A sumo bot based on the STM32F0 Discovery board.

• STM32F0 Discovery datasheet
• SN754410 H-Bridge Driver datasheet
• ULN2003 Transistor Array datasheet
• 850mAh LiPO battery
• 5v 3A switching voltage regulator (RC UBEC)
• 2 x 5v DC motor and gearbox with wheels
• 4 x TSAL7400 Infrared 5mm LEDs datasheet
• 4 x TSOP4838 38kHz Infrared Receiver datasheet
• 2 x CdS LDR Photoresistor
• Some sort of chassis, like the BoboBot

• ChibiOS Real-time operating system
• STLINK

I use OS X. It should be almost identical to Linux.

cd ~/OpenSource 
git clone git@github.com:mabl/ChibiOS.git

cd ~/OpenSource
sudo port install libusb  # sudo apt-get install libusb
git clone https://github.com/texane/stlink.git
cd stlink
./autogen.sh
./configure
LIBRARY_PATH=/opt/local/lib C_INCLUDE_PATH=/opt/local/include make CONFIG_USE_LIBSG=0  
sudo make install

cd ~/OpenSource
git clone git@github.com:mattwilliamson/yamato.git
cd yamato
make
make load  # Installs onto Discovery board

make debug
(gdb) target remote localhost:4242
(gdb) load
(gdb) continue
...

Note: on my setup, the flash will fail the first time. Press the reset button and run make load again. Reset again for the MCU to start running.

SN75441ONE

       .----------. .----------.
       |          |_|          |
       |                       | 
PB0   =| 1,2EN   1  16   VCC1  |=  5V
       |                       |
PB2   =| 1A      2  15   4A    |=  PC7
       |                       |
M1A   =| 1Y      3  14   4Y    |=  M2A
       |                       |
GND   =| GND     4  13   GND   |=  GND
       |                       |
GND   =| GND     5  12   GND   |=  GND
       |                       |
M1B   =| 2Y      6  11   3Y    |=  M2B
       |                       |
PC6   =| 2A      7  10   3A    |=  PB15
       |                       |
5V    =| VCC2    8  9    3,4EN |=  PB1
       |                       | 
       '-----------------------'

M1A and M1B are leads to the left motor. M2A and M2B are leads to the right motor.

Set PWM load on PB0 to control speed. Digital HIGH will be 100% speed.

Set PWM load on PB1 to control speed. Digital HIGH will be 100% speed.

I'm using the SRF-05 ultrasonic rangefinder. The protocol is as follows:

1. Write the trig pin for a minimum of 10 microseconds
2. Write the trig pin low
3. The echo pin changes to high when it starts measuring
4. The echo pin goes low when it stops measuring
5. Divide the duration the echo pin was high in microseconds by 58 to get the range in centimeters

Yamato uses ChibiOS's ICU Driver on TIM1 to measure the pulse width.

PA11 is mapped to trig

PA8 is mapped to echo

IR Proximity detection is pretty simple. Blink an IR LED at 38kHz and a 38kHz IR receiver's output pin will go low. Combining direction of the LED and the receiver allows us to get better accuracy of where the detected object is.

Consider this simplified example.

• Two receivers and one LED
• Receiver 1 is pointed at -45 degrees
• Receiver 2 is pointed at 45 degrees
• IR LED is pointed at 0 degrees
• Only receiver 1 goes low

The object detected is probably somewhere closer to -22.5 degrees, than 0 degrees, since we average the direction of the LED and the receiver. We can elaborate further by taking into account that the receiver can detect close to 180 degrees and the spreadof the IR beam, when enclosed with an LED holder is about 22 degrees.

The IR LEDs can use a large amount of current. More than the GPIOs can provide. We can use an ULN2003 darlington transistor array to drive them straight from the UBEC switching power supply.

ULN2003A

       .----------. .----------.
       |          |_|          |
       |                       | 
PC0   =| 1B      1  16   1C    |=  IR LED 1 GND
       |                       |
PC1   =| 2B      2  15   2C    |=  IR LED 2 GND
       |                       |
PC2   =| 3B      3  14   3C    |=  IR LED 3 GND
       |                       |
PC3   =| 4B      4  13   4C    |=  IR LED 4 GND
       |                       |
PC4   =| 5B      5  12   5C    |=  IR LED 5 GND
       |                       |
PC5   =| 6B      6  11   6C    |=  IR LED 6 GND
       |                       |
PC8   =| 7B      7  10   7C    |=  IR LED 7 GND
       |                       |
GND   =| GND     8  9    8C    |=  N/C
       |                       | 
       '-----------------------'

To detect the white line around the outside of the ring, two CdS Photoresistor cells are used. The voltage across the cells are read using the ADC1 peripheral. a 10k ohm pull-down resistor is connected to the IO pad and GND to even out the reading range.

A yellow 5mm LED with a 330 ohm resistor inline is used to illuminate the area the Photoresistors are pointed at to reduce the effect of ambient light changes. The cell seems to perform best when as close to the surface as possible.

                                        5v   / \
                                              |
                              CdS             |
                                              |
PC0 -----------------+--------([])------------' 
                     |
                     Z
                     Z   330 ohm
                     Z
                     |
                   _____
                    ---    GND
                     '