Page 168 - Build Your Own Quadcopter_ Power Up Your Designs with the Parallax Elev-8

Chapter 6: Radio-Controlled Systems and Telemetr y 147

OBJ
sig: “PWM2C_SIGEngine.spin”
com: “RS232_COMEngine.spin” ‘not discussed – for serial comm
str: “ASCII0_STREngine.spin” ‘not discussed – for text
manipulation

PUB demo
ifnot( com.COMEngineStart(_receiverPin, _transmitterPin,
_baudRateSpeed) and { } sig.SIGEngineStart(_leftServoPin,
_rightServoPin, 100))
reboot

repeat
com.transmitString(string(“Left: “))
com.transmitString(1 + str.integerToDecimal(sig.
leftPulseLength, 10))
com.transmitString(string(_clearToEndOfLineCharacter,
_newLineCharacter, “Right: “))
com.transmitString(1 + str.integerToDecimal(sig.
rightPulseLength, 10))
com.transmitString(string(_clearToEndOfLineCharacter,
_homeCursorCharacter, “Servo Pulse Length’s”,
_newLineCharacter))

This program is the driver that uses an “engine” object to perform the pulse-width
measurement and then reports the results back to the PSerT application for user display.
The heart of this program is the forever-repeating loop that sends a series of strings over
to the PSerT. The pulse-length values are acquired in the two object-method calls
sig.leftPulseLength and sig.rightPulseLength. The sig object is a reference
to a program named PWM2C_SIGEngine, which is listed below in an abbreviated manner.
I did add some comments to key code lines to help explain what was happening in
the code.

VAR
long leftLength, rightLength, stack[7]
byte cogNumber, leftPinNumber, rightPinNumber, timeoutPeriod

PUB leftPulseLength ‘’ 3 Stack Longs ‘ Returns the servo

microseconds.
return leftLength

PUB rightPulseLength ‘’ 3 Stack Longs ‘ Returns the servo

microseconds.
return rightLength