Digilent ServoMini User Manual

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Revision: June 21, 2007

Overview

The Digilent ServoMini board is useful for
programmable control of up to eight RC servos
for both students and hobbyists.

The ServoMini’s versatile design and
programmable microcontroller allows you to
implement your own algorithms to control up to
eight RC servos. This allows you to decide
what method of control may be best suited for
your application.

The ServoMini can establish serial
communication with other devices using TWI
protocol from Atmel, or SPI. This enables you
to use the ServoMini as a slave device, freeing
up the workload of the master device. Using
TWI, many ServoMinis can be linked onto a
communication bus, giving it the ability to
expand with your needs.

The ServoMini can be powered using the
screw terminal connector, the SPI port or J12.
It supports a number of programming tools
including Atmel AVR® Studio 4, and WinAVR.
The device can be programmed using one of
Digilent’s programming cables.

Features include:

• ATmega168 microcontroller

• three LEDs

• ESD protection for all I/O pins

• in-system programming support using

the Digilent parallel JTAG cable or the
Digilent USB JTAG/SPI cable

• support for up to eight RC servos

• jumper selectable dedicated servo

power supply

• TWI bus daisy chain connectors

l

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Figure 1 Digilent ServoMini Board

Various power

connectors

16k Flash

(Internal)

ATMega168

512 EEPROM

(Internal)

1k SRAM

(Internal)

4 4

J11

SPI/

ISP

Figure 2 Block Diagram

Features of the ATmega168 include:

• 16KB program flash

• 512 byte EEPROM

• 1KB internal SRAM

• master/slave serial peripheral interface

(SPI)

• Atmel two wire serial interface (TWI)

• 10-bit ADC analysis of the AVR power

supply along with the servo power
supply

• two 8-bit timer/counters

• one 16-bit timer/counter

MLF32

ServoMini

J9, J10

TWI

Chain

3 LEDs

Eight servo
connectors

®

Internal

Oscillator

SPI & TWI

ports

8

Doc: 502-102 1

Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.

Digilent ServoMini Board Reference Manual

For more information about the
ATmega168, refer to the data sheet
available at www.atmel.com

.

Functional Description

The ServoMini is designed for embedded
control and robotic applications as well as
microprocessor experimentation. Embedded
firmware, suitable for many applications, can
be programmed into the ServoMini’s
ATmega168 microcontroller.

Although the ServoMini can be used as a
stand-alone microcontroller board, it is also
designed to be part of a larger system using
distributed processing architecture.
Connectors J9 and J10 allow it to be
connected to a serial data bus using Atmel’s
TWI protocol. In this case the ServoMini can
receive instructions, such as desired positions
for any of its eight servos, and then it can
interpret that data as the designer sees fit. It
can also transmit data, such as battery voltage
information, for processing by another
microcontroller.

The ServoMini’s firmware could also be
designed to monitor a few servo channels
coming from an RC receiver and drive servos
based on those pulse-widths. By doing this,
the ServoMini could be used as a servo mixer
or to control servos based on a custom
algorithm. The ServoMini’s servo driving ability
is only limited by the user’s imagination.

Power Supply Options

When a shorting block is installed on JP2, the
servos will share the same power supply as
the ServoMini’s processor. Power can be
applied via the screw terminal connector, via
connector J12 or pins 5 and 6 of the SPI
connector, J11. The Atmega168 processor is
rated for operation from 2.7 to 5.5 volts DC.
Using a voltage outside this range could
damage the ServoMini.

Digilent, Inc.

www.digilentinc.com

Alternatively, if jumper JP2 is removed, the
servos must have their own independent
power supply connected to the screw terminals
and the ServoMini’s processor must be
powered using either J12 or the SPI port.

Device Programming

The ServoMini has one in-system­programming connector, J11. The Digilent
programming cable is connected to J11. Either
a parallel JTAG or USB JTAB/SPI cable can
be used. When connecting the programming
cable, ensure that the VCC and GND pin
labels from the cable match to the VCC and
GND pins on the ServoMini.

A power supply must be provided to the
ServoMini when programming. The Digilent
programming cable does not supply power to
the board; the board it is plugged into powers
the programming cable. The Digilent
PmodREG1 voltage regulator module can be
used, or any appropriately regulated power
supply can be connected to J12. If the
ServoMini is being used in conjunction with
another Digilent board, such as the Cerebot or
Minicon, these boards have connectors that
can be used to supply power to the J12
connector on the ServoMini using a two-wire
cable.

Programming can be accomplished using the
Digilent AVRP application, available by free
download from the Digilent web site. It is also
possible to configure the AVRDUDE
programmer in the WinAVR release for in­system-programming using the Digilent parallel
JTAG cable. See the documentation for these
applications for more information on board
programming.

Connector J11 is used for both in-system­programming and for user access to the SPI
controller. The jumper block JP1 is used to
select between the two functions. The shorting
block is placed in the RST position for in­system-programming, and in the SS position
for user access to the SPI port.

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Copyright Digilent, Inc. All rights reserved. Other product and company names mentioned may be trademarks of their respective owners.