- Arduino Pro mini
- HMC5883L Magnetometer sensor
- LED lights - 8Nos
- 470Ohm Resistor – 8Nos
- Barrel Jack
- A reliable PCB manufacturer like PCBGOGO
- FTDI Programmer for mini
Before we dive into the circuit, let’s understand a bit about magnetometer and how they work. As the name suggests the term Magneto does not refer to that crazy mutant in marvel who could control metals by just playing piano in the air. Ohh! But I like that guy he is cool.
Magnetometer is actually a piece of equipment that could sense the magnetic poles of the earth and point the direction according to that. We all know that Earth is huge piece of spherical magnet with North Pole and South Pole. And there is magnetic field because of it. A Magnetometer senses this magnetic field and based on the direction of the magnetic field it can detect the direction we are facing.
How the HMC5883L Sensor Module Works
The HMC5883L being a magnetometer sensor does the same thing. It has the HMC5883L IC on it which is from Honeywell. This IC has 3 magneto-resistive materials inside which are arranged in the axes x, y and z. The amount of current flowing through these materials is sensitive to the earth’s magnetic field. So by measuring the change in current flowing through these materials we can detect the change in Earth’s magnetic field. Once the change is magnetic field is absorbed the values can then be sent to any embedded controller like a microcontroller or processor through the I2C protocol.
Since the sensor works by sensing the magnetic field, the output values will be greatly affected if a metal is placed nearby. This behavior can be leveraged to use these sensors as metal detectors also. Care should be taken not to bring magnets near this sensor since the strong magnetic field from a magnet might trigger false values on the sensor.
The circuit for this Arduino based Digital Compass is pretty simple, we simply have to interface the HMC5883L sensor with the Arduino and connect 8 LEDs to the GPIO pins of the Arduino Pro mini. The complete circuit diagram is shown below The Sensor module has 5 pins out of which the DRDY (Data Ready) is not used in our project since we are operating the sensor in continuous mode. The Vcc and ground pin is used to power the Module with 5V from the Arduino board. The SCL and SDA are the I2C communication bus lines that are connected to the A4 and A5 I2C pins of the Arduino Pro mini respectively. Since the module itself has a pull high resistor on the lines, there is no need to add them externally.
To indicate the direction we have used 8 LEDs all of which are connected to the GPIO pins of the Arduino through a current limiting resistor of 470 Ohms. The Complete circuit is powered by a 9V battery through the barrel Jack. This 9V is provided directly to the Vin pin of the Arduino where it is regulated to 5V using the on-board regulator on Arduino. This 5V is then used to power the sensor and the Arduino as well.
Fabricating the PCBs for the Digital Compass
The idea of the circuit is place the 8 LEDs in a circular fashion so that each Led points all the 8 directions namely North, North-East, East, South-East, South, South-West, West and North West respectively. So it is not easy to arrange them neatly on a breadboard or even on a perf board for that matter. Developing a PCB for this circuit will make it look more neat and easy to use. So I opened my PCB designing software and placed the LEDs and resistor in a neat circular pattern and connected the tracks to form the connections. My Design looked something like this below when completed. You can also download the Gerber file form the link given. I have designed it to be a double side board since I want the Arduino to be in the bottom side of my PCB so that it does not spoil the look on top of my PCB. If you are worrying that you have to pay high for a double side PCB then hold on I got good new coming.
Now, that our Design is ready it is time to get them fabricated. To get the PCB done is quite easy, simply follow the steps below
Step 1: Get into www.pcbgogo.com, sign up if this is your first time. Then, in the PCB Prototype tab enter the dimensions of your PCB, the number of layers and the number of PCB you require. My PCB is 80cm×80cm so the tab looks like this below Step 2: Proceed by clicking on the Quote Now button. You will be taken to a page where to set few additional parameters if required like the material used track spacing etc. But mostly the default values will work fine. The only thing that we have to consider here is the price and time. As you can see the Build Time is only 2-3 days and it just costs only $5 for our PSB. You can then select a preferred shipping method based on your requirement. Step 3: The final step is to upload the Gerber file and proceed with the payment. To make sure the process is smooth PCBGOGO verifies if your Gerber file is valid before proceeding with the payment. This way you can sure that your PCB is fabrication friendly and will reach you as committed.
Assembling the PCB
After the board was ordered, it reached me after some days though courier in a neatly labeled well packed box and like always the quality of the PCB was awesome. I am sharing few pictures of the boards below for you to judge. I turned on my soldering rod and started assembling the Board. Since the Footprints, pads, vias and silkscreen are perfectly of the right shape and size I had no problem assembling the board. The board was ready in just 10 minutes from the time of unpacking the box.
Few pictures of the board after soldering are shown below.