Understanding the C8 Board - Part 2

Last time, we covered the very basics of the C8 board including the power inputs and the LED functionality.  If you missed these parts, you can find them here:

Part 1 - Power and LEDs

Here we will go in-depth on the inputs of the C8, including the wiring, operation, and jumper configuration.

The Anatomy of the C8 Input

Each input of the C8 has two terminals, labeled A and B.  Typically, a dry contact is placed across these terminals and a change in the state of that contact will activate the input of the C8.  However, the C8's inputs are very flexible - capable of handling almost any type of input including dry contact, voltage, or open collector inputs.  The key to the flexibility of the C8 input is in its wiring.


The A terminal of the C8 board is a resistor-limited voltage source, provided by the higher of the B1/B2 power inputs.  The resistor limits the current of this voltage to approximately 10mA maximum when directly shorted to ground.  This voltage may be used in conjunction with the B terminal for activation of the input.

The B terminal is the actual input to the C8's circuitry.  It is a voltage input, with an acceptable range of 9-30VDC for activation.  It may be activated with the voltage available on the A terminal or with any voltage common grounded with the FPO/C8.

Note that there is no ground connection on the input.  If you place a voltmeter across the A and B terminals of the input, you will see a voltage - this is normal and will not damage a dry contact due to the current limiting resistor on the A terminal.

Dry Contact Input

By far, the most common input application is a dry contact.  This contact may be the output relay of an access control panel, a momentary pushbutton, a relay output on a keypad, or any other dry contact.  The C8 will operate correctly with a Normally Open (NO) or Normally Closed (NC) contact by setting the blue jumper for the zone.  There is no requirement to use a NC input for Mag Locks and a NO input for door strikes - the C8 will work correctly for any output type with any input type, so all inputs may be wired the same regardless of the lock type being used.

Voltage Input

A separate voltage source between 9 and 30VDC may be used to activate the C8's input, by connecting it to the B terminal.  This voltage must be common grounded with the FPO system in order for it to work properly.  The FPO power supply's DC1- terminal is a convenient point to tie the grounds together.  The C8 can be set to activate on the application of a voltage or the removal of a voltage by setting the blue jumper for the zone.

Open Collector (Transistor) Input

An open collector input may be used to activate the input of a C8, though some precautions may need to be taken.  First, the activation device with the open collector output must be common grounded with the FPO system to work correctly.  If wired as shown in the first diagram below, with the diode, the C8 will work with any open collector output that can sink the 10mA maximum current of the A terminal.  This diode blocks the voltage from the A terminal from reaching the open collector.  This diode may be eliminated if the open collector output can tolerate the 24V supplied from the A terminal.  Verify with the activation device's manufacturer to be sure - many have a 12V maximum.


The second diagram below shows an alternate wiring method if the open collector output also provides a voltage source.  This is typical for open collector outputs designed to power locks - the lock is designed to be connected to the +12V terminal and the ground for the lock is provided through the open collector.  When using this type of output with a C8, use a resistor from the voltage terminal to the open collector to provide the activation voltage required by the C8, rather than using the C8's A terminal.  The resistor value isn't critical, but should be around 1K ohm.  Sometimes multiple outputs on the activation device will share a common voltage terminal - in this case use multiple resistors from the voltage terminal to each open collector output.

Typically for an open collector output, the blue jumper for the zone should be in position 1, however moving this jumper to position 2 will reverse the operation if necessary.

Blue Jumper

The blue jumper for each zone inverts the operation of the input for that zone.  This allows the input to operate either on application of voltage to the B terminal or on removal of voltage.  It is important to get this jumper set properly for proper operation of the C8.  When set up correctly, the LED for the zone should be steady when the door is locked and flashing when the door is unlocked.  It is possible to set the board up so that the LED operates in the reverse and the lock still works properly under normal conditions, however the door will not unlock when the FAI input is activated.  In this situation, simply place the blue and white jumpers into the opposite position of where they currently are.

Note that if you don't have the jumper positions memorized and don't have access to a manual, you can still set the jumpers properly by setting your activation source to the state where the door should be locked, then set the blue jumper on the C8 so that the LED is lit steady.  Verify that it is set correctly by setting the activation source so that the door should be unlocked and verifying that the LED is flashing.  After setting the blue jumper, adjust the white jumper to set whether there is voltage when the door is locked or unlocked.  This will be covered in more detail in the next part of this series.


Next part we will cover the outputs of the C8 - again going into detail on the wiring, jumper settings, and other details.  Until then, if you need any assistance, our Technical Support department is here to help.