On Monday, 30 December 2019 16:17:18 GMT Graeme Gemmill wrote: > 1. All my sensors are mounted on small circuit boards bought from (now > defunct) American company Hobby Boards. I believe the temperature > sensors are powered parasitically, though there is a 5v power injector > to feed a humidity meter. > > 2. They are connected to the Pi by a DS2490 USB-RG45 bridge, and the > software that drives them is based on the Dallas 1-wire software > implemented by a third-party, which has been in use for 10 years.
This adds another device to the system and therefore another possible point of failure. I presume that there is a Hobby circuit board for each of the sensors, which in turn, connect to the DS2490 bridge at the 1-Wire end and the data is transmitted to the Pi over USB? > 3. The second net is completely independent though same set-up, feeding > its data directly to a postgresql database. Presumably via a similar setup to the Temperature sensors? > 4. I see no reason for the values of electrical signals to have changed > unless something has happened to the Pi. In this case, unless I've completely misunderstood the function of the DS2490 bridge, the Pi only has to accept the DS2490 as a USB device; in other words, all the voltages and clock processing for the sensors is performed by the DS2490 chip inside the bridge. It is therefore entirely possible that a component in the bridge has failed (or drifted out of spec) and that is causing your problem. If the USB Port on the Pi works OK when you plug a memory stick into it then the Pi is almost certainly OK. A copy of the Data Sheet for the chip inside the bridge may be found at https://pdfserv.maximintegrated.com/en/ds/DS2490.pdf. > Anyway, this is all a bit moot, since I managed to break one of the > DS1820 leads when examining the board! ;-( > So I'll have to wait for a replacement to arrive before investigating > further. Take care with this in case the fault is taking out sensors. It might be worth also getting a new DS2490 USB-RG45 bridge (although, I notice that they are quite expensive). Alternatively, if you have any breadboarding kit, try the circuit that I originally posted at: http://www.reuk.co.uk/wordpress/raspberry-pi/connect-multiple-temperature-sensors-with-raspberry-pi/ That will isolate the sensors because you won't be using the bridge. -- Terry Coles -- Next meeting: BEC, Bournemouth, Tuesday, 2020-01-07 20:00 Check to whom you are replying Meetings, mailing list, IRC, ... http://dorset.lug.org.uk/ New thread, don't hijack: mailto:dorset@mailman.lug.org.uk
