The Jimmy has a nice little pocket in the driver's door that just fits the remote transmitter button for the garage door opener. Although the transmitters always come with a clip that you can supposedly fasten to the sun visor, that wasn't a good option on the convertible. The door pocket wasn't all that handy, either, so it ended up hanging from the ash tray, which always looked pretty tacky. The fact that the case had cracked made it look even worse.
I had already installed a button in one of the spare switch holes in the VW's dashboard (see the VW horn project), so I thought it would be a good idea to use that to trigger the transmitter and hide the workings inside the dashboard. Oh, sure, another one hour project that absolutely destroyed a weekend!
The transmitter itself uses a 9V transistor radio battery. Since I was going to hide it, I didn't want to have to dig into the car to replace the battery, especially when there's a self-recharging 12V battery already in the car. That meant I had to regulate the 12V down to 9V. I spent a couple of days looking, but couldn't find a commercial 3-lead +9V regulator at my local electronics stores, so I took a +5V regulator and used an old trick. I took a 470 Ohm resistor from the output to the reference lead, then took a 390 Ohm resistor from the reference lead to ground of the car. The 470 Ohm resistor has 5V across it because that's what the regulator is designed to do, and the 390 Ohm resistor has the same current flowing through it as does the 470 because they are in series. OK, the 390 has the quiescent current of the regulator, but that's not much. In this case, the 430 Ohm resistor drops about 4 volts, which means the output of the whole thing is +9V, which is what I needed to power the button. I put that circuit in the housing where the battery had been. I didn't need to heat sink the regulator because the duty cycle is so low and the unit is only powered for a couple of seconds at a time.
I checked out the transmitter's circuit pretty carefully, and although it wasn't real clear at the beginning, the switch just switches the power to it. When it has 9V on it, it transmits the code programmed by the D.I.P. switch, when it doesn't, it doesn't. This meant that I could simply provide 12V to the regulator and the button would transmit the code until I took the power away.
The button I had put in for the horn had been
wired to the ignition 12V, not to the battery, and I didn't want to have
to start the car with the garage door down just to open the door, so I had
to move the wire to an unswitched fuse position. I decided to mount
the transmitter unit itself to the top of the glove compartment using
double-stick velcro. I ran the wire from the button to the transmitter
through the hole the windshield washer hose had originally used.
The transmitter has worked flawlessly for over a year, and Kate thinks it's even cooler than the windshield washer!
I'd probably try to get a better button. The one I used I got for free at a trade show. It works perfectly, but it has a very short throw and very light tactile feedback. The button originally in the transmitter gave a nice resounding click when it was pressed, and this one doesn't do that.
I'd also use something a little more permanent to fasten the transmitter to the top of the glove compartment, like double stick tape, or silicon adhesive (but that takes at least 24 hours to set).
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