PIC Camera Controller

for eclipse photography

  Figure 1

The circuit is a standard configuration, taken straight from the applications data sheets with a few straightforward modifications.  A ZIF socket holds a 16C84 PIC controller to save the stress of continually inserting and extracting the device during development. 

The 8-bit input port has a set of DIP switches that allows for a variable delay between each photograph.  The 4-bit output port has LEDs to indicate when the appropriate pulses are output.  Programmable links connect three of the output lines to MAX323s, which are dual electronic make switches.  The 4th LED is used to indicate when the sequence is complete. 

The circuit operates with a 4MHz clock, derived from a resonator.  It has a stabilized +5V supply and a "large" reset switch which is used to start things off.

The program itself was written in assembly language mainly because I felt that compiling a high-level language would produce more that the 2K bytes that could be accommodated on the chip.  In fact assembly language was better because it gave greater control of the output pulses.  It was necessary to "create" trigger pulses of 2ms duration which was the settle time for the MAX323 devices.

Initially I planned 6 x 1/1000th shots to coincide with second contact and 6 with third contact having increments of 2 seconds.  Then the balance of the pictures on a 37 exposure film spread out over totality with a variable delay, incrementing and decrementing the cameras shutter speeds over the whole range.  Ideal of course for Mexico, Peru, Mongolia, Venezuela, Cornwall and Zimbabwe but the program is undergoing a re-write for Australia where there are only 29 seconds to "play" with.

  Figure 2

This picture shows the five pin connector that gives access to the shutter speed control switches and the electronic trigger.  It fits very snugly onto the base and there is just enough space inside the hand grip area to thread some wires to the desired points in the circuit.  The connector is fixed in place with a dab of epoxy adhesive.  If you don't feel up to doing the modifications yourself, you might find that a local Canon service centre would do the job for the equivalent of half an hours labour.

I chose a Canon T70 specifically because the shutter speed adjustments are done by UP and DOWN push button switches.  Good quality camera bodies can be bought for about £70 (or $100).  Mind you, if you do buy, try to ensure that your purchase has the screw dust cap or cover over the electronic cable release socket (seen just above and to the right of the external connector).  These are as rare as hens teeth and the cameras look rather grotty without them.  You might also ensure that the camera has the proper viewfinder eyecup assembly - finding the right type of rubber trimmed attachment is not easy and the bodies tends to scratch your spectacles if you are not careful.  I use angle finders anyway.

RIM - 23Jun02