Introduction: DIY LED Voltage Tester – Test Any DC Voltage With LEDs!

By Pro Maker 101
About: DIY,IoT, Electronics

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!

Supplies


  1. Old USB Device Case
  2. (Netsetter, Card Reader, or Pendrive – used as enclosure)
  3. MT3608 DC-DC Boost Converter Module
  4. (Used to step up 5V to adjustable higher voltage)
  5. 0.28-inch Mini Digital Voltmeter
  6. (To display output voltage)
  7. 2.2k Ohm Resistor (1/4W)
  8. (Optional – for load or LED indicator depending on your circuit)
  9. Banana Sockets (2 pcs – Red & Black)
  10. (For voltage output connections)

Step 1: Prepare the Case From an Old Netsetter or USB Device


  1. Take an old USB netsetter, card reader, or pendrive.
  2. Use a small screwdriver to remove the two screws holding the case.
  3. Carefully open the plastic casing.
  4. Remove the internal circuit board and discard it.
  5. Use a cutter to cut off the USB plug section from the case.
  6. Smooth the cut edges with sandpaper or a small file.


Step 2: Install USB Plug and MT3608 Module


  1. Take the cut-off USB plug from the netsetter or USB device.
  2. Insert it back into one side of the plastic case where you made the cut.
  3. Adjust and fix the USB plug so that it fits snugly in the case opening (you can use glue or hot glue).
  4. Take the MT3608 boost converter module.
  5. Carefully place the MT3608 inside the case, positioning it near the USB plug.
  6. Solder the + (VIN) pad of MT3608 to the +5V (VCC) line of the USB plug.
  7. Solder the – (GND) pad of MT3608 to the GND line of the USB plug.
  8. Make sure the adjustment potentiometer is accessible.
  9. Secure the MT3608 with glue or double-sided tape if needed.

Step 3: Install the Banana Sockets


  1. Mark two spots on the back of the case.
  2. Drill or cut two holes for the banana sockets.
  3. Insert the red and black banana sockets into the holes.
  4. Glue the sockets in place.
  5. Secure the sockets with screws from the back.

Step 4: Solder Resistor and Connect to Banana Socket


  1. Take a 2.2k ohm resistor.
  2. Solder one leg of the resistor to the positive output (VOUT+) of the MT3608 module.
  3. Solder the other leg of the resistor to the positive banana socket (red).
  4. Solder the negative output (VOUT–) of the MT3608 to the negative banana socket (black).

Step 5: Install Mini Voltmeter


  1. Take the 0.28-inch mini voltmeter (3-wire type: +, –, S).
  2. Drill a small rectangular hole on the top side of the case to fit the display.
  3. Insert the voltmeter display into the hole from the outside.
  4. Drill a small hole near the display to pass the 3 wires into the case.
  5. Feed the wires (+, –, S) inside, ready for connection.


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Step 7: Connect Voltmeter Wires


  1. Solder the black wire (–) of the voltmeter to the input GND of the MT3608.
  2. Solder the red wire (+) to the input VIN (positive) of the MT3608.
  3. Solder the S wire (sense) to the red banana socket (positive output).

Step 8: Close the Case and Add Pot Access Hole


  1. Carefully place all components inside the case.
  2. Close the case and secure it using the original screws.
  3. On the side where the MT3608 potentiometer is located,
  4. drill a small hole for easy access to adjust the voltage.
  5. Make sure the hole aligns with the pot so you can rotate it with a screwdriver.

Step 9: Power and Set Output Voltage


  1. Plug the USB plug into a USB power adapter (5V output).
  2. Use a small screwdriver to rotate the MT3608 potentiometer.
  3. Watch the mini voltmeter display and adjust the voltage to your desired level (e.g., 26V to 30V).
  4. Stop adjusting once the correct output voltage is shown.

Step 10: Test With Probe and Check LED Voltage


  1. Take a test probe or two jumper wires.
  2. Connect the probe ends to the red and black banana sockets.
  3. Touch the other ends to an LED or SMD LED
  4. The LED will light up, and you’ll see the voltage on the mini voltmeter.
  5. Use this to check LED forward voltage or test other components.

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