Also resistors are marked with coloured bands for the numbers - it takes a little to accustom yourself to the system but it works better than trying to print tiny numbers on them!
Google colour codes & print it out & stick the chart up above your bench. If not fully sure check with a multimeter on ohms range.
Also be aware that LEDs are polarity sensitive & WONT work connected in reverse
3 ways to tell
1/ the longer leg is positive
2/ the flat on the body is on the negative side
3/ looking through the body the larger "electrode" is the negative
The battery pack you have is +3.2 volts, which is correct since *unloaded* batteries are typically 1.65V and are 1.5V when loaded down.
Now in order to hook up (4) LEDs with a (minimum) forward voltage of 2.2V, you will need 4 * 2.2V = 8.8V (minimum) as a voltage source. Therefore you would need (3) dual AA battery packs that are connected in series to get 9.6V to work properly.
Next you will need to control the current thru each of the LEDs that are also connected in series. The resistor would be need to be the voltage divided by the current from Ohm's Law as follows R = V / I = (9.6V - 8.8V) / 10mA = 0.8V / 0.010A = 80 ohms
With this solution you can use (1) switch to turn off all the LEDs.
An alternate way to power the LEDs is when each of the (4) LEDs are in parallel to the single 3.2V source. Since the voltage drop of each LED is 2.2V, the resistor for each LED would be R = V / I = (3.2V - 2.2V) / 10mA = 1.0V / 0.010A = 100 ohms
Now you would need a switch to the batteries that is in series will all (4) LEDs that are in parallel to each other with their separate 100 ohm resistor. Notice that the batteries will not last as long with the LEDs in parallel as they would with the LEDs in series. The series combination is more efficient, but requires a higher voltage.
LEDs do not give off heat, but the resistor might. However, the current of 10mA is not enough to create any danger.
Lee has good answer for circuit
As far as the heat produced, yes LED's do produce heat but it reaches a constant level after a minute or so and does not get any hotter. So if you can put a bulb against your face after running 10 minutes and not feel overly warm, it will be safe on fabric also.
LED's use approximately 1/25th to 1/30th the amount of wattage as a incandescent bulb for the same amount of lumens, so it will also have 1/30th of the heat output. So if a couple of AA batteries have a few watt hours of power available then that means the heat produced is a few watts spread over 100 LED's and over two hours. That is less heat than the sun strikes your face at 4 o'clock. So the heat build up appears insignificant
Do this connection....
+3.2V ---> 100 ohm resistor -----> LED ------> negative from battery.
Make four circuits as above to light up 4 LED. Make more same circuit to light up more LED.
With AA cell, it is able to light up 100 LED at the same time for one to two hours.
For full brightness obtain from your LED but shorten its life, replace 100 ohm with 68 ohm.
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Hi, I've been trying to google-educate myself but I want to make sure of what I'm doing and ask for some expert advice, if we've any in the audience. :)
I have a battery case that takes two AA batteries (energizer if that matters), I've checked on my voltmeter and I believe it gives a DC current of 3.20v (if that's way off I may be using my voltmeter incorrectly...) And the LEDs I have are 5mm Nexxtech LEDs, which from searching I've found this information on them: 5mm (T1 3/4): Forward Voltage 2.2 V, Forward Current 10 mA (max 15 mA).
Now I want to hook up 4 LEDs to this battery pack, to be continuously illuminated. I have also got a pack of 1/4 watt 5% resistors. On the back of the pack it lists a whole slew of specs, apparently there are two of each type, but I'm not sure what the numbers mean, or how to differentiate which resistor is which. (see the summary of http://www.thesource.ca/estore/product.aspx?language=en-CA&catalog=Online&category=Resistors&product=2719018 for specifics)
I would like to know how many of which type of resistor will I need to use to run these LEDs off this battery pack and where in the sequence do I need to put them? Also, should I split four wires off from the main wire out of the battery terminal to connect to each LED (and four wires back to the neg terminal) or can I place the LEDs in sequence to one another?
Any answers, and/or explanations to these answers would be absolutely wonderful.
(Also, as this is going to be close to my face for an extended period of time, and closely laid against fabric, do LEDs give off ANY heat? I know they don't give off appreciable amounts of heat, but say after several hours of continuous use? I want to be sure I cover all my bases on fire hazards when working with electronics.)
