Receive keychain TX signals?

Larry Molter

Ok, this might be a dumb question, but I have an application in mind that requires a user to use a keychain rf transmitter (like the ones for a car) to send signals to a simple tennis scoreboard controller.· It's intended for us over-50 folks that can't seem to remember either the game score or the number of games we've won.· I'd like to press a button on a keychain xmitter to increment an LED display that's positioned court-side.· I know there is a 433MHz receiver, but what can I use as a transmitter? I only need a few buttons.

TIA,

Larry Molter

Chris Savage

Larry,
·
·· Is this a Javelin application?· RF Digital sells a Keyfob unit with 5 buttons that transmit at I believe 418 MHz to a receiver which makes one of those pins high in response to the button on the remote.· Would something like this work for you?

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Chris Savage
Parallax Tech Support

Larry Molter

Chris, thanks for the quick reply. Yeah, I forgot to mention that this would be a Javelin app.· I'll go check out RF Digital's stuff.· Sounds like the ticket.· Thanks.



Larry

Larry Molter

Chris, it looks like Linx Technologies sells a keyfob with 1-5 keys and the spec says it works with your 433MHz receiver (which makes sense since Parallax is using the Linx receiver module).· This would work, right?· Am I missing something?

The RF signaling is crucial to my 'master plan'.· The tennis player needs something small to fit in their pocket while playing.· The keyfob idea is perfect. Any other solution would not be feasible.· So, other than the LED driver stuff, which I think can be solved with the 8-digit driver chip you sell, all I have left is the (minimal) programming.

Larry

Chris Savage

Larry,
·
·· I don’t think it does work with out receiver…If so, then you would still need to decode the signals it sends.· The one we used to carry had a matching receiver which was not serial (as our RF units are) but rather had parallel outputs.

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Chris Savage
Parallax Tech Support

Larry Molter

Chris, I found a source of a simple 4-channel keyfob xmitter/receiver for about $35 from HVWTech.com. I have one now to play with, but I'm concerned that its outputs are active high. I'd like these outputs to appear as buttons to Javelin, so do I need to buffer its outputs with a transistor so that it floats high and is driven low? I don't want to burn out the stamp.

I've noticed something else that's peculiar with my stamp and its super carrier board (now that I have your attention). I can only talk with the PC serially if I'm on 9V battery power. The IDE can't communicate if I'm on wall power (RadioShack 7.5 V, 500mA supply). Same thing if I connect it with a 9V xformer. Granted, I haven't used this stamp and board for a couple of years and they've just been sitting on my workbench, but why does it work with the battery and not the dc wall supply? I can't figure it out. Of course, I'm over 50. That might have something to do with it <g>.

Larry

Larry Molter

Never mind my rambling. There's something odd with the carrier board, but if I do an Identify followed by a Test Connection, the Java IDE seems to find the stamp. As far as the outputs of the 433 MHz receiver are concerned, I just connected 4.7K resistors from the active-high outputs to ground and grabbed the signal from the top of each resistor. Works like a charm. I would definately recommend the HVWTech keyfob controller to anyone who needs a simple, low-cost 4-channel 433 MHz tx/rx pair.

Sorry about my paranoia. <g>

Larry