Digital Matter devices have a few different digital output options available. These are:
- Switched Ground Outputs (most common and widely used across the range)
- Switched Power Out
- 3.3V outputs to power sensors
Switched Ground Outputs
Digital Matter devices commonly use switched ground outputs. These provide a path to ground when on (i.e. allow a path for current, closing the circuit) and are high impedance when off (breaking the circuit). This is an example of a low side switch.
The function of the digital output can be set in system parameters. Functions include:
- Output is not used.
- Digital output:
- Can be set to on or off from the server.
- Control and external buzzer. This can be used to buzz Driver ID exceptions or over speed violations.
- Use output for Immbolisation. More information here
- Control an external LED. Be sure to use a series resistor.
Setting the function dictates what 'controls' the output. I.e. if we set the output up with the function as Immobiliser - when the immobiliser should be on according to the device, the immobiliser is on.
If we set it up as a Buzzer - this output will pulse on/off when buzzing should happen (i.e. if no driver ID is scanned) -so that if it is connected to a buzzer we will hear the buzz.
The active level setting depends on the function. This can be used to invert the output. LED's and Buzzers should generally be Active High and Immobilisers Active Low.
Switched Power Out
Some devices have a switched power output. I.e. the G120 has a 5V switched power output. When this output is ON - a certain voltage is supplied. So this could be connected to the positive terminal and power a buzzer, LED or other peripheral.
Parameters are the same as for Switched Ground outputs. Set the function to determine what causes the output to turn on or off.
The digital outputs on our devices can be used for remote switching. i.e. to turn a pump or lighting tower off or on.
One example is how a vehicle can be immobilised by sending a command from the server - which is covered here Driver ID & Immobilisation methods with Powered Devices. Telematics Guru has an 'immobilise' button, which causes a message to be sent down to the device to turn any outputs set up with function "Immobiliser" on or off. This same message can be sent from a 3rd party server using the OEM WebAPI - contact DM support for documentation.
Any outputs set up with function "Digital Output" can similarly be controlled by sending a different message to control outputs.
Remote Switching Latency
It is important to note that all of our devices (even hard-wired vehicle trackers) will sleep during periods of inactivity. For example, the G120 default tracking parameters are for the device to heartbeat hourly when the ignition is off and the asset is stationary. Between heartbeats, the device will sleep and the cellular modem will be off.
This means that a command sent down to the device will not be received until the next heartbeat, when the device next connects.
If we require low latency, to improve upon this, we can set this parameter under the upload settings, available on hard-wired devices.
This will cause the device to attempt to remain connected to the network all the time. In practice, generally the network will kill the connection after 5-10 minutes. So the device additionally needs to be set to upload often enough to keep the connection alive.
This will allow commands to toggle outputs to be received by the device within 60 seconds in most cases. It should be noted that this functionality was not designed with live control applications in mind.