I want to monitor my solar thermal system with the Jeenode. I have a solar controller, but I want to see another view of the data as well as see how it correlates to data that I collect.
First up, I need to connect a bunch of DS18B20s. I found a source online for them embedded into a stainless steel tip and waterproofed. They have a 1m cable.
The look like this:
The basic connections are:
- VDD 3.3V
- GND
- DQ
You also need a 4.7k resistor between DQ and VDD
I put together two little boards, one with 5 sensors and one with 3.
The cable pinout is:
Jeenode Code
I prefer to hard-code the ROM addresses for each sensor into the code so that I which sensor goes with which reading. It is an annoying part of the OneWire protocol that you cannot easily find out which sensor is first on the bus.
I’d use a smaller resistor when you have a source of 3.3v
Curious as to why. The datasheet suggests a 4.7k with VCC of 3-5.5V. I’ve used a 4.7k with 1 or 10 DS18B20s and haven’t had a problem running at 3.3V.
Interested in your experience.
You were right. It works fine for up to 10+ DS18B20 sensors. When I added another 10, it stopped working. I changed the pullup to a 2k and now I’m reading 20 sensors connected in a linear topology with 60m of cable (3m drops for each sensor, a few cm between each connection).
Thanks for your insight.