DS18B20 sensors stopped working


My emonpi has been working fine for over a year with six DS18B20 sensors. Recently they stopped reporting any value. After a hard restart they resumed working fine.
Until now. They are not being recognised by the emonpi on boot up. And thus no values. Nothing had been changed, nothing added or updated.

Any ideas? Thanks.

[Confusing first sentence removed - Moderator (RW)]

Welcome, David to the forum.

We have heard reports of sensors failing, of course if only one has failed but it’s preventing the OneWire bus from working, then none will be recognised.

I’d suggest you first take a look generally for physical damage, then look at the connectors (for tarnish or other corrosion) - though after only a year that’s not all that likely; and then try to find if any are working, and take it from there. Bear in mind that they are only detected at power-up of the “emon” part of the emonPi, so rebooting isn’t good enough, it must be powered down and powered up again.

In the heading, you mention emonTx. If you have one, it would be easier to use that rather than your emonPi.

Robert, where did you see his reference to an emonTx?

The only place I saw a “Tx” mentioned was in the line:

For discussions related to emonPi, emonTx, emonBase and emonGLCD hardware and Arduino firmware

which is a "default " that’s created when the category is created.
How it got in his post is another story…

That’s what I was referring to, I did recognise from whence it came. Presumably, it was put there for a reason?

I remember when I created the FAQ a post similar to said line appeared at the top of the then-empty thread.

I thought there probably wasn’t an emonTx, but then I thought it was worth mentioning it just in case David was hinting that he had those things but the temperature sensors were only relevant to the emonPi. Certainly, if he’s got an emonTx, trying the sensors one by one in that and resetting it each time is a lot easier than shutting down and starting up the emonPi each time.

No doubt about it! Faster, too. thumbsup


Thanks for the helpful comments.

For the avoidance of doubt, it is an emonpi that I have. And only an emonpi.

I did try removing all but the first sensor from the line but there was no change. No sensor was recognized on boot up.

I will go through them all systematically later after I have put some work time in.

And the hardware topic line was put in automatically to the post which I left as it was.

Thanks again.

For the avoidance of doubt, it needs to be a complete power off/on sequence for a sensor to be detected.

Robert mentioned that earlier in the thread.
I couldn’t help but wonder if that had been overlooked…

Hi, Yes I realise it has to be a complete orderly shutdown, remove power, and reboot.
A simple reboot will not work.

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Hi, cause narrowed down to connector block from Sheepwalk electronics.
By connecting in a single sensor direct to the emonpi (all connections via RJ45) confirmed no problem on emonpi. Moved that single sensor to first connector block whereupon it was not recognized (all other connections to that block removed). Swapped for another connector block - success. Extended the line to next connector block and again all worked.
The connector block that did not work had accumulated quite a quantity of fluff across the pcb and its solder terminals. It was in use near the hot water tank with stock of towels, sheets, etc. Buried as these things ever are.

Using the dubious connector in place of the transferred block returned the sensor count to zero on bootup.

So I need a new connector block. Not sure there is much to fail in the connector block but failed it certainly has.

As a request for further info, is the recognition of sensors logged in any of the log flies under /var/log?

Thanks again

Thanks all for

I think wrapping the new connector in a plastic bag might be a good idea.

All the temperature reading and conversion happens inside the “emon” part of the emonPi, only the actual numeric values are passed into the Raspberry Pi itself. I don’t think the sketch inside the “emon” front end allows for anything other than an automatic search for sensors, as explained in Learn→Electricity Monitoring→Temperature, neither does it appear to send a helpful error code like the emonTx does, so all I’d expect you to see is values of zero being recorded.

And to clarify - that means any sensor except pulse: voltage, current & temperature.

I’d get an electronics box from Bangood/Aliexpress.

I had wrapped the connector that was moved because it was near the cooker in the kitchen but didn’t think the failed one needed the precaution. Live and learn.

I’m inclined to agree with Brian.
First thought that spings to mind with a plastic bag is ESD damage.


Made in the 80s and kind of cheesy, but still good info.
The elevant part is 5:04 into the clip, but the entire clip is worth watching.