Optocoupler interface / Strobe Interface

Optically isolated inputs and outputs.

Optocoupler basics

Open 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.

Optocoupler parameters summary

Parameter	Input Value	Output Value

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
	Open Example of using the optocoupler inputs

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.

The optocoupler is guaranteed to be switched on (logical 1 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 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.

Optocoupler outputs

The CORSIGHT camera is equipped with four optically isolated output lines. One output optocoupler is fully independent, the other three 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. Whenever the optocoupler output is disconnected in the SW interface, it gets in high impedance status.

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.

TTL I/O's

Standard 5V TTL (transistor-transistor logic) interface.

After power up, the TTL outputs are driven low — and they remain driven low until reconfigured from the software interface. Whenever the TTL output is disconnected in the SW interface, it gets in driven low status. TTL inputs are pulled up to 5V inside the camera to guarantee a stable input in case nothing is connected. To generate a steep edge the TTL input driver should be capable of driving and sinking 10mA.

The TTL input's and output's logical state is understood as logical 1 when it's driven high (5V) and logical 0 when it's not driven (0V).

The TTL input lines are equipped with a debouncer to prevent generating unwanted input signals.

The delays listed in the table are setup dependent mean values, while the jitters are maximal deviations (± ) from those mean values.

TTL input/output parameters summary

Serial port interface

Standard RS232 communication interface, accessible directly from the camera's feature tree.

Configurable communication parameters are: baud rate, parity, data bits, stop bits.