Magnetometer < IoT_Course

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---+ Magnetometer and Compass
---++ Introduction

Magnetometers measure magnetic field. The electronic devices available are very sensitive, and can measure fields down to the 100 u-Gauss level. Since the earth magnetic field is roughly 0.6 Gauss, we can measure the earth magnetic field with a resolution of 1 part in 6000. Therefore, magnetometers can be used as compasses.

Several magnetometers are on the market and we use
   * the [[https://cdn-shop.adafruit.com/datasheets/HMC5883L_3-Axis_Digital_Compass_IC.pdf][HMC5883L]] [[https://duckduckgo.com/?q=qmc5883+datasheet+pdf&t=ffab&ia=web][ ]]from Honyewell
   * the [[https://www.filipeflop.com/img/files/download/Datasheet-QMC5883L-1.0%20.pdf][QMC5883]] from QST
The chips, even though pin compatible and coming on the same PCB (GY-271), are very different. Both use !I2C as communication interface, but the !I2C address and the registers are different.
| <img alt="gy-271.png" height="290" src="%ATTACHURL%/gy-271.png" title="gy-271.png" width="273" /> | <img alt="gy-271-back.png" height="253" src="%ATTACHURL%/gy-271-back.png" title="gy-271-back.png" width="365" /> |
On the photo of the GY-271 board, the !HMC5883L is mounted. The !QMC5883 is marked HA 5883.

The !HMC5883L also comes on the GY-87 board, which combines the magnetometer with an accelerometer and a gyroscope on the MPU6050 and a BMP180 barometric pressure and temperature sensor. In this case, the !HMC5883L is connected to the MPU6050 !I2C bus and can be accessed either through the MPU6050 !I2C master or directly through a bypass of the MPU6050 !I2C master.
| <img alt="gy-87.png" height="277" src="%ATTACHURL%/gy-87.png" title="gy-87.png" width="276" /> | <img alt="gy-87-back.png" height="334" src="%ATTACHURL%/gy-87-back.png" title="gy-87-back.png" width="360" /> |

---++ Connections

Here are the connection tables for the two boards
| *GY-271* | *!WeMos Pin* | *GPIO* |
| Vcc | 5V | |
| GND | GND | |
| SCL | D1 | 22 |
| SDA | D2 | 21 |
| DRDY | D3 | 27 on WROVER CPU T7 V1.5 |

| *GY-87* | *!WeMos Pin* | *GPIO* |
| Vcc_In | 5V | |
| 3.3V | nc | |
| GND | GND | |
| SCL | D1 | 22 |
| SDA | D2 | 21 |
| FSYNC | nc | |
| INTA | D0 | 16 |
| DRDY | D3 | 17 on the ESP32-WROOM<br />27 on the ESP32-WROVER-B T7 V1.5 |

---++ The magnetometer driver class

The magnetometer driver class can be found at

-- %USERSIG{UliRaich - 2022-08-24}%

---++ Comments

%COMMENT%

Attachments

Topic attachments
I	Attachment	History	Action	Size	Date	Who
png	gy-271-back.png	r1	manage	126.9 K	2022-08-24 - 10:14	UliRaich
png	gy-271.png	r1	manage	158.9 K	2022-08-24 - 09:24	UliRaich
png	gy-87-back.png	r1	manage	121.7 K	2022-08-24 - 10:08	UliRaich
png	gy-87.png	r1	manage	109.5 K	2022-08-24 - 10:01	UliRaich

Topic revision: r3 - 2022-08-25 - UliRaich