Ultimate Chicken House - Phase II - electronic circuit design

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When I set out with this project I bought a selection of PIC microcontrollers to play with. Mostly costing £1-£2 they are remarkable little devices. The original plan was just to operate the timer for the door with a small and simple device and so I chose the little 8 pin pic12f683 and used the internal oscillator to keep time. Unfortunately from experiments this lost or gained an unacceptable amount of seconds each day and despite fine tuning I realised I would have to use an external crystal oscillator for the desired accuracy. I also decided to use more pins to increase the project functionality. I managed to destroy a couple of pic16f648a and ended up with a pic16f88 which the project is based on. Just about any 18 pin pic would do (the pic16fxx would be a cheaper option) and converting the software to work on different pics is relatively easy.

The circuit needs to accomplish the following tasks:

To drive a motor forwards and backwards to open and close the hopper door.
To open/close a switch on the VSB unit to open and close the chicken house door.
To utilise as little power as possible.

I wanted to isolate the electronics of my project from the electronics of the VSB unit so this meant using a relay rather than a transistor. Holding a relay open for see
veral hoyse each day would ehave used a lot of power so I decided to use a latching relay. This operates with a small pulse (about 2 ms) of current in one direction and then the relay's contacts
remain in that state even with the power off. Thr relay is reset with a pulse of current in the opposite direction. The latching relay is perfect fot this purpose but it adds considerably yo the expense of the project, At $4.54 it is the most expensicve part of the whole circuit.

With the feeder motor and
Comments?

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