In this project, we’ll make a DIY LED Voltage Tester using simple and recycled components like an old netsetter case, MT3608 boost module, a mini voltmeter, and banana sockets. This tool lets you test LED forward voltages, check small DC loads, or use it as a compact adjustable power supply. It’s powered by any USB adapter and displays the output voltage clearly on a digital display.
This is a fun, low-cost project that’s perfect for electronics beginners or hobbyists looking to reuse old gadgets!
Step 1: Prepare the Case From an Old Netsetter or USB Device- Take an old USB netsetter, card reader, or pendrive.
- Use a small screwdriver to remove the two screws holding the case.
- Carefully open the plastic casing.
- Remove the internal circuit board and discard it.
- Use a cutter to cut off the USB plug section from the case.
- Smooth the cut edges with sandpaper or a small file.
- Take the cut-off USB plug from the netsetter or USB device.
- Insert it back into one side of the plastic case where you made the cut.
- Adjust and fix the USB plug so that it fits snugly in the case opening (you can use glue or hot glue).
- Take the MT3608 boost converter module.
- Carefully place the MT3608 inside the case, positioning it near the USB plug.
- Solder the + (VIN) pad of MT3608 to the +5V (VCC) line of the USB plug.
- Solder the – (GND) pad of MT3608 to the GND line of the USB plug.
- Make sure the adjustment potentiometer is accessible.
- Secure the MT3608 with glue or double-sided tape if needed.
- Mark two spots on the back of the case.
- Drill or cut two holes for the banana sockets.
- Insert the red and black banana sockets into the holes.
- Glue the sockets in place.
- Secure the sockets with screws from the back.
- Take a 2.2k ohm resistor.
- Solder one leg of the resistor to the positive output (VOUT+) of the MT3608 module.
- Solder the other leg of the resistor to the positive banana socket (red).
- Solder the negative output (VOUT–) of the MT3608 to the negative banana socket (black).
- Take the 0.28-inch mini voltmeter (3-wire type: +, –, S).
- Drill a small rectangular hole on the top side of the case to fit the display.
- Insert the voltmeter display into the hole from the outside.
- Drill a small hole near the display to pass the 3 wires into the case.
- Feed the wires (+, –, S) inside, ready for connection.
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Step 7: Connect Voltmeter Wires- Solder the black wire (–) of the voltmeter to the input GND of the MT3608.
- Solder the red wire (+) to the input VIN (positive) of the MT3608.
- Solder the S wire (sense) to the red banana socket (positive output).
- Carefully place all components inside the case.
- Close the case and secure it using the original screws.
- On the side where the MT3608 potentiometer is located,
- drill a small hole for easy access to adjust the voltage.
- Make sure the hole aligns with the pot so you can rotate it with a screwdriver.
- Plug the USB plug into a USB power adapter (5V output).
- Use a small screwdriver to rotate the MT3608 potentiometer.
- Watch the mini voltmeter display and adjust the voltage to your desired level (e.g., 26V to 30V).
- Stop adjusting once the correct output voltage is shown.
- Take a test probe or two jumper wires.
- Connect the probe ends to the red and black banana sockets.
- Touch the other ends to an LED or SMD LED
- The LED will light up, and you’ll see the voltage on the mini voltmeter.
- Use this to check LED forward voltage or test other components.
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