Ok thanks, i’ll use a prototype board to start with, see if It works ok with my alarm
Hi. I’m not very experienced in electronics schemes development, can you please give me an advice.
I have an old hardwired alarm system with a wired door sensor and external status led.
I want to connect and read the status of the external led and door sensor with ESP8266 without disconnecting them from the alarm system.
What do I start from? Mesure voltage on the LED and sensor? What additional components do I need?
Every system will be different but you should first read through the link I posted in the original post:
The link explains everything you need to know about how to get the signal read by an ESP/D1.
If looking only for a non-invasive way of monitoring the led then you could use a LDR (https://www.aliexpress.com/item/32476463183.html) placed near the led of the alarm system.
For software there are multiple options with ESP modules: esphome (https://esphome.io), openmqttgateway (https://github.com/1technophile/OpenMQTTGateway), espeasy (https://www.letscontrolit.com/wiki/index.php?title=ESPEasy)
There are also ESP8266 boards with LDR already soldered (however, I didn’t yet use): https://www.aliexpress.com/item/32860254874.html
Something else that can be used instead of the ESP8266 board is an Arduino Uno/Mega flashed with OpenMQTTGateway and an ethernet shield so that it improves on the reliability of connection (however, it requires running ethernet cables…).
Also, I should mention that LDR does need a little tinkering with calibration until getting the correct values in HA as that module is analog.
What kind of door sensor you want to monitor (i.e wired/wireless; if wireless what technology: RF433Mhz/Zigbee/Zwave/Wifi/etc)?
I have 2 wired sensors connected in series directly to the alarm system. There is also a wire coming to the external LED on the front door.
I’m thinking, maybe I can use optocouplers to check sensors and led state?
Here are connections that i want to connect to.
You could use a hall effect sensor to measure voltage, however you need a voltage divider to be able to connect it to an Arduino/ESP board in order to have continuous readings.
Also, keep in mind that those wires are probably running 12 V thus, although not sufficient to cause direct electrical shock problems, an incorrect wiring can lead to damages to the alarm’s motherboard or even fire hazard.
Thus, I would totally advise against messing with the wiring if not an electrician.
Instead, if able to access the led that turns on when sensors trigger (I assume that, since the two sensors are connected in series, you don’t have multiple zones for the alarm to monitor), a LDR connected to Arduino/ESP is still a solid option as it doesn’t involve any invasive wiring. LDR readings are instantly sent to the MQTT broker and you only need to take care of HA’s logic.