5. Electrical and Controller Properties

The components inside Bittle are:

the main board on the top which is covered with a plastic shell.
the servos which are installed at every joint. (The motor shaft depicts joints and the motor body is connected to the limb)
the battery which is installed at the bottom.

../../_images/dog_stand.JPG — Fig. 5.1 Standing dog

Todo

Get familiar with the provided hardware.

5.1. Main Board

../../_images/board_top_view.png — Fig. 5.2 Top view of main board

../../_images/board_bottom_view.png — Fig. 5.3 Bottom view of main board

5.1.1. Specifications

Controller Specifications:

Mainboard Name

NyBoard V1_1

Microcontroller

ATmega328P

Operating Voltage

5V

Chip frequency / Clock speed

16 MHz

DC Current per I/O Pin

20mA

Memory usage:

Flash

32KB

SRAM

2KB

EEPROM

1KB

EEPROM (I2C)

8KB

External Interface:

UART
I2C (TWI)
SPI

Additional on board components:

Component

Description

Protocol

Address / Pin

MPU6050

6 axis IMU

I2C

At 0x68

Interrupt pin

D2

PCA9685

16 channel PWM controller

I2C

At 0x40

AT24C64

EEPROM 8KB

I2C

At 0x54

VS1838B

IR Receiver

D4

Buzzer

D5

Voltage divider

A7

G1

External I2C

I2C

G2

External analog pins

Analog

A2, A3

G3

External digital pins

Digital

D8, D9

G4

External digital pins

Digital

D6, D7

LED

Single Green LED

Digital

D10

5.1.2. Board interface

../../_images/interface_diagram.png — Fig. 5.4 Interface diagram

../../_images/Bittle_servo_num.png — Fig. 5.5 Motor connection layout

5.1.3. Board power supply

The actual voltage is approximately 2x of the reading. A safe range of battery voltage is below 10V. You should charge the battery in time when the battery is lower than 7.4V.

$Voltage_{real} = \frac{ADC_{reading}}{1024} \times 5.0 \times 2$

The main chips are powered by a Low-dropout (LDO) linear regulator for noise removal and better stability. LM1117-5V and XC6206P-3.3V are used to power 5V and 3.3V chips. The 3.3V LDO is connected in serial after the 5V LDO for better efficiency.

There’s a diode between the battery and LM1117-5V to prevent damage by the wrong connection. There’s a self-recover fuse (6V 500mA) on the USB uploader to limit the current and protect the USB port.

The Raspberry Pi consumes much more power, so we choose TPS565201 DC-DC to provide a 5V 3A output. The peak output can be 5A and with high-temperature/current/voltage protection. It will cut off the power when the chip keeps outputting >4A and over 100 Celcius degrees until the temperature drops to normal.

The servos are powered by 2S Li-ion batteries directly. Pay attention not to short connect the power or any pins on the NyBoard.

../../_images/power_supply_diagram.jpg — Fig. 5.6 Power supply diagram

5.2. Servos

The servos are used to execute the robot movements. These can be turned to the required angle as they have a built-in feedback circuit. Inside a servo motor, there is an electric motor which is in connected to a potentiometer using gear train. The potentiometer is used to measure the angle of rotation of the motor shaft. The wiring of almost all servos include VCC, GND and PWM input. PWM or Pulse width modulation is used to control the motor to the specific angle.

The controller controlling the servo sends pulse signal with duty cycle which nominally ranges between 1ms to 2 ms. For example, if at 1ms the motor turns to -90° and at 2ms the motor turns at +90°, then at 1.5 ms the motor will turn at 0°.

../../_images/servo_with_gear.png — Fig. 5.7 Servo motor

5.3. Battery

Specifications of battery:

Battery type

Lithium Polymer

Number of cells

2 of 1000mAh

Total capacity

7.4Wh

Max discharge current

5A

Max output voltage

7.4V

Max recharge current

1A

Max recharge voltage

5V

Charging cable type

micro-USB

../../_images/dog_bottom_view.jpeg — Fig. 5.8 Battery location and status LED.

5.3.1. Battery Status

Battery status LED color when Bittle is running or idle.

Blue

Charged

Red

Discharged

Charging status:

Battery status LED color when Bittle is charging.

Green

Charged

Red

Charging