pxt-calliope/docs/projects/guitar/accelerometer.md

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2016-09-27 06:55:39 +02:00
# Accelerometer Beat control
### @description micro:bit guitar: using accelerometer to control tempo
### ~avatar avatar
Use the Accelerometer to control guitar tempo
* Duration: 30 - 45 minutes
* Concepts:
* Gravity
* Acceleration
* X, Y, Z coordinates
* Tempo
* Beat
* Mapping
* Graphing
* Absolute value
### ~
*accelerometer controlled tempo*
https://youtu.be/h_gPkBaVkoo
TODO: add sound to video
## Blocks
```cards
input.acceleration(Dimension.Y)
music.setTempo(120)
pins.map(0, 0, 1023,60, 320)
Math.abs(1)
```
## Accelerometer, gravity and tilting!
The micro:bit contains an **accelerometer** sensor that is able to measure forces applied to the board.
On earth, we are subject to the **gravity force** which pulls us to the ground!
https://youtu.be/0SULoTKmkhI
When the micro:bit is flat on a table, with the screen pointing up, the gravity force is aligned
with the **Z** axis of the micro:bit.
![micro:bit x, y, z axis image](/static/mb/projects/guitar/accelleration_axis.png)
If you tilt it up and down, the force will align with the **Y** axis -- this is how we can detect tilting!!!
If the force along **Y** grows, the micro:bit is tilting more and more vertically!
## Measuring Acceleration along different coordinates (X, Y, Z axis)
The acceleration block approximately measures **milli-g**, which is 1/1000 of a **g** or the
acceleration of gravity.
### Step 1: Graphing acceleration
```blocks
basic.forever(() => {
led.plotBarGraph(input.acceleration(Dimension.Y), 1023)
})
```
**Create the code** that measures the change in the Y axis acceleration as a graph on the LEDs
**Dowload the code** to the micro:bit
**Test the movements that move the graph from 1 to 5 bars on the LEDs**
### Extra
Try graphing the acceleration along the **X** and **Z** axis. Can you explain the differences?
### ~hint
## Mapping
**It is common to map one standard to another - such as with temperature**
![Fahrenheit to Celsius](/static/mb/projects/guitar/map_analogy.png "Fahrenheit to Celsius")
### ~
### Step 2: Mapping acceleration to Beat
**micro:bit sensors produce signal values between 0 to 1023. The *[map block](/reference/pins/map)* converts the signal to a desired range.**
```blocks
basic.forever(() => {
music.setTempo(pins.map(Math.abs(input.acceleration(Dimension.Y)),
0, 1023,
60, 320))
music.playTone(Note.C, music.beat(BeatFraction.Quarter));
})
```
**Create the code** that *Maps* Y axis acceleration as *tempo*
**Download the code** to the micro:bit on the guitar
**Test the movements that speed and slow the tempo**
### Step 3: Combine with light sensor tone control
**Put it all together!**
```blocks
basic.forever(() => {
music.setTempo(pins.map(Math.abs(input.acceleration(Dimension.Y)),
0, 1023,
60, 320))
music.playTone(
input.lightLevel() * 25,
music.beat(BeatFraction.Quarter)
);
})
```
**Combine the code above with the light sensor tone control code from the previous activity**
**Download the code** to the micro:bit on the guitar
### Now play the guitar adjusting tone and tempo using the light sensor and accelerometer!
### ~button /projects/guitar/pinpress
NEXT: Pin Press on/off
### ~