I have a custom board that I have developed where I am using the ESP-01 module.

ESP-01 Pin Out

I have not connected the CH_EN pin to GND or Vcc on the board. When I connect the module to the board, the red LED lights up, but the code doesn't work. When I tried to short CH_PD and Vcc pins so as to pull the CH_EN pin high, the red light started blinking very weakly and it still didn't do what it was supposed to do.

Is the CH_EN pin supposed to be pulled up or pulled down all the time?
Does the onboard red LED's blinking mean my power supply has an issue?

Please help.

  • \$\begingroup\$ I've not needed to wire the CH_EN pin on my esp01s. I'd suggest you check your power supply. The esp is very picky - you need to ensure you have enough current available otherwise it will get upset. \$\endgroup\$
    – Kartman
    Jul 17, 2021 at 11:15
  • \$\begingroup\$ @Kartman, esp-01S has on board pull-up for CH-PD. normal esp-01 doesn't. CH-PD is "enable" pin. it should be pulled up for esp8266 to work. \$\endgroup\$
    – Juraj
    Jul 18, 2021 at 5:52
  • \$\begingroup\$ @Juraj so I think in this case, my ESP-01 doesnt have CH-PD pulled high. But when I do short it with the 3.3v pin, the red led onboard the ESP board starts kind of breathing / weakly blinking. Does it have to do with power supply then? My schematic - imgur.com/Eof2UHv \$\endgroup\$
    – Amorphous
    Jul 18, 2021 at 6:24
  • \$\begingroup\$ The schematic is near unreadable both in reproduction and layout. From what I can interpret, it does look suspect. \$\endgroup\$
    – Kartman
    Jul 18, 2021 at 21:25
  • \$\begingroup\$ @Kartman its basically a 5V 200ma design based on MP150GJ-Z and then AM117-3.3V. \$\endgroup\$
    – Amorphous
    Jul 19, 2021 at 9:39

2 Answers 2


Old post but no one mentions the reset pin which on the esp-01 also must be pulled up. Indeed on the esp-01s both reset en ch_pd have internal pullups.


ESP8266 Hardware Design Guidelines Version 2.7 mentions:

1.4.2. Power-on Sequence and Power Reset Reset

Pin32 EXT_RSTB serves as the reset pin of ESP8266EX. This pin contains an internal pull-up resistor and is active low. To avoid resets caused by external interference, we recommend that you keep the PCB trace of EXT_RSTB as short as possible, and add an RC circuit at the EXT_RSTB pin.

Pin7 CHIP_EN serves as the enable pin of ESP8266EX. In this case, ESP8266EX powers off when this pin is held low. Pin7 CHIP_EN also serves as the reset pin of ESP8266EX. In this case, ESP8266EX reboots when the input level of this pin is below 0.6 V and lasts for at least 200 μs.

We recommend that you use CHIP_EN, instead of EXT_RSTB, to reset the chip.

Notice: CHIP_EN cannot be left floating.

I found several synonyms: EN (enabling), CH_PD (Chip Power Down), CHIP_EN.


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