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DIY Simple LED Voltage Level Meter

LED voltage level circuits provide visual alerts to indicate whether a certain voltage has been reached or exceeded. They may or may not show the actual amount of voltage being measured. Some of their applications include battery testing and high voltage warnings. A DIY simple LED voltage level meter can be built using a resistor, a zener diode, and an LED connected in series. The purpose of the resistor is to prevent too much current from coming into the diodes, to prevent their destruction or damage. The zener is used to provide a reference voltage. The LED functions as an indicator that will light up when the desired voltage is reached or exceeded.

Things You'll Need

Zener diode datasheet
Solderless breadboard
3 volt battery holder
9 volt battery holder
330-ohm resistor
1N4735 or 1N5234b zener diode
Green LED
Jumper wires
2 1.5 volt AA batteries
9 volt battery

Instructions

- 1
  Study the datasheet for the 1N4735 zener diode. It shows the diode has a power rating of 1 watt and provides a reference voltage of 6.2 volts. The 1N5234b has the same reference voltage, but is rated at 0.5 watts.
- 2
  Insert the red lead of the 3 volt battery holder into one of the holes alongside the red stripe at the top of the breadboard. Insert its black lead into one of the holes alongside the blue stripe at the top, and label this ground, or zero voltage. Alternatively, select two columns, label one positive and the other ground, and add the battery holder to them.
- 3
  Attach the resistor to the breadboard so it is parallel. Insert a jumper wire from its left side to a hole near the breadboard's red stripe. Insert the negative end of the zener, which is the end with the black mark, into the same column that the resistor's right end is in. When the zener diode is connected this way, it is called reverse-biased. The right side of the diode must fall into a different column.
- 4
  Insert the positive end of the green LED, which is the side with the longer lead, into the same column that the right end of the diode is in. Attach the right side of the LED to one of the holes near the blue stripe. Do this by inserting a jumper wire between the LED and the stripe.
- 5
  Place the batteries inside the holder. The LED will not light, because the voltage level of the circuit has not been exceeded.
- 6
  Remove the 3 volt battery holder, and replace it with the 9 volt one. Add the battery to the holder, and the LED will light. This is because the voltage level of the circuit has been exceeded.

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