A very useful votmeter with indicator leds witout the need of power supply! It has 5 indicators for 5 voltage levels (5,9,12,24,30 volt dc)
The kit is based on a quad opamp LM324.
All the needed power is directly from the voltage you measure.
The first led turns on when the measured voltage reaches 5V.
The other four leds are connected to the for outputs of the opamps.
With the help of a voltage divider we can reduce the measured voltage from 0-30 volt to 0-3 volt.
This new voltage is driven to the non inverting inputs of the opamp.
The voltage reference for the inverting inputs is taken from a voltage divider again.
Each opamp operates as a comparator that compares the tow inputs.
If the voltage level comes above the reference voltage ,
the output of the opamp goes high and drives the led that is connected to it.
When the measured voltage reaches 30 volts all the leds are turned on!
Reference Type Value
C1 Ceramic Capacitor 330nF
C2 Ceramic Capacitor 100nF
C3 Electrolytic Capacitor 22u
D1 3mm difussed led Red
D2 3mm difussed led Red
D3 3mm difussed led Red
D4 3mm difussed led Red
D5 Diode 1N4148
D6 Diode 1N4148
D7 3mm difussed led Red
D8 Diode 1N4148
R1 Resistor 1/4 watt 100k
R2 Resistor 1/4 watt 10k
R3-R6 Resistor 1/4 watt 1k
R7 Resistor 1/4 watt 82k
R8 Resistor 1/4 watt 22k
R9 Resistor 1/4 watt 47k
R10 Resistor 1/4 watt 10k
R11 Resistor 1/4 watt 33k
R12 Resistor 1/4 watt 1.2k
R13 Resistor 1/4 watt 1k
U1 QUAD Op. Amplifier LM324
U2 Voltage Regulator 7805
J1 Terminal Block 2 pin
construction help guide
watch the presentation of the kit
Frequently asked questions about the kit
Led Voltometer 3,6,12,24,30 vdc levels indicators
A very useful voltometer based on the lm324 quad amplifier. Every opamp is used as a comparator at the interested voltages. So if you have a power supply and every time you have to measure the output with a multimeter do this project and you are ready to display the interest levels of the voltage.