Afterburner 3.3V Arduino compatibility

[ole00]

Afterburner PCB v.3.1 (and lower versions) is NOT electrically compatible with 3.3V Arduinos. In fact, it will most likely damage your 3.3V based Arduino!

Q: Shall I be concerned?
A: No - if you use Arduino Uno R3, Arduino UNO R4 and other 5V based Arduinos and clones
A: Yes -if your Arduino has a 3.3V/5V IOREF switch. You have to keep IOREF switch at 5V. For example Sparkfun BlackBoard or Seeed Studio boards have such switch.
A: Yes - if you have ARM or ESP32 (or other ESP MCU) based Arduinos. Do not use not use those with Afterburner PCB v.3.1 and older (lower PCB version).

Q: Is 3.3V based Arduino important for Afterburner's project?
A: Possibly. It will allow to program GALs that can't operate at VCC voltage higher than 3.3V.
A: Yes, for those who already have 3.3V Arduino and want to use Afterburner without buying another Arduino.

Q: I have a 3.3V based Arduino, can I mod the Afterburner's PCB to be compatible with 3.3V ?
A: Yes, PCB version 3.1 can be modified to support 3.3V Arduinos. See the image bellow and follow these steps:

1. Cut the traces on the bottom side as indicated by the Red lines

2. Carefully scrape off fthe solder mask to reveal bare copper. Ensure the ground plane
   is not scraped, or else you might create a short. Tin the copper parts of the traces
   with a bit of flux for better solder joint.

3. Solder short wires (indicated Blue) as depicted. Do not use thin keynar wires, use a bit
   thicker AWG 30 or lower (for at least 100mA current or higher current).

4. Triple check the IOREF pin and 5V pins are not shorted

5. Triple check the IOREF pin and GND are not shorted

6. Triple check the 5V pin and GND are not shorted

Q: What does the mod do?
A: It ensures IOREF pin and 5V pin are not shorted together. Without the mod on 3.3V Arduino the IOREF pin supplying 3.3V and 5V pin supplying 5V are shorted - that's not good. The 5V based Arduinos supply 5V on IOREF pin, so such short is not a problem (usually the IOREF and 5V are shorted on the Arduino board as well). Note that the MT3608 module (voltage booster for producing VPP) is still powered by the 5V rail (for better efficiency and to not to overload the 3.3V LDO).

Q: I have a 5V based Arduino. Will this mod allow me to program 3.3V GALS that operate at maximum voltage of 3.3V (or 3.6V) ?
A: No, the above mod does not allow that. The mod ensures Arduinos that operate at 3.3V are not damaged when Afterburner is used.

Q: Will the new versions of Afterburner PCB support the 3.3V Arduinos?
A: Yes, PCB version 3.2 and higher will have the mod applied.

Q: Can any GAL be programmed by 3.3V based Arduino?
A: Yes, it looks like the C versions of Atmel GALs (ATF16V8C and ATF22V10C) can be programmed with 3.3V based Arduino. But not the ATF16V8B IC. I was able to program ATF750C as well with 3.3V Vcc. Some Atmel GALs are specifically designed to operate at 3.3V, they have LV marking. For example ATF16LV8C, ATF22LV10C or ATF750LVC. Also, I was able to program Lattice GAL16V8D with IOREF set to 3.3V. Please note that there are many clones of Lattice GALs on Aliexpress, so it may not be always possible, depending on the clone capability.

Q: I have a 3.3V based Arduino XYZ, and it does not seem to work with Afterburner, what to do?
A: Please make sure you have the above mod applied (on PCB v.3.1 or lower). Also, it may be possible that Arduinos that are too fast (above 48MHz clock) produce programming pulses that are too short for the GAL. Try to lower the MCU frequency in Arduino IDE options (if possible) before uploading the Afterburner sketch. Ensure you are programming 3.3V compatible GAL (like Atmel LVC parts - see above).

Q: Which 3.3V based Arduinos work with Afterburner and the modded PCB?
A: I have only tried it on Sparkfun's BlackBoard whith IOREF switch set to 3.3V. If you have a 3.3V based Arduino and it works for you with Afterburner (or does not work - make sure you've applied the mod first!) feel free to post some info.