Simple LED Matrix

Ok sounds good. Should i make each row a chain and then chain all the rows together? Would 6V be enough for 12 be better?

If you want them all on together then yes. The series chains only need a single resistor to set the current btw.

Graham

snipped-for-privacy@yahoo.com wrote in news:1125348994.846715.114230 @z14g2000cwz.googlegroups.com:

I don't think you'll be able to chain 8 LEDs together without using more than 12V. I'm guessing you'll be looking at 16 parallel chains of 4 LEDs each.

This tool might help you:

Joel Moore

I read in sci.electronics.design that snipped-for-privacy@yahoo.com wrote (in ) about 'Simple LED Matrix', on Mon, 29 Aug 2005:

Don't try to use an AC adapter, use a DC one. With a string of four red LEDs in series (never put two in parallel), you need about 6 V for the LEDs, and you need a resistor in series to control the current. To do this effectively, it needs to drop several volts, say 6, so you need a

12 V DC supply.

To run the LEDs at 6 mA (milliamps), which these days is likely to give you enough brightness, the resistor need to be 1 kohm (1000 ohms), and it dissipates 0.036 W (watt), so anything, even a 0.1 W part is indicated. Repeat 16 times and connect all the strings, with their series resistors, in parallel to the 12 V supply.

This means you have a total current of 96 mA, so a 12 V 100 mA supply is adequate, and you may not be able to find one that low, which doesn't matter, anything over 100 mA is OK. You should, however, use a REGULATED

12 V adapter, not an unregulated one which will give you maybe up to 18 V; nice bright LEDs but the resistors then need to be 0.2 W or more

If you are using green or yellow LEDs, or very high brightness red ones, you need less than 1 kohm resistance. If you are using blue ones, you may need up to 12 V just for the four LEDs, in which case you need an 18 or 20 V adapter and a lower resistor value, in ohms:

(Adapter voltage - LED string voltage)/(6 mA)

which can be written as 16.7 x (Adapter voltage - LED string voltage)

--
Regards, John Woodgate, OOO - Own Opinions Only.
If everything has been designed, a god designed evolution by natural selection.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Don't be afraid to do a bit of experimenting with parallel LEDs. The resistivity of many LEDs is high enough that they self-ballast and parallel quite well, especially if brightness matching is not crucial. This also accounts for the absence of series resistors in cheap LED flashlights (that, and the high impedance of small coin cells). I have designs with as many as 42 LEDs in parallel, and they share current quite democratically. YMMV, depending on LED process, luck of the draw, etc. Paul Mathews

As Joel and John said, you'd be better off with 16 x 4 if your supply voltage must be 12V. But if for some reason you must have 8 x 8 then you'll need a substantially higher voltage. And, whatever array you choose, voltage supply will depend on the *type* of LED, as seen here:

--
Terry Pinnell
Hobbyist, West Sussex, UK