MOTOTRBO Application: Simple Telemetry
What is it?
Most MOTOTRBO radios* support telemetry functionality in digital mode. Both the MOTOTRBO portable and mobile, have General Purpose Input/Output (GPIO) lines on the radio accessory connector which can be connected** to external equipment.
With this telemetry functionality, the originating radio can send a telemetry command to another radio. Sending the telemetry command can be triggered either by GPIO pins or a programmable button.
Telemetry commands instruct GPIO pins on the target radio to be set, cleared, toggled or pulsed. The telemetry commands can also be used to query the status of GPIO pins at the target radio. It also enables the target radio to display a programmed Text Status Message or act on a telemetry command received from the originating radio responding to an event at the originating radio's GPIO pins.
Portables have three GPIOs and mobiles have five. In addition, any of the programmable buttons can be set to trigger a telemetry command. In the case of the portable, a telemetry cable (PMKN4040A) is required which informs the radio that a special cable is connected.
A popular example of how MOTOTRBO can be used for telemetry is a reservoir control system. In this application, the reservoir is fitted with two float switches: one switch closes when the reservoir is full and the other switch closes when the reservoir is empty.
|Figure 1 : MOTOTRBO radios control an irrigation reservoir system.|
These switches are connected to a MOTOTRBO radio. Since there is no AC power at the reservoir, a DP4400 can be used, which is powered from a lead-acid battery and small solar panel. The radio will have minimal current drain, as it will not be party to any calls and will only transmit when either of the switches change state.
The portable is programmed as follows:
At the other end is another MOTOTRBO radio - it could be a mobile or a portable. This radio is connected to a pump**. The pump draws water from the river and fills the reservoir. This radio is powered from the AC supply to this location (solar could be used here too).
This radio is programmed as follows:
Between the pump and radio is a simple control circuit. This circuit provides soft start and power factor correction for the electric motor inside the pump. The control circuit also provides a low level input for starting and stopping the motor. When the input is high, the motor will run and as soon as the input goes low, the motor will stop.
So as the reservoir empties, float switch A closes and causes radio 1 to send a telemetry command to radio 2. Radio 2 reacts to this command by toggling the pin connected to the motor controller. The pump starts and the reservoir fills. As soon as the reservoir gets to a certain level, switch B closes and radio 1 sends a telemetry command to radio 2, which turns the pump off.
Radio 3 (not shown) also has the option to manually start the pump by pressing a pre-programmed button. Pressing the button has the same effect as closing float switch A or B. This radio would be in the hands of the farm workers allowing them to switch the pump on for whatever reason. This third radio is optional!
Radio 3 is set up as follows:
For more sophisticated systems, where exact levels and flow rates need to be monitored and controlled, I highly recommend looking at one of Motorola's SCADA products. From a simple a system like this, to a entire plant, Motorola SCADA is able to do this, and MOTOTRBO can be used to link remote stations.
* Note that the DM1400; DM1600; DP1400; DP2400 DP2600 and SL4000 do not have any telemetry functionality.
** Although the radios support standard TTL levels, it is strongly advised to make provision for electrical isolation when longer cable lengths and/or AC mains are involved.