energy is needed for electrons to move into the conduction band. This is possible with heat.
Insulators
High reisistance to the flow of electricity, which means that their valance shell is full and
Semi-conductors
These have properties that are in between conductors and insulators, hence the name semi-conductors. If a semi-conductor is exposed to head this can improve it conductivity. But there is another way to improve the conducitivty of a semi- conductor which is to add impurities to it (called doping).
If we take a look at a silicon cristal:
[* *] = covalent bond
Si [* *] Si [* *] Si [* *]
⌈*⌉ ⌈*⌉ ⌈*⌉
⌊*⌋ ⌊*⌋ ⌊*⌋
Si [* *] Si [* *] Si [* *]
⌈*⌉ ⌈*⌉ ⌈*⌉
⌊*⌋ ⌊*⌋ ⌊*⌋
Si [* *] Si [* *] Si [* *]
So we can see that we have these covelent bounds between the atoms and all of the free electrons in the valance shell are bound. There are not free electrons of "holes".
If we replace on of these atoms will an atom with only 5 electrons (like fosfor) in its valance shell what would happen:
[* *] = covalent bond
Si [* *] Si [* *] Si [* *]
⌈*⌉ ⌈*⌉ ⌈*⌉
⌊*⌋ ⌊*⌋ ⌊*⌋
*<-------------------- free electron
Si [* *] P [* *] Si [* *]
⌈*⌉ ⌈*⌉ ⌈*⌉
⌊*⌋ ⌊*⌋ ⌊*⌋
Si [* *] Si [* *] Si [* *]
It can still bound with the other 3 atoms around it but also has an additional electron left over. This free electron can now move in the conduction band. This makes this silicon cristal more conductive then before. Because we have a free electron by this process and electrons are negatively charged this is called an n-type conductor now. So that is one way we can increase the connectivity of silicon. But how about replacing an atom with something that only has 3 electrons in its valance shell:
So if we hook up a battery to this the free electron will be attracted to the positive terminal and the electrons from the negative terminal will be able to move in their place through the material (in/through the conduction band):
Si [* *] Si [* *] Si [* *]
⌈*⌉ ⌈*⌉ ⌈*⌉
⌊*⌋ ⌊*⌋ ⌊*⌋
*
+--- Si [* *] P [* *] Si [* *] <-----------+
| |
| ⌈*⌉ ⌈*⌉ ⌈*⌉ |
| ⌊*⌋ ⌊*⌋ ⌊*⌋ |
| |
| Si [* *] Si [* *] Si [* *] |
| |
| | |
| || |
+-------------> + || - -------------------------+
|
It can still bound with the other 3 atoms around it but also has an additional
So lets try with alunminum (Ai):
[* *] = covalent bond
Si [* *] Si [* *] Si [* *]
⌈*⌉ ⌈*⌉ ⌈*⌉
⌊*⌋ ⌊*⌋ ⌊*⌋
Si [* *] Ai x * Si [* *]
⌈*⌉ ⌈*⌉ ⌈*⌉
⌊*⌋ ⌊*⌋ ⌊*⌋
Si [* *] Si [* *] Si [* *]
Notice that we have a missing electron so thre is no covalent bond between the Ai atom the Ai atom to the right. This is called a p-type semi-conductor. This also conducts electricity better than pure silicon so the conductivity goes up.
In the case of N-type we know that the electrons are free to flow in the conduction band. This is not what happens for P-type, instead the electrons flow in the valance band, so if we apply a current electrons will be attracted to the positive terminal, hence they will move to holes:
Si [* *] Si [* *] Si [* *]
⌈*⌉ ⌈*⌉ ⌈*⌉
⌊*⌋ ⌊*⌋ ⌊*⌋
*
+--- Ai x * Si [* *] Si [* *] <-----------+
| |
| ⌈*⌉ ⌈*⌉ ⌈*⌉ |
| ⌊*⌋ ⌊*⌋ ⌊*⌋ |
| |
| Si [* *] Si [* *] Si [* *] |
| |
| | |
| || |
+-------------- + || - <-------------------------+
|
The holes are what allow electrons to flow and this happens in the valance band as opposed to n-type doping where the flow happens in the conduction band. With a batteri cell attached the electrons will be attracted to the positive terminal. There for electrons will fill the holes:
x o x x x
<-
x x o x x
<-
x x x o x
<-
x x x x o
Now, what I think will happen is that one electron will "leave" and and one will enter:
x <- o x x x o <-x
o x x x x
And once again the process of the electrons filling the holes will continue and a electrons will be transferred/conducted accross the valance band.
Now, lets see what happens if we combine a p-type and an n-type:
[* *] = covalent bond
x = hole
* = free electron
P-type N-type
Si [* *] Si [* *] Si | | Si [* *] Si [* *] Si [* *]
| |
⌈*⌉ ⌈*⌉ ⌈*⌉ | | ⌈*⌉ ⌈*⌉ ⌈*⌉
⌊*⌋ ⌊*⌋ ⌊*⌋ | | ⌊*⌋ ⌊*⌋ ⌊*⌋
| | *
| |
Si [* *] Ai x * Si | | Si [* *] P [* *] Si [* *]
| |
⌈*⌉ ⌈*⌉ ⌈*⌉ | | ⌈*⌉ ⌈*⌉ ⌈*⌉
⌊*⌋ ⌊*⌋ ⌊*⌋ | | ⌊*⌋ ⌊*⌋ ⌊*⌋
| |
Si [* *] Si [* *] Si | | Si [* *] Si [* *] Si [* *]
The free electron would be attracted to fill the hole
Si [* *] Si [* *] Si | | Si [* *] Si [* *] Si [* *]
| |
⌈*⌉ ⌈*⌉ ⌈*⌉ | | ⌈*⌉ ⌈*⌉ ⌈*⌉
⌊*⌋ ⌊*⌋ ⌊*⌋ | | ⌊*⌋ ⌊*⌋ ⌊*⌋
+-------------------------------- *
↓ | |
Si [* *] Ai x * Si | | Si [* *] P [* *] Si [* *]
| |
⌈*⌉ ⌈*⌉ ⌈*⌉ | | ⌈*⌉ ⌈*⌉ ⌈*⌉
⌊*⌋ ⌊*⌋ ⌊*⌋ | | ⌊*⌋ ⌊*⌋ ⌊*⌋
| |
Si [* *] Si [* *] Si | | Si [* *] Si [* *] Si [* *]
One thing that I was missing is that even though there is an extra electron, the Ai has an additional proton (remember that atoms have the same number of proton and electrons) so that side is neutral, both sides are to begin with.
And a hole can also move to the n-type side. This will create an area between these two where there are now extra electrons, or any extra holes, so there are now charge carriers in this region. This region is called the depletion region and it like an insulator.
Depletion Region
N ↓ P
+----------------+---------------+
| * * ** *** * * | o o oo ooo |
| ** * ** * * * | o o o o o oo |
| * * ** *** * |o o o o |
| * * ** *** * | o o o o o|
+----------------+---------------+
Depletion Region
N ↓ P
+--------------+----+-------------+
| * * ** *** * | Si |o o oo ooo |
| ** * ** * * | Si | o o o o oo |
| * * ** *** * | Si |o o o |
| * * ** *** * | Si |o o o o o|
+--------------+----+-------------+
Now if we hook up a power source we will not get a current flowing initially as the depletion region prevents the flow. But if the batteri has enough voltage, like > 0.7v this will overcome the.
Depletion Region
N ↓ P
+--------------+----+-------------+
| * * ** *** * | Si |o o oo ooo |
+--> | ** * ** * * | Si | o o o o oo |---------+
| | * * ** *** * | Si |o o o | |
| | * * ** *** * | Si |o o o o o| |
| +--------------+----+-------------+ |
| |
| | |
| - | | + |
+-----------------| |<---------------------------+
| |
|
Electrons will enter the n-region and there will be more electrons in that region. There will also be electrons (remember there are holes but there are also electrons in this region. Those electrons will be attracted to the positive terminal and will exit leaving more holes behind. If the batteri has a voltage
0.7 the depletion region will collapse and current can flow.
Now lets hook this up the other way, where the negative terminal is connected to the p-type region, and the positive terminal to the n-type region:
Depletion Region
N ↓ P
+--------------+----+-------------+
| * * ** *** * | Si |o o oo ooo |
+----| ** * ** * * | Si | o o o o oo |<--------+
| | * * ** *** * | Si |o o o | |
| | * * ** *** * | Si |o o o o o| |
| +--------------+----+-------------+ |
| |
| | |
| + | | - |
+---------------->| |----------------------------+
| |
|
In this case the electrons will fill the holes in the p-region, and electrons will leave the n-region, causing the depletion region to become larger:
Depletion Region
N ↓ P
+---------------------------------+
| * * ** **| Si |o oo ooo |
+----| ** * ** | Si | o o o oo |<--------+
| | * * ** * | Si |o o | |
| | * * ** * | Si | o o o o| |
| +--------------+----+-------------+ |
| |
| | |
| + | | - |
+---------------->| |----------------------------+
| |
|
As the depletion region becomes larger meaning that there are no charge carriers in this region this component will act like an insulator. So no current will flow.
If we stick an n-type region next to a p-type and then another n-type we get the following:
Depletion Regions
| |
N ↓ P ↓ N
+-------------+-+--------+-+----------+
| * * ** *** *| |o o oo o| |* * * * * |
| ** * ** * | | o o o o| | * * ** |
| * * ** *** | |o o o | | * * * |
| * * ** *** *| |o o o| | * * * * |
+-------------+-+--------+-+----------+
And say we want a current to flow through this thing:
Depletion Regions
| |
N ↓ P ↓ N
+-------------+-+--------+-+----------+
| * * ** *** *| |o o oo o| |* * * * * |
+--->| ** * ** * | | o o o o| | * * ** |-----+
| | * * ** ** | |o o o | | * * * | |
| | * * ** ** * | |o o o| | * * * * | |
| +-------------+-+--------+-+----------+ |
| |
| |
| |
| |
| | |
| - | | + |
+-----------------| |<---------------------------+
| |
|
Well this will increase number of electrons in the left-most n-type region, and some electrons will leave the right-most n-type region but there will not be a current flowing.
Lets try looking up a second power source like this:
Depletion Regions
| |
N ↓ P ↓ N
+-------------+-+--------+-+----------+
| * * ** *** *| |o o oo -| |+ * * * * |
+--->| ** * ** * | | o o o -| |+ * * ** |-----+
| | * * ** ** | |o o o -| |+* * * | |
| +--| * * ** ** *| |o o -| |+ * * * * | |
| | +-------------+-+--------+-+----------+ |
| | | | |
| | - | | + | |
| +---------------| |-----+ |
| | | >0.7v |
| | |
| |
| | |
| - | | + |
+-----------------| |<---------------------------+
| |
|
Notice that this extra connection between the left-most n-type and the p-type is the same as we hade above where we saw that current would flow through that connetion. Now, we have electrons entering from both battries. When they make these types of components the first n-type region is very heavyly doped. So once this second current starts flowing, those extra electrons can now also move through into the p-type region. Some of these electrons are going to fill in holes in the p-type region, and some are also going to be attracted to the outgoing plus terminal of the p-type region. The base is very thin (how they are manufactured) and these holes are physically close to the left-most n-type's electrons. That depletion region was created when electrons left the n-type into the depletion region which caused the n-type region to become positivley charged (remember that the number of electrons and protons match up when neutral and removing a electron will make the atom postitive). And those electrions that move into depletion region cause the p-type region to become negatively charged. The electrons that have now started flowing through the p-type region will be attracted to the positive right-most n-type region and therefor be able to flow through it towards the positive terminal output.
This component is called an NPN bipolar junction transistor:
Emitter(N) Base(P) Collector(N)
+-------------+-+--------+-+----------+
| * * ** *** *| |o o oo -| |+ * * * * |
+--->| ** * ** * | | o o o -| |+ * * ** |-----+
| | * * ** ** | |o o o -| |+* * * | |
| +--| * * ** ** *| |o o -| |+ * * * * | |
| | +-------------+-+--------+-+----------+ |
| | | | |
| | - | | + | |
| +---------------| |-----+ |
| | | >0.7v |
| | |
| |
| | |
| - | | + |
+-----------------| |<---------------------------+
| |
|
Alright, so that was the theory now lets see how we can create a circuit with such an NPN transistor:
For this example I used as button switch which is connected to the base of the transistor:
So with out a current flowing through the base and the emitter there is no current flowing though the transistor. Pressing the button will cause a current to flow:
So that is how a NPN Bipolar Junction transistor works and how we can hook it up physically. We can use two such transistors:
Now, pressing just the left button no current will flow:
And, pressing just the right button no current will flow:
But pressing both and current will flow:
Notice that what we have created here is a AND gate:
Left button | Right button LED
0 | 0 0 (Off)
1 | 0 0 (Off)
0 | 1 0 (Off)
1 | 1 1 (On)
Before any movement has occured we have the following Formal Charge for P
⌈*⌉
⌊*⌋ *
[* *] P [* *]
⌈*⌉
⌊*⌋
Bounds: 4
FC = valance electrons - (Bonds + dots)
= 5 - (4+1)
= 0
And for Ai:
⌈*⌉
⌊*⌋
[* *]Ai x *
⌈*⌉
⌊*⌋
FC = 3 - (3 + O)
FC = 0
Now, after the move of the free electron to the hole we have the following formal charge for P:
FC = 5 - (4 + 0)
= 1
This means that it has a positive formal charge. And for Ai:
⌈*⌉
⌊*⌋
[* *]Ai [* *]
⌈*⌉
⌊*⌋
FC = 3 - (4 + O)
FC = 3 - 4
FC = -1
P N
+--------------------+-------------------------+
| o o o | * * * * |
| o o o | * * * |
| o o o | * * |
| o o o | * * * * * |
+--------------------+-------------------------+
The free electrons will drift to fill in the holes:
P N
+--------------------+-------------------------+
| o o o <--* * * * |
| o o o <-- * * * |
| o o o<-- * * |
| o o o <--* * * * * |
+--------------------+-------------------------+
P N
+--------------------+-------------------------+
| o o o -|+* * * * |
| o o o -|+ * * * |
| o o o-|+ * * |
| o o o -|+* * * * * |
+--------------------+-------------------------+
P N
+--------------------+-------------------------+
| o o o | |* * * * |
| o o o | | * * * |
| o o o| | * * |
| o o o | |* * * * * |
+--------------------+-------------------------+
^
Electric field accross the PN junction
The electric field makes it difficult for new electrons on the N side to cross the PN junktion now. The free electrons still have a force acting upon them that wants to move them to the other side, but there is also a force acting in the opposite direction. When these forces are equal then no electrons will move over from the right side to the left side.
So applying a current to the N side that overcomes the force of the PN junction would allow electrons to move through to the P side and beyond if the P-side is connected to something. Reversing this process, that is connecting a voltage to the anode (P-side) will not cause any (or vary little current to flow). I'm taking about electron current here and not convertional current. So the flow of electrons can only happen in one direction.
P N
+--------------------+-------------------------+
| o o o | |* * * * |
| o o o | | * * * |
| o o o| | * * |
| o o o | |* * * * * |
+--------------------+-------------------------+
Anode Cathode
----->|---
<-- e⁻
+----+----+
anode-----| P | N |-----cathode
+----+----+
Light Emitting Diod
Notice that this is basically a Diode that can emit light.
+--+
| |
+--+
| |
| |
| |
|
Anode Cathode
When we connect these the electron current must flow through the cathode so it should be connected to the negative output of the batteri.
Bipolar Junction Transistors.
There are two (bi) junctions (think of the PN junctions in a diode as explained above):
+-----+-----+-----+
| N | P | N |
+-----+-----+------
^ ^
junction junction
1 2
The N is for N-Type, and P for P-Type which are the same as in the diode example above.
+-----+-----+-----+
E-----| N | P | N |-----C
+-----+-----+------
|
|
B
E = emitter
C = collector
B = base
So we would have free electrons in the left and right boxes, and holes in the middle box. And notice if we removed the first box we would be left with a normal diode:
+-----+-----+
| P | N |-----C (cathode)
+-----+------
|
|
B (anode)
And the addition of the first N box is basically the reversal of a diode
Metal Oxide Semiconductor Field Effect Transistor (MOSFET)
+----------------------+
| |
| P-Type Substrate |
| |
| |
| |
+----------------------+
+----------------------+
|+---+ +---+ |
|| N | | N | |
|| | | | | S = Source
|| S | | D | | D = Drain
|| | | | |
|+---+ +---+ |
+----------------------+
So at this stage we have a PN junction between the substrate and the two N-type regions. Next an oxide insulator is added between the two N-types. And on top of that a metal later is added. And this is the origin of the first part of the name, Metal for the metal plate, oxide for the insulator, and semiconductor for the PN.
----+ | +----
| | |
| ---------------- |
| ---------------- |
+----------------------------------+
|| N | | N ||
|+----------+ +--------+|
| ^ ^ |
| +---- pn junction -----+ |
| |
+----------------------------------+
Formal Charge
FC = Valance electrons - (Bonds + dots)
ARM Vector table
Contains functions pointers to handlers of exceptions (and perhaps the ResetHandler in entry 0 but that is not clear to me yet).
ARM Exceptions
This is a condition that changes the normal flow of control in a program.
Exceptions have a number associated with them and this is used as an index into the Vector Table which contains function pointer to Exception Handlers or Interrupt Service Routine (IRS). The ARM hardware will look up and call the function when an exception is triggered.
1 Reset
2 NMI
3 HardFault
4 MemoryManagement
5 BusFault
6 UsageFault
7 Reserved
8 Reserved
9 Reserved
10 Reserved
11 SVCall
12 DebugMonitor
13 Reserved
14 PendSV
15 SysTick
16 External interrupt 0
...
Each Exception also has a priority number.
All Cortex-M variants support 6 exceptions:
-
Reset This is the function called when the chip comes out of reset, like power on, or the reset button is pressed (can this be called programatically also?).
-
Non Maskable Interrupt (NMI) If an error happens in another exception handler this function will be called to handle it. It cannot be masked to be be ignore.
-
HardFault This is used for various system failures. There are also more fine grained exceptions handlers for MemoryManagement, BusFault, UsageFault.
-
SVCall This is the exception handler that will take care of supervisor call (svc) instruction is called.
-
PendSV/SysTick System level interrupts triggered by software and seem to be used mostly for RTOS.
If we take a look at the symbols we should be able to see the above handlers:
$ cargo objdump --release -- -t
Finished release [optimized] target(s) in 0.05s
app: file format elf32-littlearm
SYMBOL TABLE:
...
0000055a g F .text 00000000 DefaultHandler
00000040 g O .vector_table 000003c0 __INTERRUPTS
0000055a g F .text 00000000 BusFault
0000055a g F .text 00000000 DebugMonitor
0000055a g F .text 00000002 DefaultHandler_
0000055c g F .text 00000002 DefaultPreInit
0000068e g F .text 00000002 HardFault_
0000055a g F .text 00000000 MemoryManagement
0000055a g F .text 00000000 NonMaskableInt
0000055a g F .text 00000000 PendSV
00000400 g F .text 0000007c Reset
0000055a g F .text 00000000 SVCall
0000055a g F .text 00000000 SysTick
0000055a g F .text 00000000 UsageFault
0000047c g F .text 0000000a main
0000068e g F .text 00000000 HardFaultLoRaWAN
Is a Low Power Wide Area Network (LPWAN)
Drogue Device
The following example code is from device/examples/std/hello:
pub struct MyDevice {
counter: AtomicU32,
a: ActorContext<'static, MyActor>,
b: ActorContext<'static, MyActor>,
p: MyPack,
}
static DEVICE: DeviceContext<MyDevice> = DeviceContext::new();So in this case we are creating a new instance of DeviceContext with a specific type of MyDevice.
pub struct DeviceContext<D: 'static> {
device: Forever<D>,
state: AtomicU8,Forever is struct from Embassy and has a static lifetime and can only be written to once so it is good for initialization of things.
pub struct Forever<T> {
used: AtomicBool,
t: UnsafeCell<MaybeUninit<T>>,
}We can configure, mount, and drop a DeviceContext. When we configure we are giving the Forever a value:
DEVICE.configure(MyDevice {
counter: AtomicU32::new(0),
a: ActorContext::new(MyActor::new("a")),
b: ActorContext::new(MyActor::new("b")),
p: MyPack::new(),
});This is done by calling put which gives the Forever a value:
pub fn configure(&'static self, device: D) {
match self.state.fetch_add(1, Ordering::Relaxed) {
NEW => {
self.device.put(device);
}
_ => {
panic!("Context already configured");
}
}
}Note that self is an instance of DeviceContext<hello::MyDevice:
(lldb) expr self
(drogue_device::kernel::device::DeviceContext<hello::MyDevice> *) $5 = 0x00005555558a90c0And we can see that state is of type AtomicU8 which means that it can be
safely shared between threads. We can see that we have multiple threads:
(lldb) thread list
Process 775026 stopped
* thread #1: tid = 775026, 0x00005555555b0308 hello`hello::mypack::MyPack::new::h37a13cbcb2b29e39 at mypack.rs:14:9, name = 'hello', stop reason = breakpoint 1.1
thread #2: tid = 775029, 0x00007ffff7c8ca8a libpthread.so.0`__futex_abstimed_wait_common64 + 202, name = 'hello'fetch_add adds to the current value of this atomic integer and returns the
previous state.
This is in match so if the previous/current state state is NEW, we will call
put on the Forever giving it a value. And remember that it will also increment
the value so it will now be 1 which is CONFIGURED.
Next we have:
let (a_addr, b_addr, c_addr) = DEVICE
.mount(|device| async move {
let a_addr = device.a.mount(&device.counter, spawner);
let b_addr = device.b.mount(&device.counter, spawner);
let c_addr = device.p.mount((), spawner);
(a_addr, b_addr, c_addr)
})
.await; Notice that we are calling mount on our DeviceContext instance which is
typed over MyDevice.
pub async fn mount<FUT: Future<Output = R>, F: FnOnce(&'static D) -> FUT, R>(
&'static self,
f: F,
) -> R {
match self.state.fetch_add(1, Ordering::Relaxed) {
CONFIGURED => {
let device = unsafe { self.device.steal() };
let r = f(device).await;
r
}
NEW => {
panic!("Context must be configured before mounted");
}
MOUNTED => {
panic!("Context already mounted");
}
val => {
panic!("Unexpected state: {}", val);
}
}
} Notice that this method takes a closure. Remember that we incremented the state
previously so it is currently CONFIGURED, and we now increment it again using
fetch_add which as before will return the current value so we will enter
the CONFIGURED branch of the match statement:
(lldb) expr self->state.v.value
(unsigned char) $11 = '\x01'We then get the value of the device and pass that to the closer (so we will be back in main.rs in the closure:
38 let (a_addr, b_addr, c_addr) = DEVICE
39 .mount(|device| async move {
-> 40 let a_addr = device.a.mount(&device.counter, spawner);
41 let b_addr = device.b.mount(&device.counter, spawner);
42 let c_addr = device.p.mount((), spawner);
43 (a_addr, b_addr, c_addr)
44 })
45 .await;Next we will call each of the MyDevice struct members mount methods.
drogue-tls logging
Logging can be enabled using
$ RUST_LOG=info cargo test --verbose -- --nocaptureElectrons
An atom is composed of a necleus which consists of a core of tightly bound subatomic particles called protons (positive charge) and neutrons (neither positive of negative). Rotating around the necleus are electrons. These have orbits that are referred to rings or shells and an electron has a negative charge. The number of electrons in orbit equal the number of protons in the necleus and the atom is electrically balanced. Electrons can be manipulated, like storing or moving, and be used to produce electricity.
Static electricity
This is where one object has an excess of electrons and the other objects has a shortage of electrons. The object with the excess is negatively charge as it now has more negative electrons that positivly charged protons. There is an invisible force field called an electric field between two charged objects. The object with a shortage of electrons attracts the object with the excess electrons. When we have such a situation, where we have two objects with opposite charge we say there is an electrical potential, or a difference of potential between them. This difference is called voltage. If these two charged objects come to close to one another the electrons jump the gap between them and create a spark. This is how lightning occurs for example. The earth is positively charged and the clouds negatively
Electricity
This is the flow of electrons. The electrons flowing from one place to another is called current flow. Voltage, the difference in the charge between to object is what causes the flow. Electronics is about controlling the electrons with special components and circuits.
Electric charge
This is movement of electrons.
Voltage
Voltage is what pushes electrons arounda a circuit. Without Voltage the electrons will move randomly in any direction.
(Spänning in Swedish) is the difference in charge between two points. This is
measured in volt (V) and the symbol used is U from the German word unterschied
that means difference.
Electrons flow from the netative terminal of a voltage source around the curcuit
as they are attracted by the positive terminal.
Current
Is the rate at which charge is flowing. Is measured in ampere (A) and the symbol
used is I which comes from the French word intensite de courant which means
current strength.
The number of electrons that move past a point in a conductor during a specific
period of time is measured in coulombs (C). One coulomb of charge is equal to
1 Coulomb = 6.242x10^18 electrons
If 1 coulomb moves past a point in 1s, we say that the current is 1 ampere (A) 1 Ampere = 1 coulomb/s
Resistance
Is a materials tendency to resist the flow of charge (current). Is measured in ohm using the symbol used is capital omega Ω and resistance uses the symbol R.
Gound
In a ciruit with one battery we refer to the negative terminal as ground. And in schematics instread of drawing lines that should be connected to the negative terminal we simply use the ground symbol. For example:
+----------/\/\/--------+
| |
+ | |
----- |
--- |
| |
| |
--- ---
= -
. .
Which is the same as writing:
+----------/\/\/--------+
| |
+ | |
----- |
--- |
| |
| |
+-----------------------+
Ohm's Law
voltage = Resistance * Current U = R * I I = U/R R = U/I
Power
Is the rate, per unit time, at which electrical energy is transferred by an electric circuit. The unit of power is watt which is one joule per second.
Joule
Watt
General Purpose Input Output (GPIO)
Normally Open (NO)
Is open (broken) by default so no current flows
Normally Closed (NC)
The opposite of normally open.
Batteries
All batteries have a voltage of 1.5 V. 9V batteries are simply 6 such batteries that are connected in a series.
Radio waves
Are just another form of light (electro matnetic waves) just like light. They travel at the speed of light 300 000 000 meters per second.
Now, electrons in a wire flow with the help of atoms, in the conduction band. But radio waves/light waves or electro magnetic waves don't have a wire but Electromagnetic waves differ from mechanical waves in that they do not require a medium to propagate. This means that electromagnetic waves can travel not only through air and solid materials, but also through the vacuum of space.
Radio bands
Name Frequency Range Wavelength Range
ELF (Extremely Low Frequency) 3–30 Hz 100,000–10,000 km
SLF (Super Low Frequency) 30–300 Hz 10,000–1,000 km
ULF (Ultra Low Frequency) 300–3000 Hz 1,000–100 km
VLF (Very Low Frequency) 3–30 kHz 100–10 km
LF (Low Frequency) 30–300 kHz 10–1 km
MF (Medium Frequency) 300 kHz–3 MHz 1,000–100 m
HF (High Frequency) 3–30 MHz 100–10 m
VHF (Very High Frequency) 30 MHz–300 MHz 10–1 m
UHF (Ultra High Frequency) 300 MHz–3 GHz 1–0.1 m
SHF (Super High Frequency) 3 GHz–30 GHz 10–1 cm
EHF (Extremely High Frequency) 30–300 GHz 10–1 mm
THF (Tremendously High Frequency)0.3 THz–30 THz 1–0.1 mm
Radio waves with long wavelengths such as in the bands LF, MF, and HF can exploit interesting effects of the Earth’s atmosphere to travel extremely long distances. It is possible to reflect waves in these bands off various layers in the atmosphere and ionosphere, making intercontinental communications possible.
Notice that the lower frequency which also means longer wavelengths. When sending data this data needs to travel over a signal that oscilates over with a wave length. With the modulation techniques discussed later in this doc we will see that most of these, if not all, will use the frequency to interpret the original signal. If the wavelenght is longer less information is availaible for processing during the same time period compared to a higher frequency. So more information can be sent with higher frequencies in the same amount of time.
The general line-of-sight propagation mode can be more thought of as allowing one to communicate with something that one could see in the absence of any obstacles, that is, something not blocked by the curvature of the Earth or large geographic features like mountains.
Diffraction
Like light rays from the sun diffract in the atmosphere so can other types of EM waves. This enables them to when they hit the peak of a hill diffract (spread) out into the vallly. This can also happen with walls in ones home which happens for 2.4GHz and 5GHz radiation which is what our WiFi routes emit.
Reflection
In general, good conductors (such as metal) reflect most of an electromagnetic wave’s energy. Other materials like rock reflect some energy, and many insulators such as plastics reflect little energy. Areas covered in metal are well shielded from electromagnetic radiation, because the metal will reflect much of the incoming energy back.
Absorption
The energy not reflected by a medium will pass into the medium. Some materials allow electromagnetic radiation to pass through them without attenuation ( gradual loss) better than others. Many materials do not allow visible light to pass at all but do pass lower-frequency radio waves. Radio waves can travel through most nonconductive materials,
Modulated Signal
This example is of a computer sending data over a telephone, like when we used modems in the good old days. First thing is that a byte will be broken down into separate bits and sent one after the other. After that the will be partity bits and perhaps sync bits but that is not important to this section.
The problem is that the telefon line cannot transmit logic levels which might use 3.3V for High and 0V for low. We need to change these bits into something that can be trasmitted on the frequence of the telefon wire (300-4000Hz) which is a periodic wave that oscilates.
There are three properties of a sine wave that we can manipulate:
y(t) = A(t) * sin(2π f(t) + ψ(t))
amplitude frequency phase
So amplitude is the max distance of the trough/crest. And frequency is the number of cycles per second. Notice that the phase is added so this would be the hight of the y axis.
Amplitude Modulation (AM)
We start with an input signal which is what we want to send to the reciever. The reciever knows the frequency that this signal will be sent. The signal is then modulated into a carrier signal where the amplitude will proportional to the original signal. For example where the original signal has a higher value the amplitude of the carrier signal will be greater, and where the original signal value is lower the amplitude will be lower. On the receiving side the demodulator will interpret the amplitudes to transform the carrier signal into the original senders signal.
Just remember that we start with some signal on a wire and for this to be transported as a radio wave it has to be modulated into 30Hz-300GHz frequency without loosing the information that the orignal signal represents.
Frequency Modulation (FM)
The goal here is similar to AM where we have a signal that we want to send and instead of changing the amplitude we change the frequency. For exampl 0 might be represented by a higher frequency (shorter wave lengths), and a 1 by a lower frequency (longer frequency).
Phase Modulation
This this case a change in phase could be used to indicate 1 and no change could be 0. Visually this would look like break in the curve and it starting over in the down instead of up or vice virca.
Digial signals and frequency
A digital signal is in a specific state as high or low, 1 or 0. This state is represented by a constant non-changing voltage on the wire. Like 0V or 3.3V.
If instead this voltate varies over time we have a signal.
If the voltage is changing is a regular way, periodically way, over time we have a frequency.
Wave length
c c = speed of light
λ = - f = frequency
f
Lets say we have a signal that frequency of 200Hz. And recall that frequency is the number of waves that pass a fixed place in a given amount of time (in Hertz this is per second.
So the more waves that complete the higher the frequency. These waves are shorter and the lower frequency waves are longer.
So if we have a wave of 200Hz, that means 200 cycle per second can calculate the wave lenght using the formula above:
3 * 10⁸ m/s
λ = ----------- = 1.5 * 10⁶ m = 1500 km
200Hz
Now, a wave length is the length of one cycle, as in starting from zero going
up to the amplitude, down to zero, down to the amplitude and back to zero. This
distance is 1500km?
So would an antennna that is build to receive such a signal then have to be
1500km long to receive the complete wave. This does not work and in reality we
have small devices that have antennas which are much must shorter. What is
needed is to take this low level fequency and transform it into a higher
frequency but still retain the same information, and on the other side we take
this high frequency and transform it back into the lower frequency.
And lets take a higher frequency of 3000Hz:
3 * 10⁸ m/s
λ = ----------- = 10⁵m = 100 km
3000Hz
How does frequency and data rate relate to each other. The way I'm thinking about this at the moment is that we have a carrier wave that is of a certain frequency, but there is no change in the wave, like no change to the amplitude phase or anything like that so it does not really transport any information, or perhaps it transports the same information all the time. But if we can decide that a change in amplitute means a logical 1 and another change means logical 0 then we can send on bit of information per cycle/period. So if we have a 10Hz communication channel that would mean 10 bits of information per second?
Frequency bands
Take the FM band which is the range of frequencies from 88MHz to 108MHz:
88MHz 108MHz
|-------------|------
FM broadcast band 88 MHz (frequency of the electrical current)
88 miljon cycles per second, 88 000 000Hz
220V - - 60Hz (60 cycles per second)
- - - -
- - - -
0V -------------------------------
- - -
- - -
-
What is bandwidth
TODO:
Electro magnetic waves
Lets say you have two wires with a current running in opposite directions, this magnetic fields will cancel each other out so there will be now propagation of EM waves.
Antennas
Antennas are the interface between the world of electronics and the world of electromagnetic radiation. An antenna can transform an alternating current (AC) into a radio wave and vice versa.
https://www.youtube.com/watch?v=FWCN_uI5ygY
The below notes were take while watching https://www.youtube.com/watch?v=bwreHReBH2A.
Lets say we have a positive charge (+) and a negative charge (-) and we are going to move them vertically (but I guess without them being attracted to each other):
+ - +
| + - ↑ - + |
E | | + ↑ | ↑ - | |
| ↓ - | | | + ↓ |
↓ - + | + - ↓
- + -
-------------------------------------------------------> time
Electro field = vertial arrow
So the electric field is pointing from the positive to the negative. Notice how the electric field goes from negative to 0 to positive. So the value of the electricfield starts off negative, then goes up to zero, then changes direction and becomes positive instead, and then goes back down to zero etc.
If you look at the diagram above and visualize a curve looking something like this:
-
- -
- -
------------------------------------->
- -
- -
Wire with electric current
+ +-+
| |||
E | |||
| |||
↓ |↓|
- +-+
Recall that when we have a current there is also an magnetic field generated. Remember the right hand rule here, the current is flowing downards so your right thumb points in that direction, and you other fingers wrap around the wire and that is direction of the magnetic field. So the magnetic field goes around the wire in a circle from right to left above, coming out towards us and then back behing the wire. We can name this magnetic field B.
Now, in the same way we moved the positive and negative charges up and down, we can change the direction of the current, and we can also stop the current flow:
Wire with electric current
+-+ +-+
||| |↑|
||| +-+ |||
||| +-+ |||
|↓| |||
+-+ +-+
The middle box is supposed to represent zero current.
- - - -
- - - -
------------------------------------->
- - - - - -
- - - - - -
So have the electric field which is doing up and down, and we have the magnetic field which is coming out towards us and back into the screen. So try to visualize this as the electric field going up and down and the magnetic field is on a plane orthogonal to it.
Changing E generates B, and chaging B generates E. This makse the wave and causes the continuation of this intraction causing this "wave" to propagate. The speed it propagates is the speed of light, 3 * 10⁸m/s.
Metal wire
↓
| ↑
- - | |
- - - | | I
- - - | |
------------------------------------------> | |
- - - | |
- - |
So the above is just showing when E is positive but it will soon go down to zero and then to negative:
Metal wire
↓
| |
- | |
- - - | | I
- - - | |
-------------------------------------------> | |
- - - | ↓
- - -
Notice that the current (I) switches direction.
c = 3*10⁸m/s
But there is a relation ship between c and the frequence and the wavelenght:
c = frequence * wave length
c = f * λ
m 1
- = - * m
s s
Since c is constant if we increase the frequence then the wave length must decrease. And if the wave length increases the frequence must decrease.
The frequency of E is the same as the frequency of B.
E = cB
EM Energy
Do electro magnetic waves carry energy?
Yes, think about what happens when you sit in the sun, you get warm and if you
are like me your skin will become red and burn. We absorb that energy from the
sun.
LoRa
Is short for "long range" and provides low power consumption and long range, a low data rate, and secure transmission. Is used in small battery driven sensor devices that connect to a gateway which may be between 1km to 10km form them. These devices are expected to run on the same battery for about 2 years.
Has a greater range than celluar networks which have a range from a few 100m to 1km.
In Europe the frequencies for LoRa are 433MHz and 868MHz. Be carful when configuring this as it could be illegal to use 915MHz which is allowed in other places in the world.
LoRa is the physical layer that enables a long-range communication link. LoRaWAN is the communication protocol and system architecture for the network.
LoRaWAN
Is a Low power Wide Area Network (LPWAN)
Nodes: Gateways Network Server Application servers
*------------->+-------+ +-----+ +-----+
* *--+------>| | --------> | | ------> | |
| +-------+ | | +-----+
*------+------>+-------+ | | ------> +-----+
| | --------> | | | |
+-------+ +-----+ +-----+
(LoRa) (TCP/IP, TLS) (TCP/IP, TLS)
Protocol stack:
+---------------------------------------------------------------+
| Class A Baseline | Class B baseline | Class C baseline |
+---------------------------------------------------------------+
| LoRa Modulation
+---------------------------------------------------------------+
| Reginal ISM band |
+---------------------------------------------------------------+
| EU 868 | EU 433 | US 915 | AS 430 | |
+---------------------------------------------------------------+
BlueTooth
Peer-to-peer connection over relatively short ranges. These devices normally do not require much power so fairly low power consumption.
BlueTooth Low Energy (BLE)
TODO:
WiFi Direct
Is a peer-to-peer connection and and does not need a wifi access point. It uses the same frequency and similar bandwidth and speed as normal WiFi.
Near-Field Communication (NFC)
Other wireless devices emit radio signals but NFC communicate with an EM field (not a wave that is) between two coils. So these two coils need to be very close to each other for this to work. There can be passive tags don't have any power source of their own and instead get their power from the reader over the EM field.
Low-Power, Short-Range, Low-Data, Mesh technologies
Mesh means many-to-many so with these technologies we can send a message to a destination device without being directly connected to that device:
A ---> B --> C
In this case A want to send a message to device C but is only sending to B which migth be closer. A might be too far away to even be able to send to C. There can be many hops here and they can be spread out over fairly long distance and still have low power consuption for the devices.
Examples: BlueTooth Low-Energy, ZigBee, Z-Wave, and 6LoWPAN.
RS-232
Recommended Standard 232.
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