# mechanical vehicle speed sensor



## jmath (Nov 19, 2013)

I'm RPi computerizing all the electrics for my 93 Geo Metro EV conversion.

I finally realized that the vehicle speed sensor isn't really a sensor, it's a cable that spins in a housing that reaches, I guess, all the way up to the instrument panel.

The cable is destroyed on mine anyway, so I'd like to replace it somehow.

Any suggestions for modifying the apparatus to incorporate a real electronic sensor?


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## Sunking (Aug 10, 2009)

Most controllers have a RPM output that you can program to convert to speed. If you know RPM, you know the speed.


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## Matej (Dec 4, 2015)

You can purchase a GPS speedometer.
https://www.youtube.com/watch?v=GgHV3v7ZYDM

If you want the speed to display on the car's original gauge cluster speedometer, you can purchase a GPS speed sender and combine it with a signal converter which spins the mechanical cable drive.
http://www.dakotadigital.com/index....t_id=886/category_id=287/mode=prod/prd886.htm


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## dcb (Dec 5, 2009)

the typical speed sensor is more like a distance sensor. In the case of the metro it is a little reed switch in the speedometer triggered by a spinning magnet about 4100 times per mile. So pulses per second / 1.138888889 = mph.


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## BWA (Mar 14, 2015)

I got a GPS speedo. Works great, you don't have to worry about gear ratios, tire size, or, even what car it's in. I wired mine with a 12 volt accessory plug, and, routinely swap it from car to car.


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## Sunking (Aug 10, 2009)

BWA said:


> I got a GPS speedo. Works great, you don't have to worry about gear ratios, tire size, or, even what car it's in. I wired mine with a 12 volt accessory plug, and, routinely swap it from car to car.


Any cell phone can do that. Even works on planes.


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## BWA (Mar 14, 2015)

My Cell Phone can't do that.....


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## Sunking (Aug 10, 2009)

BWA said:


> My Cell Phone can't do that.....


It will if you download an APP. Every cell phone has GPS


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## Duncan (Dec 8, 2008)

Sunking said:


> It will if you download an APP. Every cell phone has GPS


Really? - are you sure?


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## Sunking (Aug 10, 2009)

Duncan said:


> Really? - are you sure?


Absolutely certain otherwise your cell phone would not work. 

1. It is needed for timing and synchronizing. To measure your distance from tower, location, and timing signal. 

2. Additionally required for 911 emergency service so they can find your arse when you call. 

3. So you can be tracked by UNCLE SAM or cheating spouses without your knowledge. 

Been that way for last 15 years when analog went away. Every cell phone made has GPS.


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## ken will (Dec 19, 2009)

Sunking said:


> Absolutely certain otherwise your cell phone would not work.
> Been that way for last 15 years when analog went away. Every cell phone made has GPS.


Actually...FCC Rules All Cellphones Must Have GPS by 2018


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## Sunking (Aug 10, 2009)

ken will said:


> Actually...FCC Rules All Cellphones Must Have GPS by 2018


Like I said, a cell phone will not work without GPS. I work in the Cellular Telecom sector. GSM, CDMA 1X & 3G), and LTE (4G & 5G) cannot work without GPS. It is also required for E911. 

Your phone needs to know its distance from the tower, to know how much time delay there is in the signal so your phone knows its time slot. Your cell phone needs to know distance, encryption key, and PN to decode the signal intended for it. Otherwise no talkie walkie.

There are dozens of Apps you can download from both Google and Apple for GPS speedometers. So are very good, some are just basic. If you have an Android phone Google maps will give you directions with voice prompts, tell you your speed, direction, street names, when to turn, ETA, traffic conditions and how to get around them. Every digital cell phone has GPS and is turned on anytime the phone is on. 

Your wife or husband can install a Spy program on your phone and track your every move, listen to all your phone calls, see every web page, text, email, and even turn on your mic and listen in to what is going on around you. The goberment can find you with a couple of key clicks if your phone is on. 

There is no such thing as a private phone call.


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## dcb (Dec 5, 2009)

my understanding is that cell phones have location information, but it is tower based, not satellite based, and isn't as accurate for some reason.

GPS implies the global positioning satellite network, so that might be a tripping point in the discussion, as I can turn off my gps anytime to save power, and it takes a while to get its bearings when it is enabled.

I would not consider tower triangulation to be GPS though, it is a local positioning system.

http://hackaday.com/2011/03/10/thursday-gsm-tracking-without-gps/


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## Sunking (Aug 10, 2009)

dcb said:


> GPS implies the global positioning satellite network, so that might be a tripping point in the discussion, as I can turn off my gps anytime to save power,


No you cannot turn it off, it is always on. What you can do is make it unavailable to other programs to conserve power, but it is always on. It provides the sync signal for your phone. 

There are a couple ways to be turned on for use with other apps. dial 911 and press send you will see the icon come on, and you cannot even hang up and end the call. 911 operator has to disconnect. 

Another way is you start an App that requires GPS, and usually those will ask permission.

Then there is goberment and spyware programs that can turn on high accuracy without your knowledge.

Your cell phone GPS has two modes. What you call OFF (low accuracy mode) is just receiving the timing signal from the satellites, and is always ON whenever your phone is ON. Position data is not computed in Low Accuracy or what you call OFF. What is needed is the exact distance between you and the tower to account for the time delay. Both your phone and Tower receive the GPS timing signal. Your phone needs to know when to look for its signal. 

What you call ON is when you turn it on for APPS, dial 911, and when Big Bother wants to know exactly where you are. That is high accuracy mode where position data is acquired. 

The Telco always knows about where you are at within a block or two. I can open a program, type in any phone number, and see what towers your phone is in range, and how far away it is from the tower. I can also tell you who you are talking too and where they are if so inclined. Those records are permanent and stored in databases for recall if needed. 

What you are talking about Triangulation is correct. A Cell Tower has 3 Sectors. Think of it as a Pie with three 120 degree slices. The Switch knows which Towers, Sectors, and Distance. Yu will most always be seen on more than one tower. Exception would be rural area.

But here is the deal. Each of those 3 Sectors on the tower, and all the other Towers use the exact same Carrier Frequency. In order for your phone to know which Tower, Sector and Time Slot to use requires a Sync Signal to know when to look for its unique time slot and encryption. Otherwise it would be like being in a stadium full of people yelling and you trying to talk to someone on the other side. But if you sync everyone conversation so you only hear when the other person speaks, you can hear them, and them only. Otherwise it is just a bunch of noise. GPS provides that timing. 

Want to know something really Scary. DOD can shut down all communications with a key click. How? Turn off GPS and no talkie walkie. Every phone office and Internet provider uses GPS timing. Without that timing, you no talk. 

Want to shut down cell phones in a specific area? Easy Peazy goberment can easily do it. GPS signals are weak and very easy to JAM. A kid can do it. You could do it with a hand held radio and wipe out cell phones a few miles around you. 

Every telephone company can shut down all traffic real easy and does so frequently. Have a hurricane or natural disaster, they can kill all traffic except 911 and emergency numbers in a database. 

Gotta a deactivated Cell phone? Turn it on and it can place a call to one number 911.

So when you said it is Tower Based in partially correct, but not entirely correct. There is more to it than you know and left out.


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## TooQik (May 4, 2013)

I appreciate that you work in the field Sunking but you are incorrect in saying that a cell phone must have GPS to work. If this were the case then all other devices that use the same mobile communication infrastructure would also require GPS, they don't.

I've been working with devices that require mobile modem/routers which utilised the 2G/2.5G/3G/4G networks for the last 14 years and none of these have/had any GPS componentry.

The sync signal and timing you mention are nothing to do with GPS, they're controlled by the multiplexing method using for the particular network ie. CDMA, OFDMA etc.


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## BWA (Mar 14, 2015)

IF my cellphone has GPS, it is not user accessible.

It also is not APP capable.

It's just a Cell Phone, it's not very smart (kinda like it's owner).

It's also coal fired.

I like my GPS speedo, and, would still use it even if I had a modern Smart Phone with active GPS. It is 4" diameter and, has an analog needle that swings around just like most of the other dials/gauges in the old clunkers I drive.....

It suits my old timey sensibilities.....


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## dcb (Dec 5, 2009)

that sounds neat. fwiw I think they use accelerometers and stuff too besides gps to keep things smooth (the integral of acceleration is velocity).


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## BWA (Mar 14, 2015)

I got the cheapest one I could find. It has a resolution of 30 yards, so, it only gets a ping once every 30 yards (I think that's how it works).

Even in my 68 Vauxhall, with it's 0-60 time of sometime before dinner, I can out accelerate it by a second or so up to about 50Kph.......

I can out brake it easily, and, be dead stopped while the needle is still unwinding past 40Kph..........

It's general accuracy on steady state driving seems to be pretty good.

The more expensive ones have much better resolution and, react faster to acceleration and braking much quicker.......


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