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FOB remote & receiver, long range, low power, small size.

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Newbie level 1
Jun 10, 2011
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Hi Guys,

I'm new here and i need Your help.

I have very little experience in the field of electronics - i did some supervised DIY work, but nothinh highly advanced or ambitious.

Now I MUST complete a relatively easy, or so they say, project.

Here is the outline:

- a FOB remote (as in both fob on a keychain and frequency operated button), as small as possible and with the largest possible range is to be used to turn on and off a small, battery operated lightsource.

And voila! It's amazingly simple, isn't it? I'm sure that many of You done dozens or more of such simple projects. While I have basic idea how I'd do it, and what I'd use to do it, I'm also quite convinced, that given my lack of experience in the field, my choices would be far from optimal.

That's why I'd like to ask You - how to do it?

The simplest way to visualize what the finished project is supposed to look like is to think about those lights one can see at the hospitals saying "Do Not Enter", which are turned on by the doctors whenever the patient is in the room. Only they simply have buttons and wires.

Mine needs to be remotely operated, portable & very small (like pinkie size), because it will also be mounted under RC helicopter (kind of a flying "starting stall") but it's not operated by the same person that controls the helicopter. It will operate outdoors, so it must be weather resistant. And the operator is located some distance away - 200 yards or more away. It is simply supposed to stay off, then a diode is supposed to light up RED (either one of two diodes or one color-changing diode) with a press of a button, then with another press to light up GREEN, and then it has to be turned off (also remotely) because of the rules, though I guess it will also save battery power. Another thing - there are many other radio emiters and receivers operating around (for RC models etc.) so it must not interfere with those.

So how to do it? Ideally - I'd like You to tell me which specific parts (boards and circutry, diodes, FOB remote, casing etc.) to use. But if that's not possible, just point me in the right direction and tell me where to look for similar projects and/or information on how to build such a device. One important thing is that the light must be as bright as possible, but it also has to last as long as possible without changing batteries - so I guess it's a compromise. Maybe it should be flashing light (flashing RED and then flashing GREEN - if it would be more battery-friendly solution). Also - a button cell battery has to be used - which is a good thing, I think, for it will keep the size down. I know it's probably a simple thing, but for me it will be like a megaproject 8-O

And I can't simply buy a ready one :grin: I must make it.

Thanks in advance.


Your specifications were well presented. Looks like a fun project.

As led's have gotten brighter over the years, it's become popular among pilots to light up their flying R/C machines. They just use a spare channel on their transmitter / receiver.

However to do it the way you describe will be a challenge whether or not one is experienced with radio control.

1. transmitter

An R/C transmitter needs several volts and a 3 foot antenna to send control signals to a plane several hundred feet away. Not easy to miniaturize.

There are kits containing small, simple radio transmitting circuits. which will broadcast your voice to an AM radio, or an FM radio. Several dollars through an electronics supply house. I got one that was supposed to have 100 foot range. I think it broadcast about 30 feet through walls.

If you can find such a kit on a frequency that's allowed for you to use, and it says 1,000 foot range outdoors, it might be usable. A 9 V battery might be sufficient to power it.

You might need to run a wire down your pants to serve as the antenna.

2. receiver

Are you allowed to buy a receiver unit? These have become miniaturized. $15 to 30. You install a crystal for your chosen frequency. It will run on a couple of button cells. To be fair the rules should allow you to add an antenna several inches long.

It's only fair for the rules to give you leeway about what frequency (channel) you use. Of course you don't want to transmit on the same frequency as the helicopter control. That could cause it to crash.

However it's unpredictable who will be using which channel. At flying ranges it's typical to have a display board with a flag for each frequency. Pilots cooperate by not transmitting on a channel whose flag (or lack of flag) shows it's in use.

3. control signal

How to code your control signals will be another challenge. Not sure which is easiest... to transmit the same command and use a toggle circuit in the receiver unit. Or else to transmit a different command with each press of your transmit button, and let the receiver interpret.

If your receiver is a commercial model, then you must transmit pulses in the format it expects. You may need to construct your own circuit to decide how long a pulse length means to turn off / on red led. You'll probably use a mosfet to turn on your led's.

4. LED's

LED's come in various beam widths and efficiencies. You want to obtain the most efficient LED's you can. Wide beam for best visibility from unpredictable viewing angles.
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