Simple Light Emiting Diode Circuit

First A Series Resistor Circuit With Ohms Law Examples...

WARNING: This is not a "wow look at that" circuit, but it's a basic electronic circuit that's really important to understand. This circuit is simply two 1000 ohm (1k) resistors hooked end to end (in series) across a 9 volt battery. Nothing lights up or makes a noise, but here's what we can determine about it.

The total resistance of the circuit is 2000 ohms (1K+1K=2000) and we know the applied voltage is 9 volts so using ohms law (current=voltage divided by resistance) the current flowing is .0045 amps. Next we can determine the voltage present across each resistor. Again ohms law says voltage equals current times resistance so the resistance of the resistor is 1000 ohms and the current is .0045 amps so the voltage is 1000 times .0045 which equals 4.5 volts. There is 4.5 volts present across each resistor.

When you understand this, move on to circuit 2.

The Series Resistor Light Emitting Diode Circuit

simple light emitting diode circuit project
If you ever took a computer programing class, one of the first programs you wrote displayed "Hello World" on the screen. Well this circuit is almost the same thing in basic electronics.
Take a look at the circuit to the left. It's a simple series circuit with a battery, resistor and L.E.D. (light emitting diode) all in series. The ground wire or common makes the circuit complete.

Here are some typical values for the series current limiting resistor. If the input voltage is 9 to 14 volts, then use 1000 ohms. If it's 5 volts, use 470 ohms. If you want a brighter light, use a smaller value resistor, but be careful, if you go too low. Too much current will flow, you will destroy the diode junction and the led will fail. Since led's consume such little power you can use a resistor with a very low power rating, 1/4 watt or less. This also keeps the physcal size of the resistor small.

Light Emitting Diode Circuit Construction

First lay out the parts. You should have a 9 volt battery, a 9 volt battery connector, a 1000 ohm resistor and a light emitting diode. Start with the led. All diodes have a anode and a cathode, determine which wire is the cathode. There's some kind of indicator, one lead can be longer or a small flat on the side of the led can mark the which lead is the cathode.

Now connect the cathode to the black wire from the battery connector. Solder them or use a circuit breadboard. Next the anode connects to one lead of the 1000 ohm resistor and the other lead connects to the red wire from the battery connector.

Now for the fun part, connect the battery and the light should light up. If nothing happens, take a close look at your connections and make sure they are all making contact. Then if nothing, reverse the connections to the led. If your led still doesn't light, then your battery is dead or the led is. If there's a problem, 99.9% of the time it's because the led is in backwards.

There it is, your light is on, the circuit is working! If you placed a small switch in series with, let's say the 9 volt battery and the 1K resistor, you can control the light off or on. We will do that with the next circuit, only we will use a transistor and not a regular switch.

This circuit is covered in more detail in book two of my beginning basic electronics program.

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