I have this diagram: enter image description here

The datasheet specifies I should bias the COMM+ line around 1.5V. However, when I measure the voltage at TP1 with the oscilloscope probe connected to ground, the output from the oscilloscope is always 0V (i.e Ground)

enter image description here

I want to understand which way the current flows in the given circuit and what voltage I should see for every division.

The main current source is coming from 3V3. The other source is signal coming from the Coil attached to C23 and R18.

I am trying to get 1.5V at COMM+ through a resistor voltage divider.

  • 4
    \$\begingroup\$ However, the output from the oscilloscope is always ground. ... this makes no sense ... what output are you talking about? ... what does an oscilloscope have to do with the question? \$\endgroup\$
    – jsotola
    Oct 24, 2020 at 1:05
  • 3
    \$\begingroup\$ Your circuit is missing much needed information. For example, no power sources are shown. No output is designated (where are you connecting your oscilloscope?). Current flow is normally not measured but voltage levels are. You need to revise your question so we know what you are expecting and what measurements you have made so far. \$\endgroup\$
    – Barry
    Oct 24, 2020 at 1:59

2 Answers 2


There is some missing information in your question. In any case, if you are wondering how you can calculate currents flowing through circuit branches and voltage differences across nodes you can use the constituent equations of the devices in your circuit and apply Kirchhoff's laws. Furthermore, in complex linear circuits you can apply mesh analysis.

  • \$\begingroup\$ Hi. This was really useful and made me think that my computer science degree is insufficient and I should bring up my high school electronics physics lectures. However, I did not solve the problem through this. I added an update to the question now. This was very valuable for me, however. \$\endgroup\$
    – bem22
    Oct 25, 2020 at 12:10
  • \$\begingroup\$ If you are just trying to polarize the circuit (i.e trying to bias COMM+ at 1.5 V), things are pretty simple. You should only have one current flowing from 3V3 to ground through R19 and R17. That's because capacitors are open circuits at DC. If TP1 is 0 V might be because you are tying COMM+ to ground somehow. \$\endgroup\$
    – dpalo
    Oct 26, 2020 at 10:33
  • \$\begingroup\$ YES! I solved this before your answer, and, indeed, the divider was not working correctly. It took me desoldering the resistors (and the capacitor) and trying them component by component starting at 3V3. Thanks for your suggestions \$\endgroup\$
    – bem22
    Oct 26, 2020 at 16:07

Current flow direction is kind of a convention. It is common to say that current flows from positive/higher voltage to negative/lower voltage.


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