How to read the state of a 1.8v LED?

ESPHome
1

Hi,

I’m working on trying to connect my doorbell up to Home Assistant using a wireless doorbell I bought from Amazon and following this guide but cannot get the ESP8266 to read the state of the LED in the chime when it is flashing. I have tried the + and the - side of the LED and so far nothing. When I measure the voltage on the LED when flashing i’m getting roughly 1.8v max; and am beginning to think that is too low for the ESP to register as an input. Is there anything I can do?

-Cheers,
doorbell_receiver.yaml

esphome:
  name: doorbell_sensor
  platform: ESP8266
  board: nodemcuv2

wifi:
  ssid: !secret wifi_network
  password: !secret wifi_password

  # Enable fallback hotspot (captive portal) in case wifi connection fails
  ap:
    ssid: "Doorbell Sensor Fallback Hotspot"
    password: !secret api_password

captive_portal:

# Enable logging
logger:

# Enable Home Assistant API
api:
  password: !secret api_password

ota:
  password: !secret api_password
  
binary_sensor:
  - platform: gpio
    name: "Doorbell"
    pin:
      number: D0
      inverted: true
      mode: INPUT_PULLDOWN_16
  #    mode: input_pullup
    filters:
      - delayed_off: 10ms
switch:
  - platform: gpio
    pin: D1
    name: "Doorbell Chime"

Pin D0 on the esp8266 goes to the + pad on the LED. Pin D1 goes to a 2N222 transistor in-line with the speaker to control the chime. The LEDS blink when the doorbells are pressed.

2

I should also mention. If I physically remove the wire from D0 I can see the trigger for the binary sensor sending on/off.

3

I am not sure what you mean by that.

However the led should have a resistor in series with it. The voltage across the led and the resistor combined should be readable. (Make sure it isn’t too high for the esp though,)

4

Very likely. The minimum input high voltage for 3.3v TTL is 2.0V

logic-family-voltage-table
logic-family-voltage-table951×747 174 KB

There should be a current limiting resistor connected to the LED. What voltage do you measure across the LED and current limiting resistor?

single-led-resistor

1 Like
5

Hi,

Thank you for the help. I did some tracing on the board and found three resistors. After probing either end while on ground and pressing the chime; I found one that registered 2.4v max when the button was pressed. That seems to work now as when I press the button it is registering now no problems or false positives.

Thank you again. I needed that.