jonathan_ed3

iTrader: (4)

I'm not sure where to post this, I assume this forum will contain the most electrical gurus. Feel free to move if necessary.

I have an odometer/speedo assembly from a 1992 civic mounted into an old car. For accuracy reasons, I want to run the mileage up to match the chassis.

For accessibility reasons and delicacy of the area it's mounted in, I do NOT want to mechanically do this (i.e. Remove odometer and try to manually roll mileage forward).

I tried to hook a drill mechanically to a Honda VSS but this proved too cumbersome to be reliable enough without watching it 24/7.

I also tried a DC motor attached to the VSS to spin it, worked for about a day and then fried the motor. Again, this method is too cumbersome to really be reliable.

For absenteeism needs, I want to do this process with something that I can hook up and forget for 10-20 days while it rolls forward.

The Honda speedo needs to see a square wave pulse to mimic the VSS. Doing some math shows I send to send it a 100-200hz signal. (111hz = 100mph, 144hz=130mph)

I'm not sure the mechanical limit of the speedo. Looks like maybe 150mph, which would be about 166hz.

At any rate, I need to rack up about 43k miles. This will be anywhere from 10-30 days depending on how fast I can spin the thing.

So, what is the cheapest most reliable way to send a 100-200hz square wave signal to the speedo for possibly up to a month straight?


I tried using this. It worked for about 5 minutes and blew up. I may have crossed the power leads while attempting to adjust the speed, but I'm pretty sure I didn't. I think the unit just fried itself. I'm not sure why. But something like this is certainly on the right track because it WAS working.

I have no clue about anything electrical, so please speak in laymans terms when you answer. I tried asking this question on an computer/electrical forum and their responses/questions were so far above my head that I stopped even replying. They were basically of no help whatsoever.

Blown06

iTrader: (32)

How about a fan from home depot or some ****. Can run those for days. This might be the weirdest thread on the forum.

jonathan_ed3

iTrader: (4)

I tried that also when I was trying different motors. . On high speed it was able to generate enough signal through the VSS to turn the speedo about 100mph. It burned the fan out in about 2 hours though. I guess they can't deal with very much load at all.

roastin240

iTrader: (13)

Yes a function generator will perform this. Most of the ones we use are expensive and obviously not economically feasible for your project ($10K), but I just picked up a decent one for $1K for another project at work. But these are standalone units with a user interface and have alot of additional control options as well as being able to read and display any signal under the voltage and current ratings of the device. What you linked to appears that it will work if it has the frequency range you are after. And the square wave should be 50% duty cycle like it says that one is. For $6 its worth a try if the frequency is what you need. (I didnt see a specification on that in the link)

jonathan_ed3

iTrader: (4)

Thanks for the reply. I couldn't find any specs on the frequency, but one of the Q&A responses lower on the page said it'll do 0-20,000 HZ. This appears to be accurate because when I first hooked it up it was showing about 20mph on my speedo. But then as I tried to adjust the pentiometer it blew up. This may have been due to one of my test leads contacting the other or maybe not. The entire unit is less than an inch long and the inputs are about 1/16 of an inch from eachother. I guess I'll order another couple and solder some extensions on it before I hook up any power.

aknovaman

iTrader: (7)

The NE555 pulse generator on ebay is your most affordable option at less than $2 each. I suggest you connect a simple marker lamp in series with it's output as it will provide some voltage buffering. Another option is an arduino microcontroller but that requires come effort but still less than $8 total.

jonathan_ed3

iTrader: (4)

Thanks for the replies everyone. I would like to update this thread for future searchability. I hate when I stumble on a relevant older thread with no conclusion.

I ended up ordering two more of the 555 pulse generators. I soldered some wiring extensions to the leads to make it less cumbersome for hookup and lower the chance of my accidentally touching something wrong which is what blew up my first NE555 pulse generator. I have it running off a plain old 12v car battery but I have the voltage reduced to 3.5v as the speedometer per the FSM only should be seeing 0-5v so I would rather be safe than sorry. It probably would have been okay to not reduce the voltage but I already had the voltage reducer so I figured why not.

I have a car battery feeding an LM2596 voltage reducer ($5-6 on Amazon) that I had leftover from another project to reduce voltage to 3.5 which then powers the NE555 pulse generator which then feeds to proper frequency to the speedometer signal input.


So far this seems to have done the trick.I thought it had a needle limitation on the speedometer but on closer review I was actually able to get it almost clock all
The way around before touching the 0mph resting needle (don't know the exact term). Doing some math tells me that I've got the speedometer turning at 192mph. It's been running unattended for a few days now and has already racked up over 10k miles.

I should be at my target mileage within a week. I'll update when it's done.

stevieturbo

Some USB oscilloscopes have a signal generator that would do.

Or Megasquirts JimStim should be able to give a signal that would suffice.

There are other tools for car diagnostic stuff to generate signals too, eg

http://autoditex.com/AutoSim/index.html