Value of this crystal?

What makes you think it’s a crystal?

Normally, a crystal has 2 pins.

Bob

 

So, whuts going on at 433.920 MHz?
And how in the heck did you find this, @bertus?

 

A WHOLE bunch of communications between RF data links, key fob remotes , rf switched relays, car burglar alarms, AUTOMOBILE ACCESS KEYS and GDO's.
That MURATA product logo is being the real give away to researching, and the shortened 43 is a clue as to its sharp filtering, operational frequency.

OOPSIES . . . . I now see that Sir Dave beat me by a couple of silly milliseconds . . . whilst I was poking up this response . . . . .

 

@davenn, @73's de Edd: Thanks, guys. I guess the "giveaway" was the OP's statement that it belonged to a car key. I must be getting lazy for at least not trying to Google that. And, Yikes! Forgetting about the 433 MHz ISM band... I hope the FCC doesn't use that against me and cancel my Amateur Extra ticket.

 

That's a question . . .I also would want to know . . . .on that Vaux-Opel key.
What doesn't work ? the ignition portion- the door lock/unlocks-windows ?

Since that uses that mechanical keys aspect, with its special metal linear "worm" pattern PLUS an ADDITIONAL electromagnetically coupled signal to a pickup loop, near the keyhole is required.
An then, there are the two pushbuttons that transmit a digitally modulated signal within the 433 ISM band.
AND on the ISM band there are a MULTITUDE of other channels . . . . and the particular referece that
Bertus gave you . . . doesn't even fall, centered, on a valid channel frequency.
https://en.wikipedia.org/wiki/LPD433

ONE FAMILY OF Vaux / Opel KEY UNIT . . . .




MAJOR POINTS OF INTEREST . . . . . .

Green Rectangle . . . . . u / p for system
Red Rectangle . . . . . . . RF amp Xstr
Pink Rectangle . . . . . . multidirectional RF loop xmit antenna . . . 433 mhz
Yellow Rectangle . . . . . SAW filter
RED Ovals . . . . . . . . . . " Trouble prone " Tact switches.
Yellow Star . . . . . . . . . . Transfer coupling medium to the sense pick up loop mounted around the ignition key receptacle

Thaaaaaaassit . . . . .


73's de Edd . . . . .


Last night in my dream I was peeing in bed. Dreams do come true . . . . I fully realized that in the morning.


.

 

There are a couple of possibilities to also consider. Is this the correct key fob for the vehicle it is intended to be used with? In other words, was it correctly synched with the receiver in the vehicle initially? Is there a good battery in the key fob, or did it die without warning?

These key fobs typically use some form of "rolling, encrypted, code frame" to establish a one-way channel from the transmitter in the key fob to the receiver in the vehicle. It is to be determined by the manufacturer what the exact nature of the code frame is, but the data in the frame is randomly scrambled (encrypted) each time the fob is activated by the user pressing a button. This is done to prevent anyone with a key fob receiver and a lap-top computer from recording the transmitted data frame and using the recorded data to unlock the vehicle. The transmitted code is a one-time-only use code and will change on the next key press.

A counter in the receiver keeps track of the number of button pushes (unique code frames) received. We might stipulate that the key fob also contains a counter that is incremented each time a button is pressed, and that this count is embedded in the code frame along with perhaps a unique serial number. The receiver and the transmitter both "know" the encryption/decryption algorithm, so when the receiver "sees" that the decrypted counter value transmitted by the key fob is the same value as the counter kept in the receiver, the receiver pretty much "knows" it has received a valid transmission from the key fob associated with the receiver's vehicle. To "clinch the deal" and unlock (or lock) the vehicle, the data frame may also encode a unique serial number, perhaps the vehicle VIN, in the data frame.

So what happens if the key fob counter gets ahead of the receiver counter, say from too many key presses from too far away to be received by the vehicle receiver? To accommodate this, the receiver must "look ahead" to other possible encrypted key fob counter codes to determine whether any of them match the encrypted counter code it just received. If it finds a match, it just re-syncronizes its own counter and everything is golden once again. Of course it cannot be expected to look ahead forever, but the number of "looks" can vary over a wide range of values, depending on the speed of the receiver processor and the acceptable maximum delay in key fob response before the user releases the key switch and punches it again. However, once that limit (whatever it is) is reached, the system is "bricked" and nothing will open the vehicle, start the engine, run the windows up and down, etc. until the key fob is "re-synchronized" with the vehicle receiver.

In the early days of rotating code key fobs, re-synchronization had to be performed by the car dealer. I suppose this was to somehow guard against car theft rings cloning key fobs and then somehow syncing them to car receivers. That won't work if a serial number is encoded in both the key fob and the car receiver. Anyhoo... for awhile car dealers had a nice little profit center going, bringing key fobs back to life after Junior spent an entire afternoon playing with Daddy's car keys.

So, check the owner's manual to see if there are instructions on how to re-sync the key fob to the vehicle receiver. Replace the coin cell (or whatever) battery first.