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DIY: Progressive Voltage Indicator

Progressive voltage indicators are devices that provide alerts to indicate when specific voltages have been reached. The alerts are usually visual, though they may include sound. They are useful because they can test the voltage in batteries or circuits. To build a DIY progressive indicator, use LEDs that are connected to a LM339. The LM339 is a quad comparator chip that is used to compare input voltages to a reference voltage. The chip̵7;s role in this circuit is to select which LEDs to turn off when certain levels are reached. The reference level is adjusted with a potentiometer.

Things You'll Need

4 LEDs
LM339
8 1K-ohm resistors
1M-ohm potentiometer
Battery
Power supply
Battery holders
Breadboard
Jumper wires
Potentiometer

Instructions

- 1
  Insert the LM339 into the breadboard so that it faces left, and has its pins straddling the breadboard̵7;s top and bottom sections. All of the pins must be in different columns. Select a row or column on the breadboard to be the voltage source and another row or column to be ground.
- 2
  Connect the pins 4 and 6 together. Do this by placing a jumper wire between the columns that the pins are inside of. Similarly, connect pins 6 and 8 together, and also pins 8 and 10.
- 3
  Attach a 1k resistor between pins 5 and 7. Do the same for pins 7 and 9, and 9 and 11. Connect another 1k resistor between pin 11 and ground.
- 4
  Insert an LED into the breadboard so that its two leads are in separate columns. Insert the remaining 3 LEDs the same way. Each one must be a short distance away from each other, so that their leads do not overlap.
- 5
  Connect a jumper wire between the negative side of LED1 and pin 2. Similarly, connect the negative sides of LEDs 2, 3 and 4 to pins 1, 14 and 13, respectively.
- 6
  Place a 1k resistor between the positive lead of LED1 and the voltage source. Do the same for the other 3 LEDs.
- 7
  Connect one end of the potentiometer to the voltage source, and its middle lead to pin 5. Attach pin 3 to the voltage source, and pin 12 to ground.
- 8
  Connect the power supply̵7;s red and black leads to the voltage source and ground, respectively. Switch its output to 9 volts, and turn it on so that the LEDs will light. To test the circuit, place a jumper wire vertically at pin 10, to serve as the positive input. Place another jumper wire. The two wires function as probes.
- 9
  Touch the probes to the terminals of the battery to be tested. Turn the potentiometer knob to adjust the sensitivity of the circuit. For example, adjust it for the following. All of the LEDs will remain lit if the voltage is 9.0 or higher. If the voltage is only 7.7, the first LED will not light, though the others will. If the voltage is 1.5, all of the LEDs will turn off, but if the voltage is 3.0, only the fourth one will remain lit.

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