Page 242 - Making PIC Microcontroller Instruments and Controllers

GIHECOU TERS! COU TI G ITARBLES
240 UNDEBSTANDI

Counting with an Escapement

"escapemenfbased"
counling program step by s!ep, segmenl by seg
LeCs develop the
mcnt, as we werejust aliscussing.At staft oftbe program' we need to wait for a signal
the
to slart the colrnling process. At this point, the top gale must bl} open and the lower gate
muslbe closeal. When the lirst maible amves on top of the boltom gate. wcwill be ready
to stai counting. We assume lhc other na$les are in position, but this-as we will see
may not necessarily be lhe case, meaning that our software must accommodate all
possibili!ies.
The hardware we will respond to and conlrol consisls of the follov"rng ilems connected
as indicatedl

Infrared LED power on PORTD.I
Infrared LED ground to gr,ound

power on PORTB
Phototransistor l
Photolransi stor ground to ground

signal to POmB.0
Phototransistor
Top seNo on PORTC.I to the servo pins
Bottom servo on PORTC.2 to the servo pins
We will u se switch I connected between line PORTB.4 and ground to start the count_
irg process. PORTB.4 will be pulled up internally with OPIION-REC 7=0

The rviring schematic for thc preceding description is shown in Figure 17 4'

5 VOLTS 5 VOLTS

-4

rl:FiiU.-iiSilt],4li The two ways of doing schematic wiring diagrams lor lR'LED phototransislor