Generation Of The Reference Voltage - Metz mecablitz 44 MZ-2 Servicehandbuch

Technik und Service Seite: 41
Technology and Service Page: 41
mecablitz 44 MZ-2 / 44 AF-3
ENGLISH
SCA 15 - SCA 3002 identification:
On flashguns and adapters of the SCA 3000 system, contact SCA 15 is not connected. On flashguns of the
SCA 3002 system, contact SCA 15 is connected via two 47 kOhm resistors or one 100 kOhm resistor to +5 V.
In the mecablitz 44 MZ-2, this is the resistor R4029 (100 kOhm).
SCA adapters of the SCA 3002 system are compatible with flashguns of the SCA 3000 and SCA 3002
systems. However, the adapter must know which system the flashgun uses, so that it can set its functions
accordingly. The above connection at contact SCA 15 of the mecablitz 44 MZ-2 identifies the mecablitz as a
flashgun of the SCA 3002 system and the adapter sets itself to operate in accordance with the SCA 3002
system.
SCA 16 - Auto-off and Wake-up:
Optionally, the user of the mecablitz 44 MZ-2 can set it so that it switches itself off automatically after three
minutes. If the user does nothing within this period and there is no exchange of data with the SCA adapter, the
mecablitz switches to standby mode, where it consumes as little power as possible. The quartz oscillator of the
µC IC401 is switched off in standby mode.
When the mecablitz switches to standby mode (Auto-off), the µC IC401 switches Pin 49 (+5V ON/OFF) to
HIGH, causing transistor Tr406 to cut off. The supply voltage for the SCA adapter (SCA 13) and the switched
5 V voltage (+5VG) are switched off.
The mecablitz is reactivated by an interrupt (Wake-up): pressing any of the keys on the control panel (S402 to
S407) generates an interrupt for the µC IC401.
The mecablitz belongs to the SCA 3002 system. In this system, it is possible for the SCA 3002 adapter to wake
up the mecablitz via interface contact SCA 16. If the user briefly depresses the camera shutter release, the SCA
adapter connects contact SCA 16 to ground via an (open-collector) transistor. This causes Tr429 to cut off and
Tr411 to conduct. The resulting LOW signal at Pin 51 (NSBB INTR) of IC401 generates an interrupt for the µC.
When such an interrupt is generated, the µC IC401 switches the mecablitz back to its normal operating mode
(the mecablitz wakes up). Pin 49 (+5V ON/OFF) of IC401 switches to LOW, causing Tr406 to switch the
voltage +5 VG back on.

6.2. Generation of the reference voltage:

The comparator circuit for automatic control of the light output requires an adjustable reference voltage of
about 0.5 V to 3.5 V at Pin 3 of IC404A. This voltage is generated with the transistor stages Tr423 to Tr425.
Level changes from HIGH to LOW and LOW to HIGH at Pin 57 (Charge1) and Pin 58 (Charge2) of IC401
cause the transistors Tr425 and Tr423 to conduct and cut off. In this manner, it is possible to charge capacitor
C410 quickly via R4086 or slowly via R4083. C410 is thus charged until the desired reference voltage is
reached. C410 can be discharged by switching Pin 53 (Discharge) of the µC IC401 to HIGH, causing Tr424
to conduct. C410 is then discharged via R4084 and Tr424 and the reference voltage drops,
The (reference) voltage on C410 is measured by the µC IC401 via the A/D-converter input at Pin 46
(HSS Ref A/D) and is stabilised at the desired value by controlling the levels at Pins 53, 57 and 58.