DS1820 Max Cable length ?

[dccch]

Dear all,
I'm building a temperature logger for my solar panels.
The program is running fine as long as the 1-wire Dallas sensor is connected using a reasonably short cable, e.g. 3-4m. When I try using a 20m cable then the LCD display just hangs and no temperature measure takes place. The cable is a regular power cable with 3 wires (no twisted pairs)

I've changed the far end pullup resistor (i.e. close to the DS1820) from 4K7 down to 2K2 and this seems to allow me to use longer cables (10-12m) but it still doesn't work at 20m.

The Dallas 1-wire design guide is mentionning a 100-150m radius value, so I'm confused.

My design is based around a 16F628 @8Mhz.

Anyone with similar "long cable" design experience ?

Best rgds

[CocaColaKid]

I think I ran one around 100 ft or so but I used a twisted pair and the DS18B20-PAR. I also use a 1K pull-up and switch a GP transistor to give power to the device when it does its conversion.

[BrianT]

I use the DS1620 over several (~10) metres. I found I had to terminate the data and clock lines with a 120 ohm resistor and a 0.1 uF capacitor to ground to prevent ringing on these lines which screwed up the data stream. I also put a 10 uF across the DS1620 power to ground pins.

I realise the DS1820 is not the same as the DS1620 but the ringing issue may be the same.

HTH
BrianT