A work in progress by John D.

1. Current limiting arming board

The CLAB limits the current to the firing circuits to 10 ma.  This is just enough to power the continuity test circuit but way below the required amount to fire the igniter.  So in the case of a damaged firing circuit, stuck or faulty relay or even if someone pushes the button at the LCO the igniter cannot fire.  You will see a relay on the CLAB as well as relays on the individual firing boards.  BOTH relays need to closed to launch a rocket.  If the relay on the CLAB board is closed then the attached strobes on each distribution box will start flashing.  This will indicate the range is hot and NOBODY should be on the range.  The CLAB board uses a high quality Panasonic 40A automotive relay which is protected by a 20A thermal circuit protector.

2. Wiring Distribution board

The WDB main purpose is to making the internal wiring organized and neat.  Each cable connector on the PCB is labeled to where it goes to make service easy to understand.  The other function of the WDB is the entry point for the external battery power.  The WDB uses a bridge rectifier power input which allows the battery to be hooked up with either polarity.  This makes it impossible to hook up the battery wrong.

3. Individual firing circuits, pad firing board (PFB)

The PFB, one for each pad, fires the igniter and provides a continuity check.  As mentioned earlier the PFB cannot fire an igniter by itself, it requires the relay on the CLAB to be activated as well.  For this reason there are no arming or test switches or modes needed.  The PFB is “dead” until the CLAB relay or arming switch is activated by the LCO. The PFB continuity circuit shows drives a continuity LED on the distribution box that the flyer can check after connecting the igniter.  Also the PFB has a fault indicator that will detect a fault or stuck relay on the board.  This condition is indicated by a red LED on the distribution box.  If this fault LED is lit, this indicates that that PFB is faulty and that channel should not be used.  The PFB relays are also the high quality Panny 40A relay and is also protected by a 20A thermal protector.  Additionally the active circuitry on the board are protected against static discharge with 3 TVS diodes on the lines that run outside of the distribution box (power, igniter, and launch controller cable).