GPIO / Trigger / Strobe Interface
Optically isolated inputs and outputs.
Optocoupler basics
 Diagram of basic optocoupler function | An optocoupler is a device using optical path to transfer an electronic signal between two circuits. It basically consists of a photodiode converting the input signal to light and a phototransistor converting the light again to electronic signal. The optocoupler is useful in situations where one part of the circuit needs to be galvanically isolated from the other part to prevent damage or unwanted interference. It is used to prevent ground loops or to block voltage spikes. For effective use of the optocoupler it is important to control it using an independent power supply. When the external circuit is galvanically connected to the camera (eg. when reusing the camera's power to control the optocoupler), the optocoupler's protective function is eliminated. |
Due to the schematic characteristic the signal transmitted through an optocoupler interface will be inverted. For details please see schematic below.
Optocoupler parameters summary
Parameter | Input Value | Output Value |
|---|---|---|
Operating voltage | 5 - 24 V | 5 - 24 V |
Input current | 7.5 mA | < 100mA |
External resistor requirement | No | Yes, output current must be limited to 100 mA |
ON voltage level | > 4.5 V | |
OFF voltage level | < 1.5 V | |
OFF to ON delay | < 125 ns | 750 ns |
OFF to ON rise time (10 to 90%) | 1.0-4.0 µs | |
ON to OFF delay | < 125 ns | 2.4 – 25 µs |
ON to OFF fall time (90 to 10%) | 9.0 – 140 µs | |
OFF to ON jitter | ± 5 ns | ± 20 ns |
ON to OFF jitter | ± 5 ns | ± 0.1 µs |
 | ||
Optocoupler inputs
The CORSIGHT camera is equipped with four optically isolated input lines. One input optocoupler is fully independent, the other three are connected with a common cathode (Section “I/O connector”) due to limited number of pins on the I/O connector. Each input line is protected by a current limiter circuit.
The optocoupler input's logical state is understood as logical 0 if no current is flowing through the optocoupler diode, logical 1 if current is flowing through the diode. See schematic below.
The optocoupler is guaranteed to be switched on (logical 1 input status) when the voltage applied to the input is in range of 5 - 24V (tolerance 10%). It is guaranteed to be switched off (logical 0 input status) when the applied voltage is under 1.5V. The input status is undefined between 1.5V and 4.5V, the input voltage must not exceed the 24V limit!
The nominal input current is 7.5 mA — the input signal must be able to deliver at least this amount of current.
The input lines are using fast optocouplers: The propagation time is under 125 ns, for both rising and falling signal edge (assuming input signal with strongly steep edge). The exact switching speed may vary with temperature and the used input voltage level - the listed specifications are the worst case values.
The optocoupler inputs have no protection against wrong polarity. Be sure to connect them always with correct polarity according to the documented wiring diagrams and connector pinouts.
The optocoupler inputs are TTL compatible provided that the signal source is capable of supplying the input current of 7.5 mA.
The optocoupler input lines are equipped with a debouncer to prevent generating unwanted input signals.
Trigger input
Any of the available optocoupler inputs or TTL inputs can be used for triggering. The input line mapping on the camera connectors is described in section Connector and cable description .
The characteristics and default behavior of these interfaces are described below in Section “Optocoupler interface” and Section “TTL I/O's”. Those sections also provide examples how to connect the inputs.
Schematic
If the camera serial number has an X or Y in the 9th digit (e.g. 14A2GEBAX2042013) the I/O connector has the Prototype pinout. Expand below!
The schematic of newer cameras I/O interface can be found below.
Optocoupler outputs
iam is equipped with three optically isolated output lines. One output optocoupler is fully independent, the other two are connected with a common collector (Section “I/O connector”) due to limited number of pins on the I/O connector.
After power up, the optocoupler outputs are in high impedance state and they remain in that state until reconfigured from the software interface. Automatic reconfiguration at start up can be done by means of user sets.
The optocoupler output's logical state is understood as logical 0 when its output transistor is in high impedance, logical 1 if it is in low impedance mode. See schematic below.
The rising edge (switching to logical 1) propagation time is 750 ns, the falling edge propagation time is under 25 µs. The exact switching speed may vary with temperature and the used input voltage level — the listed specifications are the worst case values.
The optocoupler output work with operating voltage range of 3.3-30 V. The maximal switched output current is 100 mA per optocoupler, higher current could damage the optocoupler output circuit.
Strobe output
Any of the available optocoupler output can be used for strobe control. The output line mapping on the camera connectors is described in section Connector and cable description .
Schematic
If the camera serial number has an X or Y in the 9th digit (e.g. 14A2GEBAX2042013) the I/O connector has the Prototype pinout. Expand below!
The schematic of newer cameras I/O interface can be found below.