The SentiBoard uses the Output Compare functionality of the on-board microcontroller to generate a very accurate trigger. The triggers are 3.3V and there is a trigger pin on each sensor port. The table below shows which trigger pins are available on which sensor port. Notice that we only have 5 different trigger ports. That means that the same trigger port can be laid out to the trigger pin of multiple sensor ports.
|Trigger port / OC port 1
The triggers can operate in two modes.
Independent mode In the independent mode the SentiBoard generates the desired trigger frequency and duty cycle only based on its internal oscillator. This means you're trigger frequency will inherit the jitter and drift of the SentiBoard oscillator
Synchronized mode In synchronized mode the trigger frequency is synchronized to an external input on the TOV pin on any sensor port. This is meant to be used with a 1PPS signal, like the one generated by a GNSS receiver. The SentiBoard will then sync up the trigger frequency on each PPS signal. This only works for 1 Hz PPS. The sensor port which you wish to synchronize the trigger with must be enabled for it to accept the external PPS. This means that if you want to synchronize oc7 (available on UART2 and RS232-1) to a PPS connected to the IC/TOV pin of RS232-2, you must also configure RS232-2 port to be enabled.
Through the USB interface the triggers can be configured.
From the main meny type
c ocX where X is the ID of the trigger port. E.g. to configure the Trigger pin on the RS232-2 port you should enter:
You will then enter the trigger config menu which has the following options
e true|falseenables or disables the trigger
s SENSORNAME|offselects which port's IC/TOV to synchronize with. Typically where your GPS is connected.
r FLOATthe rate in which the sensor is triggered in Hz
p PERIODthe period the flank should be active, 0-100 given in percent. 0% and 100% is heavily discouraged to use as 0% is never active and 100% is always active.
?Print the current configuration of the selected sensor.
xExit and return to the main menu. Saving must be done in the main menu.
The changes will not make effect until you save and reset the board.
The trigger packet
On each trigger generated by SentiBoard a packet containing the timing information of that trigger will be generated and sent over the USB interface. The packet is structured as follows:
|Rising edge TOV value (in SentiBoard time 10*ns)
|falling edge TOV value (in SentiBoard time 10*ns)