This is the revision D version of the Sonar2 module.

Sonar2 Module (Revision D)

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

1. Introduction

This is a completely optoisolated Sonar module for driving sonar modules. The Sonar modules can be from the following list:

Parallax Ping
Devantech SRF04
Devnatech SRF05
MaxSonar-EZ1

In general, any sonar that can be independentally triggered and returns a pulse width can be hooked up to this module.

2. Programming

Command
Name Bit Action Description
8 7 6 5 4 3 2 1 0

Raw Read 0 0 0 0 0 0 0 0 s Send Return the pulse length as hhhh hhhh llll llll × .2microSec.
0 h h h h h h h h Receive
0 l l l l l l l l Receive

Centimeter_Read 0 0 0 0 0 0 0 1 s Send (Unimplemented) Return the distance for senosr s as dddd dddd centimeters.
0 d d d d d d d d Receive

Millimeter_Read 0 0 0 0 0 0 1 0 s Send (Unimplemented) Return the distance for senosr s as dddd dddd millimeters. A return result of 1111 1111 means that the distance exceeds 254 millimeters (=10.45 inches)
0 d d d d d d d d Receive

Command Name	Bit	Action	Description
8	7	6	5	4	3	2	1	0
Raw Read	0	0	0	0	0	0	0	0	s	Send	Return the pulse length as hhhh hhhh llll llll × .2microSec.
0	h	h	h	h	h	h	h	h	Receive
0	l	l	l	l	l	l	l	l	Receive
Centimeter_Read	0	0	0	0	0	0	0	1	s	Send	(Unimplemented) Return the distance for senosr s as dddd dddd centimeters.
0	d	d	d	d	d	d	d	d	Receive
Millimeter_Read	0	0	0	0	0	0	1	0	s	Send	(Unimplemented) Return the distance for senosr s as dddd dddd millimeters. A return result of 1111 1111 means that the distance exceeds 254 millimeters (=10.45 inches)
0	d	d	d	d	d	d	d	d	Receive

3. Hardware

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

The parts list kept in a separate file -- sonar2.ptl.

3.1 Circuit Schematic

The schematic for the Sonar2 module is shown below:

The module is connected to the RoboBricks2 bus via connector N1. The signals come in on N1-5 and N1-6 and are connected through the CAN bus physical layer transceiver (MCP2551) at U2. The TX and RX pins of the microcontroller (PIC16F688) at U1 are connected to U2. To send a pulse to a servo, either U1-13 (RA0) is brought high, or U1-9 (RC1) is brought high. This causes current to flow through R1 (or R2) through the light emitting diode in the quad opto isolator (U3). This saturates the corresponding NPN transistors, which pulls R7 (or R8) to near 5 volts (4.8 volts is more like it.) This will trigger the sonar unit connected to either connector N2 or N3. Some sonar units combine the trigger and pulse back pins (e.g. Parallax Ping and Maxbotix MaxSonar-EZ1) and others keep the separate (e.g. Devantech SRF04.) For combined trigger and pulse systems, J1 (or J2) are shorted together; otherwise they are left open. The trigger pulse will cause current to flow through current limiting resistor R3 (or R4) and light up the corresponding light emmitting diode int the quad opto-isolator in U3. The corresponding transistor will saturate and pull the resistor R5 (or R6) up to 5 volts (again, it is closer to 4.8 volts) and feed the signal into U1-10 (RC0) or U1-12 (RA1).

3.2 Printed Circuit Board

The printed circuit board files are listed below:

sonar2_back.png: The solder side layer.
sonar2_front.png: The component side layer.
sonar2_artwork.png: The artwork layer.
sonar2.gbl: The RS-274X "Gerber" back (solder side) layer.
sonar2.gtl: The RS-274X "Gerber" top (component side) layer.
sonar2.gal: The RS-274X "Gerber" artwork layer.
sonar2.gml: The RS-274X "Gerber" mask layer.
sonar2.drl: The "Excellon" NC drill file.
sonar2.tol: The "Excellon" tool rack file.

4. Software

The following files are available:

sonar2.ucl: The µCL source code for the Sonar2 module.
sonar2.asm: The Sonar2 module assembly code file.
sonar2.lst: The Sonar2 module listing file.
sonar2.hex: The µCL Sonar2 Intel^® Hex file.

5. Issues

The following fabrication issues occured:

Pins 9 and 12 need to be reversed. The response signal should be attached to an RA pin.
The optical isolation provided by this module is dubious. The sonar modules really do not draw that much current. The amount of current being pulled by the optoisolators is more than the amount of current pulled by the sensor.
The optoisolators are really slowing things down. The 10µSec pulse to trigger is getting stretched to about 50µSec. The pulse that comes back has some RC discharge jitter added to it.
In summary, this design should be replaced by a Sonar4 or Sonar5 module with no optoisolation.