Page 73 - Making PIC Microcontroller Instruments and Controllers

ADVAICED EXERCISET COI|IROLIING !J RC SERVO FBOL THE KEYBoIRD 63

qF,ii{ili!{inilaillli: cenerates telephone key tones on the piezo speaker (555-1212)
CLEBR
DEFINE OSC 4
DIMFOUT PORtC.2, t5, 5, 5, !, 2,
ElID

The key tones generated are rough (before filtering), but you can tell that rhey mimic
the telephone dialing tones. The signal needs to go through a filter and then an ampli
fier to be clean and viable. This command has a number of constraints, depending on
the processor used and the speed of the oscillator in the circuit. See rhe PICBASIC PRO
Compiler manual for details.
The FREQOUT command can also be used to gercrate telephone dialing frequen-
cies. See the PICBASIC PRO Compiler manual for details.

Advanced Exercise: Controllins an RC

Servo from the Keyboard

Now that ws know how to generate pulses and confol the LCD, we can use the LAB
Xl to control ihe position of an RC se o connecred to po JT from switches SWl,2,
and 3 on the keyboard. Program 5.11 is designed such that . . .

Swilch I will turn tbe servo clockwise incrementally.

Switch 2 will center the servo from wherever it is.
Switch 3 will turn the se o counrerclockwise incrementally.
The circuitly for this exercise is shown in Figure 5.6.
Note that by changing a few variables that are defined up front, we can adjust the
centerposition, the incremental step value, and the extreme CW and CCWpositions of
the servo. (This program has been adapted ftom, and made simpler than, a Fogram in
the microEngineering Labs sample ptograms. It is instructive to compare this program
with the programs SERVOX and SERVOI in the sample programs.)

l]]il!.!.!!&l.ia€!!:!!:t servo Position control for an Fyc seruo from PoRTB buflons
(This program uses a servo on JumperJT)
CI.EAR
DEFTNE OSC 4
DEFINE IJCD_DREG PORTD ; define LCD connections
DEFTNE IJCD_DBIT 4 , defne LCD connections
DEFINE IJCD RSREG PORTE , de6ne LCD coanecEions
DEFTNE IJCD RSBIT O , de6ne LCD connecEions
DEFINE I|cD EREG PORTE , de6ne LCD connections
DEFINE I|cD EBIT 1 , de6ne l,CD connections
POS VAR WORD , serwo posilion variable