ESP8266 Community Forum

- Mon Nov 12, 2018 4:57 am #79099 I haven't done this myself but when I had previously looked into it I thought the LP3470 reset IC might be a good mechanism.

This simple IC will pull reset low as soon as voltage drops below a threshold (e.g. 3.65V or 3.3V) and will release it after a delay when voltage rises again (battery charging). As it is an open drain output it is easier to integrate in with other sources of reset (e.g. deep sleep). It also has a reasonably small quiescent current.

- Mon Nov 12, 2018 5:31 am #79100

I haven't done this myself but when I had previously looked into it I thought the LP3470 reset IC might be a good mechanism.

This simple IC will pull reset low as soon as voltage drops below a threshold (e.g. 3.65V or 3.3V) and will release it after a delay when voltage rises again (battery charging). As it is an open drain output it is easier to integrate in with other sources of reset (e.g. deep sleep). It also has a reasonably small quiescent current.

It seems a good choice, but a little bit expensive

What about stm1001t?

- Mon Nov 12, 2018 1:33 pm #79109

So you don't put a cap before the regulator?
And do you use decoupling cap on esp module?

I typically have a ceramic 10uF cap on the input of the regulator. The 68uF on the output is the decoupling cap for the module. I put the regulator and caps as close to the Vcc and ground connections for the ESP-12 module.

I've read that if the battery goes to low when the esp is in deep sleep, even a charge could not wake up the module, and is necessary to Make a manual reset. Do you had the same problem?

For my application (remote control) I start from reset. I don't use sleep-wake operation. I use a mosfet in series with the circuit. When a button is pushed it turns on the mosfet and provides the enable signal for the ESP8266. It starts up, I then turn on an output that provides the enable signal when the button is released. I read the buttons and act on it. After some time of inactivity I turn off the port pin that was keeping the mosfet (power) on to disconnect the power.

As far as low battery voltage. I am using a battery charger with a supervisor chip to disconnect the battery is the voltage of the battery is too low. Other than during testing, I have never let the battery voltage get too low. I put a charger on at times.

- Mon Nov 12, 2018 5:05 pm #79110 stm1001t seems very similar to the LP3470.

I didn't think there was much difference in pricing but obviously depends on the source.

If you use the 3.3V version then the regulator will be in a non-regulated region when the reset kicks in but you should still be getting >3V through to the ESP