1-wire wiring advice

3 replies [Last post]
United Kingdom
Joined: 31 Mar 2011


Before I go ahead and do somehing stupid I was wondering if someone with more electronics knowledge than myself could give me some advice on whether what I am about to do is sensible and not going to do any harm.

I want to get 1 wire devices into most of my rooms but cannot face the wiring task, I could do Jeenodes but for the number I want this would be costly.

Therefore I realised that I have already run a cat5 cable to my alarm box for bell monitoring and panic activation from the HAH. I therefore have enough free wires to get the 1-wire power,Gnd and data to my alarm box.

I want to put 1wire devices into my PIRs that are already located in good positions and disconnect their tamper wires and use them for power and Data. I will put a pull up resistor in each one to help with the cable length.

I am not bothered about loosing tamper protection.

However I am short of a ground wire but thought I could share this with the 12V gnd for the pir power lines as they are seperate systems.

Can anyone see any obvious problems with this. my electronics is getting better but still not great :)




Providence, United States
Joined: 9 Jan 2010
not sure myself

I would say this isn't a good idea as the references for GND can vary.

If you measure the voltage from +5V VCC side to the 12v(GND) you might find that you don't have 5V and if you don't I'm not sure that this is stable.  Derek?


United Kingdom
Joined: 31 Mar 2011
so far so good!


Just thought I'd post an update as I have had success with this and it seems a really easy way to get 1wire temp devices into every room you have a wired PIR device.

I have run a cat 5 cable from the HAH to my alarm box (realatively easy for my setup, thankfully) which carries the 1wire power, Gnd and data.

I have disconnected the tamper connections from the pir devices and the alarm box and used these wires to carry 1 wire data and power from the cat5 to each PIR.

I connect the HAH 1wire Gnd into the PIR 12V Gnd (effectively sharing the GND wire).

Then at each PIR I just connect a 1wire temperature device onto the reused tamper wires carrying data and Power and then connect the temperature device gnd onto the PIR gnd terminal.

I currently have two working and stable so far. I have not yet used pull up resistors but suspect I will need to when I increase the number of sensors. I then just poke the head of the 1wire temp device outside the PIR case and all is good.


Thought it might be of use to somebody. Bear in mind this does mean the tamper circuit to the PIR doesnt work anymore (I'm not too concerned about this)





Glasgow, United Kingdom
Joined: 26 Oct 2009
Not the best

If I was going down this route, I'd probably just use the existing 12v/Gnd lines & pop a 7805 regulator at each point. However, the wire that is used for alarm systems generally isn't as good as Cat5. Also, a whole series of different cable runs (as is typical in alarm systems) might make for a rather strange 'bus'.

RoomNodes would be the way to go. A bit more pricey, but in the end it's more likely to be reliable & a load more flexible for other things like 'light level sensing'.

Mentioning RoomNodes, the PCBs or these are in & looking good. Available in the next few weeks from the HAH Shop.


Hardware Info