D Infrared Light Module SM-IR-16-2
April 03. 2012 BEIER-Electronic 7
Connecting lamps/LEDs to the switch outputs
Lamps or LEDs are connected to Terminals X2/2 and X3/1 – X3/16.
These terminals are spring-tension terminals, which allow for a quick and easy
connection of the light module. To connect or disconnect a cable, simply press down
on the terminal lever with a small screwdriver. This opens up the terminal and the
cable can be plugged in or out. Cable ends should be stripped approx. 7-9mm, and
these areas should ideally be coated with tin before they are connected.
The 16 outputs of the SM-IR-16-2 are minus-switching outputs, i.e. the minus pole of
the voltage is always toggled. The plus pole of the output load is always securely
connected to the plus pole of the power supply voltage.
The switched voltage at the 16 outputs is always as high as the power supply
voltage! Therefore, dropping resistors must always be connected to the LEDs or light
bulbs!
The size of the dropping resistors depends on 3 different factors:
Supply voltage (UB) power
LED/light bulb (UL) voltage
LED/light bulb (I) current
The dropping resistance can then be calculated according to the following formula:
UB- UL
R = ----------
I
Example:
We have a power supply voltage of 7.2V, and we want to connect a white LED with
3.5V and 20mA (=0.020A).
7.2V – 3.5V
R = -------------- = 185 ohm
0.020A
However, since a resistance value of 185 ohm is not possible, we use the nearest
possible value, in this case 180 ohm.
Subsequently, one should also calculate the necessary resistance value:
P = (UB- UL) x I
P = (7.2V – 3.5V) x 0.020A = 0.074W
In this case a standard resistance with a value of 0.250W (1/4W) is sufficient.
Each LED/light bulb should have its own dropped resistor.
