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The phone remote, revisited.

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The phone remote, revisited.

Unread postAuthor: TurboSuper » Mon Jan 07, 2008 5:29 pm

I see people tossing around the idea of using a cordless phone as a remote control sometimes on these forums, yet I have never seen anyone actually do it. So, I went ahead and decided to give it a try.

I based the design off this website: http://www.angelfire.com/80s/sixmhz/rcphone.html

This design works pretty well, but it has one major flaw:

The reciever is modified with an Op Amp to increase it's amplitude to something sufficient to drive a relay. Unfortunately, phones (at least not mine), don't ring continuously. Therefore, you end up with the relay being actuated in 1-2 second bursts.

While this may be fine for a spudgun, other things, like model rockets, usually need a longer burst to ignite.

So is there a solution? Of course!

Instead of an Op Amp based circuit, I used a 555 timer in a monostable configuration, as shown here:

Image

The idea here is that the small speaker signal is applied to Q1, which acts as a switch, thus triggering the timer. The time delay is calculated as 1.1(R1*C1). J1 is a reset switch, and D1 and D2 can be a wide range of diodes, so I didn't pick specifics.

It may seem complicated, but it's actually pretty easy to wire up, (I'd post some pics but my camera doesn't seem to like Vista).

You also have the advantage of being able to convert almost any wireless device into a remote.

I tested this circuit and it worked, but I managed to somehow fry the phone reciever between the breadboard phase and the actual wiring phase :x

What think, guys?
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Unread postAuthor: psycix » Mon Jan 07, 2008 6:08 pm

And just when you walk in front of your 12x hybrid your mom calls in to ask how you are.....
:P joke


I think its a great remote control device.
Get your camera working soon :)
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Unread postAuthor: miskaman » Mon Jan 07, 2008 6:14 pm

Once you get some pictures, I will definetly try to do this.
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Unread postAuthor: TurboSuper » Mon Jan 07, 2008 6:31 pm

Thanks for the positive replies, guys!

I got some pictures now:

The transmitter:

Image

Image

The big red "fire" button is wired to the "find handset" button on the phone's board. The "arm" switch is just a power switch, it's powered by 4 AAs.

The monostable receiver:

Image

Image

This is wired to the speaker of the phone handset. I used a basic perf board for the components.

I don't see how these pictures will help ya build it, but hey, I suppose a visual aid never hurts. My process follows the link in my first post almost exactly, apart from my modification to the handset, and a big red button :D
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Unread postAuthor: jimmy101 » Tue Jan 08, 2008 2:38 pm

Nice job Turbo!

I'm a bit surprised that the 555 will source enough current to operate the relay. IIRC, 555's output is usually limited to about 200mA or so. Obviously it's working for your particular relay but for a larger relay an output transistor between the 555 and the relay's coil might be needed.
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