Can we make a Radar detector turn on only when...

[navin in KC]

I get sick of sitting at a stoplight and hearing my V1 make so many beeps that it sounds like a game of Defender.

I don't care if there are any cops or 7-11's around me when I'm going less than 30mph. If we could figure out a way to make some kind of a servo turn on and off, based upon the speed sensor wire, it would accomplish this.

Any of you electronic engineers game?

If not, do any of you guys have any ideas as to where to start in on this?

[neil.schneider]

The V1 needs an automute like the passport. Whats up with the sound system?????

[Hroussard]

Build one, connect it to a GPS system that - in the future - gives you the posted speed limit and make it work and you will be a multi-

millionnaire.

HarryR

[navin in KC]

The V1 needs an automute like the passport.  Whats up with the sound system?????

<{POST_SNAPBACK}>

I'm having a Reus system installed in a couple of months, which is the soones he can do it.

It will have: GPS, Sirius, and a bluetooth phone kit.

[Costa]

Ye Olde Williams Defender - Great game when it arrived on the scene :D

It would be reasonably simple to achieve this cutout feature with some simple electronics circuitry.

You would need to measure the frequency of the speed sensor signal at a few speed points eg 10mph, 20mph, 30mph etc. This will give an idea as to the linearity of the speed sensor signal.

Once you have this data it is quite easy (and cheap) to interface a frequency to voltage converting IC (eg LM2917 - Just a couple of dollars) to the speed sensor signal. Once this is done it will provide a voltage which is proportional to the frequency of the incoming speed sensor signal.

You can then place a voltage comparator (another cheap IC - eg LM311 etc) to check this voltage and compare it to a preset reference voltage (adjustable via a trimpot etc) so that the device will trigger at your chosen speed.

Once this is done - all you need is a simple relay (preferable) or a transistor driver which is connected to say the speaker of your radar detector so that it can disconnect the speaker when travelling below your chosen set speed trigger point.

I can knock you up a circuit if required but you will need someone to verify/measure the speed sensor signal so the circuit can be setup and calibrated for the speed ranges that the circuit will operate over....

You can also do it digitally utilising a 'PIC' microprocessor but some more diagnostic work would be required to accurately measure the incoming range of the speed sensor signal and some programming would be required for the micro. A more elegant solution which requires a little more work, but this method would be preferable if the unit was going to be produced in large numbers etc.

Edited September 20, 2005 by ZX7R

[Stefan]

If only you could connect it to the speed alert on the OBC, that would be very cool.

[navin in KC]

Ye Olde Williams Defender - Great game when it arrived on the scene  :D

It would be reasonably simple to achieve this cutout feature with some simple electronics circuitry.

You would need to measure the frequency of the speed sensor signal at a few speed points eg 10mph, 20mph, 30mph etc. This will give an idea as to the linearity of the speed sensor signal.

Once you have this data it is quite easy (and cheap) to interface a frequency to voltage converting IC (eg LM2917 - Just a couple of dollars) to the speed sensor signal. Once this is done it will provide a voltage which is proportional to the frequency of the incoming speed sensor signal.

You can then place a voltage comparator (another cheap IC - eg LM311 etc) to check this voltage and compare it to a preset reference voltage (adjustable via a trimpot etc) so that the device will trigger at your chosen speed.

Once this is done - all you need is a simple relay (preferable) or a transistor driver which is connected to say the speaker of your radar detector so that it can disconnect the speaker when travelling below your chosen set speed trigger point.

I can knock you up a circuit if required but you will need someone to verify/measure the speed sensor signal so the circuit can be setup and calibrated for the speed ranges that the circuit will operate over.... 

You can also do it digitally utilising a 'PIC' microprocessor but some more diagnostic work would be required to accurately measure the incoming range of the speed sensor signal and some programming would be required for the micro. A more elegant solution which requires a little more work, but this method would be preferable if the unit was going to be produced in large numbers etc.

<{POST_SNAPBACK}>

wow, this is very helpful. Thanks.

Most of what you said goes over my head, but could you refer me to a place or a book where I could read about this?

How do I measure the frequency of the speed sensor wire? I have a volt-meter and some basic understanding of what this means, but not sure how to measure it.

I can re-wire a bathroom, repair a digital nerve and wired up my PSE just fine, but you lose me here.

thanks again,

navin

[1999Porsche911]

For less than $20, simply put an adjustable voltage activated switch inline with the Speed sensor wire and set it for something like 2 - 3 volts. The other end of the switch is connected to a 12 volt line and away you go. The only problem with turning the detector off and on is that it will beep each time it come on unless you have one that can be silenced on startup. There is an endless aray of ways to do it. You can even put a voice activated switch in the car.

Edited September 21, 2005 by 1999Porsche911

[my996]

how about just an automatic mute when it is below 30 mph instead of turning it off?

[Costa]

I have not had a need to measure the incoming speed sensor signal myself, but I would guess that it is a square wave signal (either 0 to +5v or 0 to +12v) which varies in frequency (not Voltage) as the speed of the vehicle changes.

The best way to measure this would be to utilise an oscilloscope (which you probably do not have in your back pocket) otherwise a late model digital multimeter which can measure frequency (as welll as the usual volts/amps etc) could be used to measure the signal.

If you know a friend in the electronics field they would probably have a suitable digital multimeter that you could borrow for the measurements.

Once a few spot measurements are conducted at a few various speeds, the results can be used to draw up a function/table of speed versus frequency (speed sensor). Once this is known, I can simulate the speed sensor's output on my test bench using a signal generator which I can program to mimic the speed/frequency ranges in question and feed this in to the circuit so that component values can be calculated/prototyped to suit the required range of operation.

Measuring the speed sensor's output is the difficult bit, as it requires access to the speed sensor signal which is sent to the ECU etc. ie the seat has to be removed etc!

Note: The speed sensor signal that I am referring to is not the signal which is utilised to activate the PSE/Windows etc. It is the signal which is supplied to the ECU from the actual speed sensor. Loren may be able to supply some info on this device as I am not sure as to how it is accomplished on a 996. On many other vehicles they have a sensor (usually a magnetic - Hall Effect device) on their tailshafts etc.

Edited September 21, 2005 by ZX7R

[bavarian]

The convertibles already get a speed feed to disable the power top switch at 30mph--how about tapping into the source of that signal?

[FlashingBlade]

Are you sure this is such a good idea? Each time I turn on

any of my radar detectors they make their start up sound.

Do you really want to hear that each time you exceed 30

(or whatever)? The automute would be better, but then you'll probably

have to hack into the radar detector circuitry (probably easy, but a pain).

If you can hack into the digital speedometer circuity, then

you just need a set of leads and an or gates to see if any

of the bits beyond the 6th bit (0010 0000 =32 mph) are set to one.

[1999Porsche911]

Better yet, get a good detector and you won't have any problems. The BEL has few, if any false alarms and can go silent after initial twerp.

[navin in KC]

Are you sure this is such a good idea? Each time I turn on

any of my radar detectors they make their start up sound.

Do you really want to hear that each time you exceed 30

(or whatever)? The automute would be better, but then you'll probably

have to hack into the radar detector circuitry (probably easy, but a pain).

If you can hack into the digital speedometer circuity, then

you just need a set of leads and an or gates to see if any

of the bits beyond the 6th bit (0010 0000 =32 mph) are set to one.

<{POST_SNAPBACK}>

actually, as suggested above by ZX7R, a better way to do it would be to just make the relay turn on and off the speaker. The V2 audio accessory has an output for a speaker that could be shut on and off.

[navin in KC]

For less than $20, simply put an adjustable voltage activated switch inline with the Speed sensor wire and set it for something like 2 - 3 volts.  The other end of the switch is connected to a 12 volt line and away you go.  The only problem with turning the detector off and on is that it will beep each time it come on unless you have one that can be silenced on startup.  There is an endless aray of ways to do it.  You can even put a voice activated switch in the car.

<{POST_SNAPBACK}>

what is an "adjustable voltage activated switch" and where could I find one?

[Jimflip]

Without complicating your install, I thought about what you are trying to achieve, and I would suggest that when you build the "mute" for the detector, you would probably want a visual confirmation that it is muted (ie. an LED) ~ the LED could extinguish past 30mph, but then at least you know that your detector is "unmuted" again, as it would be disastrous to be nicked at speed with your detector on "mute" !

(just a thought)

Regards

James