Connecting to the EV1
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The diagnostic port for collecting data from the EV1 while driving is under the driver's side dash. It is an OBD II connector. This type of connector is commonly used in the automotive industry and is based on SAE standard J1850. Its difficult if not impossible to find the connector hardware unless its at the end of an $80 cable. The connector looks like the following illustration.

OBD II connector

Only pins 4 or 5, 9, and 16 are needed to gather data from the port. On the EV1 only pins 2, 4, 5, 9, and 16 have metal contacts (This should help you orient the pins correctly). You should be able to see these contacts from under the dash. The pinout is standard (or a subset of) OBD II; pins 4 and 5 are ground, pin 9 is the signal, and pin 16 is 12 volt power (really around 13 or 13.5 volts). The signal is 8192 baud at 5 volts with a base voltage low. That means it needs to be inverted first to look like a standard RS232 signal. Pin 9 is used at the factory to diagnose and reprogram the car. The interface is known as the Assembly Line Diagnostic Link or ALDL.

The easiest way to invert the signal on pin 9 and make it look more like an RS232 interface is to use two 4.7K ohm resistors and one 2N3904 transistor. Mike Schwabe came up with this circuit and is now making the small boards that are inside the connectors.

The parts should be connected as in the illustration.

the circuit

I decided to make a the adaptors with my homemade computer controlled milling machine (Robots are one of my other hobbies.)

The connectors are no longer available.

Here's a picture of the first version of the housing for the connector being milled from some polyethylene.

A router cutting plastic.

The connector consists of two halves plus the internal PC board. Here is a picture of both sides of each half plus the PC board.

Two halves held together with 4 bolts.

Heres a view from under the dash with the connector plugged in. The older units had the DB9 facing toward the rear of the car. The new ones face forward to give more room for gender changers and null modems when hooking up a PC. The new connector also fits more snugly against the sides of the ODB II connector on the EV1 so there is not longer a need to wire tie the connector to the car.

Mounted with the DB9 connector facing towards the front of the car.

Next the PalmPilot needs to be mounted somewhere in the car. Some people just set a cradle on the center console and leave it at that. Others like to mount the Palm handheld somewhere where it is easier to see while driving. If you want to make your own mounting bracket its pretty easy to do. Here's what I did.

For the real technical types that want to write their own software to decode the data coming from the EV1 I've set up a page about the data stream.

Check out the sample graphs to see what can be collected.