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Topic: Reverse engineering an accelerometer, need help (Read 195 times) previous topic - next topic


Feb 19, 2015, 11:13 pm Last Edit: Feb 19, 2015, 11:14 pm by larsmartinj

I recently got access to a wrecked newer car. We had lots of fun going over it, following wires and getting to know the internals of a car with lots of electronics. As an electronics student of course I grabbed a screwdriver and brought a few of the side collision sensors with me home. I hooked one up to my oscilloscope and to my Arduino, but I can't figure out how to get any data from it! And of course it's impossible to find any data sheets on it. The QR code only tells me it's produced by Denso, an electronics company, but the rest gave no result (QR: DENSO -4020 11P06L L2659).

The circuit is pretty simple, so I was hoping some clever minds could help me out. There are two inputs and two outputs, but only one pair is necessary (the back sensor was only connected to the RIN and ROUT pins while the front side sensor (looked identical) had the input/output of the back one connected to one pair while the other pair were connected to the "brain" in the front, i'm guessing they're parallel since one of them should be enough to set off an airbag). But I don't have enough practice interpreting circuits like this. I do believe the IC to be a single axis accelerometer, after all it's there to look for an impact from the side.

Does anyone have any idea how to hook them up? I have a few projects they'd be perfect for and would hate for them to just go to waste. Even if it would be easier to buy something WITH datasheets...  :P


The circuit in which you found that part would be very informative.


I think you will find that these sensors communicate digitally with a protocol called PSI5 which has been developed for Automotive safety sensors. It's a 2 wire bus with 5V power for the sensor.
Typically a PSI transceiver chip is needed to communicate with them such as Bosch CF190.

The sensors can be organised in various ways on the digital bus including daisy chaining which is what the second set of pins is for I think but the sensor has to be programmed appropriately for mode and address.

It may be possible in theory to get an arduino to create the correct PSI5 digital communication but I think it's going to be pretty difficult particularly without datasheets.

Typically these sensors are accelerometers (or possibly pressure sensors in the door cavity) which just stream sensor data and the Electronic Control Unit they are connected to has the algorithm that determines if the airbags need to be deployed.

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