LED Component Tester with Torch

Here is a simple tester for Hobbyists. This LED Component tester can test the integrity of electronic components from resistors to ICs before soldering. It reduces the job of testing the components using multimeter. The tester gives LED indications about the Good or Bad conditions of the components. A White LED torch is added to verify the value of the components if light is not sufficient.

The circuit layout is straight forward. Two bipolar NPN transistors are used to drive two LEDs based on their base bias. When the tester is switched on through S2, Red LED lights because T2 gets base bias through R2. At the same time, Green LED remains off because the base of T1 is floating .

When a component is placed between the Probes, electrical continuity establishes and T1 gets base current through R1. When T1 conducts, Green LED turns on and Red LED turns off since the base of T2 is grounded when T1 conducts. This indicates that the component under test is good. In short Green LED lights only when a good component is connected to the probes. If the component is bad, probes will not get electrical continuity and T1 remains off. In this state only Red LED light indicating that the component is bad. Test procedure is given below.

LED Component Tester Circuit diagram

Test Procedure

  • 1. Polarity
    Connect Red probe to positive track of circuit board and Black probe to test point. Circuit board under test should be ON
    Green LED ON – Positive supply. Green LED OFF and Red LED ON – Negative supply or No power
  • 2. Continuity
    Connect both Red and Black probes across the test points
    Green LED ON- Continuity. Green LED OFF and Red LED ON- No continuity
  • 3. Resistor. 1 Ohm to 500K
    Connect Red and Black probes on either side of Resistor
    Green LED ON- Resistor OK. Green LED OFF and Red LED ON-Resistor burned
  • 4. Capacitor Electrolytic
    Red probe to positive and Black probe to negative of capacitor
    Green LED ON and gradually fades and then Red ON- Capacitor Good. Red LED always ON- Capacitor bad
  • 5. Capacitor Disc
    Same as above.Probes can be connected either way round
  • 6. LED, Diodes, Photodiodes, Infrared diodes
    Red probe to Anode and Black probe to Cathode
    Green LED ON – Good diode and LED. Green LED OFF and Red LED ON- Diode or LED bad
    Change the direction of Probes. If the Green LED ON diode or LED is Open
  • 7. LDR
    Red and Black probes at the leads of LDR
    Green LED ON and Red LED OFF. Mask with hand. Green LED turns OFF-LDR good

Probes with Crocodile Clips


Join the conversation!

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  • Stuart

    I built this design of the LED Component Tester with Torch diagram. It turns out that the green led and the white led light up perfectly while the red led does not turn on when it is turned on, and even when testing the components in the test, the red led does not light. How to solve this problem?

  • leftywi

    Breadboard this circuit from yesterday. Works for continuity, Maybe I was doing something wrong. I checked my layout several times.component testing not to hot. Red led never goes out.

  • Ingrid Bjorklund

    Did you know that our CFL light bulbs are very toxic with Mercury? I didn’t until someone in the office asks me to properly recycle the CFL bulbs because these bulbs have Mercury on it. From there on, I told my family that we have to get rid of the CFL and have something better like LED light bulbs. The LED bulbs are made from silicon which is just basic sand. Did a lot of reading, everyone recommends these LED bulbs. Non-toxic and save for your family. Glad we found this healthy product.

    • purehash

      Did you know mercury is to dense to escape the glass unless they are broken, did you know that is such trace amounts that your more likely to get sick from mercury by eating fish?.. Did you also know that the new “high efficient” “high power” LEDs actually draw more power then a CFL for the same amount of light input? And did you know that those high power super bright LEDs actually use arsenic in the manufacturing prossess? Arsenic is more dangerous for your health then mercury. Also a light bulb is the last place you should be concerned about safety.. Have you had your furnace inspected lately? If its over 10 years old there is a good chance your heat exchanger could be cracked and little do you know is your breathing in carbon monoxide all day long.. Have you ever used a microwave oven? Do you know what kind of radiation it produces? And how harmful it is to even be in the same room as it when it’s running? Have you ever watched an old cathode ray tube television? Look on the back of it and read the radiation hazard warning… Do you realize how many radio waves and radiation is in the air that you live in? Inside, outside left right and center? How do you think your radio works? Guess what, it works on the same principals as a microwave… The microwave oven was accidentally invented when a cup of water infornt of a test radio transmitter started to boil. Meaning your exposed to more crap every day then you should even worry about…. Basically, every day of your life your in a microwave oven, bein exposed to microwaves, radio waves, and many other types of radiation. The LAST Thing you should be worrying about is a little CFL bulb.