ESP8266 Community Forum

Hi, I've got some ESP8266 ESP-14 which I use like ESP-12F (only using GPIO0)

The power supply is 5V, I'm using a LM1117 linear regulator to step down voltage to 3.3V

I have 10k pull up resistor on GPIO0 and a relay module connected to it.

This works fine but when I first power up the power supply, the esp doesn't boot up. I have to unplug the psu and then plug it again, then esp blinks and boots.

I was able to recreate the problem by plugging it to my lab power supply and increasing voltage slowly from 0V to 5V then the esp doesn't boot up.

I also tried to add a resistor to put load on it (400mA) and this doesn't help.

Does anyone see what's the problem here ?

Thanks !

The reset circuitry inside the module has a pull up to the supply and a capacitor to ground.

The intention is that the capacitor holds the reset low until the power is established and then as it charges up the reset crosses the threshold for high and the chip starts executing.

This relies on the power supply reaching operating voltage in a reasonably short time. If it ramps up too slowly then it is possible the chip does not see a low on its reset line after it has started to function properly with correct supply voltage.

It could be your power supply is starting fairly softly when first powered on but speeds up when unplugged / replugged.

I can't say I've suffered from this myself. I tend to use battery, USB or the Hi-Link HLK-PM modules if powering from mains supply.

The value of the reset capacitor is a bit of an unknown quantity but I am guessing the time constant is of the order of 100 mS or so.

Thanks for the answer, I couldn't have figured it out by myself.

Do you have any workaround for this problem or maybe put a name on it so I can google this ?

Thanks.

The LM1117 is a well-known renowned linear voltage regulator. That won't be the problem (unless it appears to be a dodgy clone).

The ESP8266 isn't that sensitive to voltage fluctuations, but it is sensitive to noise on CH_PD and RESET lines. IIRC RESET is pulled internally up, but only by the slightiest amount (> 100 kOhm equivalent) and CH_PD isn't pulled up at all. A strong external pull up resistor already helps a lot, but I found it's even better to use a ceramic capacitor. Otherwise the ESP will reset on any noise occuring in the neighbourhood (like powering on a fluorescent lamp).

Did you read the LM1117 data sheet? Some voltage regulators have peculiar demands on capacitors on the input and output sides. If the demands are not met, they tend to go oscillating.