# 1.4" lcd speedometer



## chamilun (Jun 17, 2008)

didn't know if this may be usable for an rpm sensor/reader

http://dealextreme.com/details.dx/sku.32804~r.96035782


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## Tesseract (Sep 27, 2008)

Wow - it certainly is cheap, BUT... it doesn't say that it shows RPM, and even if it did, most bike computers expect to see RPMs in the, oh, 1-100 range. Might not be fast enough to read motor RPM.


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## Jimdear2 (Oct 12, 2008)

I ordered one. 

If you look carefully you can see it's a speedometer. From what I can make out of the instructions you are supposed to measure the diameter of the wheel then input that info., then mount something (a magnet?) on the spokes and a pickup near it.

This should work well to give me the wheel speed of my pulling garden tractor. I dont know how accrate it will be but as long as it is consistant, I will have a data point I usually have to plot mathamatically. 

If it doesent work out for me, I'll give it to my brother who still rides his bike.

I'll try it out this spring and post the results in the electric bike and in the technical forum. Of course someone else may get it checked out before then. If it is any kind of accurate, it might make a easy way to incorperate MPH into a custom DIY dashborad.

For seven bucks I don't think it will be any kind of accurate or resistant to damage, but you never know. The low price probably come from the economey of scale. Probally Billions of bikes in China.


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## evcars (Mar 15, 2008)

Why not just use a GPS? They are way more accurate and you dont have to mess with the magnets and sensors.


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## Jimdear2 (Oct 12, 2008)

evcars said:


> Why not just use a GPS? They are way more accurate and you dont have to mess with the magnets and sensors.


evccars.

I guess I'll do it 

For Fun,
To find out . . .
Because this is a DIY thing
Because it costs $6.50

And finally, because I want to see wheel speed not ground speed. They are different in tractor pulling.

You all be well,


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## Salty9 (Jul 13, 2009)

Well played, Jim


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## chamilun (Jun 17, 2008)

I didn't look too carefully, but if you could use this as a motor tachometer, it would be awesome. I was never willing to pay the $100+ for a tach sender.


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## DIYguy (Sep 18, 2008)

you may be able to mount sensor on the drive shaft and enter final ratio (vs differential/wheel size).


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## Jimdear2 (Oct 12, 2008)

DIYguy said:


> you may be able to mount sensor on the drive shaft and enter final ratio (vs differential/wheel size).


To all

Well I got the little speedo today and am quite pleased with the quality of the components. Better then average for Chinese plastic stuff.

I'm afraid you will have to forgo ideas of a cheap tach. 

But you might be able to fiddle with parameters and make it work as a speedo on a car off the drive shaft.  But . . . there is no back light and the display is quite tiny. For a bicycle or for the use I want them for, I think they will be fine. For a car, find a way to light and magnify the display and WOW. 

It uses a 3 volt coin battery, the lead from the base mount to the Pickup is only about 30 inched long It comes with enough tie wraps to mount it on a bicycle. The measurement head is removable and then it becomes a kind of pocket watch. 
The unit appears to be reasonably well constructed and they claim it's waterproof (wait and see)

For 6.50 cents shipping included I think it's a pretty good deal.

A quick operational rundown:


*Continious Display*

Clock 24 H or 12 H display modes
*Other displays*

Scan: In this moe it unit steps through all of the operational modes continiously
Arrows UP and DOWN: Accelleration / Deccelleration
M/h or K/h: miles or kilometer modes
*OPERATIONAL MODES *

*SPD*: Speed in kMH or MPH
*TMR*:Timer (stopwatch) 0.0 to 999.59 hours
*RAT*: Rate (Total Riding Time since last complete reset) This is up to 9999.0 hours. Only displays the four digits
*AVS*: Average Speed (must reset for each unique measurenmt or it keeps a continious average)
*MXS*: Maximum Speed attained since last reset
*DIS*: Shows a single riding distance (not sure how this one works it might be from a reset or from 0 speed. I'll get back to you on this one
*CAL*: Calories Burned (Don't know Hhow you could use this on an EV)
*ODO*: Odometer total trip distance (don't know how this differers from DTS I'll report back when I find out.
*RPM*: Realtime display of wheel RPM up to 999
I'm satisfied with it.


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## kixGas (May 2, 2008)

Jimdear2 said:


> To all
> 
> Well I got the little speedo today and am quite pleased with the quality of the components. Better then average for Chinese plastic stuff.
> 
> ...


Jim-
Quick question. I have an electric go kart that I built for my son. I thought about using this for a speedometer. Is the minimum diameter that can be entered into the device? He has a 10" tire and I know these are intended for bikes with obviously larger wheels.

Thanks-


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## Jimdear2 (Oct 12, 2008)

kixGas said:


> Jim-
> Quick question. I have an electric go kart that I built for my son. I thought about using this for a speedometer. Is the minimum diameter that can be entered into the device? He has a 10" tire and I know these are intended for bikes with obviously larger wheels.
> 
> Thanks-


kixGas,

Your are in luck, I think it will work.

I input 254mm (=10 inches) into the wheel diameter parameter and then tried pulsing the sensor by hand with the supplied magnet. I did get a reading of around 2.5 mph. Since I can only do maybe 2 to 3 pulses per second and those are iregular It sounds close.

Figure that is the equivalent of 100 or so RPM and with a 10 inch wheel if you run that through one of the rpm to mph converters on the internet gives 2.5 to 3.0 MPH.

So, it should work for you, you might have to do a bit of fine tuning (+- a few mm) to get it spot on, but even rough speed for $6.50 is worth it. Plus you have all of those other fun setting like max MPH and time spent riding on it. 

Just came to me why the speed didn't come out right spot on. The magnet is going to be on the spokes of the wheel thats going to reduce the actual sensed diameter of the measured wheel. Like a 26 in wheel migt have the magnet describing a 23 inch circle. The programmer may have put an offset into the algorythem (excuse the spelling) to compensate.

Hope the speedo works well.


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## kixGas (May 2, 2008)

Thanks for checking Jim- I will order one right away.
BTW it doesn't matter where on the spokes (in the case of a bike) the magnet is. The controller is just counting how many times the magnet is passing the sensor in a certain time period. It then uses the input of the diameter to calculate the speed. If the magnet is 5" away from the axis or 26" away from the axis it will still pass a fixed point the same number of times at a given speed.


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## Jimdear2 (Oct 12, 2008)

kixGas said:


> Thanks for checking Jim- I will order one right away.
> BTW it doesn't matter where on the spokes (in the case of a bike) the magnet is. The controller is just counting how many times the magnet is passing the sensor in a certain time period. It then uses the input of the diameter to calculate the speed. If the magnet is 5" away from the axis or 26" away from the axis it will still pass a fixed point the same number of times at a given speed.


 
OOOOOH, slap me upside the head.

Man is my face red. 

I know that. . . Thats what I get for trying to throw out something that occures to me without thinking it through. Getting old sucks

Thanks for catching it.

By the way that site is a lot of fun to just window shop.


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## Salty9 (Jul 13, 2009)

Jim,

I've found that the only consolation to getting old is that it is better than the alternative.

Chuck


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## Jimdear2 (Oct 12, 2008)

Salty9 said:


> Jim,
> 
> I've found that the only consolation to getting old is that it is better than the alternative.
> 
> Chuck


Chuck,

Very true. Just wish it didn't hurt so much.

Jim


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