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Topic: 2-Wire Smoke Detectors (Read 305 times) previous topic - next topic


Nov 12, 2016, 01:10 pm Last Edit: Nov 12, 2016, 11:04 pm by Ripmax
Hi, I am designing a fire alarm system as a little project and I am using the Apollo Series 65 Optical Smoke Detectors, these are 2 wire smoke detectors.

If I've done my research correctly, with a 2-wire system, the power and signalling is done over the same wires. When a smoke detector is NOT in alarm, it draws very little current, however when it does go into alarm (detects smoke) it draws more current and that's how normal fire alarm panels detect that.

If possible, how would this be done with Arduino?

Apollo S65 Engineering Guide

Apollo S65 Product Page



I'll be curious to see how you get on because I am thinking of replacing the battery operated wireless detectors we have at home.

I had a brief look at the Appollo.

It does indeed appear to be a two wire system. From the information I found (more marketing than technical), it is not clear in the case of the Apollo65 what information is visible from the control unit.
The Apollo65 literature talks vaguely "including an IC based on that used in XP95 analogue addressable detectors." which hints at address information (ie which detector raised the alarm etc.) being available at the control panel.
The information abut the XP95 series is much more comprehensive, including a description of the communication to control panel.

I guess you have to decide what level of integration you want with the Arduino i.e. just detecting if an alarm was raised by monitoring the change in current to the chain of detectors  or going further to know which detector raised the alarm etc.


The XP95 series are addressable and i'm not really interested into going down that route. As they are expensive and I already have some Apollo S65'.

I'm only really interested in monitoring the current change to raise an alarm.

However, there is a way to wire them so they will trigger a relay when the detector goes into alarm. I was thinking do that, and just connect my zone wires to the C and NO contacts of the relay with an EOL resistor.

Open Circuit = Fault
Resistance equal to that of the EOL resistor = Normal
Closed Circuit = Alarm


You'll get a lot more help if you add a link to the device you are talking about.

I studied Greek Gods in school, but that was 65 years ago  :)
Regards, Terry King terry@yourduino.com  - Check great prices, devices and Arduino-related boards at http://YourDuino.com
HOW-TO: http://ArduinoInfo.Info


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