[McHUG] Running the Vail Tests with no Parts

[Rich Mitchell]

I was looking through the new QST when I happened to read the Hands-On Radio column.  It was about circuit simulation, a continuation of what he had begun in the December issue.  I dug that out and it told how to download LTspice and use it to model a voltage divider.  The January issue models a common emitter amplifier.  

Anyway, I downloaded the FREE simulator and set up a voltage divider circuit to simulate the problem we encountered in the PICetSat Lite - where we could not use a voltage divider to monitor battery health because the PICAXE reference was its own voltage in.  I set up R1 to 10k and R2 to 4.7k - the values we had in the PICetSat Lite.  I added a DC voltage source that I varied from 5 to 1 volts a volt at a time.  I then divided the divider voltage by the input voltage and the result was a rock solid 31.97% showing how the divider could not detect a change in battery voltage.

Next I substituted D1 for R2, D1 being a 1N914 diode and varied the voltage source as before.  I again divided the divider voltage by the input voltage and the result increased from 10.96% to 45.26% as the voltage decreased.  This shows that using a diode in the voltage divider circuit provides a simple way to monitor battery health in a PICetSat Lite.  The chart is below.

VoltageR2 VdevR2 %D1 VdevD1 %
51.5986431.97%0.54775710.96%
41.2789131.97%0.53632413.41%
30.95918431.97%0.52111117.37%
20.63945631.97%0.4983424.92%
10.31972831.97%0.4525645.26%


LTspice looks like a fun tool to add to a McHUG tool bench and a big help when reading through EE101.  On to amplifiers!

73,
Rich, N3III

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