CCTV Camera Long Exposure Control Circuit

The circuit was designed to control long exposures of the CCTV camera using a simple AT89C2051 microcontroller. It can be used with modified B/W cameras based on Sony chips CXD2463R ( CCD timing control ) and CXA1310AQ ( CCD signal processing ). These ICs may be found with Sony HAD CCD sensors in small board cameras with "1004" or "1043" designations.

The circuit contains slightly more transistors and resistors than necessary. It is useful to have the camera in the "normal" autoexposure mode when the MCU is started or even if the MCU socket is empty. Software functions are controlled and monitored by five push buttons and three LEDs. MCU ports assignment may be different - it depends on software. The schematic described below allowed me to design a simple single sided prototype PCB. There are four unused port pins for future developement : UART RX/TX for the remote control ( computer serial port connection ) and analog comparator inputs which may be used e.g. for supply voltage checking.

Exact values of resistors are not critical as well as types of transistors and diodes. I used BC547 ( NPN ) and BC557 ( PNP ) transistors, 1N4148 diodes and SMD resistors and capacitors with values listed in the schematic. I can't provide a PCB layout of the daughterboard because the original prototype design was slightly different ( more complicated ) and I modified it using the original PCB which is now not optimal for this final version. I'll prepare some "production model" in the future.

The CXA1310AQ amplifier gain control circuit ( at the top - one switch, potentiometer and two resistors ) is optional. It is not related directly to long exposures but it helps to obtain a desired image brightness when the AGC output is not optimal. Sometimes a minimum noise is more important than the maximum gain.

I/O description

Connections to the camera board are denoted by the IC pin numbers. "A" means the CXA1310AQ chip, "D" means CXD2463R and "C" is for CCD sensor pins. Following camera connections are used :

SYNC and BLK signals were originally brought to drive an embedded digitizer and capture circuit which is not completed yet ( I have a problem digging up some special parts ).

It is necessary to decouple +5V, +12V and +15V power supplies by capacitors because the MCU frequencies interference may cause some strips or noise in the CCD signal. If there are problems with a correct decoupling I recommend following measures :

It is possible to test the circuit without any MCU in the socket. Control ports P1.4 .. P1.7 ( pins 16 .. 19 ) are pulled high and the camera should work in the "normal" mode without the MCU. Shorting the pins to the ground ( pin 10 ) should switch corresponding functions.

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M.P. 2004