User`s manual

30 • Part I: PC2-CamLink Board PC2-CamLink User's Manual
3.3V
Opto2_Trig +
Opto2_Trig -
Opto-Coupler
1.33k (1W)
221
(0.1W)
3.3V
Opto-Coupler
Trigger
Controller
J3: opto2
J4: opto2
Opto1_Trig +
Opto1_Trig -
1.33k (1W)
221
(0.1W)
J5: opto1
J6: opto1
Figure 6: Opto-coupler
When current flows inside the LED, the emitted light acts as a base current for the transistor.
Depending on the amount of light that is being emitted, the transistor can be turned ON, just like a
switch. The information, in the form of a voltage, is transmitted from one side to the other as a
transistor being turned ON or OFF. The opto-coupled input is an inverting circuit; PC2-CamLink
software compensates for this when specifying the polarity.
The surrounding circuit that converts the voltage to current and into the LED is therefore crucial to the
performance of the opto-coupler. If the current flowing through the LED is too small, the emitted light
will not turn the transistor ON.
HPCL-0531 is the typical opto-coupler on the PC2-CamLink. It is designed for high-speed TTL/TTL
applications. A standard 16mA TTL sink current through the input LED will provide enough output
current for one TTL load. Maximum rates are given below:
Electrical
parameters
Description Value
I
F avg
Average forward input current 25mA
I
F peak
Peak forward input current 50mA
V
R
Reverse LED input voltage 5V
t
pHL max
Maximum propagation delay from high to low 1.0μs
t
pLH max
Maximum propagation delay from low to high 1.0μs
Note: TTL signals are approximately 0 and 5V corresponding to logical 0 and 1, respectively. A
standard TTL output can sink 16mA and could be used as a sink to drive an opto-coupled input. In