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content/notes/10-orientation-sensors.md
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@ -5,7 +5,8 @@ tags:
- info305 - info305
--- ---
> [!INFO] Location sensors dont know > [!INFO]
> Location sensors dont know what direction you are looking
Accelerometers Accelerometers
- Measures proper acceleration (acceleration it experiences relative to freefall. gravity), felt by people or objects - Measures proper acceleration (acceleration it experiences relative to freefall. gravity), felt by people or objects
@ -14,6 +15,11 @@ Accelerometers
- iPhone range: ±2g, precision 0.018g - iPhone range: ±2g, precision 0.018g
![g forces|300](https://i.imgur.com/l4DnMSN.png) ![g forces|300](https://i.imgur.com/l4DnMSN.png)
> [!INFO]
> measure accelerationi with respect to gravity
> measure gravity along three axis
> tradeoff large range with high precision
Accelerometers Accelerometers
- Acceleration is measured on 3 axes - Acceleration is measured on 3 axes
- Orientation of sensor (and coordinate system) varies among different device - Orientation of sensor (and coordinate system) varies among different device
@ -24,14 +30,17 @@ Accelerometers
- Measuring flowing current over an differential capacitor indicates the acceleration - Measuring flowing current over an differential capacitor indicates the acceleration
![|300](https://i.imgur.com/UIS4zDV.png) ![|300](https://i.imgur.com/UIS4zDV.png)
> [!INFO]
> dont need to fully understand how MEMS work
Accelerometers Accelerometers
- Advantage: - Advantage:
- Fast update rate - Fast update rate
- Relatively accurate - Relatively accurate
- Disadvantage: - Disadvantage:
- Can’t easily identify certain kind of acceleration (small value range) - Can’t easily identify certain kind of acceleration (small value range)
> [!INFO]
> only give you direction to the center of the earth (from gravity)
![two phones|300](https://i.imgur.com/s45a4TF.png) ![two phones|300](https://i.imgur.com/s45a4TF.png)
Compass / Magnetometer Compass / Magnetometer
@ -40,6 +49,11 @@ Compass / Magnetometer
- iPhone 4 magnetometer range: ±2mT - iPhone 4 magnetometer range: ±2mT
- Pro tip: prolonged exposure to a fridge magnet decalibrates your phones’ magnetometer for at least a week ;-) - Pro tip: prolonged exposure to a fridge magnet decalibrates your phones’ magnetometer for at least a week ;-)
![field strength examples|300](https://i.imgur.com/00VV74x.png) ![field strength examples|300](https://i.imgur.com/00VV74x.png)
> [!INFO]
> doesn't directly measure north
> measure magentic fielf of earth and aligns with magenetic north
> earth field is very weak so we need sensitive magnetometer
>
![Error around metal/magnetic objects](https://i.imgur.com/YIJAcGS.png) ![Error around metal/magnetic objects](https://i.imgur.com/YIJAcGS.png)