View Full Version : Controlling an array of LEDs

09-14-2008, 12:11 PM
I am trying to create a project which contains a large array of LEDs, most likely a number in the 100's. I considered using the 40pin Stamp2 microcontroller along with the Parallax Professional Development Board. Many of the LEDs would be connected in series so 32 I/O ports should be enough.

What I'm concerned about though is the voltage supplied. Having 100's of LEDs would require a good amount of voltage, and as far as I can tell, the microcontroller can only handle and supply up to 12V. Is there any way to output more voltage? If anyone has any input to offer, I would appreciate it.

09-14-2008, 02:33 PM
i am sure someone that has vastly more experience the I will come along and correct me if i am wrong, but

to my knowledge the bs2 cannot supply 12 volts, it can source or sink 5 volts but i don't know of any that can do 12volts

it would help to know more about your project

how many leds in series are you planning

how many groups and all that

i suspect that using a driver chip will be needed the number of which escapes me just know, but it is a package

of several darlington pairs that can handle about a half amp at 12volt output using the stamp pin logic to drive the chip

also you could use a 4099be chip setup right to demulitiplex and drive 7 or 8 outputs using only 3 pins off the stamp

and there is likely better demultiplexer chips than the 4099 for your needs, it is just the one i am most familiar with.

it would have to drive the darlington however because it can't handle enough current to do what you want i would suppose.

again, there will be some very bright and intelligent folks that will lead you to more elagant solutions to your project, but i suspect

they will ask the same questions i have and maybe more.

bob g

Dream it, design it, engineer it, build it, and

do what is necessary to make the damn thing work!

09-14-2008, 04:49 PM
Hope this will help you.


Jack Jordan
09-14-2008, 11:21 PM
Interesting link on LEDs

As for the voltage and curreent requirments for 100s of leds, you might consider the TIP12x, (100v, 5A) or the TIP14x, (100V, 10A) darlingtons.

If i'm not mistaken the series are 5v control logic.

09-15-2008, 06:02 AM
Why would you use 100v for a led it's not the volts it's the amps you could lite all the leds you would want to with with 5 volt power supply that can put out say 20amps that would lite a 1000 of them. If you just want to turn on 100 it would take 2 amps at 20mA. If you layed out your leds to lite 20leds from a pin. you use 5 pins on a basicstamp 2 all you need is 5 power transistor like a tip120 and 5 mps2222a that would give you 25amps of led liteing power. Use the transistors to switch the leds on from a 5 volt 3amp power supply .And just 1 more thing to think about 25amps even at 5 volts can kill you. so be carefull with this thing.

Post Edited (be80be) : 9/14/2008 11:14:55 PM GMT

Jack Jordan
09-15-2008, 06:42 AM
The darlingtons are rated for 100v, you dont have to supply that much.

Maybe I am missing something here: Each LED drops ~2v each. Thats 2 1/2 leds for every 5v?

Mike Green
09-15-2008, 07:57 AM
You're missing the current requirement and the fact that there are no fractional LED voltages.

LEDs require an amount of voltage that depends on the materials used to manufacture it and sometimes how they're assembled. This voltage is pretty much fixed although it does vary somewhat with the amount of current through the LED and the temperature of the LED. The graphs for this are generally included with LED datasheets. Red LEDs usually require 1.7V. Blue LEDs usually require something on the order of 3V. Other colors (green, yellow, orange) are somewhere in between.

Most LEDs operate in the range of 10mA to 20mA. They'll product light at lower currents and they may be damaged with higher currents except for devices specifically made for much higher currents.

A Stamp I/O pin generally can handle 20-25mA max. Groups of 8 I/O pins (like 0-7, 8-15) can handle a total of about 50mA. The Stamp chip as a whole can handle roughly 100mA. More than this can damage the chip. The wiring on the chip is not made to handle more.

Handling large numbers of LEDs is usually done with external transistors or external LED drivers which are designed for handling the current involved. There was a project (see the Completed Projects forum) using the Propeller to drive a large multicolored array of LEDs for a video display. You could use some of the same techniques to drive a smaller array at much lower speed with a Stamp.

Post Edited (Mike Green) : 9/15/2008 1:03:36 AM GMT

09-15-2008, 08:49 AM
A led will drop volts but your not going to wire them up in series you wire them in parallel ? I added a schematic the leds need resisters added in front of them but you should be able to get a idea how it would work. I added the resistors to the drawings

Post Edited (be80be) : 9/15/2008 4:39:09 AM GMT

09-15-2008, 10:50 AM

something doesn't look right to me!

how do you limit the current and drop the voltage to the led's in your sketched circuit?

looks like a good way to burn up led's to me, but maybe i am missing something?

bob g

Dream it, design it, engineer it, build it, and

do what is necessary to make the damn thing work!

09-15-2008, 11:07 AM
I said I didn't put the resisters in front of the led's it just to show how you would go about doing it

09-15-2008, 05:01 PM
· For driving high current loads from a Stamp, look at the High Side Drivers developed for microprocessor controlled automotive applications.

They work with up to 26 to 36 volts depending on which one, have current capacities up to 60 amps and can be driven with 5v logic right from an I/O pin.

They can drive inductive as well as resistive loads.

Some examples I've used·would be:


· Darlene

09-16-2008, 09:19 AM
Here you go dig in to this site it tells you all you need to no about hooking up a lot of leds.

09-16-2008, 03:10 PM
As for what be80be 5V 25A being able to kill is in-acurate. it takes 30V .007A before coming real dangerouse. Thats not to say you shouldn't be careful. there is still high line voltage in the power supply that can kill.

Post Edited By Moderator (Chris Savage (Parallax)) : 9/16/2008 3:15:13 PM GMT

09-17-2008, 12:36 AM

Thanks for the sharing the tip about the high-side drivers from the automotive industry!


09-18-2008, 09:21 PM
Do they all turn off and on simultaneously via one control line?

A wise man told me; "All electronics are made to work by magic smoke.

Don't ever let it out as it's·very difficult·to get it back in."