User's Manual

The EXT_KEY_OUT signal is TVS-protected by diode CR35 before routing to pull-down resistor R9 and
transistor Q1. Resistors R10 and R11 bias the LED of opto-coupler U2 while diodes CR33 and CR34
transient protect the transistor outputs of opto-coupler U2. The transistor outputs are labeled
EXT_KEY_OUT+ and EXT_KEY_OUT- before routed to terminal block TB1.
The MON1_AUDIO_ID and MON2_AUDIO_ID are transient protected by diodes CR30 and CR31 before
being voltage-divided by resistors R1/R3 and R2/R4. The lower voltage level signals are called
DET_IDENT1 and DET_IDENT2 before being routed to terminal block TB2.
1.3.2.9 AC Monitor CCA Theory
Refer to Figure 1-15. The AC Power Monitor CCA provides a means for the DME system to measure the
AC current and voltage levels of the obstruction lights and of the DME system itself. A photo switch
bypass is also incorporated for the obstruction lights in the event manual operation is desired.
T1 is a current-sense transformer in series with the obstruction lights line supply from TB1-4 and TB1-5.
AC current through the primary of T1 induces a current in the secondary. The secondary is connected to J1-
3 and J1-4. A resistor on the BCPS CCA converts this current to voltage for measurement.
T3 is a voltage step-down transformer connected in parallel to the obstruction lights supply at TB1-4 and
TB1-6. The transformer primary is strapped to accept a nominal 220 VAC. AC voltage on the primary is
stepped-down on the secondary and current-limited by R1 and R2 in the unlikely event of an accidental
short-circuit. The secondary is center-tapped and is routed to J1-1, J1-2, and J1-13.
T2 is a current-sense transformer in series with the DME’s line supply from TB1-10 and TB1-11. AC
current through the primary of T2 induces a current in the secondary. The secondary is connected to J1-7
and J1-8. A resistor on the BCPS CCA converts this current to voltage for measurement.
T4 is a voltage step-down transformer connected in parallel to the DME’s supply at TB1-9 and TB1-10.
The transformer primary is strapped to accept up to 220 VAC. AC voltage on the primary is stepped-down
on the secondary and current-limited by R3 and R4 in the unlikely event of an accidental short-circuit. The
secondary is center-tapped and routed to J1-5, J1-6, and J1-14.
An external SPDT switch is connected at TB1-1, TB1-2, and TB1-3. This switch in the OFF position
allows an external photo switch to control the application of power to the obstruction lights. When in the
ON position the obstruction lights are turned ON continuously.
Earth ground is also connected to the AC Monitor CCA via the board’s mechanical mounting holes and
TB1-12.