ESP8266 not working to drive relay

Question

I am trying to drive a 5V Relay using ESP8266-01 module.

Following image is the circuit diagram i have uploaded.

My sketch is about connecting the esp to the mentioned Access Point and controlling the relay from esp.

When i power my device ( same as the connections given in the image below ), the esp turns on (blue led is turned on on esp) but it does not work according to the sketch.

When i remove the connection between GPIO2 (of esp) and R3, the esp works according to the program logic but in that case i wont be able to control the relay from GPIO2 (of esp).

Can anyone guide me resolving this issue ?

Answer 1

One problem that I can see with your circuit is that the 2N2222 transistor may not have sufficient current gain to turn the relay on (and keep it on).
The relay may need anywhere from 60 to 100mA, the transistor gain is guaranteed around 50 at around 100mA AND (this is VERY important) 1.0V across the collector-emitter junction.
This means that you might have only 4V available to the relay, and some 5V relays need at least 4.5V to turn on.
It is not clear from your question whether by the circuit "not working" you mean the relay or the IC?
I would suggest using a low voltage MOSFET (even a regular one should work since it needs to drive a small current) instead of a bipolar transistor like 2N2222, as that would solve both problems at once: it would not load the IC output and it would have almost no voltage drop (giving the relay the full 5V for its operation).
Check the voltage on the output pin when the transistor is connected, and check the voltage on the collector pin when the transistor is on, and let us know what you got!

P.S.: Some of my values above may be somewhat incorrect, but the issues mentioned are present.

Answer 2

I have checked some info on the ESP8266-01, and your problem is that BOTH the GPIO and GPIO2 need to be pulled UP for the chip to start working. The GPIO2 in your case is pulled DOWN through the base of the transistor. The chip at startup checks the GPIO pins, and then it makes them available for use as inputs and outputs. That's why your chip works without that resistor connected, and doesn't work when you connect the resistor.

I have searched and searched, but I had to come up with my own solution to your problem. Here it is:

You might get away with simply adding the R2 and C3 to your board.
C3 here acts as an RC delay circuit with R3, giving you a positive pulse at GPIO2 at startup. Apparently, ESP-01 pauses for 40ms during the power up sequence, sends some bytes through GPIO2 for 100ms, and then it boots into normal program. This means that you only need to hold the GPIO2 at the logic high level for more than 140ms, and this CR combination should give you more than 200ms.
The R2 is needed here to prevent the C3 from discharging through GPIO2 at more than 12mA (maximum allowable current for GPIO pins) when GPIO2 goes to logic high.

If you don't want the relay to turn on shortly when powering the circuit, you could add the C4.
R1 and R2 could be used to ensure the C3 and C4 discharge in about 5 seconds after power off, so that they function as designed if you power the circuit back on within 10 seconds (but not sooner than after 5 seconds have passed).

This RC combination will also give you a slight delay in switching the relay on and off (should be less than 0.3 seconds or 300ms), but that should be fine for most purposes.

P.S.: For anyone asking, here is a datasheet for this module from MicroChip: http://www.microchip.ua/wireless/esp01.pdf
Here is also a little more about the boot modes: https://www.forward.com.au/pfod/ESP8266/GPIOpins/index.html

P.S.: I realize that C2 could be 10uF, so just use that!