DS18B20 problem - 127°C

[dudo02]

Hi,

I would like to ask you for help.
I have conected LAN CONTROLER as you can see in schematic.
I have got problem, when I switch thermostat contact ON/OFF the value of temperature is jumping UP/DOWN and in finally turn to 127°C.
Doesnt help reboot - value 127°C after reboot still there.
I must disconect power suply, then everithing working(value of temperature is OK), but when I switch thermostat - same prolbem again.

[pat]

The problem occurs when thermostat switch on/off or off/on, or in both cases?

[dudo02]

I am not sure.I have to chek it on the site, but I think about both cases.

[adzik]

Try use flyback diode parallel to relay!

[dudo02]

Yes I will do that.
I thought that somebody else had same problem...

[wilkxt]

You have connected termostat to relay contact on LK?

[pat]

Disconnect the relay's power and check the sensor reading. If it works - you need to change the cable - the power supply should not be in the same bundle as the sensor.
How long is the connection between LK and the sensor?

[dudo02]

Willxt-Yes,thermostat is simply mechanical thermostat mounted on the wall and contact is conected in series connection with OUT0 - as you can see in schematic. Also OUT1 and OUT2 connected in the same way with another two thermostats...

pat - DS18B20 is digital senzor so there should not be a problem with interferences. I have similar connection on diferent site where senzors and power for relay goes in CAT5 cable and there is no problem.
And also on another site - sensors are conected separerly on 4wire tephone cable and sometimes I saw same problem...

But here when I switch thermostat ON/OFF one time the temperature first time reach 80C and then go back to normal value.
But if I switch termostat few times in short time then temperature reach 127C...

[wilkxt]

you have 12V relay on schematic, what is it for?

[pat]

It's not about interference of digital signal but the induction of too high voltage on lines DS18 when switching the relay.