Motor Speed Selector

Photograph of the prototype hardware:

Circuit diagram:

Controlling program:

(*$d 2313 - device of choice *)

(*$c 4 - clock rate *)

(* Demonstrate use of the PWM output to drive a DC motor

and keypad to enter the speed *)

PROGRAM MotorSpeedController;

(* Function: Waits for a keypress on the numeric keypad; sets the speed of

a dc motor to one of 10 rates: 0 = slowest, 9 = fastest.

'#' zeroes the display,

'*' ends the program.

Author: C.A.G.

Date: 21/05/02

Version: 1.0 *)

USES

Keypad, PWMgen; (* import library modules *)

VAR

speedCode : byte; (* key stroke entered on pad *)

(* import from Keypad *)

PROCEDURE InitKeyPad; LIBRARY;

FUNCTION GotKeyPress(VAR keyPress:BYTE):BOOLEAN; LIBRARY;

(* import from PWM *)

PROCEDURE InitPWM(freq, dutyCycle: BYTE); LIBRARY;

PROCEDURE PWMon; LIBRARY;

PROCEDURE PWMoff; LIBRARY;

PROCEDURE SetDutyCycle(dutyCycle:BYTE); LIBRARY;

BEGIN

InitPWM(#2,#0); (* set prf to ~1kHz[4MHz clock], duty cycle=0 *)

InitKeyPad;

PWMoff;

REPEAT

(*wait for a keypress*)

REPEAT

UNTIL GotKeyPress(speedCode);

(* check which key is pressed *)

IF (speedCode <= #9)AND(speedCode >= #0) THEN (* scan display *)

BEGIN

speedCode := #10*(speedCode+#1); (* convert to duty cycle 10..100 *)

SetDutyCycle(speedCode); (* update motor speed *)

END

ELSE IF speedCode = #11 THEN (* its a '#'so stop motor *)

PWMoff

ELSE IF speedCode = #10 THEN (* its a '*'so start motor *)

PWMon;

FOREVER;

END.

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