## Absolute Acceleration

You can get the equivalent of the MakeCode `acceleration strength`

block with a tiny bit of math in CircuitPython. The key is to take the square root of the sum of the squares of x, y, and z, similar to the hypotenuse of a triangle but in three dimensions. In vector math, it is getting the magnitude of the acceleration in 3D.

The following CircuitPython code will get the readings from the accelerometer and calculate the absolute acceleration and print it on the serial monitor and plot it in Mu.

import time from math import sqrt from adafruit_circuitplayground.express import cpx def show_value(val): # Show value 0-9 on CPX NeoPixels for i in range(val): cpx.pixels[i] = (50, 0, 0) # Red for i in range(val, 10): cpx.pixels[i] = (0, 0, 0) return # Main loop gets x, y and z axis acceleration, gets the absolute # acceleration, then a normalized value to the number of Gees # prints the values, and displays on NeoPixels Normalize_To = 9.8 * 2 # Normalize to 2 Gs, change 2 to 1, 4, 8, etc. while True: x, y, z = cpx.acceleration # Get acceleration from board abs = sqrt(x*x + y*y + z*z) # Get absolute acceleration abs = min(abs, Normalize_To) # Normalize to max acceleration normalized = abs / Normalize_To # Get fractional normalized accel print((abs,normalized)) # Print to Mu Serial show_value(int(normalized * 10)) # Show on NeoPixels on CPX time.sleep(0.5) # Wait a bit then do again

Now shake the accelerometer. Mu will show you the absolute acceleration and the normalized acceleration, here to 2g although you can change this to any value you want, usually 1, 2, 4, 6, 8, 16, etc.

Press the Plotter button and you get a plot. The screen below shows shaking in various directions.

## Color Glow Accelerometer

You can use the acceleration values to make a fun light up project with the NeoPixels. There are three acceleration values, and the LEDs have three color values. Let's see what we can do with that!

Copy the following to a file named **code.py** and save to your Circuit Playground Express **CIRCUITPY** drive.

from adafruit_circuitplayground.express import cpx # Main loop gets x, y and z axis acceleration, prints the values, and turns on # red, green and blue, at levels related to the x, y and z values. while True: if cpx.switch: print("Slide switch off!") cpx.pixels.fill((0, 0, 0)) continue else: R = 0 G = 0 B = 0 x, y, z = cpx.acceleration print((x, y, z)) if x: R = abs(int(x)) if y: G = abs(int(y)) if z: B = abs(int(z)) cpx.pixels.fill((R, G, B))

Move the slide switch to the right if it isn't already. Lights! Now move the board in different directions to see the colors change!

Let's take a look at the code. First we `import`

the `adafruit_circuitplayground.express`

library as `cpx`

.

Inside the `while True:`

loop, the program checks to see `if`

the switch is to the left. If it is, we `print`

`Slide switch off!`

and turn off all the LEDs. This creates an "off switch" for the project in case you'd like to leave it sitting around but not have the lights on. `continue`

tells the code to keep checking the switch until the state changes, i.e. you move the switch to the right. Once that happens, the code moves on.

Next is the `else`

block. First, three variables, R, G and B are created. These will be used to set the colors. They are assigned 0 to start. Then, the code assigns `x, y, z = cpx.acceleration`

and prints the values. If you look at the serial output, you'll see how fast the values are scrolling. This is why one typically includes a `time.sleep()`

in the code, to slow those values down to a readable speed. However, this project works best without a `sleep`

, so it has been left out.

The next section has three parts. Each do the same thing but for a different axis. It is time to take the acceleration values, and use them to represent color values. Begin with `x`

.

The value of x is modified a little with `abs(int(x))`

. This returns the absolute value of the whole number value of `x`

. Absolute values are explained here. Since color values are all whole numbers, use `int(x)`

to return only the nearest whole number value of `x`

, instead of a long decimal which is often what acceleration returns. Since color values are all positive, take the absolute value of `int(x)`

to remove any potential negative numbers from the mix.

Then take `abs(int(x))`

and assign it to `R`

. Now we have our `R`

value to use for red! Then we do the same thing for `y`

and `z`

, except `abs(int(y))`

is assigned to G and `abs(int(z))`

is assigned to B. This gives us three color values!

We then set `cpx.pixels.fill((R, G, B))`

to set all the pixels to these color values. As you move the board around, the acceleration values change, and that causes each of our color values to be different. Now, depending on what angle you hold the board, you'll get a different color combination!

Remember the earlier example, where we explained that if the board is laying flat, the returned values are (0, 0, 9.8). This means, if the board is laying flat, facing up, while this code is running, the color values are `(0, 0, 9.8)`

. So, you'll see if it's laying flat on your desk, it's blue!

If you hold it so the USB cable is on the top and pointed downwards, the values are, `(0, 9.8, 0)`

, so the LEDs are green.

If you hold it so the USB cable is sideways, pointing left or right, the values are `(9.8, 0, 0)`

so the LEDs are red.

As you move the board around at different angles, you'll find every color between!

We also explained that if you shake the board, you'll get back higher values from the accelerometer. This means that the LEDs will be brighter if you shake it. Give it a try!

## Accelerate Other Projects

Here are some projects that use acceleration: