A little on channel steering

It is possible to remotely change the channel on a MOTOTRBO mobile by applying a high or low to the accessory connector pins that are configured as Channel Select.

In this example pins 17; 19; 20; 21 and 22 are set as Channel Select 1 to Channel Select 5. The active level is set to High which means that in order to trigger that function, the input needs to go logic high. Since these inputs are set to Channel Select, applying a high to the pin will make the radio go to the channel that is represented by the binary weight. The following truth table explains this better.

If all the pins are low, the radio will remain on whatever channel it is or whatever it scans to (i.e. its in a "don't care" state). If say Channel Select 5 went high, the radio would go to Channel 16 (or the channel in the 16th position, if one exists). If all the pins went high, the radio would go to Channel 31. In other words the BCD number of the channel.

Debounce prevents a bad electrical contact from producing a false trigger. The debounce time can also be set and the default of 100ms works for 99% of applications. If you are triggering these inputs with a transistor or IC, you dont really need to be concerned about debounce.

Logic low is 0-2Vdc and logic high is 5-12Vdc. The input goes into a transistor so if you're going to be connecting this to external equipment some distance away or powered from a different supply line then you should seriously consider electrical isolation (optocoupler). If you want to switch channels by means of a remote up down switch, you can use a microcontroller or a counter IC like this one.

Here are the pin locations:

The plug for this connector is PMLN5072 - it comes with crimp type pins.