ESP32 Forum

Custom PCB design, very clean 3.3 volts going to Vcc with no ripple detected, excellent grounding and decoupling capacitors placed throughout, EN pin pulled up via 4.7 Kohm pull-up resistor to Vcc, GPIO 8 and GPIO 9 pulled up each with 4.7 Kohm to Vcc. Monitoring the TX UART pin and expecting to get at least "flash reset" or "boot mode" on UART at 115200 baud when pressing a reset button which temporarily pulls the EN pin down to 0V, then release, back to 3.3 V very quickly (quickly since I removed a capacitor which would have slowed this down.)

Pressing and releasing reset does nothing, other than bringing some outputs like TX and RX down to 0v while it is pressed, then TX goes up to 1.5V and RX goes up to over 3V when reset button is released. UART TX and RX are connected to nothing else.

Don't you have to pull GPIO 9 low when toggling reset to enter bootloader mode ?

Yes you do - and I have another button which controls that pin. I have tried pulling it low as well, but still there is nothing on TX. Even if it was left HIGH the TX should say something when reset is triggered, like "cant find vector of code" or whatever it says when there is no code on the flash at all.

So I've tried both and neither works

Sounds like you did everything right, tbh. Are you sure the C3-Mini is soldered in correctly?

I had them done by JLCPCB so I'm really concerned that there might be bad ESP32-C3-mini modules out there. I've done several other designs with the exact same module and no problems at all. JLCPCB usually does an amazing job with the soldering. And normally they have very good component stock.

It's just very odd that the reset button would make it behave that way. I know what I should normally see. And also most of these modules come pre-programmed so a WiFi access Point usually appears when they are powered and reset. But to get absolutely nothing from the UART TX pin on reset is very concerning

Also this isnt just one module. I had 2 prototypes that were done by JLCPCB. The modules are dead-center perfectly aligned on the PCB. So I tried 2 different PCBs with the module and got the same wrong results

Schematic?

Are you sure your monitor config is correct? Correct port selected? Do you get output from a known-good board?

Can you use an ammeter to confirm ~0mA when EN is low and ~20mA when released high?

Used a 1.5 ohm shunt directly off the LiPo battery at 4.2 V (regulator was consistently outputting 3.30V clean clean throughout the test). On the input-to-regulator side, started at 6 mA (milliamps) when reset not held in. Once reset held in, total input current drops to 0.26 mA (260 uA). Then after releasing reset, current jumps back up to 6mA. That is input current to the reg, not output current. Regulator is ME6211C33M5G-N ... a very capable regulator with 500 mA capable output.

Note there are a few other passive elements that are biased which probably take a tiny bit of current

Monitor is good - I use it daily on other ESP32C3 circuits. On top of trying the 115200 monitor built in to VS-Code terminal, I also closed that and tried PuTTY. PuTTY gave no response at 115200 baud, and only a single wavy block ascii character at 921600 baud (which I have seen before as an artifact from a simple voltage spike)

I haven't used a C3 specifically but 6mA is very suspicious. That says to me that it's not booting correctly. I know from experience that the ESP32 can sometimes be stuck drawing about this much with a bad boot (eg. if EN is high from my attached ESP-PROG before 3V3 applied).

The lipo is also potentially an issue. What's the capacity? Do you have a power supply to use instead for testing?

Can you capture EN and 3V3 with an oscilloscope as the button is released? I suspect this will be very telling.

Is GPIO2 high?