There is an Indiegogo campaign to sell a kit for learning electronics that seems to have better pricing than most of the similar kits I’ve seen: BE MAKER! KIT plus FREE lessons on electronics, from Zero to Internet of Things | Indiegogo.

The most popular product they are selling seems to be a $69 kit with a microprocessor board (a clone of the Arduino Leonardo); a “shield” with an LCD display driver, pushbuttons, microSD card reader, 2 servo connections, RGB LED strip driver, and Ethernet adapter; a bunch of useful electronics parts (including an LCD display for the shield and an RGB LED strip); “lessons” (which are probably just assembly instructions for different projects, but may be more tutorial) and a box to keep all the tiny parts in.

As Arduino and Arduino-compatible kits go, this one looks pretty good.  Forget about it for holiday gift-giving though, as they don’t expect to deliver until February 2014.  If you want something similar for this year, look at the somewhat more expensive kits from AdaFruit or SparkFun.

There is an Indiegogo campaign to sell a kit for learning electronics that seems to have better pricing than most of the similar kits I’ve seen: BE MAKER! KIT plus FREE lessons on electronics, from Zero to Internet of Things | Indiegogo.

The most popular product they are selling seems to be a $69 kit with a microprocessor board (a clone of the Arduino Leonardo); a “shield” with an LCD display driver, pushbuttons, microSD card reader, 2 servo connections, RGB LED strip driver, and Ethernet adapter; a bunch of useful electronics parts (including an LCD display for the shield and an RGB LED strip); “lessons” (which are probably just assembly instructions for different projects, but may be more tutorial) and a box to keep all the tiny parts in.

As Arduino and Arduino-compatible kits go, this one looks pretty good.  Forget about it for holiday gift-giving though, as they don’t expect to deliver until February 2014.  If you want something similar for this year, look at the somewhat more expensive kits from AdaFruit or SparkFun.

Who knew Lego characters had to be somewhere in a hurry? Adafruit did, as it just whipped up a minifig-sized train schedule. The invention mates one of Adafruit's own 1-inch OLED boards with an Arduino Uno controlling the schedule behind the scenes. It looks to be a straightforward project for the DIY types, although the display is currently all show: the schedule doesn't (yet) pair up with the train tracks to automatically let your minifigs know if their trip to the pirate spaceship castle has been delayed by ghosts. You can check the source link for the full instructions. Duplo builders, alas, are kept out of the loop.

OLED Lego train station emerges from Adafruit and Arduino gear, minifigs to get home on time originally appeared on Engadget on Tue, 26 Jun 2012 00:07:00 EST. Please see our terms for use of feeds.

For the Santa Cruz Robotics Club, I’ve bought three sensors for their underwater ROV: a magnetometer, an accelerometer, and a pressure sensor.

Originally, we were going to an ADXL335 accelerometer (with a breakout board by Adafruit Industries) and an MPXHZ6250A pressure sensor (no magnetometer), for which I designed a small PC board, but once the specs for this year’s mission came out, we saw that they wanted us to determine compass headings for a “sunken ship”, so it seemed a natural thing to add a magnetometer to the hardware.  After looking at what was available, I chose the MAG3110 breakout board from Sparkfun, because it provided a triple-axis magnetometer for only $15.

The MAG3110 is an I²C interface, which means we need only 2 wires to hook it up (and the wires can be shared with other I²C devices).  If we are going to all the trouble of figuring out an I²C interface, I figured we might as well use it for the accelerometer as well, so I got a MMA8452Q breakout board from Sparkfun also.

I decided to do a simple test program for the I²C parts before handing them over to the robotics club, so that they could be sure they had working parts.  It was a good thing I did, because I spent more than an entire day trying to get the parts to work.  I finally gave up on the “Wire” library from the Arduino website, and tried using the i2c.h file from Sparkfun (example code linked to from the accelerometer web page).  I got that working and rewrote the library as a proper .h and .cpp file, so that it could be installed as a normal Arduino library, adding some of the utility calls that had been buried in the MMA8452 demo code.

The MMA8452Q code was working fine, so I tried using the same i2c library for the MAG3110 magnetometer.

I had gotten MAG3110 working with the Wire library, but running at 5v (I’d not noticed that it was a 3.3v part—rather, I thought I’d checked that it was a 5v part, but I was wrong).  I’d left it powered at 5v all night, and I think I burned it out, as it was quite warm in the morning.  Today, I can read and write the registers of the MAG3110, but the xyz values are not coming out reasonable at all—I frequently get the same values (like 0xF9F9)and 0x1DF9), independent of the orientation. If I read all the registers, a lot of them come out as 0xF9 or 0x1D.  Even the WHO_AM_I register (which should be 0xC4) often comes out 0x1D.  I seem to get intermittent correct values for registers, but mostly bogus values.

I’ll feel stupid if I order another part and it turns out to be a software bug, but I’m pretty sure the chip is fried.  But I guess it is time to do another Sparkfun order. (I owe them some business, after calling them for the replacement photointerrupter.)

Incidentally, I tried finding a usable pressure sensor with an I²C interface, but it doesn’t look like anyone is making them except for barometric pressure ranges for dry gases.  I suppose Freescale will eventually come out with a full range of I²C pressure sensors, but my guess is that will be a long time coming, as the automotive and industrial applications have a pretty long product design cycle (unlike consumer electronics, which is driving the barometric pressure sensors).

I expanded the HexMotor.cc and HexMotor.h library today, so that I can use the same library with both my HexMotor board and the Adafruit Industries motor shield.  The only differences from a user’s standpoint are

• Declare an AdafruitMotorBoard instead of HexMotorBoard.
• Use motors 1,2,3,4 instead of 0,1,2,3,4,5.
• motor.release() works on the AdafruitMotorBoard, but is not usable on the HexMotorBoard, which only brakes when off.

I also figured out a way to get some debugging capability into the library, so that people could check that their configuration is consistent (though there is no way to check whether the jumpers and wiring are actually what the user says they are supposed to be).  I can’t use “assert” statements the way I’m used to, so I did explicit if-statements and provided output through Serial.print() calls.  This only works for tests that come after the Serial.begin() call, so I put the tests in the HexMotorBoard::setup() method, assuming that it would be called after Serial.begin() in setup().

The tests can be turned off by commenting out the #define HEX_MOTOR_DEBUG 1 line in the HexMotor.h file, reducing the size of the downloaded program by 860 bytes.  Actually, almost everyone will have to turn the debugging off, since every run() command sends debugging output to the serial line, so the default is to have the debugging off.

The software library is pretty much done for controlling brushed motors, except for changing PWM frequency.  Currently motors 0 and 1 (1 and 2 on the Adafruit board) run at 490Hz, while motors 2 and 3 (3 and 4 of the Adafruit board) run at 976.5Hz and motors 4 and 5 at 490Hz.  I don’t want to mess with the PWM for motors 2 and 3, since that timer is also used for the delay() and millis() calls, so I probably want to change the PWM frequency for the other PWM pins.

Update 8 October 2011: Since I’ve just found out how to put source code into WordPress blogs, let me put the latest versions of HexMotor.h and HexMotor.cpp here:

// HexMotor.h
// copyright Kevin Karplus 8 August 2011
// Creative Commons license Attribution-NonCommercial
//	http://creativecommons.org/licenses/by-nc/3.0/

#ifndef _HexMotor_h_
#define _HexMotor_h_

#include <inttypes.h>
#include <avr/io.h>

// Define HEX_MOTOR_DEBUG if you want to get error messages from setup() for erroneous setup.
// #define HEX_MOTOR_DEBUG 1

// Declaring a HexMotorBoard gives the jumperable configuration for the board.
// The relevant jumpers are which pins drive the motor speed inputs
// and whether the H-bridges are configured for lock antiphase or sign-magnitude.
//
// IN2 of the H-bridge is always connected to SIGN XOR MAG
//
// IN1 of the H-bridge can be connected to either SIGN  or MAG.
//		If IN1 is connected to SIGN, then the TLE-5206 H-bridge will
//			be running in a sign magnitude mode, with the Speed pin low meaning BRAKE
//				and Speed pin high meaning RUN (with the sign bit indicating which way to turn).
//		If IN1 is connected to MAG, then the TLE-5206 H-bridge will
//		    be in lock antiphase, running if the SIGN bit is high and BRAKING if the SIGN bit is low.
//			The MAG bit determines which way the motor runs.
//      If the MAG bit is not a PWM output, then IN1 should be connected to MAG.
// Note: on the rev 1.3 boards, the silkscreen for the jumpers is misleading.  
//      The center of the 5 holes for header pins is MAG and the outer one is SIGN.

// The PWM frequency for all channels defaults to 1kHz (actually 16Mz/ 2^14 = 976.56Hz)
// Changes could be made in the HexMotorBoard::setup() routine if other PWM frequencies are needed.


class HexMotorBoard
{ protected:
	uint8_t SpeedPins[6];
	    // which pins are connected to the "speed" (MAG) inputs of each H-bridge?
	    // Numbers 0-54 are for Arduino pins
	    // Numbers 0xA0..0xA7 are for the low byte of the serial output latch
	    // Numbers 0xA8..0xAF are for the high byte of the serial output latch
		//		(on rev2 or later)
		// Number 0xFF means that the MAG bit is tied to +5V
	    // 
	    // Note: all SpeedPins should be connected to something.
		
	
	    // Note: on Arduinos other than Mega, using the Servo library means that pins 9 and 10
	    // are not PWM pins.  If used, they should be set up as ON/OFF pins. 
	
	
	enum{NOT_THERE, SIGN_MAG, ANTIPHASE, FORWARD_BACKWARD_BRAKE, ONE_BIT, ADAFRUIT} MotorMode[6];	// MotorMode[i] is
				// NOT_THERE if motor_i is not usable on this board
				// SIGN_MAG if IN1 of motor i is connected to SIGN, and MAG is assumed to be PWM
				// ANTIPHASE if IN1 of motor i connected to MAG and MAG is a PWM bit
			    // FORWARD_BACKWARD_BRAKE if IN1 of motor i connected to MAG, but MAG is ON/OFF, not PWM.
				// ONE_BIT if IN1 is connected to MAG, which is tied to +5v, so the
			    //		the motor is always either running forward or backward, controlled by the SIGN bit
				// ADAFRUIT if this is not a HexMotor board, but an Adafruit Motor shield
				//
	
	uint8_t LatchPin, ClockPin, DataPin;
		// which Arduino pins are used for talking to the Hexmotor shift register?
	
	uint16_t ShiftRegister;  // the current or future contents of the HexMotor shift register
	
	uint8_t Version;	// which model of board is used
	
	// set (or clear) a bit in the ShiftRegister corresponding to the specified motor
	inline void set_signbit(uint8_t motor, bool value=1)
	{   digitalWrite(0xA0+motor, value);
	}  
	
	void serial_out(void);	// transfer the shift register to the HexMotor board.
  public:
	HexMotorBoard(
				  const char *antis, 
				  const uint8_t *pins=0,	// defaults to {11, 3, 6, 5, 9,10}
				  uint8_t version=1,
				  uint8_t clock=4, 
				  uint8_t data=8, 
				  uint8_t latch=12);
	    // An array of pins is given to indicate where the MAG output for each motor goes.
					
	    // The 6 antis characters are 
		// '-' for NOT_THERE
		// 'S' or 's' for SIGN_MAG (IN1==SIGN)
	    // 'A' or 'a' for ANTIPHASE (IN1==MAG) 
	    // 'F' or 'f' for FORWARD_BACKWARD_BRAKE (IN1==MAG, but MAG is not PWM bit)
		// 'O' or 'o' for ONE_BIT
		// 'M' or 'm' for ADAFRUIT motor shield
		
		// The version is the integer part of the board rev number (rev1.3 is 1, rev 2.3 is 2).
	    // This indicates, for example, whether the board has 8 or 16 bits of shift register.
		// Use rev 0 to indicate an Adafruit motorshield.
	    // latch, data, and clock are Arduino pins that are used for the serial output to the shift register. 
	
	void setup(void);
	    // makes sure that PWM frequencies are appropriately set and turns all motors off.
	    // Should be called during the global setup() procedure.
	    // QUERY: should PWM frequency be settable here (or even as separate call?)
	
	void digitalWrite(uint8_t pin, bool value);	// write a single bit to a pin (using SpeedPins naming convention)
	friend class HexMotor;
};



// Declaring an AdafruitMotorBoard sets up the HexMotorBoard interface for an AdaFruit Industries Motor Shield, 
// rather than for a HexMotor board.
// The declaration has no parameters, as the AdaFruit motor shield is not configurable.
// For compatibility with the M1 through M4 labeling on the motor shield, motors 1 through 4 are used,
// rather than 0 through 3.

class AdafruitMotorBoard : public HexMotorBoard
{  protected:
	typedef enum{FORWARD, BACKWARD, BRAKE} MotorDir;
	void change_motor_bits(uint8_t motor,  MotorDir control);
  public: 
	AdafruitMotorBoard(void);
   	friend class HexMotor;

};



class HexMotor 
{  protected: 
	uint8_t Motor;
	HexMotorBoard* Board;

  public:
	HexMotor(HexMotorBoard &board, uint8_t motor_num);
	
	void run(int speed);
	// speed is between -256 (full reverse) and 255 (full forward)
	// 0 is off (braking on HexMotor, released on Adafruit)
	
	void brake(void);

	void release(void);		// Available on Adafruit Motor shield,
							// but not on HexMotor boards rev1 or rev 2
							// since the TLE-5206 chips do not have a Hi-Z output
};


#endif

// HexMotor  library
// Kevin Karplus
//copyright 8 August 2011
//	http://creativecommons.org/licenses/by-nc/3.0/

#include <avr/io.h>
#include <pins_arduino.h>
#include <WProgram.h>
#include "HexMotor.h"

// The PWM frequency for all channels defaults to 1kHz.
// Changes could be made in the HexMotorBoard::setup() routine if other PWM frequencies are needed.

// The frequencies below are approximate.
// The actual frequency in fast PWM mode is f_clk/(256*prescale)
// For the 16.000MHz crystal of the Arduino, the frequencies are
// 62.5KHz, 7.125KHz, 1.9531 kHz, 976.56Hz, 488.28Hz, 244.14 Hz, and 61.035Hz

// Don't mess with timer 0, since it is used for "delay()" and "millis()"
#define OCR0_64KHz (1)  // no prescale
#define OCR0_8KHz (2)   // divide by 8
#define OCR0_1KHz (3)  // divide by 16

// Timer 1 (and Timers 3, 4, 5 on Arduino Mega) have limited
//	prescale choices, because they allow external clock as well.
#define OCR1_62KHz	(1)	// no prescale
#define OCR1_7KHz	(2)	// divide by 8
#define OCR1_1KHz	(3)	// divide by 64
#define OCR1_240Hz	(4)	// divide by 256
#define OCR1_61Hz	(5)	// divide by 1024

#define OCR2_62KHz	(1)	// no prescale
#define OCR2_7KHz	(2)	// divide by 8
#define OCR2_2KHz	(3)	// divide by 32
#define OCR2_1KHz	(4)	// divide by 64
#define OCR2_490Hz	(5)	// divide by 128
#define OCR2_240Hz	(6)	// divide by 256
#define OCR2_61Hz	(7)	// divide by 1024

// The Adafruit Motor Shield has an extra output bit for its serial interface:
#define AdafruitEnablePin (7)

/////////////////
// HexMotorBoard
/////////////////
const uint8_t defaultPins[6]={11, 3, 6, 5, 9,10};

HexMotorBoard::HexMotorBoard(
							 const char *antis,
							 const uint8_t *pins,
							 uint8_t version,
							 uint8_t clock,
							 uint8_t data,
							 uint8_t latch)
{
	if (pins==0) {pins= defaultPins;}
	// Save all the jumper information.
	for(int8_t i=5; i>=0; i--)
	{   SpeedPins[i] = pins[i];
		switch (antis[i]) {
			case 'A': case 'a':
				MotorMode[i] = ANTIPHASE;
				// should check that pins[i] is legal PWM pin
				break;
			case 'S': case 's':
				MotorMode[i] = SIGN_MAG;
				// should check that pins[i] is legal PWM pin
				break;
			case 'F': case 'f':
				MotorMode[i] = FORWARD_BACKWARD_BRAKE;
				// should check that pins[i] is consistent with board version
				break;
			case 'O': case 'o':
				MotorMode[i] = ONE_BIT;
				// should check that pins[i] is 0xFF (indicating MAG tied to +5v)
				break;
			case 'M': case 'm':
				MotorMode[i] = ADAFRUIT;
				// should check that 1<=i<=4 and pins[i]=AdafruitDefaultPins[i] and version==0
				break;

			default:
				MotorMode[i] = NOT_THERE;
				break;
		}
	}
	Version=version;
	ClockPin=clock;
	DataPin=data;
	LatchPin=latch;
}

void HexMotorBoard::setup(void)
{
	// setup the serial output pins and clear the shift register
	pinMode(LatchPin, OUTPUT);
	pinMode(DataPin, OUTPUT);
	pinMode(ClockPin, OUTPUT);
    if (Version==0)
    {   pinMode(AdafruitEnablePin, OUTPUT);
    }

	ShiftRegister=0;
	serial_out();

	for (int8_t m=5;m>=0;m--)
	{
		switch (MotorMode[m])
		{   case NOT_THERE: case ONE_BIT:
#ifdef HEX_MOTOR_DEBUG
			    if (SpeedPins[m]!=0xFF)
			    {   Serial.print(m,DEC);
				    Serial.println(" motor shouldn't have speed pin");
			    }
#endif
		        continue;

			case FORWARD_BACKWARD_BRAKE:
				if (SpeedPins[m] >= 0xA0)
				{
#ifdef HEX_MOTOR_DEBUG
					if (Version<2 && SpeedPins[m]>0xA7)
					{   Serial.print(m,DEC);
						Serial.println(" motor has SpeedPin>0xA7");
					}
#endif
					continue;	// no need to set pinMode for HexMotorPins
				}
				pinMode(SpeedPins[m], OUTPUT);
				continue;	// no PWM to check

			case ADAFRUIT:
#ifdef HEX_MOTOR_DEBUG
				if (Version!=0)
				{   Serial.print(m,DEC);
					Serial.print(" mode M, but board version");
					Serial.println(Version,DEC);
				}
#endif
				break;

			default:
				break;

		}

		if (SpeedPins[m] >= 0xA0)
		{   // A HexMotor shift register output or tied to +5v, can't do PWM.
#ifdef HEX_MOTOR_DEBUG
			Serial.print(m,DEC);
			Serial.print(" motor has one-bit speed in mode ");
			Serial.println(MotorMode[m]);
#endif
			continue;
		}

		//real Arduino pin (not HexMotor shift register)
		pinMode(SpeedPins[m], OUTPUT);

		// Set up PWM frequency
		switch (digitalPinToTimer(SpeedPins[m])) {
			case NOT_ON_TIMER:
#ifdef HEX_MOTOR_DEBUG
				    Serial.print(m,DEC);
					Serial.print(" pin ");
					Serial.print(SpeedPins[m]);
					Serial.println(" not a PWM pin");
#endif
				break;

			// timer 0 is used for delay() and millis(),
			// so don't mess with its frequency
			case TIMER0A:
				TCCR0A =  (TCCR0A & 0x30) | _BV(COM0A1) | _BV(WGM00) | _BV(WGM01); // fast PWM, turn on OC0A
				OCR0A = 0;
				break;
			case TIMER0B:
				TCCR0A =  (TCCR0A & 0xC0) | _BV(COM0B1) | _BV(WGM00) | _BV(WGM01); // fast PWM, turn on OC0B
				OCR0B = 0;
				break;

			// Timer 2 is used for pins 11 and 3 of Arduino (not Arduino Mega)
			// default pins for motors 0 and 1, (M1 and M2 on Adafruit Motor shield)
			case TIMER2A:
				TCCR2A = (TCCR2A & 0x30) | _BV(COM2A1) | _BV(WGM20) | _BV(WGM21); // fast PWM, turn on oc2a
				TCCR2B = OCR2_1KHz & 0x7;
				OCR2A = 0;
				break;
			case TIMER2B:
				TCCR2A =  (TCCR2A & 0xC0) | _BV(COM2B1) | _BV(WGM20) | _BV(WGM21); // fast PWM, turn on oc2b
				TCCR2B = OCR2_1KHz & 0x7;
				OCR2B = 0;
				break;

			// Timer 1
			case TIMER1A:
				TCCR1A = (TCCR1A & 0x3C) | _BV(COM1A1) | _BV(WGM10); // fast PWM 8-bit, turn on oc1a
				TCCR1B = (OCR1_1KHz & 0x7) | _BV(WGM12);
				TCCR1C = 0;
				OCR1A = 0;
				break;
			case TIMER1B:
				TCCR1A  = (TCCR1A & 0xCC) | _BV(COM1B1) | _BV(WGM10); // fast PWM 8-bit, turn on oc1b
				TCCR1B = (OCR1_1KHz & 0x7) | _BV(WGM12);
				TCCR1C = 0;
				OCR1B = 0;
				break;
#if defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
			// Timer 3
			case TIMER3A:
				TCCR3A = (TCCR3A & 0x3C) | _BV(COM3A1) | _BV(WGM10); // fast PWM 8-bit, turn on oc3a
				TCCR3B = (OCR1_1KHz & 0x7) | _BV(WGM12);
				TCCR3C = 0;
				OCR3A = 0;
				break;
			case TIMER3B:
				TCCR3A  = (TCCR3A & 0xCC) | _BV(COM3B1) | _BV(WGM10); // fast PWM 8-bit, turn on oc3b
				TCCR3B = (OCR1_1KHz & 0x7) | _BV(WGM12);
				TCCR3C = 0;
				OCR3B = 0;
				break;
			case TIMER3C:
				TCCR3A  = (TCCR3A & 0xF0) | _BV(COM3C1) | _BV(WGM10); // fast PWM 8-bit, turn on oc3c
				TCCR3B = (OCR1_1KHz & 0x7) | _BV(WGM12);
				TCCR3C = 0;
				OCR3C = 0;
				break;

			// Timer 4
			case TIMER4A:
				TCCR4A = (TCCR4A & 0x3C) | _BV(COM4A1) | _BV(WGM10); // fast PWM 8-bit, turn on oc4a
				TCCR4B = (OCR1_1KHz & 0x7) | _BV(WGM12);
				TCCR4C = 0;
				OCR4A = 0;
				break;
			case TIMER4B:
				TCCR4A  = (TCCR4A & 0xCC) | _BV(COM4B1) | _BV(WGM10); // fast PWM 8-bit, turn on oc4b
				TCCR4B = (OCR1_1KHz & 0x7) | _BV(WGM12);
				TCCR4C = 0;
				OCR4B = 0;
				break;
			case TIMER4C:
				TCCR4A  = (TCCR4A & 0xF0) | _BV(COM4C1) | _BV(WGM10); // fast PWM 8-bit, turn on oc4c
				TCCR4B = (OCR1_1KHz & 0x7) | _BV(WGM12);
				TCCR4C = 0;
				OCR4C = 0;
				break;

			// Timer 5
			case TIMER5A:
				TCCR5A = (TCCR5A & 0x3C) | _BV(COM5A1) | _BV(WGM10); // fast PWM 8-bit, turn on oc5a
				TCCR5B = (OCR1_1KHz & 0x7) | _BV(WGM12);
				TCCR5C = 0;
				OCR5A = 0;
				break;
			case TIMER5B:
				TCCR5A  = (TCCR5A & 0xCC) | _BV(COM5B1) | _BV(WGM10); // fast PWM 8-bit, turn on oc5b
				TCCR5B = (OCR1_1KHz & 0x7) | _BV(WGM12);
				TCCR5C = 0;
				OCR5B = 0;
				break;
			case TIMER5C:
				TCCR5A  = (TCCR5A & 0xF0) | _BV(COM5C1) | _BV(WGM10); // fast PWM 8-bit, turn on oc5c
				TCCR5B = (OCR1_1KHz & 0x7) | _BV(WGM12);
				TCCR5C = 0;
				OCR5C = 0;
				break;

#endif
			default:
				break;
		}

	}
}

void HexMotorBoard::serial_out(void)
{
#ifdef HEX_MOTOR_DEBUG
	Serial.print("shift 0x");
	Serial.println(ShiftRegister,HEX);
#endif
	digitalWrite(LatchPin,LOW);
	// Output high order bits first
	if (Version>=2)
	{	shiftOut(DataPin,ClockPin, MSBFIRST, highByte(ShiftRegister));
	}
	shiftOut(DataPin,ClockPin, MSBFIRST, lowByte(ShiftRegister));
	// rising edge on latch pin transfers shift register to output register
	digitalWrite(LatchPin, HIGH);
	if (Version==0)
	{   digitalWrite(AdafruitEnablePin, LOW);	// enable output
	}
}

void HexMotorBoard::digitalWrite(uint8_t pin, bool value)
{
	if (pin<0xA0)
	{   ::digitalWrite(pin, value);
		return;
	}
	if (pin==0xFF)	return;	// pin is +5v and can't be changed
	uint16_t pos = (1 << (pin-0xA0));
	bool old_bit = ShiftRegister & pos;
	if ((value && ! old_bit) || (!value && old_bit))
	{   ShiftRegister ^= pos;
		serial_out();
		return;
	}
}

//////////////////////
// AdafruitMotorBoard
//////////////////////

const uint8_t AdafruitDefaultPins[6]={0xFF, 11, 3, 6, 5, 0xFF};

AdafruitMotorBoard::AdafruitMotorBoard(void): HexMotorBoard("-MMMM-",AdafruitDefaultPins,0)
{
}

// Map the motor number to the two control pins for the motors, based on the
// mapping from the AFMotor.h file:
//      MOTOR1_A 2
//      MOTOR1_B 3
//      MOTOR2_A 1
//      MOTOR2_B 4
//      MOTOR3_A 5
//      MOTOR3_B 7
//      MOTOR4_A 0
//      MOTOR4_B 6

const uint8_t AdafruitMotorAPin[5]={0, 1<<2, 1<<1, 1<<5, 1<<0};
const uint8_t AdafruitMotorBPin[5]={0, 1<<3, 1<<4, 1<<7, 1<<6};

void AdafruitMotorBoard::change_motor_bits(uint8_t motor,
										   MotorDir control)
{
    if (MotorMode[motor] != ADAFRUIT) return;	// error
	switch(control)
	{    case FORWARD:
			ShiftRegister |= AdafruitMotorAPin[motor];
			ShiftRegister &= ~AdafruitMotorBPin[motor];
			break;
		case BACKWARD:
			ShiftRegister &= ~AdafruitMotorAPin[motor];
			ShiftRegister |=  AdafruitMotorBPin[motor];
			break;
		case BRAKE:  // set both outputs low
			ShiftRegister &= ~AdafruitMotorAPin[motor];
			ShiftRegister &= ~AdafruitMotorBPin[motor];
			break;
	}
	serial_out();

}

/////////////////////
// HexMotor
/////////////////////

HexMotor::HexMotor(HexMotorBoard &board, uint8_t motor_num)
{
	Board=&board;
	Motor=motor_num;
}

// speed is between -255 (full reverse) and 255 (full forward)
// 0 is off (braking)
void HexMotor::run(int speed)
{
	// clip to legal range
	if (speed>255) speed=255;
	else if (speed<-255) speed= 0-255;
#ifdef HEX_MOTOR_DEBUG
	Serial.print(Motor, DEC);
	Serial.print(" motor running at ");
	Serial.println(speed);
#endif

	switch (Board->MotorMode[Motor])
	{
		case HexMotorBoard::NOT_THERE:
#ifdef HEX_MOTOR_DEBUG
			Serial.print(Motor, DEC);
			Serial.println("motor NOT_THERE. Can't run");
#endif
			return;
		case HexMotorBoard::SIGN_MAG:
			// (Sign-magnitude) IN1 is connected to SIGN, and MAG is assumed to be PWM
			Board->set_signbit(Motor, speed<0);
			analogWrite(Board->SpeedPins[Motor], speed>=0? speed: 0-speed);
			return;
		case HexMotorBoard::ANTIPHASE:
			// (MotorMode) IN1 is connected to MAG, and MAG is PWM
			if (speed==0)
			{   // Brake
				Board->set_signbit(Motor,0);
				analogWrite(Board->SpeedPins[Motor], 0);
				return;
			}
            Board->set_signbit(Motor,1);
			analogWrite(Board->SpeedPins[Motor], (256-speed)>>1);
			return;
		case HexMotorBoard::FORWARD_BACKWARD_BRAKE:
			// (Forward/Backward/Brake) IN1 is connected to MAG, and MAG is ON/OFF only
			if (speed==0)
			{   // Brake
				Board->set_signbit(Motor,0);
				return;
			}
			Board->digitalWrite(Board->SpeedPins[Motor], speed<0);
			Board->set_signbit(Motor,1);
			return;
		case HexMotorBoard::ONE_BIT:
			// IN1 connected to MAG=+5V
			Board->digitalWrite(Board->SpeedPins[Motor], speed<0);
			return;
		case HexMotorBoard::ADAFRUIT:
			// shift_register pins are interpreted differently by Adafruit board
			if (speed>=0)
			{   static_cast<AdafruitMotorBoard*>(Board)->change_motor_bits(Motor,AdafruitMotorBoard::FORWARD);
				analogWrite(Board->SpeedPins[Motor],speed);
			}
			else
			{   static_cast<AdafruitMotorBoard*>(Board)->change_motor_bits(Motor,AdafruitMotorBoard::BACKWARD);
				analogWrite(Board->SpeedPins[Motor],0-speed);
			}
			return;

	}
}

void HexMotor::brake(void)
{
	switch (Board->MotorMode[Motor])
	{   case HexMotorBoard::ADAFRUIT:
			static_cast<AdafruitMotorBoard*>(Board)->change_motor_bits(Motor,AdafruitMotorBoard::BRAKE);
			analogWrite(Board->SpeedPins[Motor],255);
			return;
		case HexMotorBoard::NOT_THERE:
		case HexMotorBoard::ONE_BIT:
#ifdef HEX_MOTOR_DEBUG
			Serial.print(Motor,DEC);
			Serial.println("motor NOT_THERE or ONE_BIT. Can't brake.");
#endif
			return;	// no such operation exists
		default:
			run(0);
			return;
	}
}

void HexMotor::release(void)
{
	switch (Board->MotorMode[Motor])
	{   case HexMotorBoard::ADAFRUIT:
			static_cast<AdafruitMotorBoard*>(Board)->change_motor_bits(Motor,AdafruitMotorBoard::BRAKE);
			analogWrite(Board->SpeedPins[Motor],0);
			return;
		default:
#ifdef HEX_MOTOR_DEBUG
			Serial.println("Not Adafruit motor shield, can't release.");
#endif
			run(0);	// not a release, but a brake on HexMotor boards.
					// The closest the TLE-5206 chips can get.
			return;
	}
}

The hexmotor rev 1.3 boards before cutting them apart.

The printed circuit boards for hexmotor rev1.3 came today from 4pcb.com. I ordered the boards on July 21, so the total turnaround time from order to delivery was only 12 days. No wonder the company is so popular for student projects—low prices and fast service will do that!

The boards looked pretty good, so the first thing I did was to check some crucial dimensions:

• I put headers into the holes for the connection to the Arduino board and checked that it would plug in.  No problem!
• I checked that I could spread the pins of the TLE-5206-2S chips to fit the holes where they were supposed to plug in.  No problem!  In fact, it was surprisingly easy to get the right spacing, by using the board itself as a tool for bending the pins.
• I checked that I could put in both the MTR2 TLE-5206-2 chip and capacitor C5 without conflict (as I’d noticed that the silk screen outlines overlapped only after I’d sent in the order).  This also turned out not to be a problem
• I checked that the mounting holes on the board lined up with those on the Arduino.  Only 2 out of 3 do.  What is going on???I got the hole placement from the Adafruit library for Eagle, and it has 3 holes, but they are not in the same places as the Arduino board.  It turns out that two of the holes correspond to holes on the Arduino board, and two to holes on the Arduino Mega board, which has holes in different locations.  Neither pair corresponds to the holes on the  Adafruit motor shield, which has only 2 diagonally opposite holes, the two holes that are actually in common between the Arduino and the Arduino Mega footprints.  For the next revision of the boards, I have to decide whether to use the 3-hole design of this board, or to go with the pair of diagonally opposite holes.  Or put in 4 holes, so that either Arduino or Arduino Mega can be securely attached with 3 screws. I think that there is room for the fourth hole, if I move one of the electrolytic capacitors.
• I also did some continuity checks on the power lines.  The power and ground lines connect to the right pins on the TLE-5206-2 footprints, and they aren’t shorted.  The 6.25v and 5v lines also seem fine.
• I had to make some Eagle library components for the screw terminal blocks I was using, and they seem to be fine, except for two little problems: I put a silkscreen mark for the bump on the side of the 5mm block on the wrong side, and the holes specified by the manufacturer seem a bit too big for the pins.  I’ll specify a smaller drill hole (closer to the spec for the pin size) in the next revision.  Neither of these little problems will interfere with functionality.
• I checked out the Sparkfun header pattern, with the slightly staggered holes to hold the headers while soldering.  The holes must be a bit bigger than Sparkfun gets from their manufacturer, or my headers smaller, because the headers were not held by the staggered holes.  They fit fine, but the holes are loose enough that they aren’t held.

Tonight, I’ll fix up my Eagle library to have a 4-hole Arduino template and to have a better 5mm screw terminal component.

Here's a 12" board shear that costs $379 from Circuit Specialists.

Tomorrow I’ll go up to campus and see if I can cut the boards apart with the board shears.

I took a look at  printed circuit board shears on the web (you need to include “printed circuit” if you search, or you get book-binding equipment), and they range in price from $125 to $500, depending on size and quality.  I don’t plan to buy one for myself, but it seems like the sort of low-price, special-purpose tool that a place like Makers Factory ought to get.

The PC board for the hexmotor H-bridge is ordered and supposedly going to arrive soon, and I’ve ordered all the components from Digi-Key. The total coast of the project is looking like about $180 (including the PC board and shipping) for 2 fully populated boards (not counting an enormous amount of my time). I’ve already started designing a revised board (rev 2.0) that will be designed around the TLE-5206-2 from the beginning, and will have more versatility. I’m thinking that I’ll populate one rev 1.3 board for testing, finalize the rev 2.0 design, and send it out for fab, rather than populating a second rev 1.3 board.

Here is a preview of what my panel of 4 boards should look like.

In addition to the 6 TLE-5206-2 H-bridges, both boards have 74HC594 serial-to-parallel converters for control signals and 74HC86 XOR gates. The serial-to-parallel conversion is similar to that of the Adafruit Industries motor shield (which I have, but which does not have enough current capacity as it uses L293D H-bridges, which only support 0.6A per channel, and I need at least 2.5A per channel).

Copying the choices on the Adafruit board, I made the pin mapping LATCH=Arduino pin 12, DATA=Arduino pin 8, CLOCK=Arduino pin 4. I was wondering at first why they did not use the built-in SPI interface (which would simplify the programming of the serial output), but then realized that the output bit of the SPI interface (MOSI=pin 11) is also OC2A, one of the PWM outputs. Since there are only 6 PWM outputs (one per motor), and the serial interface does not need to be very fast, using software control of other pins is a good idea.

I’ve also brought out all the PWM signals to 3-wire servo connections, so that I can use each PWM signal as either a servo control or a motor speed control. All the connections to the Arduino digital pins are jumpered, so I can reconfigure the board if needed. For example, if I just want forward/backward/brake control of a motor, without speed control, I can rewire the input that would normally be to a PWM bit to be to a different digital pin, and free up that PWM bit for servo control.

On the hexmotor rev 2.0 board I added another 74HC594 chip (in series) so that I have 16 control bits available. Six of them are used for motor control, as on the rev 1.3 board. Another 6 are brought out to header pins adjacent to the speed control pins, so that those pins can be jumpered either to the Arduino PWM pins or to the shift register outputs, allowing 6 motors and 6 servos to be controlled by the board, as long as only 6 continuous values are needed, and the servos don’t exceed the 1.5A capacity of the switching regulator. The remaining 4 of the 16 parallel bits of the rev 2.0 will be brought out to individual header pins, so that they can be used as arbitrary digital outputs. (Also, the hexmotor 2.0 board will have an LED to indicate that 5v power is properly being provided—if the board is used as intended, with the Arduino powered from the switching regulator on the hexmotor board, this tests that all the power connections are made and the Arduino board plugged in.

I will have to start writing software for the hexmotor board soon. I’ll probably base some of the software on the Adafruit AFMotor package, to make it easier for the robotics club to switch between the Adafruit motor shield and the hexmotor board, but there will be some important differences. Since the hexmotor board has several jumpers that can customize it, but no way for the Arduino to read that configuration, I need an easy way to tell the software how the board is configured. I want software that will work with either revision of the hexmotor board. Since the rev 2.0 board has more possibilities for configuration than the rev 1.3 board (thanks to the 8 extra output bits), I’ll design the software for that, making sure that the rev 1.3 board is covered as a special case.

I’m going to have to dive into both the ATMega328 data sheet and the Arduino code to find out how to get access to all 6 PWM signals.  I already know that the Arduino initialization messes with the PWM frequencies, so the AFMotor.h control for the PWM frequencies doesn’t work.  It may turn out that using OC1A and OC2A (which the Adafruit board does not use, but which I use for motors 4 and 5) interacts in some unpleasant way with other Arduino functions.  I may have to put up with some constraints on PWM frequency, as I want to retain clock and analog input capabilities.