multiple ds18b20 sensors = not working

Other Hardware Sensors
1

I am hoping someone can assist me with an odd ds18b20 issue :grin:

I have 3 ds18b20 sensors that I bench tested by manually wiring them all 3 to power then the signal pin of each went to a breadboard that had a 4.7k resistor between them and a pin on my arduino. It worked great, all 3 sensors registered temps at the same time.

After that I wired two of the sensors up on the end of the same cable (sharing power/ground/signal) and connected it and confirmed it worked as expected (two temps shown). When that was done I wired up the final sensor and confirmed it also worked as expected.

Unfortunately what is not working is having both cables (all 3 sensors) connected at the same time. Either one works by itself but as soon as I plug the second signal connection in the arduino acts like it cannot see any sensors.

FWIW I am using the onewire example code and an arduino mega connected to pin 53.

Any ideas?

2

The 4.7K resistor does not go "between" the DS18B20s and the Arduino pin, it's a pullup resistor from the data pin to Vcc. Any chance of posting a schematic?

3

Dropped down to a 1k resistor and it is working now :slight_smile:

4

This is the wiring schematic I used: http://bildr.org/2011/07/ds18b20-arduino/

Cheers