I might have a cheaper answer to it all but it depends on what radios exist in the fleet. If they are anything like the Kenwoods, they'll have built in dtmf & 2 tone encoders/decoders. I believe some Motorola mobiles have this as well.
Program the units to encode either dtmf or 2 tone on a front panel button. I've done this with the Kenwood mobiles & port's. If you have Fleetsync or MDC signaling that will work as well...Provided you have the rcvr for it. The key click counter is ok as well. I regularly sell & install S-Com's AGI1100's in airports just for pilots to remote dial a phone line & other functions using the proper number of ptt's. If you go with the ptt counter, use the Pl/dpl detect or TOR (kenwood) output instead of a carrier det only. This way, you are actually counting the correct PL/DpL hits & not a noise or distant co-channel user. If you build a ptt counter, bear in mind that commercial units offer a programmable window of opportunity within which your ptt's must arrive or the system resets. The usual windows are setup for 1 ptt per second for the number of ptts necessary. If any of the ptts arrive outside that window, you have to start over. Other than the rather pricey (for this job) S-Com units, I don't know who else makes such a device commercially. In my applications I require very dependable, bullet-proof units that I can set & forget for years. I haven't had an S-Com AGI1100 fail yet after the hundreds installed or the years in service.
