18 Make your own Instruments
Suppose you were stuck without access to meters and oscilloscopes? How far could you get with just your microcontroller board to test your circuits?
Measure DC Voltage
A multimeter measures the difference between two DC voltages. One of them might be a ground potential, but it doesn’t have to be. The ADC on our microcontrollers measures only the absolute voltage of an input relative to ground, so we will need to measure two voltages and calculate the difference.
Measure Continuity
Measuring continuity is simply measuring resistance, and beeping if it’s low enough to represent a direct connection, so let’s just add a beep to our resistance measurement whenever it is less than 5% of full scale. That will also remind us to change the scale for better accuracy.
Measure Resistance
The usual way to measure resistance is to run a small current through the load and see what the voltage drop is. We can do exactly the same thing and have our sketch do the calculations.
Measure Transient Voltages
Oscilloscopes can follow voltages up to very high frequencies, faster than the analog conversion rate of a microcontroller, but a lot of important things happen more slowly and we could still watch them.
Adding Displays
One of the things that makes real instruments so convenient is their built in displays so you don’t need to drag along a computer.