So I connected a DS18B20 directly to the screw terminal block on one of my emonTx (powered by an AC adapter). It’s generally reporting sensible values, but occasionally, and more often than I’m comfortable with (3 today, one yesterday, 6 the day before …), is reporting high values. Typically single sample spikes, but sometimes the spike persists for multiple samples. The high value are typically over 100°C but sometimes as low as 30°C or so (this is my garage and reality is low single digits) but vary and don’t appear to be ‘magic’ values. So I’m looking for the cause.
My research indicates there can be problems caused by powering down the sensors and not leaving enough time to stabilise the readings. There can be problems from faulty readings that should be caught by the CRC check. And of course there could be a faulty DS18B20 or faulty connection.
But https://wiki.openenergymonitor.org/index.php/EmonTx_V3.4 doesn’t seem to be clear about whether the sensor power is cut when using an AC power source. And the URL given in the sketch source for the library used to read the sensors resolves to a cloudflare security error page, but poking beyond that leads to a library that doesn’t have the string CRC in it. So can anybody clarify exactly what is the actual situation? Or suggest how to find the source of this problem?