Smoke detectors

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Polygontrauma
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Joined: 10 May 2021, 09:24

Smoke detectors

#1 Post by Polygontrauma » 10 May 2021, 09:27

Hey there!
I wanted to build a fire alarm system for my house using wired EI650C smoke detectors.
Those smoke detectors have two wires; if one detects smoke, it gives 5v on the wires.
In addition, if you put 3-5v on the wires, the smoke detector gives an alarm.
So you should be able to either read the alarms as well as send alarms to the other smoke detectors.
Instead of wiring them directly, I want to wire them to Wemos D1 Mini and use ESP Easy to integrate them into my smart home system (domoticz).
So here is what i did:
- connect the GND wire from smoke detector output to GND on Wemos D1 Mini
- connect the other wire from smoke detector output to GPIO16 as well as to GPIO14
- configured devices in ESPEasy as well as in domoticz (one device for reading alarms, one for sending alarms over http)
As long as I have only one wire (GPIO16 or GPIO14) attached, it works - I then can either receive or send alarms. As soon as I connect both, nothing works.
So this seems to be an electronics issue - does anybody know how to solve this?

Best regards,
David

TD-er
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Re: Smoke detectors

#2 Post by TD-er » 10 May 2021, 09:38

I guess you want to use GPIO-16 to wake the ESP from deep sleep?
That pin is a bit tricky and in a lot of respects different from any other pin on the ESP8266.

If you connect it to RST to wake the ESP from deep sleep after some time, then you will also trigger resets when the smoke alarm is activated.
So I assume you do not use it like that.
I guess you should use 2 diodes to split the signalling, but then you may also loose some voltage due to the voltage drop introduced by the diode.
This can be compensated by a "level converter".

Polygontrauma
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Posts: 4
Joined: 10 May 2021, 09:24

Re: Smoke detectors

#3 Post by Polygontrauma » 10 May 2021, 15:08

Thanks for the fast reply! I also tried other pins, without success.
I know level converters, but can you please explain how I can split the signal using diodes?

Thanks in advance!

Best regards,
David

TD-er
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Posts: 4931
Joined: 01 Sep 2017, 22:13
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Re: Smoke detectors

#4 Post by TD-er » 10 May 2021, 18:19

I guess you want to use GPIO-16 as "input" to start the ESP?
And GPIO-14 as "output", to send the "high signal".

What you need is one diode "pointing" to GPIO-16 and one diode "pointing" away from GPIO-14.
Those connect to the same bi-directional level shifter, with the high-voltage side voltage connected to 5V.

Polygontrauma
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Posts: 4
Joined: 10 May 2021, 09:24

Re: Smoke detectors

#5 Post by Polygontrauma » 12 May 2021, 22:23

Thanks a lot for your help, integrating the diodes solved the problem, I didn't even need a level converter. Now I can start wiring all smoke sensors :D

TD-er
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Re: Smoke detectors

#6 Post by TD-er » 12 May 2021, 22:40

Ah great :)
I wasn't sure if the voltage would be high enough since the diode also has some voltage drop and the output voltage of the ESP is already close to the lower limit of 3V you mentioned.

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