Arduino Circuit Debugging Methodology

Question

I am a mechanical engineering graduate that has been learning more about EE through personal Arduino projects and I am relatively unexperienced in Arduino circuit debugging. I have a circuit (see below) that I have been using with an N channel p30n06le mosfet and push button to heat up a strand of nitinol wire (muscle wire)(In my diagram I have an LED in its place).

(Source)

I have used a 9V battery to successfully heat the wire. To increase the current output and move to larger wires, I ordered two Samsung NCR18650b batteries and soldered two battery cases in series to increase the voltage to around 8.4V. When I substituted the 9V for the battery pack, the wire does not heat.

I am unsure how to debug the circuit and discover the problem. I have measured the voltage across the battery pack and it is around 8.4 V so I assume I soldered correctly. I also have checked to make sure I went positive terminal to negative of the other. Both batteries are new from a trusted retailer and fully charged with an XTar VC2.

I am wondering what other possible errors I could be making in my circuit or debugging methodology that I could perform to find more information on the error?

Any help is appreciated!

Answer 1

You are wondering about some things to try so :

Continuity Tests

Have you done continuity tests at connections within the circuit? I'm not sure if this is breadboarded or not -- if it is breadboards often have connections that are unreliable. But even if it is soldered you could have a cold solder joint that is causing a problem.

Make sure the battery is disconnected or at least it is not on and turn your multimeter to continuity and test along the circuit. It really could be as simple as that. I have had numerous hobbyist circuits that should work only to learn that one place in the circuit (usually due to a breadboard connection) was not connected.

Multimeter : Measure Voltage

Next hook up your battery, turn on the circuit and check voltages across all resistors? Are there any places where you do not get a reading? That could be the problem.

Multimeter : Measure Resistance

Again, make sure the circuit isn't powered up and set your multimeter to Ohm resistance and measure each resistor and see if they match what you think they should be.

Multimeter : Measure Current

Finally, power up the circuit and insert your meter (red and black probes) into the circuit and measure current at different locations throughout. Are the values what you expect? Is there a good current reading?

Most likely if you really try all of these you will find the problem in 30 minutes or so. It'll probably be the continuity one. Good luck.

Here's an image showing how continuity test can be run through the circuit. Start at a location, keep moving one probe through. Of course continuity cannot be tested through some components and you'll have to move the other probe too.