From: "Dave D"
Subject: Re: help! ultra compact, simple transmitter
Date: Thu, 17 Oct 2002 11:18:23 +0000 (UTC)
Organization: BT Openworld
NNTP-Posting-Date: Thu, 17 Oct 2002 11:18:23 +0000 (UTC)
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"limahl" wrote in message
> Hi y'all!
> I'm hoping for some input on a very simply transmitter, a device,
> which has a switch and once it is triggered it sends a simple signal
> (wirelessly) 100' - 150' away to a receiver which will then illuminate
> a light or make a simple sound.
> How compact could that transmitter be made, and could it be powered by
> a single "AAA" 1.2v
> nicd battery?
> Thank you in advance for any input, suggestions, scematics... please
> keep it simple - I'm electronics challenged ;-)
> Please reply to
At 1.2v it is difficult to get any sort of decent power level out of a
transmitter. A major problem will be frequency drift as the battery runs
down, it will be horrendous. However it is certainly possible to get that
range with a decent receiver, efficient antenna and the correct frequency
band. Radio mikes acheive at least that range and in the UK run an ERP
(IIRC) of only 2mW.
The problem is for a novice this is going to take some engineering so a much
better alternative is to use one of those camera or alarm key fob 12v
batteries and a standard 'bug' style transmitter which work on the FM
broadcast band, the schematics are very plentiful on the web. If this isn't
being used for prolonged transmitting, the battery should last a while.
You'd need to modify a receiver to output a switching signal when it detects
a carrier, which without a schematic will be trickier than building the
If you go for a 12v type battery (these are shorter but fatter than an AAA)
I would feed it through a 78L09 regulator, that should minimise frequency
drift to an acceptable level. I have made these bugs about half the size of
a disposable cigarette lighter, the component count is very low.