I want to test my Hall sensor and injectors with an LED light. I know the recommendation has been a 3.3v LED and 470 ohm resistor in series, but all I could get was a 2.2v light. What resistor am I going to need? I picked up a 40 pack of assorted resistors, so I sure hope in there will be the one that someone here is going to recommend.

This is not rocket science.

A 2.2v LED is rated for 0.02 amps. you have to drop the voltage by 10v. To calculate the value of the resistance, use the ohm law formula: Resistance = Volts divided by Amps = V/I = 10/0.02 = 500 ohms.
Your source of power being the battery, the voltage is not exactly 12v. If the engine is running, the alternator will deliver up to 13.5v.
At 13.5v, you should drop the voltage by 11.3v. The value of the resistance will be 11.3/0.02 = 565 ohms
In practice, anything between 470 or 560 ohm will work for the common LED requiring 2.2 volts

The two leads are called: a (or +) for anode and k (or -) for cathode (yes, it really is k, not c, for cathode). The cathode is the short lead and there may be a slight flat on the body of round LEDs. If you can see inside the LED the cathode is the larger electrode (but this is not an official identification method). The resistor has to be installed on the anode (+).

How do you know all this stuff?

Should we go into colour codes for the resistors although the multimeter should put you in the ballpark.

The kid at 'The Source' where I bought the resistors showed me how to read them, but I like Phil's idea better. I just have to go through 40 of them to find the one I want (40 for $4)...

Here is a very nice small free software to give you the color code for a resistor.

Bert

One minor issue it does not matter which lead the resistor goes on the LED will not be affected. One can also purchase for very little money a 12 volt regulated LED intended for car use which is tolerant of the voltage swings on a car or bike which needs no resistor and can be incorporated into a voltage test light instead of a filament lamp usually inside them. The LED can also be put across the injectors and because the turn on and off so quickly one can easily see if the injector is receiving a stream of firing pulses. All in all a handy diagnostic tool to carry on the bike. As is a cheap digital meter.
Regards,
K-BIKE

Or the old fashion way, memorization.

Politically incorrect diddely

When I was taking electrical engineering, we used a rather politically incorrect diddely to remember the order of colours. It probably is less used nowadays. It was a very male oriented profession in the day. It worked because I've remembered the colour code to this day using it.

It's 2010, do we still say this stuff?

Also, Wattage might need to be considered...
20mA through say 470 Ohms (P=I squared x R) approx = 200mW
My 2 Ohms worth!...

Ulrich_Grabau wrote:My 2 Ohms worth!...

And what would be the color of your resistance? faded?

Lets not confuse people. 470 to 560Ohms is what you need.

robmack wrote:Or the old fashion way -- memorization

I'd love to comment, but this is a public forum and I would have to moderate myself!
This is just a 'funny' way to remember the order of the color code. We cannot always take statements to the first degree.

To reply to K-Bike, you are right about the resistance being installed on any lead.
Using the Anode is just the way that I always use to regulate the voltage. Just my choice.
Sorry about this 'misinformation'

Here is the basic of electricity. It applies to your bike, car, house........
Electricity is something that you cannot see, but if you touch it you feel it. Why is that?

Using the following triangle makes an easy way to determine the relationship between voltage, current and resistance when making Ohm's law calculations. Just cover the unknown quantity to determine the needed calculation.
As Ulrich_Grabau stated, we could go further, but these basic formulas should be enough for everybody's needs:

E = Voltage (pressure) in volts
I = Current (flow rate) in amperes
R= Resistance (friction) in ohms.



The interpretation of this triangle is:
E=IxR
I= E/R
R=E/I

alles klar? (Yes we are riding a panzer and when I talk to my bike, I sometimes speak German to her -she's a lady-) Alles Klar means "all clear" in German.

Ah yes, the old Ohm's Law. In Oz industry we (Fitters) have a saying about electricians - What's the difference between a computer and an electrician ? Answer - you only have to punch the information into a computer once.

Dennis wrote:Ah yes, the old Ohm's Law. In Oz industry we (Fitters) have a saying about electricians - What's the difference between a computer and an electrician ? Answer - you only have to punch the information into a computer once.

Now Now that is unkind as I am both. I did an apprenticeship (for want of a better word) with the old PMG as a tech and then an Adult apprenticeship with Hornibrooks as a fitter in marine engineering from 73 to 76 so who ya gonna punch now Nah nah nah nah nah nahhh