Using a older smartphone in a car to use as speedometer?

[Startux]

Hello there! First time posting here! I have a 2004 Scion XA that has a (very annoying) center mounted speedometer. I find it highly distracting.
Is it possible to use a old (Huawai) smart phone with a GPS based Android speedometer? I'd like it to turn on and off with the ignition switch, and only run this one program exclusively. I can run the phone with out the battery, plugged into the cigarette lighter. I have read of something like this on the Hackaday website, but the main questions are about the phone powering on, and exclusively running only one app on power on. Can anyone give me some pointers? Thanx!

[Mechanical Menace]

but the main questions are about the phone powering on, and exclusively running only one app on power on. Can anyone give me some pointers? Thanx!

Depends on the phone. If you can unlock the bootloader then you can install a custom Android build that launches the app you want instead of a launcher. If you can't you can root the phone and faff about a bit.

EDIT: If you don't care about the bundled apps still been on the phone this looks promising and you don't need to root the phone. If you do care you could still use that but root your phone and uninstall the bundled apps using a root mode app uninstaller.

[Fraser]

Just be aware that the GPS capabilities of the phone are affected by its antennas view of the sky and GPS does not cope well in built up areas like cities. Expect to lose the GPS speed readout now and again. If you place the phone under any metal it will lose sight of the satellites and fail to provide GPS functionality.

Aurora

[Rick Law]

It also depends on the hardware and software of the GPS.

GPS uses longitude and latitude to find out where you are, and compares it to last long/lat to find out where you were.  The linear distance and the time difference give you the speed.

- Reliability is an issue.  There is no hard wire connection to the satellite, so signals could be blocked, you may be also be receiving reflected signals causing false readings.

- The time-between-data-points is another issue and that depends on your hardware/software.

- The interpolation is another issue - My GPS after successful satellite acquisition, will use interpolation for momentary lost of satellite view.  So, until lost of satellite view exceeded certain time limit,  "GPS data" is not real.  My GPS will interpolate for a long time as long as just one satellite is in view, and interpolate for well over a minute if just one satellite is in view.

- How about roads your GPS map doesn't know?  When I turned onto a newly made road, my TomTom's error correction puts me on the nearest road almost 100 meter away - it just can't understand why I am driving on water, I suppose.  Imagine how they would calculate when map data doesn't match satellite data.

[Fraser]

We own a Nissan X-Trail that also has the binnacle in the mid point of the dash board.

I also have a Mini Moke though, and that has a centre mounted speedometer, so the X-Trail format was not so much of a shock, but it did take some getting used to.

I can state that after a little while, the new location of the instruments does not phase me and I switch between a conventional position in my Audi and the centre position in the Nissan. Give it some time before deciding that you can't use a centre mounted instrument cluster.

Aurora

[saturation]

GPS or any consumer wireless methods are not reliable enough for mission critical instrumentation. Even short range bluetooth will be subject to some interference as you drive through cities.  Android was also not meant to be fault tolerant. 

You can try a popular Android bluetooth app called Torque with a clone bluetooth OBDII adapter to check it out, adapter sells for $US5-20 and a freeware version of Torque can be downloaded from Play Google. 

To get hardwired reliability, you can get a wired OBDII instrument cluster were you can program anything you wish to see supported by OBDII.   If this is a permanent mount you can get a passthrough ODBII port cable or splitter.  Pay version Torque does something similar for far cheaper but the bluetooth connectivity and Android creates long term problems if used as real time instruments.

http://www.corral.net/index.php/tech/articles/122-drew-technologies-dashdaq-obd-ii-gps-programmable-gauge-cluster

[Startux]

I want thank saturation, Aurora, Rick Law, and Mechanical Menace for for some quick replys and some good suggestions...Although Aurora, it MAY come at some point that I can get used to it, but I doubt it!

[rs20]

It also depends on the hardware and software of the GPS.

GPS uses longitude and latitude to find out where you are, and compares it to last long/lat to find out where you were.  The linear distance and the time difference give you the speed.

Do you know this to be true, or are you speculating? For some reason I was under the impression that GPS velocity is based, at least partially, on direct speed measurements through doppler shifts and suchlike. Though maybe some GPS devices don't do this properly; and maybe still others have a GPS chip inside providing them this data, but they don't realise its value and discard it and recompute it the dumb way.

Or, I'm just wrong.

This is a nitpick, of course, it would still suffer from reflections and all that. OBD-II is definitely the preferred solution.

[cdev]

a small car-puter based around a raspberry pi or similar combined with a $10 USB GPS would be able to give you a speed and direction display, but many jurisdictions do and should have laws against using any kind of computer or phone- not just if it forces you to take your eyes off the road. Almost all kinds of computer use in cars are unsafe. I have seen studies that explain why, use of any kind of electronic device increases your chance of having an accident many fold.

For that reason i think you should return to the traditional odometer solution. .

[Rick Law]

It also depends on the hardware and software of the GPS.

GPS uses longitude and latitude to find out where you are, and compares it to last long/lat to find out where you were.  The linear distance and the time difference give you the speed.

Do you know this to be true, or are you speculating? For some reason I was under the impression that GPS velocity is based, at least partially, on direct speed measurements through doppler shifts and suchlike. Though maybe some GPS devices don't do this properly; and maybe still others have a GPS chip inside providing them this data, but they don't realise its value and discard it and recompute it the dumb way.

Or, I'm just wrong.

This is a nitpick, of course, it would still suffer from reflections and all that. OBD-II is definitely the preferred solution.

First - Given satellites are orbiting at thousands of miles an hour (14,000km/hour), the addition of your extra few tens of miles an hour in random direction (relative to the satellite orbit) is so insignificant with doppler it will be in the rounding error.  Also, doppler (from one source) only works if you are moving in parallel to the satallite's orbit.

A speedometer will give you speed reading even when you are not moving directly parallel to a satellite's orbit.  So, you would still need multiple sats as for sure.  Angled motion relative to the satellite's orbit makes doppler shift a trigonometry problem with different shifts from different sats that software must deal with.   Could they implement hardware to do it, sure, but it would be nuts to do so from a cost standpoint.

I am not speculating on it having software timing but reasoning - based on experience and reading their manual, I know they are not all alike in how their software/hardware works. 

My first has 2 channels, scanned to get the view of 12 satellites.
My second has 4 channels to scan for 12 satellites.
My last TomTom while has one of the most popular chipset at the time, has I don't know how many channels - by then, I didn't care to find out.

All three of them will show signal from all x of 12 visible satellites.  With a different number of receivers, they have different hardware.  Thus they will have different software and timing.

The TomTom can tell me where it thinks I am when there is only 1 satellites locked (by looking at TomTom's data stream, I know how many they have locked and the sat data).  You need at least two to get actual position (assuming sea-level) and three to get position that is altitude-accurate.  So, it stands to reason that the GPS is interpolating.  And we all know from experience -- and would guess from experience that a pair of twins writing the same program will likely not have the same bugs.  So, accuracy will highly depends on how their software is constructed.

Some (older) phone-based GPS is cell-tower assisted triangulation.  And some phone GPS was pure cell-tower triangulation - GPS without satellites at all.  This was from phone specs.  When my wife was interested in that, I looked at their specs carefully.  Useless system if you are out in the country (no signal).

So, it would depends on how old the OP's old GPS is and how that darn thing works within.

EDIT - Disruptions caused me to lost track of my thought and missed the "why" GPS would likely have very different correction scheme depending on age and thus position estimation algorithm would likely changed depending on age of GPS.

The thing that made older GPS particularly sensitive to age is changes to the GPS signal quality  (by policy, not technology nor science).

When GPS was first opened for civilian use by President Reagan (KAL007 incident had something to do with it), an artificial error was inserted (~100meter) into the civilian signal.  For civilian signal to get accuracy, it has to average over time for a while.  The insertion of the error is so civilian signal could not be use for say cruise missiles by regimes not friendly to us.

The inserted error has been reduced and reduced over time.  So, older GPS error correction methods (if any) would likely changed rather significantly over time.

If MS Windows is a guide, I bet you enough of them still carries the legacy code that deals with the correction that would have been necessary 5-10 years ago.

[rs20]

I'm sorry to be so harsh, but seems to be an exhibition of poor reasoning. Unless this guy is just making stuff up, you're completely wrong, at least in general. Again, what the GPS in a phone is doing is a whole different question, although technology has moved a long way in the last few years. Apparently my phone can receive GLONASS as well, just for laughs.

First - Given satellites are orbiting at thousands of miles an hour (14,000km/hour), the addition of your extra few tens of miles an hour in random direction (relative to the satellite orbit) is so insignificant with doppler it will be in the rounding error.  Also, doppler (from one source) only works if you are moving in parallel to the satallite's orbit.

A speedometer will give you speed reading even when you are not moving directly parallel to a satellite's orbit.  So, you would still need multiple sats as for sure.  Angled motion relative to the satellite's orbit makes doppler shift a trigonometry problem with different shifts from different sats that software must deal with.   Could they implement hardware to do it, sure, but it would be nuts to do so from a cost standpoint.

Frequency isn't like voltage or current, it's very easy to measure accurately, since you're just counting pulses. So, seeing one mile per hour is not in the noise of 14,000 kph, not even close. Loosely speaking, the GPS channels are measuring phase; and the rate-of-change of phase is frequency. It comes for free, and with extreme precision at that.

And turning this phase data into location and velocity readouts is just software running inside the GPS receiver -- the extra software to calculate the output velocity as well comes for free. It all comes for free, except for the bit where you launch dozens of satellites with ultraprecise atomic clocks on board .

I am not speculating on it having software timing but reasoning - based on experience and reading their manual, I know they are not all alike in how their software/hardware works. 

My first has 2 channels, scanned to get the view of 12 satellites.
My second has 4 channels to scan for 12 satellites.
My last TomTom while has one of the most popular chipset at the time, has I don't know how many channels - by then, I didn't care to find out.

All three of them will show signal from all x of 12 visible satellites.  With a different number of receivers, they have different hardware.  Thus they will have different software and timing.

The TomTom can tell me where it thinks I am when there is only 1 satellites locked (by looking at TomTom's data stream, I know how many they have locked and the sat data).  You need at least two to get actual position (assuming sea-level) and three to get position that is altitude-accurate.  So, it stands to reason that the GPS is interpolating.  And we all know from experience -- and would guess from experience that a pair of twins writing the same program will likely not have the same bugs.  So, accuracy will highly depends on how their software is constructed.

What on earth are you talking about ? When there's only 3 (I think you mean 3, not 2) satellites available, it assumes sea level, and can get a fix that way. Three unknowns (lat, lng, time), three satellite signals, single solution. With 4 satellites, it can get altitude (lat, lng, altitude, time).

This is trilateration, which has nothing to do with interpolation (estimating a value based on previous and subsequent values in a sequence; I'm not sure what kind of sequence you're proposing here).

Accuracy is determined by phase noise in the receivers, if software were the weak link in the process that would be some very terrible software. I'm going to be charitable and assume I completely misunderstood this whole paragraph.

Some (older) phone-based GPS is cell-tower assisted triangulation.  And some phone GPS was pure cell-tower triangulation - GPS without satellites at all.  This was from phone specs.  When my wife was interested in that, I looked at their specs carefully.  Useless system if you are out in the country (no signal).

So, it would depends on how old the OP's old GPS is and how that darn thing works within.

Yeah, Android (and I'm sure many other systems) combines Wi-Fi data in as well. I think any half decent phone does have real GPS as well though. I certainly agree with you that Wi-Fi is not suitable for estimating velocity directly.

[Rick Law]

[EDIT:]

Moved this paragraph (which was already an edit) from last to first..

So, in a nut shell, you are talking about new technology.  I am talking old ones, so we are confusing each other.  May be I should have just ask the OP at the get-go, how old is your old GPS that you want to use...

* * *

This part is Physics: When you are not moving in parallel motion with the satellite's orbit, doppler doesn't work with one source!  You need multiple source to make it work.   With multiple source, you must use trigonometry to figure out which direction you are going by evaluating your speed relative to satellites in view.

This part is my estimation it doesn't make cost sense to do it in hardware.  You already have the last-position and time, current position and current time.  Calculating time delta and linear distance is simple.

As I said, it could be implemented in hardware, I think it doesn't make sense from the cost standpoint particularly since the primary function for GPS is to give position.  But that would really depends on what kind of GPS you got.  Older the GPS, the less would be done in hardware as hardware keep dropping in cost.

So, what is in the OP's GPS, who knows unless we do a tear down on the OP's GPS.

And GPS's position estimation is still questionable in my mind based on what I see on my GPSes.  Thus my paragraph (you quoted) about position estimation - each of those issues introduces error in position thus error in speed.

By the way, it was not WiFi - the phone GPS were actually using cell-tower phone signal to triangulate "GPS" position.  Verizon had it (10 years ago, I think) as a monthly service on old non-smart phones.  But you don't really need the phone company - you don't need a phone plan to pick up their cell phone signal.  If the OP's old GPS uses any of those, he got no chance of using that as speedometer once out of cell-tower view.  Again, who knows unless we know what old GPS the OP was using.

[paragaph moved to top]

[mzzj]

Yeah, Android (and I'm sure many other systems) combines Wi-Fi data in as well. I think any half decent phone does have real GPS as well though.

Have to say that there is huge differences in the GPS sensitivity and accuracy even in recent models. For example my current LG G2 mini is about same level of uselessness as 15 years old garmin handheld. (Pretty much useless in urban enviroment)  Previously had Lumia 820 and it was way way ahead of G2 mini in GPS usabilitity. With G2 mini you have to be standing in middle of open park for minutes to get a fix whereas the old Nokia 820 had no problems unless you were 10 meters below ground in sealed rf testing chamber 

[amyk]

a small car-puter based around a raspberry pi or similar combined with a $10 USB GPS would be able to give you a speed and direction display, but many jurisdictions do and should have laws against using any kind of computer or phone- not just if it forces you to take your eyes off the road. Almost all kinds of computer use in cars are unsafe. I have seen studies that explain why, use of any kind of electronic device increases your chance of having an accident many fold.

For that reason i think you should return to the traditional odometer solution. .

"Using" as in... frobnicating one, not just having it display information about the car which would be legally required for the driver to know anyway or otherwise useful to driving; otherwise GPS units would be banned too.

The main problem, as others have pointed out, is accuracy.

Have to say that there is huge differences in the GPS sensitivity and accuracy even in recent models.

That's likely antenna-related; here's a thread on another forum about modding existing GPS antennas on cheap smartphones and getting far better results than the original.