Hello,
I have the problem that I have 5 DS18B20 temperature sensors in my heating system. Now I have ordered 5 more and wanted to integrate them into the dashboard. The only problem is, if I connect all 10 sensors together to GPIO 4, I don't get a value from any sensor. But if I only plug in the 5 new ones or only the 5 old ones, they are all displayed to me and I also get a value. I use the node-red-contrib-sensor-ds18b20 palette. Unfortunately, it didn't work with others either. can someone help me why it doesn't work?
Show us how you have connected them to the pi. If you have a pull-up resistor what resistance is it?
There is a thing called pin loading. This has to do with how many devices a pin on some device can sink before it becomes non responsive. This number is different for all devices and depends on how much each individual device connected to it draws or consumes and how much the pin can deliver. I don't know what that figure is for a pi or how much each sensor is pulling but you may be over the limit. If that's the case there is nothing to be done as it is an electrical limit. I think @Colin is heading for a misconfiguration and that may be the case. But you may be over the pin's ability to handle the draw.
Thanks in advance for the feedback.
But because of the number of sensors, if I connect an old and a new one, I can't see one displayed and no values.
I'll test that with the other resistor tomorrow.
I have VCC at 3.3V, GND at GND and I have the data pin at GPIO4 with a 10k (may have been a 4.7k) resistor to VCC.
I'll measure it tomorrow and swap it for a different one.
Much too big. Try 1.5k
Though I am not convinced that you will get it to work with 10.
Have you daisy chained as you are supposed to?
Here is the circuit diagram of how I connected it.
I'll try 1.5k tomorrow and report back.
I'm just surprised that when I clamp a new sensor and an old one together, it doesn't work and when I take two old ones or two new ones, it works. Then it can't normally be due to the resistance?!
Hopefully the resistance and wiring will help. But there are a lot of fakes out there that may have a variety of problems. Eg see GitHub - cpetrich/counterfeit_DS18B20: How to tell original from fake DS18B20 temperature sensors.
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That was my first thought!
I bought 2x the same ones from the same manufacturer, there is only a time difference of half a year between them.
I ordered these from a normal good manufacturer from Germany:
Unfortunately, that is not a manufacturer but a re-seller. Amazon sellers are not automatically a good choice. As @dceejay stated, there are a lot of fakes, I have also had a delivery of bad sensors from Amazon.
As others have said, you probably have some fakes and they are interacting in some way.
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