Amplify Remote control IR signal

[Al Skierkiewicz]

Originally Posted by Lavapicker

Our students built a 60 LED array with a magnifier all jammed into a 5-inch PVC pipe so that it looks like a bazooka.

I saw one of these at Boilermaker and the team thought it worked pretty well. However, I have heard some students say that want to take a lens out of a slide projector to narrow the beam. Some of the lenses are designed to absorb IR. Be sure to check the output with the lens out and then again with the lens in place. However, with 60 LEDs, I bet it will heat your hand if you put in front of the output side.

[efoote868]

Originally Posted by billbo911

I believe it is called a MOSFET.
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That sounds about right. Our EE mentor built a circuit for us containing 8 IR LEDs, that were powered off 12 volts, and 650 mA each.
The standard 2 in the remote were powered off of 3 volts, and about 30? mA each.

Anyhow, to make a long story short, the new thing is stylish, and is about 300 times more powerful. We got its range out to 20x the other one, and gave up testing the limits (we ran out of hallway). If I can scan the schematic in the next week or so I'll post it.

[Jared Russell]

Originally Posted by Don Rotolo

I am also interested in the circuits that teams have used to pick off the IR drive signal and send it to several IR LEDs.

I have an idea to use an Op Amp, but surely there's a simpler circuit out there?

Thanks,
Don

You don't need an op amp. You have two options.

One, if the remote's LED driver has a lot of muscle behind it, just hook up additional LEDs in parallel.

Two, if the LED driver isn't as strong (more likely), add in a transistor buffer integrated circuit (IC) to pull power directly from the remote's power supply.

There are a few ways to do this. Two inverters in series would work, as would a specialized buffer IC. Or even a tri-state buffer.

[Don Wright]

Just an FYI...

If you are trying to get more distance out of your remote, then making the remote more powerful will help.

But, if you are trying to stop interference from other remotes, making it more powerful won't help.

Since the IR signal is a series of pulses, it relies on an ON state, and an OFF state to send those pulses.

So, even if your ON state can be seen on the moon, when your remote is in the OFF state (your IR LED not illuminated), other remotes could be in an ON state and transmitting IR which would also be picked up by your receiver... This would be still seen as a signal from you...and would confuse your receiving system.

There is very little you can do to help with this...besides totally different transmitting and receiving systems.

[bobabot1]

I am trying to rig up an LED array for my team but so far, I'm having some troubles. I want to make a 20 IR LED array but I know the transistor I will need to use to boost the signal voltage of the remote I'm using. Here's my schematic thusfar (sorry for crude ASCII drawing. -|>- is an LED and -/\/\/- is a resistor. The circuit is four parallel groups of five LEDs in series)

+----|>|----|>|----|>|----|>|----|>|---/\/\/----+ R = 15 ohms
+----|>|----|>|----|>|----|>|----|>|---/\/\/----+ R = 15 ohms
+----|>|----|>|----|>|----|>|----|>|---/\/\/----+ R = 15 ohms
+----|>|----|>|----|>|----|>|----|>|---/\/\/----+ R = 15 ohms

I've heard that I can use a 2N3904 transistor. Would that be what I'm looking for?

[billbo911]

Originally Posted by bobabot1

I am trying to rig up an LED array for my team but so far, I'm having some troubles. I want to make a 20 IR LED array but I know the transistor I will need to use to boost the signal voltage of the remote I'm using. Here's my schematic thusfar (sorry for crude ASCII drawing. -|>- is an LED and -/\/\/- is a resistor. The circuit is four parallel groups of five LEDs in series)

+----|>|----|>|----|>|----|>|----|>|---/\/\/----+ R = 15 ohms
+----|>|----|>|----|>|----|>|----|>|---/\/\/----+ R = 15 ohms
+----|>|----|>|----|>|----|>|----|>|---/\/\/----+ R = 15 ohms
+----|>|----|>|----|>|----|>|----|>|---/\/\/----+ R = 15 ohms

I've heard that I can use a 2N3904 transistor. Would that be what I'm looking for?

I believe the 2N3904 may be a little under rated for this unless you use one per leg of your circuit.
Alternatives are: the IRL3103 MOSFET (One of these can handle the entire circuit without breaking a sweat. It's continuous drain current rating is 40A.) and the ZTX603 Darlington (continuous current rating is 1A).

If you can get the IRL3103, you will be in good shape. The ZTX603 is lower rated, but will do just fine if you do the math right.

So, for the math:
What voltage will be driving this beast?
What is the Vf of each LED?
How much current does each LED require to turn on fully?

Find this information out and the math is as simple as E/R=I.

[bobabot1]

Originally Posted by billbo911

I believe the 2N3904 may be a little under rated for this unless you use one per leg of your circuit.
Alternatives are: the IRL3103 MOSFET (One of these can handle the entire circuit without breaking a sweat. It's continuous drain current rating is 40A.) and the ZTX603 Darlington (continuous current rating is 1A).

If you can get the IRL3103, you will be in good shape. The ZTX603 is lower rated, but will do just fine if you do the math right.

So, for the math:
What voltage will be driving this beast?
What is the Vf of each LED?
How much current does each LED require to turn on fully?

Find this information out and the math is as simple as E/R=I.

I was looking at the 2N2222 which seems to be the same as the 2N3904 except rated at 1A but I will definitely look into the suggestions you made.

I designed the circuit for a plain 9V battery. All the math works out for 1.5V, 100mA LEDs but I'm going to see if I can make it even less power-consuming. The Vf for the LEDs will be either 1.5 or 1.2 with a forward current of either 100mA or 20mA. My first choice would be the 1.2, 20mA LEDs but I need to see if I could get them delivered before our team goes to Atlanta.

[Al Skierkiewicz]

Bob,
You need to check the ratings on the LEDs. It is unusual to have a stock LED listed at 100 ma unless it is a multi LED in a single package. Second, I usually use a 2 volt Vf as a rule of thumb unless I am dealing with a special device of known specs. So using a 9 volt battery will not allow 5 LEDs in series. I actually question the need for this much output. However, 3 LEDs in series with a 120 ohm resistor in each string should work fine. The 2N2222 is fine for this service as well. If it seems that the transistor is getting too warm, you can use two transistors by paralleling the base of each transistor. Although you do not show the transistor in your diagram, normal operation uses the emitter tied back to the negative terminal of the battery. You would then tie the left side of your diagram to battery positive and each of the resistors to the collector of the transistor. When you use multiple transistors, do not tie the collectors in parallel. Tie one or two LED strings to each collector and you should be fine. Build up a driver board with several transistors and terminals for each collector. Then add a string and see if that gives you the desired result. Add a string and try again. No current will flow in an open circuit collector. Battery drain is going to be significant but you should have enough reserve in a 9 volt battery for a weekend of fun. You could even add a "power" switch to turn on the strings. i.e. 1, 2, 3, and "ludicrous power!"

[bobabot1]

Thank you so much! Hopefully with your help, I'll be able to make a working array.