Technik und Service
Seite: 35
Technology and Service
Page: 35
mecablitz 44 MZ-2 / 44 AF-3
ENGLISH
If the flash is terminated by a TTL pulse from the camera (TTL pulse on contact SK4) during the TTL gate time,
µC IC401 switches pin 53 (IGBT-DRIVE) to LOW to prevent the ITGBT from conducting again. At the same
time, "OK" (correct exposure confirmation) is displayed on the LC display of the mecablitz and the µC briefly
activates the illumination of the display. If the flash is not terminated by a TTL pulse from the camera, pin 53
switches back to LOW after a maximum of about 14 ms and the IGBT cuts off. At this time, the energy stored
in the flash capacitor is exhausted.
5. Microprocessor and Periphery:
Switched supply v5VG
In order to reduce the power consumption of the mecablitz in standby mode, the switched supply voltage
+5VG for various parts of the electronics is switched off when standby mode is activated. In normal operating
mode, µC IC401 switches pin 49 (+5V ON/OFF) to LOW. Tr406 therefore conducts and enables the switched
supply v5VG at its collector. In standby mode, pin 49 switches to HIGH, Tr406 cuts off and the supply
v5VG is switched off.
Reset circuit
IC402, pin 2 monitors the 5 V supply voltage for the µC IC401. If the µC IC401 receives a sufficiently high
supply voltage (>4.2 V) at pin 1 (+VDD), the FET at the output pin (1) of IC402 cuts off and the reset input
(pin 67) of the µC IC401 is HIGH.
If the supply voltage drops below 4.2 V, IC402 switches pin 1 to ground. The reset input of the µC changes to
LOW and the µC thus receives a RESET signal. Execution of the program in the µC is stopped until pin 1 of
IC402 switches back to HIGH.
User controls:
The mecablitz has three buttons: "Test" (S402), "Mode" (S403) and "Zoom" (S404). These buttons are
connected via R4024, R4025 and R4026 to the +5.0 V supply voltage and to pin 78 (TEST), pin 79 (MODE
IN) and pin 80 (ZOOM IN) of the µC IC401, which are normally HIGH. When any of the buttons is pressed,
the corresponding pin of the µC IC401 is switched to ground or LOW. The µC IC401 thus detects that a
button has been pressed and executes the appropriate routines.
LC display:
The LCD module Az401 of the mecablitz is driven by the pins 7 to 30 (LCD-CONTROL) of the µC IC401. The
module requires three voltages for operation. The µC IC401 generates a voltage of +5 V at pin 2 (BIAS). The
voltage divider consisting of R4068, R4069 and R4070 derives the necessary three voltages from the +5 V at
pin 2 and these are available at the pins 3 (VLC0), 4 (VLC1) and 5 (VLC2) of the µC IC401.
