This is the Revision B version of the Servo4 module. The status of this project is that it has been replaced by the Revision C version.

Servo4 Module (Revision B)

Table of Contents

This document is also available as a PDF document.

• 1. Introduction
• 2. Programming
• 3. Hardware
  • 3.1 Circuit Schematic
  • 3.2 Printed Circuit Board
• 4. Software
• 5. Issues

1. Introduction

The Servo4 module allows for the control of up to 4 hobby grade servos.

2. Programming

The Servo4 module can independently control up to 4 servos. Each servo has 1) an enable bit and 2) a current position. The position is represented as an 8-bit number. Some experimentation is needed to determine how the 8-bit numbers correspond to actual servo positions. All servos are initialized to have the enable flags off.

.

Command	Send/ Receive	Byte Value								Discussion
		7	6	5	4	3	2	1	0
Set High	Send	0	0	h	h	h	h	s	s	Set high order 4 bits of servo ss to hhhh and set the remaining 4 low order bits to zero.
Set Low	Send	0	1	l	l	l	l	s	s	Set the low order 4 bits of servo ss position to llll.
Increment	Send	1	0	0	i	i	i	s	s	Add iii to the position of servo ss.
Decrement	Send	1	0	1	d	d	d	s	s	Subtract ddd from the position of servo ss.
Set Position/Enable	Send	1	1	0	0	0	e	s	s	Select servo ss and set its position to ppppppp and enable flag to e.
	Send	p	p	p	p	p	p	p	p
Set Enable Flag	Send	1	1	0	0	1	e	s	s	Select servo ss and set its enable flag to e.
Read Position	Send	1	1	0	1	0	0	s	s	Return the current position pppppppp for servo ss.
	Receive	p	p	p	p	p	p	p	p
Read Enable	Send	1	1	0	1	0	1	s	s	Return the enable bit e for servo ss.
	Receive	0	0	0	0	0	0	0	e
Read Enables	Send	1	1	0	1	1	0	0	0	Return the enable flags eeee for all four servos.
	Receive	0	0	0	0	e	e	e	e
Set Enables	Send	1	1	0	1	1	0	0	1	Set enable flags for all four servos to eeee.
	Send	0	0	0	0	e	e	e	e
Shared Commands	Send	1	1	1	1	1	c	c	c	Execute shared command ccc.

3. Hardware

The hardware consists of a circuit schematic and a printed circuit board.

3.1 Circuit Schematic

The schematic for the Servo4 module is shown below:

The parts list kept in a separate file -- servo4.ptl.

3.2 Printed Circuit Board

The printed circuit board files are listed below:

servo4_back.png

The solder side layer is shown below:

servo4_front.png

The component side layer is shown below:

servo4_artwork.png

The artwork layer is shown below

servo4.gbl

The RS-274X "Gerber" back (solder side) layer.

servo4.gtl

The RS-274X "Gerber" top (component side) layer.

servo4.gal

The RS-274X "Gerber" artwork layer.

servo4.drl

The "Excellon" NC drill file.

servo4.tol

The "Excellon" tool rack file.

4. Software

The Servo4 software is available as one of:

servo4.ucl

The µCL source file.

servo4.asm

The resulting human readable PIC assembly file.

servo4.lst

The resulting human readable PIC listing file.

servo4.hex

The resulting Intel^® Hex file.

5. Issues

The following fabrication issues came up:

• Provide an alternate power source for the servos. When they hit the stops they mess up the logic supply. Think about putting in diodes with pull up resistors as well so the servo supply can get higher (and lower) than 5 volts.
• The holes in N1 are too large (size 3) and should be made smaller (size 2.)
• The labeling could be made a little clearer.
• Think about adding color codes for common servos.
• Think about adding some LED's for direction specificaiton. This would require upgrading to a '505.
• Think about adding a voltage regulator for the external battery.
• Think about adding an A/D converter to measure servo current draw.