Test Instrumentation

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When working with data acquisition systems, many times a signal doesn't behave as expected.  When diagnosing the problem, it's nice to have a reference voltage to test your inputs.

I made up this quick "MinMax" test box for quickly testing analog inputs.  The MinMax is built from four simple parts, a set of banana jacks for input voltage, a BNC output jack, a variable resistor, and a box.

I have one with a 1K 1 turn pot, and one using a 10 turn 100K pot for testing opamp circuits. VCC can be 3.3V, 5V, 12V, or whatever your circuit needs.  I made one up with a 1A analog meter inline also.

*** Note *** there is not a current limiting resistor inline, or a fuse, so if you short the BNC, you can short your power supply.

 

To use the box:

1) Apply power and ground to the red(+) and black(-) banana jacks

2) Connect BNC to DAQ input, and connect in parallel to voltmeter if needed.

3) Adjust output from 0-100%

 

Here's a schematic:

Here's the unit:

 

Simple, but useful.

Add a micro:bit, some switches, and display, and you have a programmable analog test instrument.

Since you sent me a micro:bit, here's a simple voltage output device program.

If button "B" is pressed, the voltage output is increased, if "A" is pressed, the voltage is decreased.

The voltage is approximated by the LEDs as a bargraph.