Capacitors Looking Suspect? Build This Simple 555 Timer-Based Tester!
Hardware debugging is tricky, which is why you may want to follow Phil B’s guide to create a simple 555 timer-based capacitor tester.
Electronic components, especially discrete components, are manufactured very well these days and it is quite rare to receive a defective resistor, diode, or capacitor. But it does happen occasionally and it is certainly possible for you to damage a component yourself. A defective component in your circuit can be frustrating to track down, but you can follow Phil B’s Instructables tutorial to assemble a simple 555 timer-based capacitor tester to help with the job.
555 timers are some of the common IC (Integrated Circuit) chips in existence, because they’re so versatile. As the name suggests, the most basic function of a 555 timer is to generate pulses at precisely timed intervals. It doesn’t keep time like the crystal in an RTC (Real Time Clock), but instead generates pulses when the voltage on a trigger pin exceeds the voltage on a threshold pin. If a capacitor is connected to the threshold pin, then the pulse will be triggered when the capacitor is discharged below the control voltage. If, when triggered, the 555 timer recharges the capacitor, you can achieve continuous oscillation. This is a “monostable multivibrator” circuit.
To build this tester, you simply need to take advantage of those operating principles to determine if a particular capacitor is working properly. The capacitor is connected to the circuit using a pair of alligator clips that are attached to the leads. A single LED is connected to the output of the circuit, and should blink at steady intervals if the capacitor is working properly. If the capacitor is damaged, the LED will remain either lit or unlit. As a bonus, the time between blinks is directly correlated to the value of the capacitor and resistors used. A longer interval indicates a higher value capacitor. Phil B’s design lets you select resistors of varying values, so you can test a wide range of capacitors. If the proper resistance is selected, you can simply count how many seconds the LED remains lit to calculate the value of your tested capacitor!