Temperature sensor power

4 replies [Last post]
Lawrencezarb
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Joined: 7 Mar 2012

I have been having trouble with HAH board locking up, and after discussion on this forum I have come to the conclusion it is caused by my extensive network of temperature sensors possibly cause a spike on the 1 wire bus.

To resolve this I tried to use a separate 5v power source to power the temperature sensors, but when I connect it up all the sensors show "?". If I unplug the 3.5mm sensor lead and plug my test sensor directly into the port it reads correctly, so I know that the 5V line is wired and working correctly.

Why is it that my multiple temperature sensors only work with the HAH sourced 5v line?

steve
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Joined: 28 Feb 2011
Are the gnd's connected

Are the gnd's connected together ? i.e new PSU and HAH's

Do you have a quick schematic

Steve

Lawrencezarb
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Joined: 7 Mar 2012
Hi Steve, Yes the grounds are

Hi Steve,

 

Yes the grounds are together. As I tried to explain, when I disconnect all the multiple sensors and connect only 1 which is fitted directly onto a 3.5mm plug it works.

 

I have no schematic as all I did was take the 15v from the power supply and feed it into a 7805 regulator, so that the temperature sensors are independant from the HAH 5v.

garrydwilms
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United Kingdom
Joined: 31 Mar 2011
Mines ok

I had the same issue with my very long and poorly shielded 1wire bus. 

I added a 5v line using a regulator on a nearby 12v line and reduced the number by a few devices. 

All been ok for 12 months now. 

 

Double check your wiring as it can be done. 

 

Garry

steve
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Joined: 28 Feb 2011
One wire topology can be an

One wire topology can be an art, OK so no schematic, so I'll take a guess your using a backbone cable (what type of cable and length) and then jointing off of this at required points (if so how & how many) thus a linear topology.

With such a system you can get a lot of signal reflections due to cable impedance, and resistance from the joints adding more impedance so fitting a 100ohm resistor on the data lead of the sensor reduces reflections here's a link http://www.maximintegrated.com/app-notes/index.mvp/id/148 see (Distributed Impedance Matching) from the Maxim website hope this helps.

I understand connecting a test sensor direct to the 3.5mm jack works OK, short lead direct connection min. impedance etc. but try connecting your furthest sensor first on your network if OK then start loading it up.

 

Steve

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