The not so Automatic 100
A computer controlled shutter for the classic 100-series Packfilm camerasMany Photographers would like to have control over shutter speeds and aperture settings of their camera.
The popular folding packfilm cameras of the 1960s are fully automatic. The three manual models (180,190,195) are scarce and very expensive.
The exposure in the automatic cameras is controlled by an analog computer that integrates the current through a light sensitive resistor.
Once the integral reaches a certain value the shutter snaps shut.
Some people have successfully modified the exposure circuit with a potentiometer in place of the photoresistor to set the shutter speeds. I tried this but the results were not so good.
So I threw the analogue electronics out altogether and replaced them with a microcontroller that does the shutter timing.
This works well with shutter times 1, 1/2, 1/4, 1/8, 1/16 1/32, 1/64, 1/128, 1/256, 1/512 seconds and Bulb
Apertures are set by the film speed and Sunny/Dull settings to f/8.8 , 12.5 , 17.5 , 25 , 35 , 50
The modified Automatic 100 works when set with a Light meter.
MicrocontrollerThe PIC12F629 from Microchip is very small and cheap.
Six of its eight pins are freely configurable inputs and outputs with interrupts on change.
A 4 Mhz oscillator is on chip.
The 8 Pin DIL package is convenient for hand soldering. There is also a very small SMD package available.
It runs from a 3V> to 5V supply. I chose 4,5V like the original shutter so it can run on 3 AAA cells.
The PICKIT2, a complete development platform for many PIC controllers, is inexpensive and includes all the necessary hard- and software.
SwitchShutter speeds are set through a BCD (direct, "1" = closed)coding switch.
External 56K pull-up resistors are used because the internal weak pull-ups did not work. The resulting bit pattern is inverted - 0=1111 1=1110 2=1101 etc. A complementatry encoder would result in a BCD pattern but those switches are more scarce and more expensive.
Magnet DriverThe shutter magnet is driven through a "open collector" NPN darlington transistor. I used a MJD122 but any high gain (>1000) type would do.
Shutter contactsWe need the shutter contact that closes on shutter cocking and opens when the first blade has snapped open, the button coontact for "B" mode and the X-sync for the flash connector. All three contacts share a common "ground" wire.
Mechanical qThe circuit goes where the analog circuitry was before. The encoder switch could either be in the front of the shutter or on top of it.
ProgramThe Assembler program , (assembled HEX file) initializes the PIC first.
When the main loop starts the PIC goes into sleep mode and waits until the shutter is cocked (shutter switch goes low).
On cocking shutter(switch goes low) the PIC turns the holding magnet on and reads the dial switch, then continuously tests for shutter open (shutter switch high).
When the shutter has opened the program calls the exposure table where it finds the value to start the timer with,starts the timer and cuts off the magnet ->shutter closes.
If the dial switch is "9" the program jumps into the "BULB" routine , which holds the shutter open as long as the button contact is pressed.
The button switch uses an input of the dial switchg that is open at "9".
Then the program jumps back into the main loop and the PIC goes to sleeop until the shutter is cocked again.
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Pretty Cool!:) I always wanted to convert a 35mm film camera to Digital, back in the early Digital Days. When they were so expensive. I Use to have a Kodak and a Polaroid Instamatic... The Pics fade after a few years though:( I gave them both to a friend who was collecting old cameras. I Still have my Kodak Pocket 110, 8mm Movie Camera, Bell and Howell 8mm Projector and a newer Projector that I bought in the 80's. And who knows what else is out there in the Garage!:)