GOAL: Convert 80s style user interface ( 8031 based ADP Product: chicklet keyboard and 2x20 lcd ) to pi zero based terminal/console using i2c based io expanders.
Looking under the keyboard membrane and tracing the connectors we can get the following key map under a 4x12 array (16 pins).
0123456789A(10)B(11)
--------------------
0) *# ZXCVBNM/ <STOP>
1) -LASDFGHJK<N/C><ENTER>
2) 0912345678<BS> <START>
3) POQWERTYUI<CAN><DIAL>
| * | # | Z | X | C | V | B | N | M | / | STOP | |
| - | L | A | S | D | F | G | H | J | K | N/C | ENTER |
| 0 | 9 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | <---- | START |
| P | O | Q | W | E | R | T | Y | U | I | CANCEL | DIAL |
For this we look at the AW9523 GPIO expander with 16 pins of io.
Since the LCD is a 5v circuit requiring either 8 or 12 pins we look at the Microchip MCP23017 on the Adafruit GPIO Expander Bonnet which we can wire either using both ports or one port in nibble mode.
root@somepi1:/home/feurig# i2cdetect -y 1
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- 58 -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --
After putting the board in the box I realized that the grey paint was conductive and that I almost let the smoke out of the pi zero. (you could smell it). So I went out in the garage and found a piece of plastic from a previous project. And then I was like OH SHIT I have Noritake 2x24 VFD thats a close fit..
root@somepi1:/home/feurig# pip3 install adafruit-circuitpython-charlcd
...
I am not thrilled about the way its wired but, whatever, because wiring it up according to the above schematic should let us write away. It't a bit jenky... I would like to be able to easily remap the pins without rewriting the library but I am not there.
But it works.
Now on to the keyboard. If it werent for the fact that there was a readymade lcd library for the mcp23017 I would have swapped the io expanders. The aw9523 has no internal pullup or pulldown resistors. Fortunately I have piles of 10k resistors and apparently I have time. (Not enough time to make fritzing make part to wire connections look good it seems)
Here is a simple circtuitpython program which presents a prompt and then puts characters scanned by the keyboard onto the display.
import time
import board
import busio
import adafruit_character_lcd.character_lcd_rgb_i2c as character_lcd
import adafruit_aw9523
keymap=[]
keymap.append('*# ZXCVBNM/\001')
keymap.append('-LASDFGHJK\r\n')
keymap.append('0912345678\010\002')
keymap.append('POQWERTYUI\030\004')
lcd_columns = 24
lcd_rows = 2
i2c = busio.I2C(board.SCL, board.SDA)
lcd = character_lcd.Character_LCD_RGB_I2C(i2c, lcd_columns, lcd_rows)
lcd.message = "PiTerm 1986 v0.0\nOk >"
aw = adafruit_aw9523.AW9523(i2c)
row_pins = [aw.get_pin(8),aw.get_pin(9),aw.get_pin(10),aw.get_pin(11)]
for pin in row_pins:
pin.switch_to_output(value=True)
col_pins = [aw.get_pin(0),aw.get_pin(15),aw.get_pin(14),aw.get_pin(13),
aw.get_pin(12),aw.get_pin(7),aw.get_pin(6),aw.get_pin(5),
aw.get_pin(4),aw.get_pin(3),aw.get_pin(2),aw.get_pin(1)]
for pin in col_pins:
pin.switch_to_input(value=True)
old_row=0;
for pin in row_pins:
pin.value=1
switch_state = [[0,0,0,0,0,0,0,0,0,0,0,0],
[0,0,0,0,0,0,0,0,0,0,0,0],
[0,0,0,0,0,0,0,0,0,0,0,0],
[0,0,0,0,0,0,0,0,0,0,0,0]
]
while True:
for r in range(4):
row_pins[old_row].value=1
row_pins[r].value=0
old_row=r
for c in range(12):
if (col_pins[c].value==0 and switch_state[r][c]==0):
switch_state[r][c]=1
print(keymap[r][c])
lcd.message+=keymap[r][c]
if (col_pins[c].value==1 and switch_state[r][c]==1):
switch_state[r][c]=0
time.sleep(0.01) # debounce
- https://learn.adafruit.com/adafruit-aw9523-gpio-expander-and-led-driver
- AW9523 Datasheet
- https://learn.adafruit.com/gpio-expander-bonnet/overview
- MCP23017 Datasheet
- https://protostack.com.au/2010/03/character-lcd-displays-part-1/
- https://www.electronicsforu.com/technology-trends/learn-electronics/16x2-lcd-pinout-diagram
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