TomCat39

Hi all,

Did a search and didn't find anything specific.

Wondering if anyone ever found out what the specification was on the 92-95 speedometer as far as what voltage for what speed?

The VSS is a micro generator called a bobbin and puts out frequency based voltage based on transmission speed. That voltage is then fed to the speedometer which then moves the needle depending on the amount of voltage it receives. Well, the voltage actually comes from the speed sensor part of the circuit.

On a replacement speedometer I have pulled the needle off and I don't like the idea of running the car without the gauge faceplate and hope that one of those speed signs is accurate let alone catching my car out of the 15 cars in range at the time to try and set the needle.

I'm thinking if we know what voltage is suppose to be say 100 KPH (62.5 MPH) we could apply that voltage to the meter and push the needle on in the proper spot.

Was there ever any information about what voltage equals what speed on a 92-95 speedometer?

Nevermind, looking deeper into this, seems the speedo gets a 5 volt square wave, so seems I would need a squarewave generator and know what frequency means what speed to the speedo.

I don't have a squarewave generator nor the components to build one so this thread is pretty pointless as far as I can tell.

TomCat39

Upon second thought, this info (if anyone has it) may come in handy for someone.

Moved to misc./tech as it's not a single car specific as much as a generation and could potentially cross generations.

Does anyone know what frequency 5v square wave correlates to a specific speed on the speedometer?

averyvm

iTrader: (1)

I think the frequency of the wave increases as speed increases. The voltage or amplitude stays the same. And I believe it's 4 cycles per tire rotation

FrostyEG

iTrader: (1)

Check the FSM, it shows that at 1205 RPM of the VSS, the speedometer should read 60 mph. The VSS sends 4000 pulses per mile if you want to count pulses.

Hope that helps.

TomCat39

Never noticed the 4000 pulses per mile.

Using that, at 60 MPH you are doing a mile a minute. So should be doing 4000 pulses a minute, which is when the VSS is doing the 1205 RPM or 60 MPH on the speedo.

So essentially, 4000 5 Volt Square Wave pulses should be 60 MPH on the speedometer. (4Khz 5V Square Wave=60 MPH).

Is my mind grasping the math properly or am I really screwing it up in my head?

Is the 4000 pulses per mile in the FSM? I don't remember seeing that tidbit.

raverx3m

iTrader: (1)

wouldn't it be easier to do it on a dyno?
I mean cheaper as in time saved

TomCat39

I was thinking about those times you've pulled the speedo to change the face, if you have a square wave generator, you can set the needle before it even goes back into the car.

Much easier than what I've seen others do with gauges in car with no clear cover plate, using gps and holding 60 mph on the free way and push the pin on.

I'd say your dyno suggestion to be far safer than what usually happens.

By the way, I just stumbled across a signal generator (square, sine, sawtooth) for 42 bucks. So it's not as expensive as an hour dyno rental.

FrostyEG

iTrader: (1)

I don't believe the 4000 ppm is in the FSM. Not sure where I got that tidbit. I've been collecting RPM and Speedo data for my cluster swap. You can get a brand new (not oem) VSS for less than $10 on eBay. Hook it up to your speedo and spin it with a drill. You should get some movement. To calibrate it, you'll need some way to measure the pulses or the RPM, I'm going to use either an Arduino or a cheap digital HUD. Let us know how the pulse generator works out.

raverx3m

iTrader: (1)

I guess its not bad. for that price.

other way is to pace your friend while you sit in pass side and put the needles in but that's also a pain in the ***. I never knew it was pulse I thought it was voltage

TomCat39

Me too until I googled about the VSS.

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Whooops, I made a huge error. Hertz is cycles per second not minute. So if 4000 pulses per mile means 4000 pulses a minute at 60 mph, we have to divide 4000 by 60 to get the pulses per second at 60 mph. 4000/60=66.666666 pulses a second.

So 60 MPH should be 67 Hz 5V square wave.

Using the following formula:
I first tried 100 MPH which = 1.66666666666 mile s a minute.
Then I found that 99 MPH = 1.65 miles a minute

x=99/60=1.65 miles per minute

So for exact Hz to MPH the two below work perfectly mathematically:

1.65 miles * 4000 pulses per mile = 6600 pulses a minute / 60 seconds per minute = 110 Pulses a second (110 Hz).

Therefore 110 Hz should equal 99 MPH.

Now going in reverse, 100 Hz should be 90 MPH.

I knew knowing that tidbit about 4000 pulses a mile should help solve the Hz to Speed formula but I'm so rusty with my math that I couldn't piece it all together right away.

Cool deal. Thanks.

It will be a awhile before I spend money on a signal generator but when I do, I have a working untouched speedo in my closet that I can use to verify this theory.

Thanks again. :D

raverx3m

iTrader: (1)

Could also put the car on bricks and chock the wheels
Then keep it at steady rpm and slap the needle in
Ive done that
Cars not goin anywhere if its on cement blocks

azchris

The VSS pulls the signal to ground as it rotates.
I have a 95 Accord and I tested the Speedo/Odo on the bench.
(it requires only 3 connections, Ground, IGN @+12v, and the VSS/sense signal)
I connected a function generator providing a square wave to pull the Speedo/Odo sense signal to ground.
I measured the pulse at 15ms period (66.67Hz) when the speedo read 60MPH.
(and at 9.92ms period, the speedo read 90MPH)
-> So, yes, I can confirm that sensor signal of ~10ms period (100Hz) gives 90MPH.

This corresponds to 66.67/sec* 60sec/min = 4000 pulses per minute.
That matches what was stated "about 4000 pulses per mile", because 60MPH is one mile per minute.

In general, the Speedo MPH = approximately 900/(period of signal in milliseconds).

The Honda factory manual states that the speedo indicates 60mph@1026RPM of the VSS.
That would be 1026rev/min * (1min/60sec) = 17.1Hz or 58.45ms.
However, that does NOT seem to match what I measured.
(scaling my measurement, 58.45ms period would give about 15MPH).
However, due to the 4 pulses per revolution, that explains the factor-of-4 difference.
So,
1026 rev/min * (1min/60sec) * (4 pulses/revolution) = 68.4 pulses/sec @ 60mph
1 / (68.4 pulse/sec) = 0.01462sec = 14.62ms period at 60MPH.
Since the period and MPH are inversely-related,
14.62 ms * 60MPH = 877.193 ms*MPH = Constant.
so, using Honda's 'exact' value:
mph = 877.193 ms * MPH / (signal period in mS)
The matches pretty closely to the measurements I took.
Period (ms) = 877.193 (ms*mph) / 60MPH = 14.62 ms (vs. measured value of 15ms)
Period (ms) = 877.193 (ms*mph) / 90MPH = 9.75 ms (vs. measured value of 9.92ms)

(My speedo reads a bit fast anyway!)

It Wasn't Me

This thread is from 2015.

azchris

yes but I'm adding some info I feel might be useful to others. For example, if someone wants to test their speedometer off the car like I did,
to test accuracy or if it's not working.
These cars seem to have bad solder joints in the control board at the back of the speedometer
e.g. https://honda-tech.com/forums/honda-...epair-2087284/
and there are various videos and forums discussing resoldering the board and 'pin 10' on the IC#1.
So I wanted to be able to test my speedo without having to jack the car up and run it to actually test it.