Copyright © Parallax Inc.
Parallax Continuous Rotation Servo (#900-00008)
v2.2 10/24/2011 Page 4 of 8
Calibration – "Center" the Servo
The servo has a pot entiometer access port, right above the plac e where the cable attaches to the case.
The port allows the user to adjust the servo to hold completely still when receiving a 1.5 ms pulse width.
This is the value in the "center" of the range of control pulses the servo will accept.
To center the servo, program your host device to deliver a 1.5 ms pulse, continually refreshed ever y
20 ms. S ample calibration code is giv en below f or all BASIC Stamp model s, Spin for the Propeller
™
P8X32A microcontroller, and SX/B for the SX chip. All are avail able for downl oad from th e 900-00008
product page at
www.parallax.com
.
Connect the servo to your microcontroller's I/O pin. The example programs below specify an I/O pin.
BASIC Stamp Calibration Code - for all BS2 models
√
Connect the servo to BASIC Stamp 1/O pin P12, or update the ToServo PIN declaration.
√
Run the program, and gently twist the potentiometer adjustment screw until the servo does not
turn or vibrate.
NOTE: Calibrating the servo may take some patience. The potentiometer is very
sensitive so a very light touch will be required.
' CenterParallaxCrServo.bs2
' {$STAMP BS2}
' {$PBASIC 2.5}
#SELECT $Stamp
#CASE BS2, BS2E, BS2PE ' PULSOUT Duration units are 2 us for these models
Center CON 750
#CASE BS2SX, BS2P, BS2PX ' PULSOUT Duration units are 0.8 us for these models
Center CON 1875
#ENDSELECT
ToServo PIN 12 ' connect servo to I/O pin P12, or change it here
DO
PULSOUT ToServo, Center ' ToServo pin outputs 1.5 ms pulse
PAUSE 20 ' refresh pulse every 20 milliseconds
LOOP
Propeller Chip Calibration Code – for P8X32A
√
Download and unzip the Propeller code file from the 900-00008 product page.
√
Connect the servo signal pin to Propeller I/O pin P0.
√
Run the program CenterParallaxServo.spin, and gently twist the potentiometer adjustment screw
until the servo does not turn or vibrate.
NOTE: Calibrating the servo m ay take some p atience.
The potentiometer is very sensitive so a very light touch will be required.
{{ CenterParallaxServo.spin
For centering Parallax Continuous Rotation Servo
or holding Parallax Standard Servo at 90° position.
Sends a 1.5 ms pulse approx every 20 ms }}
CON
_clkmode = xtal1 + pll16x ' System clock
→
80 MHz
_xinfreq = 5_000_000 ' Using 5 MHz external crystal oscillator
servoPin = 0 ' Servo signal to this I/O pin-change if needed
PUB CenterServo | tInc, tc, tHa, t
