DARKROOM TIMER PIC & 7seg drivers

This section is the 'brains' controlling 'timing' with Push Buttons
and directs (from the PIC 16F84) the BCD output to the CD4511
a very ordinary 7 segment decoder driver so as to operate the
a,b,c,d,e,f,g segments on each multiplexed 7 seg LED Display
a FND 500 or FND 560 (1/2") (12mm), a very common LED.

The PIC is controlled by a 4meg xtal, whose accuracy I have
tested to about 8 seconds error over 1 hour, and that is
really no error to be bothered with or even considered in
the common use of this timer function, as repeatability is
the issue in making exact exposures, copies (negs or ristons)
not idiotic military/scientific accuracy in 'timing'

The 3 Push Buttons from Left to Right are as follows.....
1. BLACK, the Program Timing Selector (up to 10 pre-timed operations)
2. GREEN, The 'GO' start function of a pre-programmed timing function.
3. RED, the end timing routine, Emergency STOP, used with the preset.

At the end of any timed 'used up' function, the unit will 00000, (zero)
then halt / hold for a few seconds, before PIC resetting the time set
routine for the next exposure, during this sequence, the safe light
will come back on for you to clean up get ready for extra exposure.
A 'FOCUS' switch is provided, and this can be used is you are using
an enlarger to do photographs, or provide extra manual exp. time

With a little bit of carefull thinking, and no interuptions, are needed for the
pre-programming of the Darkroom Timer, it is not easy but not really hard.
And as programming is a rare occurance, costs are better to spent with
Push Buttons, rather than a fancy, memory consuming type of computer
style keypad entry idea, which was considered, but to use a steam roller
to crush wall-nuts, then Push Buttons won out at the end of the $$$
We at RCS may even supply the PIC with a standard set of timings already
pre-programmed (or ask nicely and we may be able to put in your choice)
for a few extra dollars, but the re-programming at any time, is not fixed and
any body can sit down and plod through the steps, (with no interuptions).
One of the features of this PROTIME project is, what-ever time you have
programmed or last used, then when Power Off and Power Back ON, it
will 'remember' in the static RAM, the 'last time used' or Time Program #1

The 5 x PNP transistors are used to multiplex control the 5 x 7 Segment
Displays on this and if needed 'external' LED Displays, more discussed
on this feature later on. You will notice over on the Right Hand Edge
there is a 34way (common floppy drive style set of pins) connector so
as the circuit board can be used in a smaller case and permit the LED
Display readouts to be 'above' this board for better use in a darkroom.
The PROTIME board can be left as 1 single board for studying and
developing up an *.asm & a *.hex file for the PIC 16F84 or cut into 4
separate boards for inclusion into a 'more economical' Panel Box housing.
The project has been carefully designed for student & real work use.
If only local FND 500/560 LED readouts are used then a 5v/6vDC is
needed, but if you are going to plug in 5 of JAYCAR's large 2.3inch
(58mm) readouts ZA1850, then you are going to need a 12vDC plugpack
and a 7805 (TO92) style regulator so as the 5vDC looks after the PIC
and the CD4511 and local FND500/560 Display LEDs, where as the
34way ribbon cable will carry the 12vDC up to the JAYCAR LARGE LEDs.
That way, every one in the darkroom can see the event timer working.
misc. items like DC smoothing Electro. Caps & small RF Disc Ceramics
are placed on the circuit board to eliminate 'possible annoyances' as well
as the simple LED on the DC power supply, (cheaper than a voltmeter)

Don't forget, a fully programmed PIC microcomputer can be purchased
for this project after you have 'correctly' soldered in all the required comps.
plus any extra FND LED Displays you may wish to use as 'plug-ins'.

As outlined on the main DARKROOM Timer page, this project is both for
educational (in PIC Programming) and commercial in its capable useage.
Every one of the 12+1 In/Out - RA/RB pins are used, with no luxurious
waste of a function, sorry no beeps and burps, just isol. relay switching.

Section A
PIC CPU 'brain', 7 Segment Decoder plus MUX LED driver

PIC 'timing' & 7 Seg. LED Decoder Driver

Don't forget to send in an S.A.E. for an
A4 checkplot of the circuit board etc.