This is the revision B of the MidiMotor2 module.

MidiMotor2 Module (Revision B)

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

1. Introduction

The MidiMotor2 module is designed to drive to medium (aka midi) sized motors with a maximum current of 3.5 Amperes per motor. The logic circuitry is separated from the motor H-bridges via optoisolators.

2. Programming

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

Motor1 Speed Read 0 0 0 0 0 0 0 0 0 Send Return the speed of motor1 as ssss ssss a signed 2's complement number between -128 and 127.
0 s s s s s s s s Receive

Motor1 Speed Set 0 0 0 0 0 0 0 0 1 Send Set the speed of motor1 to ssss ssss which is a signed 2's complement number between -128 and 127.
0 s s s s s s s s Send

Motor2 Speed Read 0 0 0 0 0 0 0 1 0 Send Return the speed of motor2 as ssss ssss a signed 2's complement number between -128 and 127.
0 s s s s s s s s Receive

Motor2 Speed Set 0 0 0 0 0 0 0 1 1 Send Set the speed of motor2 to ssss ssss which is a signed 2's complement number between -128 and 127.
0 s s s s s s s s Send

Duty Cycle Read 0 0 0 0 0 0 1 0 0 Send Return the duty cycle of the pulse widths as ppp. (000=32µS, 001=64µS, 010=128µS, 011=.25mS, 100=.5mS, 101=1mS, 110=2mS, 111=4mS)
0 0 0 0 0 0 p p p Receive

Duty Cycle Set 0 0 0 0 0 1 p p p Send Set pulse width duty cycle to ppp. (000=32µS, 001=64µS, 010=128µS, 011=.25mS, 100=.5mS, 101=1mS, 110=2mS, 111=4mS)

Common
Commands 0 1 1 1 1 1 1 x x Send Standard common command. See specifications for details.
0 a a a a a a a a Receive

Select 1 a a a a a a a a Send Select the module with an address of aaaa aaaa. A time-out indicates that the module is not selected. (FIXME: 0xa5 is currently returned.)
0 0 0 0 0 0 0 0 0 Receive

Command Name	Bit	Action	Description
8	7	6	5	4	3	2	1	0
Motor1 Speed Read	0	0	0	0	0	0	0	0	0	Send	Return the speed of motor1 as ssss ssss a signed 2's complement number between -128 and 127.
0	s	s	s	s	s	s	s	s	Receive
Motor1 Speed Set	0	0	0	0	0	0	0	0	1	Send	Set the speed of motor1 to ssss ssss which is a signed 2's complement number between -128 and 127.
0	s	s	s	s	s	s	s	s	Send
Motor2 Speed Read	0	0	0	0	0	0	0	1	0	Send	Return the speed of motor2 as ssss ssss a signed 2's complement number between -128 and 127.
0	s	s	s	s	s	s	s	s	Receive
Motor2 Speed Set	0	0	0	0	0	0	0	1	1	Send	Set the speed of motor2 to ssss ssss which is a signed 2's complement number between -128 and 127.
0	s	s	s	s	s	s	s	s	Send
Duty Cycle Read	0	0	0	0	0	0	1	0	0	Send	Return the duty cycle of the pulse widths as ppp. (000=32µS, 001=64µS, 010=128µS, 011=.25mS, 100=.5mS, 101=1mS, 110=2mS, 111=4mS)
0	0	0	0	0	0	p	p	p	Receive
Duty Cycle Set	0	0	0	0	0	1	p	p	p	Send	Set pulse width duty cycle to ppp. (000=32µS, 001=64µS, 010=128µS, 011=.25mS, 100=.5mS, 101=1mS, 110=2mS, 111=4mS)
Common Commands	0	1	1	1	1	1	1	x	x	Send	Standard common command. See specifications for details.
0	a	a	a	a	a	a	a	a	Receive
Select	1	a	a	a	a	a	a	a	a	Send	Select the module with an address of aaaa aaaa. A time-out indicates that the module is not selected. (FIXME: 0xa5 is currently returned.)
0	0	0	0	0	0	0	0	0	Receive

3. Hardware

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

3.1 Circuit Schematic

There is a separate parts list file.

3.1.1 Logic Schematic

The logic section of the MidiMotor2 module is shown below:

The logic power and CAN signals come in from N4 pins 3 through 8. The CAN signals are connected to the MCP2551 CAN physical layer IC, U5. The transmit and receive pins of the microctroller, (U4 pins 5 and 6) are connected to the other side of U5. Lastly, the RC0 through RC3 are used to drive the quad optoislator, U3, through current limiting resistors R5 through R7.

3.1.2 Power Schematic

Please note that U3 optoisolator shows up in both schematics. There is only one optoisolator, it is just easier to understand what is going on if the optoisolator is present in both schematics. There is no shared ground between the two sides of the optoisolator.

The power section of the MidiMotor2 module is shown below:

Each L298 (U1 and U2) is a dual H-bridge in a Multiwatt-15 package. As per recommended practice, the two H-bridges are ganged together to form a single H-bridge with 3.5 Amp capacity. Power comes in on N3. The dedicated regulator VR1 provides 5 volts for the logic ciruitry. The H-bridge circuitry is always enabled. The Schottky diodes (D1-D8) are used to clamp out unwanted voltage spikes that occur as a result of switching. Each H-bridge is connected to two optoisolators in U3 to allow independent switching of the H-bridge.

3.2 Printed Circuit Board

The printed circuit board files are listed below:

midimotor2_back.png: The solder side layer.
midimotor2_front.png: The component side layer.
midimotor2_artwork.png: The artwork layer.
midimotor2.gbl: The RS-274X "Gerber" back (solder side) layer.
midimotor2.gtl: The RS-274X "Gerber" top (component side) layer.
midimotor2.gal: The RS-274X "Gerber" artwork layer.
midimotor2.gml: The RS-274X "Gerber" mask layer.
midimotor2.drl: The "Excellon" NC drill file.
midimotor2.tol: The "Excellon" tool rack file.

4. Software

The following files are available:

midimotor2.ucl: The MidiMotor2 µCL source code. There is not much actual code here, since most code is implemented in libraries.
midimotor2.asm: The MidiMotor2 assembly code listing
midimotor2.lst: The MidiMotor2 assmbley listing file.
midimotor2.hex: The µCL MidiMotor2 Intel^® Hex file.

5. Issues

The following fabrication issues came up:

It would be nice to have some artwork that indicates which lead is positive on the N3 connector.
The pins for the 1×2 headers are reversed.