Page 245 - Making PIC Microcontroller Instruments and Controllers

soME REIL-WOR| D ||OTES 243

(Cort nued)
,tif-6lCi!f :li:Lilt Program lo count marbles with an escapement
DISABIJE ; disable interrupts
INT_ROIITINE: ; the interrupL rouLine is called
, everv 1/60
PULSour PoRTC.1, POTo ; of a second and pulses both servos
i . a
PUT-SOtxr PORTC.o, POT1 ; theii se! values. Then ir
Iri|l!coN.2=o ; resets the interrupt flag for Tinero
R.ESUME ; resune progran
ENAaLE ; enable inLerrupts
PAUSER: ; this routine is read fron POTo and
FOR AIPI{A =1 TO Pqr2 ; delernines how long it is betveen
PAUSE 2 ; inslruciions !o lhe servos-
NEXT AI-PEA ; adjust it uith POl'o
RETURN ; do no! nake it !o shor!
E N D ^ ' l p . o o , a s - - d - \ D .

The program starts out with both gates closed.
"wallloop"
The code in Program l7-2 wiil stay in the ntil switch I is pressed.
That opens the top gate and the system is ready to count.

As soon as a marble stops againsl the lower gate, the marble is detectsd. the top gate
closes and the bofton gate opens.

One is added to the counl3r (.at this point a dnot dny soo er or later).
The botton gate closes.
The top gate opens and the cycle is repeated.
When there are no more marbles. the system stops.

Press reset to staft over.

Some Real-World Notes

If we were designing for a real world situation. we would add some type of detectors
!o makc swe thc gates actually went in and out as intendcd. Proximity detectors of some
sol arc rhe detectors of choice in thal they have no moving pa s. we would probably
use pneumatic actuato$ and run fte operation lrom a prcgrammable logic controller
(PLC), though as we saw in this exercise, aPIC wouldbe much cheaper and would do
thejobjust line. The system could also, ()1-course.
be designed !o use two solenoids wilh
appropriate IN/OUT detectors.
The preceding is the simplest way to count the marbies, but it is pdi,l4rlb rlorr. Slow
enoush to be counted with an exDensive PLC!