▲ 6 r/synthdiy
Hi all,
I want to make a clock generator and divider using a Lilygo T-QT Pro, which is sized perfectly for a 4HP module. The board is based on an ESP32 so 0-3.3V at the GPIO pins.
I am still not sure how to design the hardware to prevent accidentally frying the ESP32. Currently, I plan to use NPN transistors to isolate the GPIO pins. This inverts the logic but can be easily inverted back via software.
Planned design for a gate/trigger input: https://is.gd/grZZed
- 100k resistor for high input impedence
- diode to block negative input voltages
- 27k resistor as voltage divider to increase level needed for a trigger to about 3V (instead of 0.6V)
- transistor to isolate the ESP32 from the hot input signal
- 10k to limit current through transistor / into ESP32
Planned design for gate/trigger output: https://is.gd/JnlUJq
- 10k resistor to limit current through transistor
- transistor to raise 3.3V out to more standard 5V out for gates/triggers
- transistor also ensures that current drawn by other modules comes from the 5V rail instead of the ESP32
- 2k resistor to limit current through transistor but still have low-ish output impedence (3k in total)
- diode to protect transistor from negative voltage, if an input is accidentally plugged into this output (and 1k to limit current into that diode)
As you can see, the circuits are not only for protection but also adjusting the voltage levels to better interface with other modules.
Now I am wondering:
- Am I missing something here or should this work reliably?
- Is this overkill and there is a simpler way?
Thanks!
u/GonnaChangeThisL8er — 10 days ago