khwas / ua315 Goto Github PK

UTFT board up-converter dies when powered without LED connected.
To resolve the issue, the next iteration should include 30V zener to limit output voltage in no-load situation.

Hand soldering thermal profile is too high >200C. There is need to use automated oven with 160C-170C MAX in profile to avoid scorching of white plastic 40P component.

Up-converter inductor is too close to board's edge. Same with capacitors.This makes the panel hole cutting dimensions unnecessarily too accurate. All needs to be moved 3-5 mm closer to center of the board. Also large 40P connector is too close to the edge.

Replace square plastic spacers and plain screws with steel matte wide head (flat) screws

Add the 7-15 mil wide insulation tape to back side of UTFT board, covering all the traces completely

Inductor pads on digital board should be larger for more solder. Or may be preheating needs to be longer for inductor to heat up for better solder wetting

Add 4 notches in board outline to match the extruded plastic part.

• Currently the plastic parts require manual cutting in 4 places

This "LOW PRIORITY issue"
Study, how come the board has survived inverted DC power polarity mistake.
The DC was 5V limited to 160mA. The duration was about 0.5 sec.

• Look at schematics and see what and why allowed the board to sirvive

Silk screen must include URL, version, Pb-free symbol and other symbols.
Also may be copyright, year, logo

Software clocking details for UTFT, fuses changes for Atmel, voltage 3.4V must be documented.

• Fuses are programmed differently to Arduino Mega R3
• Main UTFT library has no example for 8MHz clocking - add it.
• External clocking for SSD1963 has special requirement for wiring of unused inputs - note it.
• Voltage 3.4V is a compromise - a highest acceptable voltage by Solomon chip and potentially lowest acceptable voltage for Atmel chip when unofficially overclocked from 8MHz to 10-12-16MHz (in future).
• Consumed current is 150 mA with local up-converter running
• Consumed current is 30-40 mA with local up-converter not running
• OK symptom: Consumed current is ~120 mA with local up-converter running and when Atmel chip is not programmed.
• FAULT symptom: Consumed current is 130-140 mA with local up-converter running and when Solomon chip is miswired.
• FAULT symptom: Consumed power is >200mA and LM regulators are hot, when there are shorting bridges.

6-pin ISP connector is located too close to main 34P connector. It needs to be moved 7-10 mm from current location.

Add white block area to silk screen to mark the manufacturing date and serial numbers by hand.

• Establish dates labels (week / year), serial numbering and online journaling for future stats about faults, components supplier batches, soldering profiles, supplementary materials, packing materials
• Attempt to trace climatic conditions / elevation (barometric) / temperature / humidity / winter freezing cycles for potential faults caused by ROHS materials ("tin whiskers") over next 5 years
• Attempt to trace mechanical stress / vibration for same data about ROHS caused faults *tin whiskers from vibration, Pb-free fragility, Pb-free slow flow of cold solder.

For next iteration of stencil use guiding coaxial holes for square "nail guides".

• The number of holes is 4 for board + 2 for stencil and board
• The 4 board only holes are for deep nails with tops of nails and board being coplanar and can stay on path of the squeegee
• The 2 additional shared holes are for board and stencil together. The CAD data for stencil must include special via pads with external diameter equal to diameter of the hole.
• The placement of holes is away from solder squeegee path + approx. size of the solder paste bead
• The diameter should match size of standard straight square pin of popular 0.1" header
• The "anti-coining" support panels must be pinned or glued with 1-2 mm play distance from board

Consider testing UTFT board for FCC compliance

• It is possible to ballpark the compliance with crude tools like AM/FM radio, selective level meter 0-30 MHz, etc

0603 capacitor are mismatching expected 0805 footprints. All filter 0.1uF capacitors must be replaced with 0805 ones.

Solder mask is too crude to 0.5 and 0.4 mm pitch.

• Consider better supplier with capability for finer solder mask between fine pitched pins.
• Consider better supplier with capability of solder mask with better adhesion - no flaking off

LOW PRIORITY
Consider adding epoxy filled variation of UTFT with custom gasket
This may be not environmentally friendly, ruggedized, high cost option for demanding applications

Board is exactly 1.6mm thick, better to reduce the board thickness if possible. To improve mechanical tolerances, reduce the board thickness to 1mm or less. Check if 4 layers boards exist for this thicknesses.

LOW PRIORITY
Consider using ARM based arduino chip.

• The ARM one has higher clocking speed
• ARM may be more electrically noisy
• Information to study the ARM design could or could be not more easy to find, it may turn to be more secretive than expected

• Review BOM, identify and add evidence of ROHS for every component
• "LOW PRIORITY" Add column in BOM about "bright tin" vs "dull coarse tin" plating to have the awareness about "tin whisker" faults in 150 days - 5 years

• This is "LOW priority issue"
  ESD mitigation for users, who confuse screen to being a "touch screen".
• Study the existing solutions for proper ESD protection of TFT screen
• Consider adding controlled impedance path from TFT to metal panel and circuit ground (1KV 1000pF cap in parallel with 1MOhm resistor). To do so, choose most appropriate TFT pin or group of pins
• Or add high value resistors (and caps if possible) from all pins to ground
• Or add low value resistors in series to all pins (?) of TFT subassembly

• Add the silkscreen info table with explanation of jumpers.
• Add pinout silkscreen text for 40P 0.1" MAIN connector
• Add pinout silkscreen text for 6P 0.1" ISP connector