[cpw]

All right guys. Keep in mind that I'm a total moron when it comes to cicuit design, schematics, etc.
I'm trying to help my daughter build a school project (a robot) and we want to put some lights on it. I got a little assortment pack of LEDs from Radio Shack and I want to hook up 7 or 8 of 'em to a battery with a switch and, if it's not too tough, to make 'em blink.
I did buy a little "Blinking LED Module" (Radio Shack part# 276-299) which has a battery pack w/ a switch and a red LED that blinks. It takes 2 AA batteries so I assume they're in series and it's a 3v deal. The assortment pack of LEDs is part# 276-1622 and no voltage or amperage values are listed. There are 20 LEDs of various colors in the package.
Can I just cut one of the wires from the battery pack and insert more LEDs in the circuit? Should they be in series or in parallel?
Do I need to start over or can I make this thing work?
Thanks for helping a poor dad.
CPW

 

[DolbyR]

i believe you could make that and put the leds in parallels but i'm not quite sure, so lets wait somebody wizer to confirm.

 

[grasshpr]

The LED's should be placed in parallel connection with the power supply. Each LED should have the same voltage applied to their terminals otherwise in a series connection, you will see voltage drops after each LED terminal. This will result in a series of LED's with diminishing light output.

One concern: Do you know if they have a resistor somewhere with the battery pack or is it on the LED assembly? This is typically placed in the circuit to control the current applied to the LED's. Without it, the LED's may fry.

If it is with the battery pack than you shouldn't have any problems. However, if the resistor is on the LED assembly then cutting the terminals to this assembly and connecting your LED's to the batteries may short out your LED's. You might want to check that out before connecting anything. Good luck!

 

[mono]

Quote:

Originally Posted by cpw All right guys. Keep in mind that I'm a total moron when it comes to cicuit design, schematics, etc. I'm trying to help my daughter build a school project (a robot) and we want to put some lights on it. I got a little assortment pack of LEDs from Radio Shack and I want to hook up 7 or 8 of 'em to a battery with a switch and, if it's not too tough, to make 'em blink.

The problem with an LED assortment pack is that there is the potential that several (if not all) of these LEDs have different properties like forware voltage drop. That means that (without lots of random experimentation and luck) you would need them in series, each with hand-matched resistor so they're all staying in the current range they can tolerate and still have acceptible brightness. In other words it's far easier to start out with X number of identical LEDs, that have a spec sheet or clearly spec'd properties.

Quote:

I did buy a little "Blinking LED Module" (Radio Shack part# 276-299) which has a battery pack w/ a switch and a red LED that blinks. It takes 2 AA batteries so I assume they're in series and it's a 3v deal.

I don't have one and have no idea what the circuit is like inside but suspect it's not a simple 3V driver as most super-bright LEDs start out around 3V forward drop and it would be a very short runtime on the batteries. I'd suspect some kind of voltage boost circuit inside of it, and that the circuit has a certain limit in current output, that it was not just a matter of the batteries suppling more current. I could be wrong though, again it's hard to know about THAT LED it uses without xpecs. You might be able to open the blinker and reverse engineer it enough to figure out how it works.


Quote:

The assortment pack of LEDs is part# 276-1622 and no voltage or amperage values are listed. There are 20 LEDs of various colors in the package. Can I just cut one of the wires from the battery pack and insert more LEDs in the circuit? Should they be in series or in parallel?

I mentioned two primary issues already. They would need be in parallel, voltage drop across even two in series is almost certainly too high.

Quote:

Do I need to start over or can I make this thing work?

I don't know exactly what your target effect is, but it could take a whole lot of work and fiddling with various resistors to come up with something using assorted mystery LEDs. At some point you might have to decide if you're going the "be a safe scientific engineer" route, or the "hook it up and see if it POPs" route. It's not likely to be a safety issue if it POPed, would just kill the blinker box.

If you were able to take a very good hi-res picture of the guts of the blinker box, "maybe" somebody here can determine what you're dealing with and it would inspire something. Maybe not. It's probably need be stored elsewhere, the picture (attachment) size limit on head-fi is too low for good/large pictures.


IMO, the easiest solution that might give a good effect would be trying to put a second (as identical as possible) super-bright LED in parallel with the original and settling for only 2 LEDs. It's still unknown if the black box will "like" this higher load, and you would probably need a low value (under 6 OHm) resistor added in series with each parallel LED to equalize their current a little.

 

[BPRJam]

I know that ratshack also sells individual LEDs that are "flashers", meaning that it looks like your run-of-the-mill LED, but when you hook it up to a battery - Wallah! you have a flashing LED. Like this one, for instance:
Radioshack red blinking LED

My suspicion, actually, is that the flashing LED thingy you bought is a battery holder hooked directly up to a flashing LED - no additional circuitry required.

All you really have to do is buy a couple of identical flashing LEDs, wire them up in parallel, and apply the appropriate voltage. Bingo, you have a bunch of flashing LEDs with no fancy circuitry required.

BPRJam