This is the Revision A version of the Compass8 Module. The status of this project is that it has been replaced by the Revision B version.

Compass8 Module (Revision A)

Table of Contents

This document is also available in PDF format.

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

1. Introduction

The Compass8 Module is a Module that can be used to connect to a Dinsmore Instrument Company digital compass. The compass can report the 8 bearings (N, NE, E, SE, S, SW, W, NW.)

A picture of the unpoplulated board is shown below:

I currently only have one of the digital compass modules and it has less than ideal behavior. My compass module works best in an envionment which has some vibration, otherwise the compass is prone to sticking and can be off by as much as 90 degrees. There is some significant hysterisis as rotation is changed; trying to steer a robot straight by aligning the robot with a bearing boundary (e.g. between N and NE) will not yield a very straight course due to this observed hysterisis effect. Of course, I may have a `lemon' module and other people might have different experiences with their moduels. However, if all you want is basic compass bearing, the Dinsmore digital compass module does seem to meet that requirement at a very reasoable cost.

If you want a more accurate compass module, you might want to try the CMPS01 magnetic compass module available at: Robot Electronics.

2. Programming

The basic operation is to send a query to the Compass8 Module to read the 3 bits of bearing data.

The Compass8 Module supports Module Interrupt Protocol. The interrupt pending bit is set whenever the the formula:

B&M

• B is the bearing expanded out into an 8-bit vector with only 1 bit turned on,
• M is the interrupt mask, and
• & is bit-wise AND

The Compass8 Module supports both the standard shared commands and the shared interrupt commands in addition to the following commands:

Command	Send/ Receive	Byte Value								Discussion
		7	6	5	4	3	2	1	0
Read Bearing	Send	0	0	0	0	0	0	0	0	Return bearing bbb (N=000, NE=001, E=010, SE=011, S=100, SW=101, W=110, NW=111)
	Receive	0	0	0	0	0	b	b	b
Read Interrupt Mask	Send	0	0	0	0	0	0	0	1	Return interrupt mask mmmmmmmm (N, NE, E, SE, S, SW, W, NW)
	Receive	m	m	m	m	m	m	m	m
Read Raw	Send	0	0	0	0	0	0	1	0	Return raw data abcd
	Receive	0	0	0	0	a	b	c	d
Set Interrupt Mask	Send	0	0	0	0	0	0	1	1	Set interrupt mask to mmmmmmmm (N, NE, E, SE, S, SW, W, NW)
	Send	m	m	m	m	m	m	m	m
Read Interrupt Bits	Send	1	1	1	0	1	1	1	1	Return the interrupt pending bit p and the interrupt enable bit e.
	Receive	0	0	0	0	0	0	e	p
Set Interrupt Commands	Send	1	1	1	1	0	c	c	c	Set Interrupt Command ccc.
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 Compass8 Module is shown below:

The parts list kept in a separate file -- compass8.ptl.

3.2 Printed Circuit Board

The printed circuit board files are listed below:

compass8_back.png

The solder side layer.

compass8_front.png

The component side layer.

compass8_artwork.png

The artwork layer.

compass8.gbl

The RS-272X "Gerber" back (solder side) layer.

compass8.gtl

The RS-272X "Gerber" top (component side) layer.

compass8.gal

The RS-272X "Gerber" artwork layer.

compass8.drl

The "Excellon" NC drill file.

compass8.tol

The "Excellon" tool rack file.

4. Software

The Compass8 software is available as one of:

compass8.ucl

The µCL source file.

compass8.asm

The resulting human readable PIC assembly file.

compass8.lst

The resulting human readable PIC listing file.

compass8.hex

The resulting Intel^® Hex file.

5. Issues

The following fabrication issues came up:

• The holes for N1 are too large (size 3) and should be made smaller (size 2).
• Think about upgrading to a PIC12C505 and adding three or four indicator LED's; sort of like shaft2.