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

# Accelerometer Beat control

### @description @boardname@ guitar: using accelerometer to control tempo

### ~avatar avatar

Use the Accelerometer to control guitar tempo
* Concepts:
     * Gravity
     * Acceleration
     * X, Y, Z coordinates
     * Tempo
     * Beat
     * Mapping
     * Graphing
     * Absolute value

### ~  

## Duration: 30 - 45 minutes  
  
*accelerometer controlled tempo*  
https://youtu.be/kA0HpqCWsjs

## Blocks

```cards
input.acceleration(Dimension.Y)
music.setTempo(120)
pins.map(0, 0, 1023,60, 320)
Math.abs(1)            
```

## Accelerometer, gravity and tilting!

The @boardname@ 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 @boardname@ is flat on a table, with the screen pointing up, the gravity force is aligned
with the **Z** axis of the @boardname@. 

![@boardname@ 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 @boardname@ 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 @boardname@ 
  
**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
**@boardname@ 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 @boardname@ 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 @boardname@ 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
### ~