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Arduino-powered tachometer/scan gauge over OBD II CAN bus

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# Real time diagnostics OBD Scan gauge tool using MCP2515

This is the Arduino IDE sketch for a CAN bus scanner with bitmap display of tachometer and other data. It uses the CAN bus interface to send requests to the ECU using OBD protocol. Currently configured for TOYOTA Prius 2020.

## Resources

Please [visit this project on Instructables](https://www.instructables.com/TachometerScan-Gauge-Using-Arduino-OBD2-and-CAN-Bu/) for further instructions.

Desktop utility is [available here on GitHub](https://github.com/neiman3/obd_rtd_desktop).

## Disclaimer
Use of this code and instructions herein is at your own risk. Possible risks to unauthorized/unintended use of vehicle interface could include damage and/or unintentional operation of your vehicle.

# Operation and Explanation
The MCU (microcontroller) uses SPI serial interface to communicate with the MCP2515 CAN controller. This is easily available as a breakout/eval module thatn can be connected with jumper wires.

The OBD protocol over CAN works like this: 1. MCU sends out a msg on the CAN bus with a CAN ID of `0x7DF`. That means "request". Encoded in that message is your PID that you are requesting.Look at function called requestDataOBD(). The third byte is the PID you are asking for. The ecu will then send a return message on the CAN bus with an ID of `0x7eA` with your requested PID encoded.

Each PID corresponds to a different measurement. Look at the #define starting w/ PID to see some various different values that can be requested from the ecu. If you're getting wrong/no data, try changing the PID that you are requesting. To find PIDs for your vehicle, you can visit [Excel sheet of codes for Prius and some Subaru](https://docs.google.com/spreadsheets/d/1QYWdWkLg0O4tg-ANYdTwwEMhpjkYAI_5JpBfTR1JfQ0/edit?hl=en&hl=en#gid=6) (switch to appropriate tab on sheet for your vehicle) and [Wikipedia: general codes for most vehicles](https://en.wikipedia.org/wiki/OBD-II_PIDs#Service_01). Keep in mind that you must adjust the draw functions for size/position so that the values fit on the screen.

| Device | Pin | Bus |
|--|--|--|
| MCP2515 | 13 | SCK |
|  | 11 | MOSI |
|  | 12 | MISO |
|  | 10 | CS |
| OLED | A4 | SCL |
| |A5 | SDA|
| Both | VCC | 3.3v / 5v
| | GND | GND|
 
OLED not showing up? First upload an I2c scanner sketch. Google it if you need the code. If it shows up on the scanner, make sure your i2c addres in THIS sketch has been changed to match the address of your oled. That could be the issue!
 
Hook the CAN Hi and Lo up to the CAN bus of your car. Next, hook the GND into the vehicle. There are signal gnd and chassis gnd in the obd port by default. You can use the chassis ground as CAN is fairly noise tolerant.

Next, you need to apply power to system. I used a fuse tap on the windshield wiper circuit since my prius has many circuits fused in a box right next to OBD port. You can use the Vbatt on the OBD port, but beware! That is hooked to the battery, so the device will never turn off. Depending on the current draw of the regulator, it may kill your battery in a matter  of days or weeks if you let your car sit. You may have a vehicle with an ACC/ignition power pin on the OBD port. Lots of pins are manufacturer specific. However, you need to correctly differentiate between a 12v logic level pin (J1699) and a power pin. Use test equipment to verify before connecting MCU power to any other pin besides batt on the OBD port.

Once you hook everything up, run a wire up the steering column (or even thru the dash) for your OLED. Be cautious of knee curtain airbags, parking brake, pedals, etc.

I have 3d printable housing designs. one for the microcontroller and one for the oled. It is nicely sloped so that the screen is perfectly angled with my dashboard above the steering wheel. Try designing your own for a custom place in your vehicle!

# Note on Operation
The device will poll for RPM data every 1,430 ms. It will poll for engine temp every 9,930 ms. Different refresh rates for temp and RPM simplified debugging and software architecture when I wrote this program. The important takeaway is this: the engine temp only updates at roughly ten second intervals. When  you turn the device on, there will be no data for temp. I set the default value for temp to be 999. If the arduino sees this value, it will not be drawn. However, the RPM updates once a second. By the time the welcome screen has dissapeared, the 1430ms period has elapsed, and the arduino will immediately request engine RPM. My point is this: if you turn your car on and see 9999 RPMs, something is wrong! That means that the arduino is not communicating with your vehicle. You should see engine temp come on the screen after about ten seconds.

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