Speedometer sensor

Hi all

I am wondering where the speedometer sensor is placed or how I can find it?

My idea is to build a small electronic kit to measure speed exactly and show it digitally.

Sonnich

Reply to
Sonnich Jensen
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make? model? year? country?

most vehicles have sensor output on the transmission so it can get a read off the crown wheel. some have it inside the cabin at the end of the speedo cable. older cars don't have a sensor so you'll have to make your own by attaching something to an output. magnets on the driveshaft for instance.

as an electronics project, it's a fine exercise. but on a modern car that has electronic gauges, it's not going to offer you better accuracy as the gauges are fed by the engine computer. for a vehicle like this, if you want digital out rather than analog gauges, make a reader for the obd output.

Reply to
jim beam

Let's try naming the car, first.. Often the speed sensor is built into the tranny. There are certainly some other variants. Once you get the speed signal located, it is no problem to devise a counter circuit and a digital display.

Reply to
hls

Ford Escort Tournier (station wagon), 1999 december

Reply to
Sonnich Jensen

I assume you are in the UK (or Europe). I have read that many European Fords from the late 1990's on have the same sort of OBDII port as US Fords,. If so, all you need to do to get a digital speed readout is buy something like a scan gauge

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and plug it in to the OBDII port.

Ed

Reply to
C. E. White

I had a 95 Caprice with a digital Speedo and once I got used to it I loved it. Much better then analog. And you can see trends on it just as you would on an analog, it's just different and you have to get used to it. One of the key factors is the size of the display. I also had some other car, can't recall which, that had both digital and analog display but the digital was much smaller then the Caprice's and it was too hard to focus on it.

Reply to
Ashton Crusher

I have had a couple of Buicks that had the digital dashes. Different strokes for different folks, I guess. I saw there were some issues with the digital speedo, and didnt really care for them. I dont agree that there were either better or worse than analog......just different.

Reply to
hls

How about a gizmo that will count the revolutions of one of the rear wheels on my Dodge van when I am driving? I have a digital bicycle speedometer.I wonder if I could rig that up? cuhulin

Reply to
J R

Sure, you can count the rotations of a wheel, using a sensor to generate a pulse, and then calibrate this number in mph.

Considerable work, though, for very little payoff.

Reply to
hls

it's likely just a science project - it's fun to do things like this. pretty much perfect for someone learning microcontroller programming for instance.

Reply to
jim beam

I could put a chalk mark at the top of one of the rear wheels/tires on my van and move my van untill that chalk mark makes one revolution and whatever that distance is, calculate that to approximately one mile.I am not too hot at calculating though. cuhulin

Reply to
J R

Most bicycle computers accept an input value for distance traveled per wheel rev, measured just as you note above.

Range is typically 1 to 2.2 meters entered in mm, 4 places. Output usually offered in km or miles per hour. The bimetallic sensor may not respond fast enough at typical driving speeds but no harm in trying since you own it already,

Reply to
AMuzi

One of the first things to do is write the specification. "Exactly" is not achievable. How many decimal digits of precision do you want? 20? 50? 245??? How many decimal digits of accuracy do you want? And how are you going to calibrate it? How much "time lag" between actual speed and displayed speed can you tolerate?

GPS comes to mind for few digits and long lag.

I once had a boat tachometer that was basically an AM radio that listened to the ignition noise from the engine and converted that to RPM. For a manual transmission in a fixed gear, that's directly related to speed.

I've considered wrapping a coil around the speedometer, but never got around to trying it.

If you have ABS brakes, there's probably a signal there. Something scary about messing with a car's braking system tho...

I hate interfacing mechanical systems if there's any other way.

Reply to
mike

some of the bicycle computers are cheap and work just fine. if that's the objective - a bike computer is not a science project.

bike computers are commonly used on motorcycles, particularly older ones where the gauges are either inaccurate at higher speeds, or just don't work at all.

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they generally use reed switches as the sensor. bimetallic strips are usually thermostatic sensors.

Reply to
jim beam

Sorry, I was hasty. You're right, two adjoining strips, one copper one steel. Switch closes with the magnet's pass, incrementing one revolution.

Reply to
AMuzi

no, the strips are both coated steel [or something ferro-magnetic] - they need to be so the induced n-s attraction brings them together. they're coated for conductivity. usually tipped too for contact longevity.

Reply to
jim beam

on the road, sure, more or less. but on a boat, it's not a linear relationship so rpm/speed translation would have to be mapped for a whole bunch of different variables.

the brakes still work even if you disconnect a sensor. you just lose the anti-lock function. tapping into a sensor connection to listen in on the signal doesn't disconnect it.

if you want data, you /have/ to interface!

Reply to
jim beam

Yes, I had digital in my '84 Lebaron, and it was terrible. All two-digit numbers look alike when your eyes are on the traffic.

Plus the temp and oil pressure gauges only had 4 segments.

Reply to
micky

Yes, I put one of those in about 3 weeks ago, and although my eyes can't be in two places at once, the speed on the Toyota tachometer seems to match what the scangauge says I haven't tried looking at the mph and speedometer.

Reply to
micky

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