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www.digilentinc.com
Revision: 06/08/05
215 E Main Suite D | Pullman, WA 99163
(509) 334 6306 Voice and Fax
Doc: 502-082 page 1 of 2
Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.
Overview
The Digilent PmodCON3 Servo Connector
Module Board (the CON3™) makes it easy to
drive up to four servo motors from any Digilent
system board.
The CON3 conveys signals between a 6-pin
header and one of four servo-motor
connectors. A terminal block and jumpers are
provided so that an external motor power
supply can be used.
Features include:
• a 6-pin header connector
• four servo motor connectors
• flexible power delivery to servo motors
• small form factor (1.00” x 0.80”).
Functional Description
The CON3 can drive up to four servo motors
like those used in radio controlled airplanes
and cars. The servo motors can be powered
by 4.5V to 6V sources, while being controlled
with TTL-level logic signals.
The CON3 can be used in conjunction with
Digilent system boards and embedded
controller boards for robotics and distributed
systems.
The CON3 can be used with most servo
motors including those that deliver anywhere
from 50 to 300 ounce/inches of torque.
Servo motor power can come from a system
board (for low power applications) or from an
external power source (for higher-power
applications). A jumper setting determines the
power source.
Servo motors attached to the CON3 can be
driven individually or in groups of two or more.
Servo motors are used in a number of robotic
applications, including steering, movement,
and rotation. Servos are designed to move to a
precise desired position and then stop.
P1
P2
P3
P4
J1 Connector
Vcc
VF
P1
VS
GND
P2
VS
GND
GND
VS
VS
GND
P4
P3
VS
Servo Motor Connectors
J2
J3J4
J5
3-Pin Servo Motor Connectors
GND
GND
CON3 Circuit Dia
g
ram
CON3 Reference Manual Digilent, Inc.
www.digilentinc.com page 2 of 2
Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.
Servo Control
A servo is composed of a control board, motor,
sense potentiometer, and gears that connect
the motor and output shaft. A digital signal is
sent to the control board which then drives the
motor until the sense potentiometer verifies
that the output shaft is in the correct position.
A pulse width modulation signal controls the
direction and degree of rotation. A pulse signal
ranging from 1ms to 2ms is sent to the servo’s
control board, which recognizes the pulse and
begins the process of turning the servo’s
output shaft. A pulse of 1ms causes the servo
to turn all the way in one direction, a pulse of
2ms causes the servo to turn all the way in the
other direction, and a pulse of 1.5ms causes
the servo to turn to the center or to a neutral
position (see the diagram.)
To avoid problems with the servo, the pulse
signal should be sent at a period of 30-60
pulses per second. The pulse width (1.5ms,
1ms, or 2ms) controls the direction.
While different manufacturers produce servos,
all servos are made to the same pulse signal
specifications. A pulse signal between 1ms-
2ms is the safe range for a servo. Most servos
will function outside of this range but the
amount varies depending on the manufacturer
and the servo. A signal that is either too narrow
or too wide for a servo will cause the servo to
try to go beyond its rotational range and can
damage the servo. Always check the
manufacturer’s instructions for a servo’s
rotational range.
Using the CON3
The CON3 can be used with small servo
motors requiring 50-70 ounce/inches of torque
and large servo engines requiring 200-300
ounce/inches of torque.
The CON3 has a power jumper that routes
power to the servo motors through either the 6-
pin header or a screw terminal (when using an
alternate power source). When the power
jumper is in the VCC position it routes power
through the 6-pin header. When the power
jumper is in the VE position it routes power
through the screw terminal.
When plugging a servo motor into the CON3’s
servo connector, the white or yellow wire of the
servo should connect to the signal portion of
the connector, and the black wire should
connect to the ground portion of the connector.
The CON3 has a 6-pin header for easy
connection to a Digilent system board. For
example, some system boards like the Digilent
Pegasus board have a 6-pin header that can
connect to the CON3 with a 6-pin cable.
To connect the CON3 to other Digilent system
boards, a Digilent Modular Interface Board
(MIB) and a 6-pin cable are needed. The MIB
plugs into the system board, and the cable
connects the MIB to the button module.
For more information see www.digilentinc.com.
Servo Control Diagram
2.0 m s
Pulse
Width
1.5 ms
Pulse
Width
1.0 ms
Pulse
Width
Pulse
Period
Servo Position
Set by Pulse
Width
