Yea, both fobs were sitting for a couple months during my recovery, and really all winter before that. So I think the best thing to do is just replace the batt every couple yrs/it's simple enough.....or just buy a new Vette every year!!!

 

I'm just a lot skeptical about his response. The RKE reacts to a transmitted signal but I'm not thinking it's going around broadcasting signals to talk to the car! If you push a button, it transmits, period. The RKE doesn't even need a battery in it to start the car. It needs a battery to get the door open but it reacted to the car asking for an RKE to be in the area and the correct RKE in the area.

My 2014 RKEs made it until this year and my battery died. I replaced both batteries and 3 years from now, I'll replace both of them again.


Elmer

 

I agree. I think the car finds the fob, not the other way around.

 

Your perception is correct, but for a different reason. Yes, the batteries don't last as long but at least part of the reason is these fobs demand a higher voltage than older fobs. The battery I removed from my fob read "Good" on my trusty battery tester, but was not as strong as a new battery, according to the testing device. Just for laughs I stuck the old battery from my fob in a cyclocomputer on one of my bikes. It's still going strong two months later.

 

^^^
Found the same with a 1 1/2 year old battery requiring more voltage than my tester showing just in the "good" area. Not good enough! That tester loads the battery depending on the voltage selected.

Also I recall the FOB on my '88 went to "sleep" and stopped transmitting when it wasn't moving,-as when in a draw! If you left the FOB in the car you had to shake the car to wake it up! With my HD suspension it took rocking it pretty hard!

Now the FOB is transmitting all the time, probably in pulses but even when I'm not using the car.

 

The RKE is passive. It does not do squat (it does NOT transmit any signals) until it is woken by the car.

A driver can touch the car door and it will unlock the vehicle (passive entry). Pressing a start button on the dashboard will allow the driver's car to start. Both these actions begin an authorization process with a fob in the driver's pocket or purse. A low-frequency (LF) signal from the car awakens the fob. This is called the LF downlink. The fob measures the field strength vectors and sends the data back to the vehicle. Since the fob orientation is arbitrary, it must measure the field in the X, Y, and Z axes. This provides 3D data which can localize the fob as being either inside or outside of the car. If the system determines the fob is outside, it unlocks the door. If the system senses the fob being inside the car, it starts the engine. Passive Entry / Passive Start (PEPS)


http://www.atmel.com/applications/au...ive-start.aspx


Also, another point. What happens when the RKE battery is dead? You can't get in the car right? So, you trundle to the rear, insert the laser cut key in the key hole, turn and unlock the trunk/hatch. You pull the handle and get in the car. Can you now start the car with a dead and NON TRANSMITTING RKE? We all know the answer is yes by putting the RKE into the slot in the steering column. The car starts without the RKE transmitting any signal. The RKE does not transmit unless you push a button on the RKE OR you touch the pressure pad on the inside handle of the door OR you sit in the car and press the START button.

The main killer of a RKE battery is the convertible top button. You must unlock the doors and press and HOLD the top down button for the entire time it takes for the top to fully go down. If you don't use passive door locking and use the RKE, you're killing the battery in the RKE. You should (with the door open) press the lock button and get out and the door will lock behind you without pressing the lock button the RKE. The more you use the RKE, the sooner the battery will be depleted and stop functioning as required. The battery life is one of the reasons I bought the SmartTop gadget. I hold the unlock button for 5 seconds and release. The windows will go down and the top will go down. If I hold the LOCK button for 5 seconds and release, the top will go up and the windows will go up. I save a lot of battery power that way.


Elmer

 

This.

 

In any case, the fob is either always receiving, or transmitting, so it uses battery power even if it sits in a drawer unused.....

 

Yes and no. Yes it can be woken to transmit a signal to the car by a signal from the car OR you can make it transmit by pushing a button. It does not transmit at all unless called upon to transmit. It is NOT killing the battery by listening 24/7 for radio signals. There is NO battery drain until:

1) you push a button on the RKE
2) you touch the door to open the car
3) you press the start button

Elmer

 

But the fob always has to be 'on' to RECEIVE the signal... so the fob isn't 'dead'/"not doing squat"... it's always 'on' and listening/in receive mode. Battery power is needed for receiving too, not just transmitting.

Not quite. The only magic in the slot is an antenna near the slot to pickup even the weakest or induced signal from the fob. The slot has no way of knowing if the fob is authorized to start the car without a way to gather the fob's ID. The C7 will not start without a recognized fob ID. If having 'something' in the slot negated the need for the fob to be transmitting its ID, the C7 would be the easiest car in the world to steal -- stick *any* fob (or even a piece of plastic) in the slot and the car would start. It doesn't work that way.

 

It is an induced signal from the RKE. You can remove the battery from the RKE and start the car with the RKE in the slot.


Please click and read the link in post #26

Elmer

 

Yup. Read that. I appreciate the link.

What I didn't read anywhere in that page was where it stated that the fob draws 0.0 volts/amps when just 'listening', thus putting into question the notion that "the fob uses no battery power at all if you are not pressing a button or if the car isn't actively pinging".

i.e., "low power" does NOT equal "no power".

My point? In my estimation, a battery installed in a totally unused C7 fob will drain faster than a battery on the shelf (or faster than one in an unused old-school active RKE) because the C7 fob constantly draws a small amount of power to listen, albeit at a reduced draw rate that is non-zero and yet measurably higher than the unloaded natural discharge rate of the cell.

We are on the same page when it comes to the induction/transmission used in the column slot, where the coil and receiver are within a centimeter or two of each other. Are you saying that the C7 fob power-on state is not triggered by a low-power receiver circuit, but rather is triggered by induction, even at the distance from the transmitter that is typical for passive entry (a meter or more)?

 

Power induction, to power-up the RFID IC in the fob (so that it can transmit a burst of its unique ID code) only works over a small distance, perhaps an inch at best. This is the failsafe back-up start method where the fob is inserted into the slot, if the battery in the fob is dead. For normal operation of the fob, with a good battery, the fob has to have either an always ON RF receiver, or periodically transmit a coded RF burst, so that the car (or the fob) can detect when they are in a few feet proximity.

 

Of course, you could buy one heck of a lot of batteries for the cost of the SmartTop. I do love my SmartTop, but for reasons of convenience, not battery life.

 

Thanks for the explanation and reference. Unlike my 1988 Vette where the FOB went to sleep when wasn't moving, the C7 FOB as you say it not transmitting until turned on by the car as does not consume any "significant" energy. Good reference. They call it Ultra Low Power!

Not an EE or radio wave expert but it still must have a circuit so the car can detect when the FOB is near so it can "turn it on." (Doubt it blows in it's ear!)

May be an ultra low current draw but must be some. Or guess it could contain a permanent magnet that the car detects? The link has 16 PDF's in the reference section but have a feeling if I download I would not fine out or understand!

 

If I get really bored this weekend I will leave one of my fobs sitting next to my Tektronix spectrum analyzer to see if it is periodically emitting bursts of energy. But I expect even with the current drought and no need to mow 5 acres I can still find plenty to keep me busy outside this weekend.

 

I eagerly await your test results.

Elmer

 

I would be interested in knowing the frequency that you capture. There has to be some radiated signal detected on the SpecAn.

 

A little data. The C7 RKE fob operates on 435 Mhz. and I believe the earlier fobs are on 315 Mhz. as is the one for my 2014 ATS. Pressing any button on the fob creates a burst of energy at 435 Mhz. but I let it sit for 10 minutes and it doesn't produce any output in this range when a key isn't being pressed. I expect the passive entry frequency is in the VLF range and I will try to set up an experiment to identify this and see what it does later today but right now I am going back out to do battle with the Japanese beetles that are trying to decimate my fruit trees.

Iphone cameras are definitely not great for capturing a shot from a scope.

 

So far, it doesn't transmit unless you press a button, correct?

I'd like to see what happens when you press the door pad to open the door. The VLF to wake it up and the response from the RKE.

You're doing great!


Oh, DEATH to all Japanese Beetles! They are definitely nasty to fruit trees!



Elmer