# BerryIMU Python Code Update - Kalman Filter and More

We have updated to the python code in our git repo.

It now includes;

• The elusive Kalman filter.
• Math needed when the IMU is upside down
• Automatically calculate loop period.

What is a Kalman filter?  In a nutshell;
A Kalman filter is, it is an algorithm which uses a series of measurements observed over time, in this context an accelerometer and a gyroscope. These measurements will contain noise that will contribute to the error of the measurement. The Kalman filter will then try to estimate the state of the system, based on the current and previous states, that tend to be more precise that than the measurements alone.

A Kalman filter is more precise than a Complementary filter. This can be seen in the image below, which is the output of a complementary filter (CFangleX) and a Kalman filter (kalmanX) from the X axis plotted in a graph.

The red line (KalmanX) is better at filtering out noisep;

The code can be found here in our Git repository here
And  can be pulled down to your Raspberry Pi with;

pi@raspberrypi ~ \$ git clone http://github.com/ozzmaker/BerryIMU.git

A summary of the code;

```
def kalmanFilterY ( accAngle, gyroRate, DT):
y=0.0
S=0.0

global KFangleY
global Q_angle
global Q_gyro
global y_bias
global XP_00
global XP_01
global XP_10
global XP_11
global YP_00
global YP_01
global YP_10
global YP_11

KFangleY = KFangleY + DT * (gyroRate - y_bias)

YP_00 = YP_00 + ( - DT * (YP_10 + YP_01) + Q_angle * DT )
YP_01 = YP_01 + ( - DT * YP_11 )
YP_10 = YP_10 + ( - DT * YP_11 )
YP_11 = YP_11 + ( + Q_gyro * DT )

y = accAngle - KFangleY
S = YP_00 + R_angle
K_0 = YP_00 / S
K_1 = YP_10 / S

KFangleY = KFangleY + ( K_0 * y )
y_bias = y_bias + ( K_1 * y )

YP_00 = YP_00 - ( K_0 * YP_00 )
YP_01 = YP_01 - ( K_0 * YP_01 )
YP_10 = YP_10 - ( K_1 * YP_00 )
YP_11 = YP_11 - ( K_1 * YP_01 )

return KFangleY

```

# Add Colour to Text in Python

To make some of your text more readable, you can use ANSI escape codes to change the colour of the text output in your python program. A good use case for this is to to highlight errors.

The escape codes are entered right into the print statement.

```print("\033[1;32;40m Bright Green  \n")
```

The above ANSI escape code will set the text colour to bright green. The format is;
\033[  Escape code, this is always the same
1 = Style, 1 for normal.
32 = Text colour, 32 for bright green.
40m = Background colour, 40 is for black.

This table shows some of the available formats;

Text color Code Text style Code Background color Code
Black 30 No effect 0 Black 40
Red 31 Bold 1 Red 41
Green 32 Underline 2 Green 42
Yellow 33 Negative1 3 Yellow 43
Blue 34 Negative2 5 Blue 44
Purple 35 Purple 45
Cyan 36 Cyan 46
White 37 White 47

Here is the code used to create the coloured text in the title image;

```print("\033[0;37;40m Normal text\n")
print("\033[2;37;40m Underlined text\033[0;37;40m \n")
print("\033[1;37;40m Bright Colour\033[0;37;40m \n")
print("\033[3;37;40m Negative Colour\033[0;37;40m \n")
print("\033[5;37;40m Negative Colour\033[0;37;40m\n")

print("\033[1;37;40m \033[2;37:40m TextColour BlackBackground          TextColour GreyBackground                WhiteText ColouredBackground\033[0;37;40m\n")
print("\033[1;30;40m Dark Gray      \033[0m 1;30;40m            \033[0;30;47m Black      \033[0m 0;30;47m               \033[0;37;41m Black      \033[0m 0;37;41m")
print("\033[1;31;40m Bright Red     \033[0m 1;31;40m            \033[0;31;47m Red        \033[0m 0;31;47m               \033[0;37;42m Black      \033[0m 0;37;42m")
print("\033[1;32;40m Bright Green   \033[0m 1;32;40m            \033[0;32;47m Green      \033[0m 0;32;47m               \033[0;37;43m Black      \033[0m 0;37;43m")
print("\033[1;33;40m Yellow         \033[0m 1;33;40m            \033[0;33;47m Brown      \033[0m 0;33;47m               \033[0;37;44m Black      \033[0m 0;37;44m")
print("\033[1;34;40m Bright Blue    \033[0m 1;34;40m            \033[0;34;47m Blue       \033[0m 0;34;47m               \033[0;37;45m Black      \033[0m 0;37;45m")
print("\033[1;35;40m Bright Magenta \033[0m 1;35;40m            \033[0;35;47m Magenta    \033[0m 0;35;47m               \033[0;37;46m Black      \033[0m 0;37;46m")
print("\033[1;36;40m Bright Cyan    \033[0m 1;36;40m            \033[0;36;47m Cyan       \033[0m 0;36;47m               \033[0;37;47m Black      \033[0m 0;37;47m")
print("\033[1;37;40m White          \033[0m 1;37;40m            \033[0;37;40m Light Grey \033[0m 0;37;40m               \033[0;37;48m Black      \033[0m 0;37;48m")

\n")
```

# Raspberry Pi, 1.8" TFT, RF Receiver and Temperature Sensor

Below is some detail regarding the latest project I have been working on. Which is near completion.
I plan to wire it up permanently, place within a case and wall mount it.

` `

Some of the images don't come up too great in the video, I have included the actual images used here;

I created a simple one line bash script that polls for the temperature every 5 mins.

The main python program uses pygame to write to the TFT via a framebuffer and Matplotlib is used to create the Graphs.
The display can be changed by either the button on the breadboard or via the remote FOB.