week 6

Week 6

Just as you dial your telephone to reach another person, you can use transmit DTMF signals over a radio, and turn things on and off, flash lights, control motors, cameras, activate warning systems, turn on irrigation systems, open gates, and in general control the world! You may have heard some tones at the start of some National News Broadcasts. These are DTMF tones that CBS or others like them send out at the start of the broadcast to transfer (or alert to transfer) their audio onto the local affiliates airwaves. Basically, it turns on a master switch. Used over two-way radios, you can transmit a DTMF "phone number". You have the same "phone number" programmed in a decoder hooked up to a radio receiver at a remote location. When the decoder sees its "phone number" come in over the radio, it wakes up and gets to work controlling the things you have hooked it up to.

With the better decoders (of course all the Genave decoders are the better ones) you are able to take phone numbers a step further. You can use Wildcard characters in the phone number. A wildcard allows you to actually embed information in the phone number. This information is usually used to control multiple locations with one DTMF signal. If, for instance, you use DTMF codes to open the overhead doors on your fire stations in the City. When you have a small fire, you send the DTMF code that opens only the door on fire station #1. But when you have a BIG fire, you don't want to waste radio air-time to transmit 15 DTMF codes to open all 15 overhead doors. So you program your decoders so that, of course, each one can be controlled individually, but using a correctly placed wildcard, they will all respond to a master "Open" signal. They can also be set up to respond to another signal for a medium size fire that opens only the doors on fire stations #1, #5 and #7. This group, sub-group, sub-sub-group relationship is just a fraction of power and flexibility when using DTMF to remotely control equipment.