I’m trying to use VM110 with the temp sensor module (VM132) and noticed that the temp value returned is never constant (even over small periods of time).
Measuring the voltage from the temp sensor it does seem constant.
I then tried using the VM110 in test mode using RV1 and Sk2 back in place (and removing the VM132 inputs), and the output shown using the test application jumps +/-1 or +/-2 once the RV1 has been adjusted as the display updates.
Any suggestions on how can I remove this random element?
You may reduce the noise by adding a large capacitor between the analog input and GND.
In the software you may do averaging: Read samples to a ring buffer and calculate average over the samples.
Could you suggest a value for the capacitor that would give the best effect?
Is the problem noise or instability of the circuit?
I’m intending to use the VM110 to control a heat pump. To gain the control required the relative temp returned needs to be accurate to a fraction of a degree, to allow the system to sense the temp beginning to swing up or down, hence I choose the recommend VM132 temp module. I’m finding that the noise is leading to an accuracy of ±1 degree each reading, and this loss of accuracy will undermine the whole system - any help in obtaining accuracy of a fraction of a degree is much appreciated!
You may try 1000uF or larger electrolytic capacitor.
Software averaging will increase the stability of the reading. That way you can get better resolution of the reading than one bit.
I think it must be the board that is bad. When I try reading from the 2 input the noise is significantly worse.
The same voltage measured by input 1 and input 2 results in very different values being returned - should they not both report the same for the same input voltage?
For input 1 when averaged over 1000 reads the result is workable. For input 2 the noise varies so much that the reading is swamped.
Any other ideas? Can I return the board to have it fixed, or is the board just not able to be used for temp measurements?
I suspect RV2.
Is the RV2 in its max position? Does the adjusting of it do any change to the variations?
Is there a difference in the noise and fluctuation of the results between the channels if you remove the temperature sensor and install jumpers SK2 and SK3 and adjust the trimmers RV1 and RV2 to about middle position?
The best filtering you get by adding 10uF capacitors from IC1 pin 3 and IC1 pin 5 to GND. If there is still variations in the result of input 2, it may indicate that the PIC microcontroller may be defective.