BT Communication Structure

Brief Description of Bytes

• A byte is usually represented in hexadecimal format, or Hex for short.
• Hex numeral system is the base 16 representation of number values.
• It is called base 16 as it is represented in a range of 16 Values: 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F

Integer	Hex	Binary
0	0	0000
1	1	0001
2	2	0010
3	3	0011
4	4	0100
5	5	0101
6	6	0110
7	7	0111
8	8	1000
9	9	1001
10	A	1010
11	B	1011
12	C	1100
13	D	1101
14	E	1110
15	F	1111

• As opposed to binary, which is base 2, as it represented with two values: 1 or 0
• Bytes are generally represented as a pair of 4 bit arrays with the prefix "0x" : i.e. 0xFA = 1111 1010

NOTE : 8 bits is referred to as a byte, and 4 bits is referred to as a nibble.

Project - BT Communication Structure

All messages will be 8 bytes long

Requests & Response payloads

• "Request" will be used to refer to messages sent from the Pi
  • The status byte will just be empty in requests
• "Response" will be used to refer to messages sent from the Arduino

  • The status byte in the response will help with error messaging:

    bit7	bit6	bit5	bit4	bit3	bit2	bit1	bit0
    byte0 error	byte1 error	byte2 error	byte4 error	byte5 error	byte6 error	byte7 error	Fail (1)/Success(0)

Full Request structure

Example : [FA,8A,00,00,00,00,00,00]

Description	[byte 0]	[byte 1]	[byte 2]	[byte 3]	[byte 4]	[byte 5]	[byte 6]	[byte 7]
sanity bt	Command	Dummy	Dummy	Dummy	Dummy	Dummy	Reserve	Status
sanity servo	Command	Dummy	Dummy	Dummy	Dummy	Dummy	Reserve	Status
sanity sensor	Command	Dummy	Dummy	Dummy	Dummy	Dummy	Reserve	Status
sanity servo/sensor	Command	Dummy	Dummy	Dummy	Dummy	Dummy	Reserve	Status
sanity PID	Command	Dummy	Dummy	Dummy	Dummy	Dummy	Reserve	Status
Run PID controller	Command	Constants Multiplier	Balance Set point	Kp	Ki	Kd	Reserve	Status

Command Byte - Sanity Check BT

• bit7 : test type flag [1 = sanity check, 0 = regular PID run]

Sanity

• bit5 & bit 4 : test type

bit5	bit4	sanity check
0	0	BT Echo
0	1	Servo Position
1	0	Sensor Read
1	1	Tilt & measure

Sero Position

• bit3, bit2, bit1, bit0 : Servo Target Angle

bit3	bit2	bit1	bit0	angle
1	1	0	0	180
1	0	0	0	150
0	1	0	0	120
0	0	0	0	90
0	0	0	1	60
0	0	1	0	30
0	0	1	1	0
0	1	1	0	sweep

Tilt & Measure

• bit3 Tile direction [1 = full left tilt, 0 = full right tilt]
• bit2, bit1, bit0

bit3	bit2	bit1	wait time
0	0	1	5s
0	1	0	10s
1	0	0	15s

Sanity Check Command Bytes (Full)

Hex	Binary	Test Type	Action	LED	Details
0x8X	1000XXXX	BT Echo	Blue LED on Arduino should blink	Blue	the last 4 bits can be anything
0x9B	10011100	Adjust Servo	Servo Tilts Left	Both
0x96	10010110	Adjust Servo	Servo Centers	Both
0x93	10010011	Adjust Servo	Servo Tilts Right	Both
0x99	10001001	Adjust Servo	Servo should loop left tilt->center->right tilt twice	Both
0xAX	1100XXXX	Read Sensor	Sensor reading is made	Yellow	the last 4 bits can be anything

PID Messages

PID Command Bytes (Full)

The upper nibble is to trigger a PID command [bits 4-7]
The lower nibble is to set the start position of the balance beam [bits 0-3]

Hex	Binary	Start Position	Action	LED	Details
0x4A	01001100	full left	PID Controller Starts tilted left	Blue	Kp, Ki, & Kd values required
0x46	01000110	centered	PID Controller Starts centered	Blue	Kp, Ki, & Kd values required
0x43	01000011	full right	PID Controller Starts tilted right	Blue	Kp, Ki, & Kd values required

PID Multiplier Byte (Full)

The upper nibble represents which constants to multiply by [bits 4-7]
The lower nibble represents where to move the decimal place [bits 0-3]

HEX	Binary	Constants to Multiply	Decimal place position	Example Input (pi)	Expected Output (Arduino)
0x0E	00001110	Null/Default	Null/Default	[125,125,125]	[125,125,125]
0x1E	00011110	Kd	Null/Default	[125,125,125]	[125,125,125]
0x2D	00101101	Ki	1 to the left	[125,125,125]	[125,12.5,125]
0x3B	00111011	Ki & Kd	2 to the left	[125,125,85]	[125,1.25,0.85]
0x4E	01001110	Kp	Null/Default	[125,125,125]	[125,125,125]
0x5E	01011110	Kp & Kd	Null/Default	[125,125,125]	[125,125,125]
0x6E	01101110	Kp & Ki	Null/Default	[125,125,125]	[125,125,125]
0x7E	01111110	Kp, Ki, & Kd	Null/Default	[125,125,125]	[125,125,125]

Things to Consider:

• Multipliers should only be set on non-zero values.
• Default constant values should be zero.
• Each constant will have a range of 0-255 (including the multiplier).
  • Currently all tested values are floats less than 3.00.