Using the P7 Outputs

Using the P7 Outputs

The outputs in the M73 and S74 IO Interface board are of a new design using an Optocoupler with an open collector.

These outputs will require the use of an external DC power supply up to 50 volts with a pull-up resistor and support a maximum current of 10mA. They are not capable of dry connect closure or direct use with AC power.

Here are some examples of how the outputs can be used.

The first is a simple low voltage low current application such as switching an LED on and off. Using the P7 Outputs

The outputs in the M73 and S74 IO Interface board are of a new design using an Optocoupler with an open collector.

These outputs will require the use of an external power supply with a pull-up resistor and support a maximum current of 10mA. They are not capable of dry connect closure or direct use with AC power.

Here are some examples of how the outputs can be used.

The first is a simple low voltage low current application such as switching an LED on and off.

For the pullup resistor: Its value depends on the forward voltage of the LED at the specific current you want to run through it. The characteristic curve for the LED will show what current is needed to achieve a specific forward voltage.

  • Here is one example of this calculation
    • Amperage through LED: 10mA
    • LED Forward Voltage @ 10mA: 2 V
    • Power supply: 12V DC
    • Resistor value = (12V – 2V) / 10mA = 1 kOhm

In the next example the output device requires a higher current than 10mA so a power supply and relay must be employed. The Flyback diode in parallel to the input of the relay may be included in the relay itself. Because the inductor of the relay may provide a resistance the pull-up resistor may not be necessary in this case. Depending on the Relay a resistor may be need to limit the current for the P7 output.

The next example involves switching devices on the high voltage AC mains. A DC power supply must still be used in order to switch the relay through the P7 output.


And of course the last example is how to create a simple dry contact closure with a P7 output.

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Just a heads up; in the last example noted here, we were able to trigger an Input on an older Viking Auto Gate Opener without the use of the Form C Relay on this diagram (in Gray). Not sure how this worked but the client did not use a Relay and just landed the two conductors onto the Input terminals of the Viking Opener.