# Circuit Playground Express Compass
## Overview
The Circuit Playground Express has a 3-axis LIS3DH accelerometer on board which can be used for all sorts of projects. This chip has the advantage of being very small and fits nicely at the center of the Circuit Playground boards. Sometimes, though, "just" being a 3-axis accelerometer is a disadvantage. Times like those when you need compass-like capabilities. An accelerometer **only** tells you how the board is moving (the forces acting on it, to be precise), but not how it's oriented relative to the magnetic north pole of whichever planet you're on. For that, a **magnetometer** is needed.
Magnetometers do come as separate chips (the BBC Micro:bit has one, for example) but it doesn't seem as easy to find on a breakout board. However, breakouts containing a single chip with both an accelerometer and a magnetometer are easy to find. Specificity, there are breakouts containing the LSM303 in both the usual rectangular header-strip format as well as a Flora breakout.
In this guide we'll add the Flora LMS303 breakout to a Circuit Playground Express and use it to build a compass.
Coding in C (Arduino), you can actually use any breakout whose supporting library conforms to the Adafruit Unified Sensor Library and provides magnetometer readings. The project is also programmable in CircuitPython and demonstrates use of the accelerometer.
The NeoPixels on the Circuit Playground Express will be used to indicate North.
## Calibration
During calibration (when all the pixels are green) move the box in a figure eight and rotate it around the x, and y axes multiple times.
By sampling a range of readings. we can get a sense of the expected range of values. Using that, we can calculate the center on the range on both the X and Y axes. The distance of that from (0, 0) can be used to correct subsequent readings to be relative to (0, 0).
When calibrating from the original code (i.e. you haven't tweaked the min/max arrays) or if you ask for a recalibration (by pressing button A until the pixels turn green) the result will be printed on the console. You can copy these two lines and replace the similar ones near the top of the code. Rebuild it (if using the Arduino code) and load it onto your compass.
## Operation
We can then map each corrected reading to the range -100 to +100, and pass these normalized values to the atan2 function that gives us a heading, the angle as shown in the range -Pi to Pi.
Then we find which 30 degree wedge the heading falls into. We start by adding 180 to the angle from above, giving us something between 0 and 360. We add 15 (because the lowest segment is centered on zero) and divide by 30.
And that's how we know which NeoPixel to light up.
## Parts
### Circuit Playground Express
[Circuit Playground Express](https://www.adafruit.com/product/3333)
**Circuit Playground Express** is the next step towards a perfect introduction to electronics and programming. We've taken the original Circuit Playground Classic and made it even better! Not only did we pack even more sensors in, we also made it even easier to...
In Stock
[Buy Now](https://www.adafruit.com/product/3333)
[Related Guides to the Product](https://learn.adafruit.com/products/3333/guides)
### JST PH 2-Pin Cable – Male Header 200mm
[JST PH 2-Pin Cable – Male Header 200mm](https://www.adafruit.com/product/3814)
For a really long time we assumed that the JST PH didn't have a free-hanging male header version. But then we found this **JST-PH 2-pin Male Cable,** and we were like, _this is perfect!_ It's not a genuine JST connector, but it's 100%...
In Stock
[Buy Now](https://www.adafruit.com/product/3814)
[Related Guides to the Product](https://learn.adafruit.com/products/3814/guides)
### JST PH 2-Pin Cable - Female Connector 100mm
[JST PH 2-Pin Cable - Female Connector 100mm](https://www.adafruit.com/product/261)
Red and black tinned wires with a 2-pin JST PH connector on the end. 4" / 100mm long. Matches up nicely with our Lipoly chargers!
[We have the socket 'mating' version of this cable](https://www.adafruit.com/product/3814) over here,
In Stock
[Buy Now](https://www.adafruit.com/product/261)
[Related Guides to the Product](https://learn.adafruit.com/products/261/guides)
### Breadboard-friendly SPDT Slide Switch
[Breadboard-friendly SPDT Slide Switch](https://www.adafruit.com/product/805)
These nice switches are perfect for use with breadboard and perfboard projects. They have 0.1" spacing and snap in nicely into a solderless breadboard. They're easy to switch no matter what size fingers you have, but not so easy that they'll get flipped by accident. Work great as...
Out of Stock
[Buy Now](https://www.adafruit.com/product/805)
[Related Guides to the Product](https://learn.adafruit.com/products/805/guides)
### Lithium Ion Polymer Battery - 3.7v 150mAh
[Lithium Ion Polymer Battery - 3.7v 150mAh](https://www.adafruit.com/product/1317)
Lithium-ion polymer (also known as 'lipo' or 'lipoly') batteries are thin, light, and powerful. The output ranges from 4.2V when completely charged to 3.7V. This battery has a capacity of 150mAh for a total of about 0.6 Wh. If you need a larger battery,
In Stock
[Buy Now](https://www.adafruit.com/product/1317)
[Related Guides to the Product](https://learn.adafruit.com/products/1317/guides)
### Silicone Cover Stranded-Core Wire - 2m 26AWG Blue
[Silicone Cover Stranded-Core Wire - 2m 26AWG Blue](https://www.adafruit.com/product/1878)
Silicone-sheathing wire is super-flexible and soft, and its also strong! Able to handle up to 200°C and up to 600V, it will do when PVC covered wire wimps out. We like this wire for being extremely supple and flexible, so it is great for wearables or projects where the wire-harness has to...
In Stock
[Buy Now](https://www.adafruit.com/product/1878)
[Related Guides to the Product](https://learn.adafruit.com/products/1878/guides)
## Supplies and Tools
- Hot Glue & Glue Gun
- Solder and Soldering Iron
For the build described here, you'll probably want a case for the Circuit Playground Express. If you have a 3D printer or have access to 3D printing facilities, [this guide](https://learn.adafruit.com/case-for-circuit-playground) shows how to produce a nice one.
- [Next Page](https://learn.adafruit.com/circuit-playground-express-compass/hardware.md)
## Featured Products
### Circuit Playground Express
[Circuit Playground Express](https://www.adafruit.com/product/3333)
**Circuit Playground Express** is the next step towards a perfect introduction to electronics and programming. We've taken the original Circuit Playground Classic and made it even better! Not only did we pack even more sensors in, we also made it even easier to...
In Stock
[Buy Now](https://www.adafruit.com/product/3333)
[Related Guides to the Product](https://learn.adafruit.com/products/3333/guides)
### FLORA Accelerometer/Compass Sensor - LSM303
[FLORA Accelerometer/Compass Sensor - LSM303](https://www.adafruit.com/product/1247)
Add motion and direction sensing to your wearable FLORA project with this high precision 3-axis Accelerometer+Compass sensor. Inside are two sensors, one is a classic 3-axis accelerometer, which can tell you which direction is down towards the Earth (by measuring gravity) or how fast the board...
No Longer Stocked
[Buy Now](https://www.adafruit.com/product/1247)
[Related Guides to the Product](https://learn.adafruit.com/products/1247/guides)
### Circuit Playground Express - Base Kit
[Circuit Playground Express - Base Kit](https://www.adafruit.com/product/3517)
It's the **Circuit Playground Express Base Kit!** It provides the few things you'll need to get started with the new [Circuit Playground Express](https://www.adafruit.com/product/3333). This version of Circuit Playground is super powered, and will...
Out of Stock
[Buy Now](https://www.adafruit.com/product/3517)
[Related Guides to the Product](https://learn.adafruit.com/products/3517/guides)
### Circuit Playground Express Advanced Pack
[Circuit Playground Express Advanced Pack](https://www.adafruit.com/product/2769)
**Circuit Playground Express** is the next step towards a perfect introduction to electronics and programming. We've taken the original Circuit Playground Classic and made it even better! Not only did we pack even more sensors in, we also made it even easier to program....
Out of Stock
[Buy Now](https://www.adafruit.com/product/2769)
[Related Guides to the Product](https://learn.adafruit.com/products/2769/guides)
### JST PH 2-Pin Cable - Female Connector 100mm
[JST PH 2-Pin Cable - Female Connector 100mm](https://www.adafruit.com/product/261)
Red and black tinned wires with a 2-pin JST PH connector on the end. 4" / 100mm long. Matches up nicely with our Lipoly chargers!
[We have the socket 'mating' version of this cable](https://www.adafruit.com/product/3814) over here,
In Stock
[Buy Now](https://www.adafruit.com/product/261)
[Related Guides to the Product](https://learn.adafruit.com/products/261/guides)
### JST PH 2-Pin Cable – Male Header 200mm
[JST PH 2-Pin Cable – Male Header 200mm](https://www.adafruit.com/product/3814)
For a really long time we assumed that the JST PH didn't have a free-hanging male header version. But then we found this **JST-PH 2-pin Male Cable,** and we were like, _this is perfect!_ It's not a genuine JST connector, but it's 100%...
In Stock
[Buy Now](https://www.adafruit.com/product/3814)
[Related Guides to the Product](https://learn.adafruit.com/products/3814/guides)
### Breadboard-friendly SPDT Slide Switch
[Breadboard-friendly SPDT Slide Switch](https://www.adafruit.com/product/805)
These nice switches are perfect for use with breadboard and perfboard projects. They have 0.1" spacing and snap in nicely into a solderless breadboard. They're easy to switch no matter what size fingers you have, but not so easy that they'll get flipped by accident. Work great as...
Out of Stock
[Buy Now](https://www.adafruit.com/product/805)
[Related Guides to the Product](https://learn.adafruit.com/products/805/guides)
### Lithium Ion Polymer Battery - 3.7v 150mAh
[Lithium Ion Polymer Battery - 3.7v 150mAh](https://www.adafruit.com/product/1317)
Lithium-ion polymer (also known as 'lipo' or 'lipoly') batteries are thin, light, and powerful. The output ranges from 4.2V when completely charged to 3.7V. This battery has a capacity of 150mAh for a total of about 0.6 Wh. If you need a larger battery,
In Stock
[Buy Now](https://www.adafruit.com/product/1317)
[Related Guides to the Product](https://learn.adafruit.com/products/1317/guides)
## Related Guides
- [Adafruit Circuit Playground Express](https://learn.adafruit.com/adafruit-circuit-playground-express.md)
- [Infrared Hand Gesture Robot Control Glove](https://learn.adafruit.com/cpx-ir-infrared-hand-gesture-robot-control-glove.md)
- [MakeCode Course for Circuit Playground Express](https://learn.adafruit.com/makecode-circuit-playground-express-course.md)
- [CRICKIT WobblyBot](https://learn.adafruit.com/crickit-wobblybot.md)
- [Circuit Playground Gizmo Ornaments](https://learn.adafruit.com/display-ornaments-with-circuit-playground.md)
- [NeoPixie Dust Bag with Circuit Playground Express](https://learn.adafruit.com/neopixie-dust-bag-cpx.md)
- [Combo Dial Safe with Circuit Playground Express](https://learn.adafruit.com/combo-dial-safe-with-circuit-playground-express.md)
- [AdaBox 008](https://learn.adafruit.com/adabox008.md)
- [Halloween Sentry-Bot with CRICKIT for CPX](https://learn.adafruit.com/halloween-sentry-bot.md)
- [Circuit Playground Express Automatic Sunglasses](https://learn.adafruit.com/circuit-playground-express-auto-sunglasses.md)
- [Infrared Receive and Transmit with Circuit Playground Express](https://learn.adafruit.com/infrared-ir-receive-transmit-circuit-playground-express-circuit-python.md)
- [Interactive Map with Circuit Playground Express](https://learn.adafruit.com/interactive-map-with-cpx.md)
- [Circuit Playground Express Perk-up Ears](https://learn.adafruit.com/perk-up-ears.md)
- [CircuitPython Made Easy on Circuit Playground Express and Bluefruit](https://learn.adafruit.com/circuitpython-made-easy-on-circuit-playground-express.md)
- [Musical Walking Stick with Circuit Playground](https://learn.adafruit.com/musical-cane-walking-stick.md)
- [Circuit Playground Musical Glove](https://learn.adafruit.com/cpx-musical-glove.md)