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  • Author Author: Jan Cumps
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A Smart Car Key - What's Inside?

Jan Cumps

I opened an end-of-life smart car key.

It uses radio for locking / unlocking and IR to switch the vehicle off and on.

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A deep dive is available here.

 

The type of key here is one that you can use from a distance to open or close the car, but that you have to physically plug into a dashboard slot to start the engine.

When the key is removed, the engine stops.

 

The locking /  unlocking mechanism works from a distance. A few 10s of meters. It's a radio circuit powered by a coin cell.

(true story: if you press the key against your temple when using it, the range is extended by several 10s of meters)

 

To activate the car and be able to run the engine, you have to insert the key into a dedicated receptacle in the dashboard.

A bidirectional infrared bridge communicates between dashboard and key. That circuit is powered via induction.

The coil on the key gets power from a coil in the receptacle.

image

 

Let's see how many components can be identified. Chime in if you have more info.

 

1: unknown function

Maxwell 1436 PQT 711011 Q2 W

The only reference I could find was other similar keys.

 

2: unknown

ROBINIE 441KP14

I saw the following different codenames on the internet: FICHTE, APFEL, WEIDE

All are German names for trees:

Acacia, Fig, Appel, Willow

Probably an ASIC or mistified OEM.

 

3: memory

5ACAT 439YTHS

This is a Microchip 25AA640A SPI EEPROM:

image

 

4: Schottky diode

45 SOT-23 package is a jellybean Schottky

 

5: tantalium capacitor

476 6K 430

47 µF, problably 6.3 V, 1411 package

 

6: oscillator

manufacturer: Nihon Dempa Kogyo Co., Ltd. (NDK)

18.000  :49

Crystal or resonator, 18 MHz?

 

7: NPN transistor

H1 SOT-23 package is a jellybean NPN.

 

A: red LED

B: inductor: extracts power from the car. Powers the IR circuit when starting and while driving. Takes care that the IR circuit doesn't need coin cell power. 190 µH.

C: I saw this before and forgot what it was. I bet it's a fuse. edit: no a TVS. edit no it's a 6.7 nF capacitor.

D: IR sender and receiver. There's a matching inverse pair in the dashboard of the car.

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Using my tablet as a detector (digital cameras see iR), I found that the left 2 pins are cathode and anode of the LED.

 

The two buttons are to open and close the door locks.

 

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Parents

  • Hello Jan,

    Thank you very much for sharing the information with us. I hope you can view this message after 2 years of this topic being posted.

    My key fob is out of order and one of the capacitors is detached and visibly broken. Finally, it was lost during trying to re-soldering it back to see if the fob functioned again.
    I'm going to buy a new capacitor for repair. But the newly bought multi-functional meter doesn't give me a solid figure about the capacitance value of the same size capacitor on the board. Furthermore, I have no idea what the voltage of the capacitor should be.

    Do you have any idea what capacitor is inside the blue circle? Thank you.

    image

  • in reply to apronxy

    I have no idea. I don't have the key anymore to check. That one is a decoupling cap, so the value shouldn't be critical.

    Check if you can measure one of the oder decouplers, and try the same value:

    image

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