Make a Voltage Divider Circuit
When making a portable circuit, such as a remote control, you may need to use a smaller voltage source than you can usually find off the shelf. Many simple electronic components can only withstand 5V, even though one of the most common voltage sources for this type of circuit is a standard 9V battery. This article will show you a simple way to turn a 9V battery into a 3V source for your portable circuit if it does not draw much current.
Steps
- Connect one lead of the 20-ohm resistor to the exposed part of the red lead of the 9V battery snap-on connector using an alligator clamp.
- Repeat Step 1 to connect the black lead of the snap-on connector to one lead of the 10-ohm resistor.
- Twist together the free end of each resistor. This will be the easiest way to make sure that there is a solid connection between the resistors.
- Clamp the last alligator clamp over the twisted leads of the resistors to ensure they stay in place.
- Connect the snap-on connector to the 9V battery so that the red wire is connected to the positive (+) terminal and the black wire is connected to the negative (-) terminal.
- Hold the negative (black) lead of the voltmeter against the alligator clamp touching the negative (black) lead of the snap-on connector.
- Hold the positive (red) lead of the voltmeter against the alligator clamp holding the twisted resistor leads in place.
- Turn on the voltmeter. The screen should read 3V.
- Use the connection where the twisted resistor leads are located as the positive voltage terminal for your circuit. The negative terminal of the battery will still be your negative source for the circuit.
You now have a voltage divider for your 9V battery.
Tips
- You must also take into account any loading the external circuit may have on the divider.
- Be Careful.
- As you work with different types of circuits requiring a voltage divider, the schematic to the right can help you develop different output voltages for this application. The equation
Vout = Vin * (R2 / (R2 + R1))
is the equation describing how the output voltage is related to the input voltage in this type of circuit. Vin is written as 9V in this equation for a 9V battery. - The divider shown places a huge drain on the battery. From Ohm's law we have: (9 volts) / (20+10) ohms = 0.3 amps. Your battery will not last long with these resistors attached. Also, the 20 ohm resistor will dissipate 1.8 watts, so use at least a 3 watt power resistor for it.
- A better choice of resistors would be the same ratio but higher values, like 200 ohms and 100 ohms, but then there would be more loading (lowering of the voltage) from your device. The best choice would be to buy a small battery clip allowing two 1.5V batteries to be placed in series, producing about 3V with no divider necessary and no loading (and much longer battery life).
- This type of circuit can easily be created on a standard prototyping board, but clamping the components together is sufficient for quickly assembling a voltage divider.
Warnings
- The values chosen here waste a lot of power. The resistors generate a total of V2/R = 92/30 = 2.7 watts, so they could get very hot. Your battery voltage may sag well below 9 volts due to the heavy load even without any device connected to your voltage divider.
- Be sure to unhook one end of the voltage divider (or unplug the battery) when not in use to prevent your battery from draining.
- You should always use caution when working with electrical devices that plug into a wall outlet to reduce the risk of electrocution. However, there is not much danger of electrocution from a 9V battery.
Things You'll Need
- Standard 9V battery
- 1-9V battery snap-on connector
- 1-10ohm resistor, 2 watts or higher dissipation capability
- 1-20ohm resistor, 3 watts or higher dissipation capability
- 3 alligator clamps
- 1 digital voltmeter
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