Volvo PCC Key Fob -- How does it work?

[Halcyon]

I drive a Volvo (don't hold that against me) which comes with the PCC (Personal Car Communicator) key fob. Among the functions, there is a button when pressed, illuminates LEDs on the key which gives you various status information about the condition of the locks/alarm when you aren't near the vehicle.

Volvo claims that this function works up to 100 metres from the car and just wondered how this system works?

Given that its a key is powered by two CR2430 lithium cells, I find it unlikely that it actually transmits anything back to the car in this mode, however I could be wrong. Could such a transmitter built into a key fob provide decent battery life and transmit over such a distance or does the car just broadcast constantly at specific intervals and the key just listens for the signal from whatever car it's programmed to? It takes 5-7 seconds for the key to "read" the data from the car.

[SeanB]

Well, the key does have a transmitter in it to send data, and likely also has a very low power radio receiver, probably kept in sleep mode to reduce current, and this then receives a signal from the car where the power budget is a lot higher so a stronger transmitter than the keyfob, that sends a status byte which probably has a serial number of the pair and a single byte of status and a checksum. 100m is not a problem for a 50mW transmitter, below the legal max for this band of 100mW EIRP, so very easy.

As well the car likely only transmits a few bursts of this data, probably for 5 minutes after you arm or disarm, and the keyfob enables the receiver for a few times after a keypress is sent, so as to get the status, and stores this value, and then when you interrogate it it listens to see if the car is transmitting ( likely will also transmit on alarm activation and manual unlock as well as a backup) and then displays the status, otherwise showing out of range.

Anyway, with 2 CR2430 cells that is a lot of power stored, plenty enough to actually have the fob provide a 50mW transmit power to get the 100m range, though I think that range is only achieved under ideal conditions with a clear line of sight.

[Halcyon]

Well, the key does have a transmitter in it to send data

I realise it has a transmitter in it (for locking/unlocking doors and activating lights), but I'd imagine this would be very low power so that it's kept to the 20 metre range as specified in the manual.

To then "interrogate" the car over 100m maybe it then enters a "high power" mode to send out the required packet for the car to respond to (at a higher power level/gain).

I just thought it was interesting that's all. It doesn't notify when it goes out of range. If you hit the button and it doesn't get a response from the car, after 7 seconds of the LEDs "spinning around" it shows nothing.

[Halcyon]

This explains it a bit better although there is no technical information. It does state that it's 2-way communication however.

[nali]

You could try downloading a BLE utility for your phone such as nRF Connect to see if it's doing anything with Bluetooth?

[cgroen]

I have a 1 yr old Volvo XC70 with PPC, and I got curious   
If I hold my keyfob near my spectrum analyzer (rigol DSA1030ATG) and presses the "I" button on the keyfob I see a transmission at 868.03 (ca) almost instantly after the button is pressed. Then the "light show" comes on, the red/green/yelow LEDs flashes in turn, and near the end of this sequence there is yet another transmission from the keyfob.
It is on the same frequencies that are used when locking/unlocking the doors with it.

[mikeselectricstuff]

How is this a power problem? - unit draws no power til you press a button. When you press the button, it asks the car for status, stays awake for a few secs to get the reply.
Power during transmit isn't an issue as it only happens when the button is pressed. Just needs to be able to supply the peak current, so may need a cap to hold it up.  Could easily have a 100mw transmitter.

[cgroen]

How is this a power problem? - unit draws no power til you press a button. When you press the button, it asks the car for status, stays awake for a few secs to get the reply.
Power during transmit isn't an issue as it only happens when the button is pressed. Just needs to be able to supply the peak current, so may need a cap to hold it up.  Could easily have a 100mw transmitter.

and, I would guess the keyfob only has it receiver active for a very short time after it has transmitted its ID as it knows that the car will respond within xxx milliseconds of the transmission. so no power issues here (I bet the LEDs consume more power as they are on for quite some time as compared to the needed "RF time")

[SeanB]

Thewre probably is a NFC component for the keyless entry and exit, and the 800MHz is longer range ( NFC likely is 10m range) comms, with a SAW filter on the antenna to provide both a transmitter filter and a recieve filter then a simple super regen receiver to listen for the reply. Same SAW filter and transistor can be both, just have 2 bias circuits to drive either very high power for transmit with the SAW doing frequency control, or low power oscillation so receive RF energy does the detector function. Car side can have a separate receiver and transmitter, with a small PIN diode switch, and a better antenna as well, with no limits other than legal ones on transmit power, so you can easily do 100m.

Never taken a Volvo one apart, though have done a few Toyota, Peugot and VW ones to replace batteries and switches in them.

[cgroen]

Thewre probably is a NFC component for the keyless entry and exit, and the 800MHz is longer range ( NFC likely is 10m range) comms, with a SAW filter on the antenna to provide both a transmitter filter and a recieve filter then a simple super regen receiver to listen for the reply. Same SAW filter and transistor can be both, just have 2 bias circuits to drive either very high power for transmit with the SAW doing frequency control, or low power oscillation so receive RF energy does the detector function. Car side can have a separate receiver and transmitter, with a small PIN diode switch, and a better antenna as well, with no limits other than legal ones on transmit power, so you can easily do 100m.

Never taken a Volvo one apart, though have done a few Toyota, Peugot and VW ones to replace batteries and switches in them.

You are probably right, I checked my keyfob if there is any transmissions going on when no buttons are pressed and it seems there is no activity (I have keyless entry in my car, I just need to have the keys with me when I pull the door handle and the car unlocks by itself. So some form of NFC must be active (not bringing my Spectrum analyser with me outside in the current weather to check )
According to the manual, there are receivers all over the car, one at each door and one at the back of the car (to allow you to open the trunk while just having the keyfob in your pocket). You have to be pretty close to one of the receivers in order to open the door (and only the door close to you reacts to the keyfor when you try open it)

[PA0PBZ]

(and only the door close to you reacts to the keyfor when you try open it)

That is interesting, on my Peugeot you can open any door as long as the key is close to one of the receivers.

[cgroen]

(and only the door close to you reacts to the keyfor when you try open it)

That is interesting, on my Peugeot you can open any door as long as the key is close to one of the receivers.

I'm actually not sure if you can change a setting in the car so it also works this way in the Volvo! But even if so, I'm not going to change it, the look on my wife's face when she reaches out for the handle on other side of the car before I have pulled the handle on the drivers side is priceless 

[SeanB]

Easy to do if you have 3 receivers in the car, and all of them have a RSSI for the NFC signal. Then you can easily detect side of car or rear, and wait for the doorlock touch, which would be another sensor in each door, that is a capacitive sensor, probably always running and tracking the residual capacitance to discern between dry, wet and snow accumulation, and only armed to unlock the door when the NFC fob is near and a sudden change is detected, then release the lock till the handle is pulled to open the door.

[Halcyon]

Easy to do if you have 3 receivers in the car, and all of them have a RSSI for the NFC signal. Then you can easily detect side of car or rear, and wait for the doorlock touch, which would be another sensor in each door, that is a capacitive sensor, probably always running and tracking the residual capacitance to discern between dry, wet and snow accumulation, and only armed to unlock the door when the NFC fob is near and a sudden change is detected, then release the lock till the handle is pulled to open the door.

It seems to operate this way on my S60. A friend was driving my car on the weekend but the keys were in my pocket. I could unlock the doors from passenger side but he couldn't. According to the manual there are 6 antennas placed around the vehicle.