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Step 5Science!
This Instructable wouldn't be instructive without science, so here's a schematic diagram I made in the free version of Eagle CAD. The triangle-and-line symbol is the generic DIODE symbol, and the lightning bolt means that LIGHT is EMITTED. Now you know what LEDs are!
There is a general direction to the LED symbol as well; the flat side is closer to the ground, or minus, side, and the triangle base is closer to the plus side. Take note of these directions, as there's another twist coming up.
The V+ symbol shows where the voltage comes in, and the GND shows where the negative end of the battery is, which is by definition zero volts. So, with a 9 Volt battery, LED1 gets 9 Volts on its plus end. (That's called the anode; now don't you feel scientific!) Remember that the voltage at the bottom of of LED4 (that's the "cathode") is zero? Well, if all the LEDs are about the same, then we can assume that the "voltage drop" across each LED is about the same, or about 9/4=2.5 volts. That's a little high for green LEDs, which is why we suggested a slightly depleted 9V battery or a resistor. So let's try it again with 8.4V, giving us 2.1V drop across each LED. That should keep the green LEDs happy.
So, here's an exercise: If v+ is 8.4V and GND is 0V, what's the voltage in the middle?
You give up already? It's just 4.2V.
If you have a voltmeter and want to do more science yourself, try it and see!
There is a general direction to the LED symbol as well; the flat side is closer to the ground, or minus, side, and the triangle base is closer to the plus side. Take note of these directions, as there's another twist coming up.
The V+ symbol shows where the voltage comes in, and the GND shows where the negative end of the battery is, which is by definition zero volts. So, with a 9 Volt battery, LED1 gets 9 Volts on its plus end. (That's called the anode; now don't you feel scientific!) Remember that the voltage at the bottom of of LED4 (that's the "cathode") is zero? Well, if all the LEDs are about the same, then we can assume that the "voltage drop" across each LED is about the same, or about 9/4=2.5 volts. That's a little high for green LEDs, which is why we suggested a slightly depleted 9V battery or a resistor. So let's try it again with 8.4V, giving us 2.1V drop across each LED. That should keep the green LEDs happy.
So, here's an exercise: If v+ is 8.4V and GND is 0V, what's the voltage in the middle?
You give up already? It's just 4.2V.
If you have a voltmeter and want to do more science yourself, try it and see!
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