Adding an extra thermistor

  • Thanks Ian will try it, have a print running right now, good idea though. although why the bed and hotend work without them is still a mystery.

  • Print wasnt looking good so I cancelled it.

    With M305 P2 T100000 B3950 R4700 in use for H2

    It now reads 7841.8 deg C, so whilst its not fixed it has changed something, though it seems to make no difference whether the thermistor is attached or not.

  • administrators

    You said that it is a second hand Duet WiFi with a fault on the H0 thermistor channel. What I suspect is that it has experienced some trauma that has damaged the ADC multiplexer in a way that affects more than one channel. I suggest you try the remaining thermistor inputs on the expansion bus (with a 4.7K pullup to +3.3V again) to see if one of them works. Failing that, you could switch your hot end to a PT100 so that you can use the E1 thermistor channel for the chamber temperature. Or find someone who can replace the processor (user W3DRK can but he lives in the US).

  • Dj is much closer to you than the states David he is in Bristol

  • David thanks for the advice I'll try the other channels. It's no problem really, it prints beautifully and I got it for a swap for a few piezo modules so I didn't pay full price by any means. I do have a pt100 board and sensor from e3d but I suspect that connects via a thermistor input so I might invest in a duet pt100 daughter board if none of the other thermistor channels work.

    Ian just wondering why use thermistors to monitor your drivers/processor when those heater channels are built in?

  • @DjDemonD:

    Ian just wondering why use thermistors to monitor your drivers/processor when those heater channels are built in?

    I only monitor the step[per driver chips, not the processor. I did it a long time ago, before anything was implemented in the firmware. AFAIK, the driver chips only report a high temp alarm and I don't know what temperature that is set at. I want to keep things cool and turn on fans, well below any high temperature warning threshold so I use 45 deg C as the threshold above which the fans come on.

  • administrators

    The driver chips flag a temperature warning at nominally 100C and report shutdown at nominally 150C. But as with most silicon temperature sensors that are not laser trimmed, there is quite a wide tolerance on these figures.

  • Hi Ian that makes sense, I'd want to fire up the fans before I hit 100 deg C for sure. Though I find one 40mm fan blowing under the board which is vertically mounted seems to keep it pretty cool. I'm moving a little less mass around though.

  • Simon,

    I have both the duet and duex5 mounted vertically one above the other so that their Vin terminals are opposite each other and close together if you get my meaning. I have an 80mm fan blowing air on to the back of each board and each fan is controlled via a thermistor stuck to one of the stepper chips. The fans are virtually silent but not particularly high flow. Today, I've seen the highest ever chip temperature at 56 degC (measured at the surface you understand) with the ambient in my study at 35 deg C. That was on one of the XY steppers on the duet main board and pushing a print speed of 260mm/sec with my heavy gantry. (Yes you did read that right - a print speed of 260mm/sec - not pretty but doable - blog post and video coming soon).

    The duex5 only drives extruders and I've never yet seen the chip get above 45 degC to trigger the fan.

  • Just to finish this of by saying I ordered the pt100 daughter board (hopefully nothing is amiss with that system). I tried H7 but when I enabled it as my second tool numbered 99, in tool definitions the DWC was now displaying 7 tools of which 4 (h2-h5) showed 1970 deg C and 2 (h6 and H7) error with or without a thermistor attached, the two working ones are handily bed and h1. So thanks for the advice but yes it seems as though something is amiss with the adc system though thankfully not the heaters, motors or anything else.


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