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Installing a Terratrip (or Brantz) to Subarus

10/03/08 | by admin [mail] | Categories: Technical

If you ever wanted to fit a Brantz or Terratrip to your Subaru without having to worry about fitting an extra sensor, then why not make use of the cars existing wiring?
Here's my collection of datasheets for Subaru WRX, Forester and Outback, as well as the all important interface circuit you need to make it all work. (If you try to connect directly without the interface circuit, your speedo will stop working.)

I can't take credit for the interface circuit, as I found it by chance one day on the 'net, but it works perfectly so I thought I should include it for completeness.
Thanks to the guys at Subaru Motorsport for supplying some of the wiring diagrams.

Let me know if you need any help, as I've made a couple of these now and they work brilliantly..

20Apr08 UPDATE: Glen McAliece was able to supply a wiring diagram for the Hyundai SantaFe's vehicle speed sensor. The speedo signal is easily available on the OBD-II diagnostic connector at the base of the steering column. When combined with the interface circuit, it makes installing a Terratrip on these vehicles a 5 minute job! Email me for the diagram. Matt




Comment from: tegar nyoto

Hi there,
I have a question for installing an electronic speedometer interface to a micro controller which then i use it to tun my rally program on a laptop.
My corolla 1993 speedometer has 10 volts current.
When i connect it to the micro controller, the current drop to 6 volts.
I tried using your speedometer interface, but the current still stayed at 6 volts.
How do i make it to 10 volts so my speedometer will also work together with the micro controller?
Thanks for helping me.

19/04/08 @ 11:35
Comment from: mswan  

Yep, this sounds like a similar problem I initially got when I tried to wire the cars speedo signal directly into the terratrip. You “accidentially” pull the cars speed sensor signal to ground and as a result the cars speedometer stops working.
The interface circuit described in the pdf uses the terratrips power supply (at the Collector) to switch the Emitter (the terratrip input) using the cars speedo input on the Base. The 10k resistor essentially isolates the whole thing from the rest of the vehicles electronics by limiting the current draw.
Maybe you should look at some Basic Stamp or PIC forums for other circuit ideas on how to interface a digital input to your microcontroller as the concept of using a transistor to isolate the input should be pretty common.
Matt (not an electrical engineer!)

20/04/08 @ 09:18
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