Digital Tachometer for Harley Davidson Sportster (Part 2 - Communication Bus and sensors)

04 Jul 2016 - 0 Comments

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In this second part we will focus in the motorcycle electronics and in knowing what we can/cannot use.
Nowadays, all vehicles with a minimum of technology have a communication bus that connects all different control units. The main advantadge is pretty clear, if each control unit had its own sensors, the weight and cost of the vehicle would be higher due to some sensors and harnesses would be redundant. With a communication bus, each control unit can have a mínimum of sensors attached and then broadcast the information through the bus to the other control units and in case it needs other information, find it there.
Until 2014, HD used to have a 1-wire bus communication based in the SAE J1850 VPW (Variable Pulse Width) at 10,4 kbit/s as communication protocol. In order to understand how this protocol works, please check the following post . Since 2014, all HD use another communication bus called CAN bus (Controller Area Network).

HD model	Model Year	Comm bus
Sportster 883/1200	2001 - 2013	1-wire J1850
Sportster 883/1200	2014 - current	2-wires CAN bus

In a HD Sportster (2007-2013) we can find the following ECUs (Electronic Control Units):
* ECM (Engine Control Unit)
* Display
* Body Control

In this project we will be focus only in the information broadcasted by ECM because it will give us the RPMs and the current gear. In order to access the J1850 VPW bus we will use the DLC (Data Link Connector), located under the battery cover (rear left side).

Pinout of the connector is:
1-
2- GND
3- Bus J1850 VPW
4- IGN (+12V when key ON, not related to emergency switch position)

Project Index:
Part1 / Part2 / Part3 / Part4 / Part5 / Part6 / Part7 / Part8 / Part9 / Part10 / Part11 / Part12 / Part13 / Part14 / Part15