esp32-wroom-32 start on battery power on without requiring boot button

[ewgoncalves]

Greetings,

I have a custom board that integrates the esp32-wroom-32 with minimal peripherals. This device's application demands that the chip remains in deep sleep (~5uA) for most of the time.

I currently have it operating with some batteries however, whenever I place a new set of batteries, I always need to press a button that straps the CHIP_PU pin to GND for it to initiate, after that, it cycles between 'deep sleep' and 'operating' modes regularly.
I would like to know how to start the device automatically just by plugging in the batteries, thus not depending on the button.
Is there any special strapping for this pin (preferably a static strapping)? Or is there any bootloader modification to be performed?

Thank you and best regards,

[Beowulff]

Do you have a capacitor and pullup resistor on the /EN pin?

[ewgoncalves]

Hello Beowulff and thank you for your reply,
Yes, I have a 10k Resistor from EN to VDD (the same power supply as batteries) and a 0.1uF capacitor to GND.

Screenshot from 2020-06-16 16-24-49.png (10.03 KiB) Viewed 10396 times

Best regards,

[mikemoy]

Check out section "2.1.2 Power-on Sequence and System Reset" of the esp32 hardware design guidelines.
https://www.espressif.com/sites/default ... nes_en.pdf

[ewgoncalves]

Hello mikemoy,

Thank you for your reply,
By following that suggestion do you mean that by applying an RC circuit to delay the activation of CHIP_PU? "...The chip should be activated after the power rails have stabilized. This is achieved by delaying the activation of CHIP_PU (Pin9) after the 3.3 V rails have been brought up..."

I have used the same RC combination as in the devkit schematic (0.1uF / 10kOhm).
If there is something else please enlighten me.

Best regards,

[PaulVdBo]

I have the same problem. I noticed that when I disconnect the power, and reconnect it within a few seconds, the ESP boots normally. When the power is disconnected for a longer time, the ESP won't start until I press the EN button ...
I've been browsing through the internet to find a solution, and I've found MANY "so called" solutions, but I can't find THE solution. I only find things like : try this, and try that and then maybe ... or sometimes it works, or most of the time it works...
Is there any one here that (for once and for all) can say what to do, and what certainly ALWAYS works ? I' can't hand over a finished ESP32 system to my clients telling them that when it shouldn't start, that they have to get a screwdriver, open the box, find that little button and press it.
It should be : POWER ON => RUN. Always, EVERY time.

Thanks in advance.

PS :
- my boards don't have a GPIO0...
- I tried the condenser "trick" on the EN pin -> same result.
- I've read through many "official" PDF's...
- I use a good power supply that delivers 3.3V/2A.

[ewgoncalves]

Hello,
I had a solution from espressif support after exchanging some details of my circuitry.
My issue was with the fact that I kept a capacitor attached to IO0. I used the dev kit schematic as a guideline, however, I think that in the latest update they also removed it. That capacitor does not let the IO0 shift as fast as necessary which messes up the strapping when powering the chip. The issue was solved after the removal of the capacitor attached to IO0.
Hope this helps,
Best Regards

[PaulVdBo]

My issue was with the fact that I kept a capacitor attached to IO0

Thanks for your fast reply !
BUT ... I don't see a IO0 on my board ... ???
I attach a pic of my board.

[esp32-user]

Paul, did you ever get a reply? I have a similar issue, not sure what I need to do to make sure that my board boots every time it gets power.