DIY Telematics Box

Telematics boxes (aka Black Boxes) are used to record and log various attributes of a moving vehicle. They have been primarily used in airplanes to log various attributes of an aircraft, for example, air speed, heading, fuel levels, radio chatter etc. It is the first reference point for any aircraft incident, as it holds all the aircraft data leading up to the incident. This method of monitoring vehicle performance, condition, and movement has since been transferred to cars, allowing insurance companies to obtain a better estimation of driving styles in order to present the correct premiums to their customers.

Some companies ask for an additional fee for installing one, others will do it for a reduced insurance price. This instructable is designed to give a step-by-step instruction on how to build a custom Telematics box for driving vehicles.

DISCLAIMER: This custom-made black box may not always be valid evidence in a court of law. Some countries/states/local laws may not allow installation of custom monitoring units into moving vehicles unless authorised by an approved installation team. For these reasons, and any other associated to tampering with the OBD port, the author(s) of this article and website hold no responsibility over the outcome of your driving, your car, your car’s electronics (including on board computer), and any other incidents occurred with a custom-made monitoring unit fitted.

UPDATE/WARNING: I went away for a week, but left all the electronics plugged in. What I didn’t realise was that the OBD port is always powered. Because the OBD port uses a Bluetooth port and Bluetooth consumes a fair amount of power, the car battery will drain…

Step 1: Acquire Materials!

For this project, you will need:

  • 1x ELM327 OBDII Bluetooth adapter – Ebay
  • 1x Arduino Mega* – Ebay
  • 1x HC-05 Bluetooth module** – Ebay
  • 1x SD card reader module – Ebay
  • 1x Neo-6M GPS module – Ebay
  • 1x GPS antenna (with SMA connector) – Ebay
  • 20x Male-Female 10cm jumper wires – Ebay
  • 1x UFL Mini adapter – Ebay
  • 1x 3D printed case – (design) SketchUp, (print) 3D Hubs
  • 6x 5mm spacers – Ebay
  • 4x M3 10mm nuts and bolts – Ebay
  • 6x M3 12-16mm nuts and bolts – Ebay
  • 1x SD 8GB card – Ebay
  • 1x Car USB adapter – Ebay

Thank goodness for Ebay! More information on some of the modules will be detailed in the next steps.

* There is an argument to use the Uno, but because I needed multiple serial ports, and program space was limited, I opted out of the Uno. There is also an argument to use the Due, as it is more powerful. The Due uses 3V3 for its IO pins, which may be damaged by other 5V components. Hence, use the Mega.

** Don’t mistake the HC-05 for the HC-06! The HC-06 is a slave-only module, and cannot be configured to be a master. Get the HC-05! IMPORTANT: make sure the HC-05 module has a Key pin to be able to switch into AT mode, otherwise this whole project won’t work!

Step 2: How Does It Work?

How are we going to read data from the car? Most cars (if not all cars) after 2003 must have and OBD port to talk to the engine (check before buying!). OBD stands for On Board Diagnostics, and is used mainly to determine any faults with the car. For example, when your engine light switches on, a fault code is logged. When you take it to the garage, the mechanics will have an OBD reader which will read the fault code, so they will know what to fix.

From the OBD port, you can also read live data. The live data available depends from car to car, but most car should allow you to read the basic stuff like speed, rev-count, distance traveled etc. For the purposes of this project, I chose to read the vehicle speed, the engine’s RPM, and the throttle depression.

When you get your ELM327, find your OBD port. This will different for every car make. For my Ford Fiesta, it was between the steering wheel and the driver’s door. If you can’t find it, look up [car brand] [car model] obd port on Google, where there should be a number of videos/pictures showing where your OBD port is. Once located, plug your ELM327 in.

You can test the OBD port easily if you have an Android phone. Go to the Play Store, and download an app called Torque. There is a paid version and a free version. The free version will suffice for demo purposes. Simply connect to your ELM327 by Bluetooth, select the desired PIDs you want to read, and turn your car on. You should instantly see the readings on your screen.

Step 3: Make a Box!

Materials required:

  • a model of a box

Result: a 3D printed box and base


Before starting on the electronics, I recommend 3D printing a box (or making your own!) with its own mounting holes. It will be much easier to fix the Arduino in place without all the components in the way!

I designed a simple case (*.skp files) to hold everything in place. The model is made in SketchUp, and the design was 3D printed using the 3D printing services of 3D Hubs, where they will print your models at pretty good quality for relatively cheap.

Print this box out, so that you can place your electronics inside.

Step 4: Assemble the Base

Materials required:

  • Arduino Mega
  • 3D printed base
  • 3x spacers
  • 3x M3 nuts
  • 3x M3 washers
  • 3x M3 12mm bolts

Result: assembled base


Starting with mounting hole number 1 (mounting hole between the 6-pin ICSP header and the Comms pins, see image), place a washer on the top side of the board, and a spacer between the board and the base. Put the screw through the washer, board mounting hole, spacer, and out through the base. There are hexagonal ut-outs under the base to fit the nuts in. Tighten up, but leave enough space for placing the other spacers.

Repeat for each mounting hole.

When all three mounting holes are done, tighten up the screws so that the board is firmly in place with the base. The other mounting holes are not necessary. I could not fit other screws, as they would clash with pin/component placements. These three should be enough to keep the board in place.

Step 5: Wire Up!

Materials for this step:

  • Assembled base
  • HC-05
  • Neo-6M
  • UFL mini adapter
  • SD card reader
  • 16x jumper wires

Result: base electronics assembly


The first step is to connect everything to the Arduino Mega. You will find the basic connection diagram in one of the pictures attached. We will be making use of the Serial ports, the SPI bus, and some of the IO pins.

If you’re curious to know how each module works, you can connect each module individually to test them out. Otherwise if you’re confident everything will be OK, just connect everything up.

SD Card Reader

Connect the following:

  • CS – pin 53
  • SCK – pin 52
  • MOSI – pin 51
  • MISO – pin 50
  • Vcc – 5V pin near pin 22
  • Gnd – ground pin near pin 52


Connect the following:

  • GPS TX – pin 15
  • GPS RX – pin 14
  • GPS Gnd – ground pin closest to power socket
  • GPS Vcc – 5V pin closest to power socket
  • Connect the UFL mini adapter to antenna pin of the module
  • (Optional) GPS PPS – pin 2


Connect the following:

  • Bluetooth TX – pin 17
  • Bluetooth RX – pin 16
  • Bluetooth Key – pin 3
  • Bluetooth Vcc – pin 19
  • Bluetooth Gnd – pin 18

Step 6: Compress It Down!

Materials required:

  • Base electronics assembly


Now that everything has been wired up, twist the modules so that they all fit inside the boundary of the Mega, but without disconnecting the wires. You may want to cover exposed pins and electrical components with electrical tape to avoid short-circuiting. Be careful!


Twist the wires until the top of the GPS module is facing the communication pins of the Mega.

SD Card Reader

Basically, bend/fold the wires over so that the top of the SD card reader module is facing down over the Reset button.


The Bluetooth module will “wrap” itself around the GPS module, and end up on the other side of the board, by the analogue pins.

Step 7: Assemble the Box

Materials required:

  • Assembled electronics base
  • 3D printed box
  • 4x M3 nuts
  • 4x M3 washers
  • 4x M3 10mm bolts

Result: Fully assembled box


Get the other end of the UFL mini adapter and plug through the hole in the box, securing it in place with the nut. Make sure it is tight, as we don’t want the antenna to twist it off!

Merge the two assemblies together, making sure none of the wires have disconnected. Align the four corner holes and fit the M3 nuts into the hexagonal holes beneath the base. Place the M3 nuts through the holes and screw the box together.

Step 8: ELM327

Materials required:

  • Full assembly
  • ELM327 Bluetooth OBD adapter
  • Portable computer


On GitHub, you will find a short program (BluetoothScanner) that will scan for some of the closest Bluetooth devices. It will display the MAC address and the SSID (name) of each device. It will also allow you to manually send commands to your car.

MAC Address

For the HC-05 to automatically connect to the ELM327, you will need to find the adapter’s MAC address. This is usually different for every module. This is to avoid connecting to the wrong device!

Simply upload the code to the Mega, turn your car on, and run the code. On the terminal output, you should see the results. The code attempts to automatically bind the module to the MAC address selected, but sometimes this does not work. Simply make sure you get the correct MAC address. The address should look like 1D,A5,68988B. Your MAC address may be different, but should be in the same format. Save this for the next step!

Response Offset

You will also need to determine the resulting format of the data that is coming out of the OBDII adapter. Using the code you’ve just uploaded (in this step), send down the characters 0100. The is the command to determine what data your car can send back to you. The full list of commands is found on Wikipedia.

You will need to check the format of the returned data. In my Ford Fiesta (2012) the command was echoed before the results:

  • Command Sent: 0100
  • Response Received: 0100BE1FA813

However, in a Renault Clio (2006), the command was not echoed:

  • Command Sent: 0100
  • Response Received: BE1FA813

The response may be different depending on the car. You will need to remove any preceding characters from the response. Ideally, your response should look like the Clio example above. If you have other characters, remember the number of characters preceding the response. You will need this in the next step!

Source: DIY Telematics Box

About The Author

Muhammad Bilal

I am a highly skilled and motivated individual with a Master's degree in Computer Science. I have extensive experience in technical writing and a deep understanding of SEO practices.

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