I work at a counseling center where it's best to limit phone calls for the mental well-being of the residents. Is there any way to detect a cell phone in the building, either by an available device or a homebrewed circuit? Is there a way to find a hidden or lost cell phone? Is there a way to log cell phone presence, signal usage, and strength? Just show whether there was a signal, the time, and the strength (how close).
I built a Jeopardy game console for use in a classroom setting. The console works quite well and can accommodate up to four players or teams. The issue I have is that the player buttons are attached to the console via cables and this gets cumbersome in class. I'd like to find a wireless solution where the push of a button would wirelessly close an associated relay in the console. I've looked at commercial solutions and they are all north of $200. Can anyone suggest a circuit that I could use that would be relatively inexpensive and easy to build? I would be willing to consider a commercial solution but, as I said, all the ones I've found so far are out of my price range.
For wireless control, it is tough to beat the low cost of Sony TV remotes from the local Goodwill, teamed with the IR-D15A 15-Bit Sony® IR Decoder IC from Reynolds Electronics. For RF remote control, there are multiple articles on how to use PIC or Atmel (Arduino) processors using serial communication, simply search or stop by the Microchip site.
An alternate encode/decode is the TX-2/RX-2 "RC car" remote control IC sets available from eBay. Recommend the TX-3/RX-3, and buy in pairs. If using RF instead of infrared, consider the WRL-10535 and WRL-10533 transmitter/receivers from www.sparkfun.com, which I personally use with the TX-2/RX-2 "RC car" set for fan control. The TX-2 can connect directly to an RX-2 for debugging, and it is easy to scope the output. A PIC (16F88) or ATmega32x (Arduino) will probably help for "who clicked first". Holtek also produces inexpensive encoder/decoder pairs. www.allelectronics.com has Sharp IR decoders which work fine with the Sony remotes, AVRs, and much more.
A solution that worked for me several years ago was to use a wireless doorbell. These generally have a jumper that you can move to avoid interfering with a neighbor that has the same model. You would have to purchase four units and then set each to a different "channel". If your console is not made of metal, you could mount the base units inside the console. Disconnect the speakers if you do not want them to chime. A quick check on Google shows these are available in the $10 to $15 price range. The Honeywell RCWL105A is one that might work for you.
There are both 120VAC and battery operated base units. The push buttons are battery operated in either case. The advantage of the 120 VAC units is that you do not have to purchase batteries and also remember to remove them when not in use. The disadvantage is it may be more difficult to interface these to your console.
I used an AC powered base and added a small 5V relay to provide a contact closure to operate my garage door opener. Note that this will be a momentary contact closure. I could not find a schematic for the unit I used but was able to use an oscilloscope to find a pin that changed state when I pushed the button. The relay takes too much current to be driven directly so I added a FET to act as a low side driver. An optical isolator might also work instead of the relay. These can be driven with only a few mA if the output transistor only has to sink a few mA.BE VERY CAREFUL and don't even attempt to connect an oscilloscope to an AC powered unit unless you have an isolation transformer since these units may operate directly from the 120VAC with no isolation. The relay or optical isolator will provide the isolation once you have found a place to connect it. You can contact me via email at firstname.lastname@example.org if you have questions.
Figure 1 is a schematic I drew of the IC in question. I have not been able to find any IC that would connect in this circuit. There is only a date code on it. Nothing else at all. Pin 6 is obvious, but with pin 5 to ground and pin 7 not connected, I am stumped. The only IC I thought it could be is a serial Flash memory. Any other suggestions?