Need mentor for electrical projects

[wayacoyote]

I've a very limited experience in electricity (I can wire a house, repair a lamp, and do continuity testing... very basic, I know). I've been post-poning some projects hoping to find someone who'll coach me in them. Nothing that would fry myself or burn a house down, I'm just trying to get some LED's to run off a car battery for example.

Waya

[Jim Fischer]

You want to search Amazon and ABE books for the
various "cookbooks" written by the Blacksburg
Group, and published by Sams.

Here's a "catalog" of sorts:
http://www.bugbookcomputermuseum.com...ok-Titles.html

The 555 Timer, Phase-Locked Loop, and OpAmp books
are classics, and contain all sorts of handy
little circuits that you can copy, adapt, and
find useful. They date from the 1970s, but
I still have my copies, and find them useful.

[nsmith1957]

I have a number of years work experience in Electronics/Electrical, as a technician. Your LED example is a very simple application.

Wire a resistor (700-750 ohm range) in series with LED. This limits current to the 15-20 mA range for a 12 Volt source. Which is what most LED's need to operate.

[David Stewart]

nsmith,
Would that be one resitor per LED or could you run a string of them?

[nsmith1957]

You could run a string of them (series), by reducing the value of the resistor. Each LED will take about .7 volt to bias it, which reduces the current as each LED is added to the string (dimming all).

If you parrallel the LED's with one resistor, the LED's will split the total current between them and get dimmer. Also, each LED will bias at a slightly different voltage and will cause the current to split unequal.

For ease of setup and operation, as long as space was not an issue, I would just use 1 resistor for each LED. Resistors are cheap.

[Edit] If you are using a LOT of LED's that are on at the same time. From a power usage standpoint you would string them together in series and use the appropriate size resistor to limit the current to the 15-20 mA range.

[size="1"][ January 06, 2007, 03:41 PM: Message edited by: nsmith1957 ][/size]

[Jim Fischer]

There are LEDs with built-in resistors that can
be directly attached to common voltages (5 VDC,
12 VDC, 15 VDC, perhaps others).

Check out Digi-Key and the other online electronic
supply houses.