Introduction: LED Speedometer

Picture of LED Speedometer

My Peugeot 504 speedometer came to an end,  with a wire & wobbly needle. I don't like it anyway.
I made an LED RPM gauge before. I think an LED speedometer would be fine too. The main obstacle for me was the speed sensor. I thought of using variable reluctance magnetic pick up sensors or automotive ABS sensors. They operate on the same principle, fixed sensor over a rotating toothed ferrous wheel. As the teeth pass by the sensor, up & down electrical impulses are generated, as the speed increases, the frequency goes up too. Then we need to convert this frequency to voltage (using the LM2917 as in a tachometer), the increasing voltage will drive 30 LEDs through 3x LM3914 ICs. Good
I didn't spend much time looking for ABS sensors. I had a stepper motor from an old inkjet printer. I tought it can generate similar signal to be interpretted by LM2917. Later I found this motor can generate increasing voltage as the car speed goes up. So, I don't need a frequency to voltage converter (LM2917)

What to do:
1- remove the old speedometer with its wire
2- mount the speed sensor underneath the car to get movement from where the old wire got it
3- building the circuit
4- calibration
5-  finish

Step 1: The Speed Sensor

Picture of The Speed Sensor

There are many Ideas when it comes to the speed sensors.

1- Variable reluctance magnetic pick up (ABS sensors)
2- IR LEDs & IR detectors
3- In my case, a stepper motor as a generator

I took this motor from my old ink-jet printer. It had two stepper motors, this is the stronger one in terms of size, weight, sensitivity & output voltage
The most challenging step is to mount the motor to the car transmission where the old speedometer cable used to be. So that the motor gets driven as the car move.
There should be:
1- Mechanical linkage between the motor head (gear) & the rotating speedometer rod inside the transmission
This was achieved using a small peice of copper folded upon itself. one end being rotated by the transmission, the second end to be inserted in a groove I made in the center of motor head (gear)
no welding needed :)
2- Good method for mounting the motor centrally in place. No shaking or to & fro movement is accepted
At my mechanic's, I drilled a 4mm hole in the transmission body, passed a screw & nut. Later on, I filled the gaps with epoxy resin glue. That was enough for good  fixation.

Now I have a speed sensor with a 4 wires cable :)
I took wire No 1 as a signal, wire No 2 as a ground

This motor can generate up to 48 Volts as I tested it. But When mount to my car's transmission, it rotates at near top speed generating 28 Volts. This is good. The relation betweed the car speed & voltage increase is linear. This is great.

Step 2: Building the Circuit

Picture of Building the Circuit

Attached the circuit schematics

12 Volts : from car battery
Ground :  Car chassis
Signal : from the sensor "stepper motor" 

The No 5 Pin of LM3914 can withstand up to 35 Volts input. I added a 47K ohm trimpot potentiometer in series with signal input for calibration
Calibration was done using GPS equippied cellphone to get the car speed

:::::::::::::::::::: List of components: ::::::::::::::::::::::::
Integrated Circuits:
3 x LM3914 This is LED display driver. Each one can drive 10LEDs in either bar mode like this project or dot mode. Switching between both modes can be done, more instructions in datasheet.
1 x 7809 Volt regulator (outputs +9 Volts)

31 LEDs of any color you want. I used bright white ones. You can use some green, some yellow & some red for the red zone. You MUST use bright ones if you are planning to put paper covers over the LEDs or they are going to be simply invisible
 The first LED is continously lit as long as the +12V source is connected. The remaining 30 will be lit one by one as you increase the engine speed. I didn't connect the first one by the way

1 x 1N4007
2 x 1 Kohm
3 x 2.2 Kohm

Electrolytic Capacitors:
1 x 470 µFarad 25 Volts (µ = micro)
Polypropylene Capacitors:
2 x 100 nF (nano)
:::::::::::::::::: List of other things you need: ::::::::::::::::::::::::
Soldering equipment
Digital multimeter
Circuit board
Aluminium heatsink
A lot of patience

Step 3: Dashboard Work

Picture of Dashboard Work

See photos :)


Mjtrinihobby (author)2016-07-15

In my country it is highly illegal to make mods to the OEM safety and process critical systems. Nice instructable but for us here that will land us in serious trouble with the law.

EMANHIGOY (author)2016-03-15

the stepper motor you used, is it DC volts output? or AC Volts?

EMANHIGOY (author)EMANHIGOY2016-03-17

how did you put the 47k trimpot? i think the trimpot will burn if the voltage is too high

Greasetattoo (author)2010-11-11

Great Instructable!

Does the 160 LED work?
I didn't see it light up in the video! lol

Great job!

abo_hosni (author)Greasetattoo2010-11-11

maybe next time when I use higher octane fuel & run on a better road.

EMANHIGOY (author)abo_hosni2016-03-15

you can just jack up the rear portion of your car since your car is an RWD, jack up your rear wheels until fully hanging up then startup the engine and step on the throttle like you do on highways and watch the speedometer until it reaches 160 :D

stinkybob1965 (author)2014-11-16

Awesome job and I'm sure maaaany hours! I'm trying to use a 2013 chrysler speedometer in my 1969 camaro. the 2013 gauges are controlled by an on board computer and extensive circuitry which I obviously don't have. If i remove everything but the stepper motor and gauge face do you think your circuit or similar could drive the motor accurately? basically I'd be replacing your led's with a motor to turn a needle.

Habayeb (author)2014-07-05

Abo_Hosni ... Assalamo Alaikom ...

How about adding an Odometer and TripMeter .. your project is great and it would be perfect if you can add those two instruments ... simple using passive components like your SpeedoMeter and TachoMeter ...

Thank you man ..

nts5109 (author)2014-05-30

what do the letters and numbers like "D2" correspond to? can I get a list of the circuits that they represent?

TankMorph (author)2013-05-14

Very cool project. I did something similar, but just used GPS and an LCD display instead.

n33r (author)2012-04-02

will this work with magnet and reed switch ???
If yes what changes do i need to make in circuit ???
am just beginner so please explain in detail, Thanks.
& btw u really are creative like ur idea !!!!

TankMorph (author)n33r2013-05-14

It would work, but a reed switch would wear out eventually. A Hall effect sensor is a better choice.

Ortzinator (author)2012-08-12

On newer cars you can use a scanner tool to get the speed straight from the sensor.

toyds (author)2012-05-08

hello hosni

how do we determine the wires from a stepper motor of a printer that it is No1 and No2?or output and ground?thanks a lot (author)2012-05-01

Is this mostly accurate, and does it drop out at high speeds when the stepper reaches its max

chaluska (author)2010-12-16

could you draw a new diagram showing how this could be hooked up from a cars existing electronic speed sensor (AC Voltage) also, your in KMH, is there any difference between KMH and MPH? im guessing on the calibration of the potentiometer?

chaluska (author)chaluska2010-12-21

actually, i just read about the diode bridge.. that is extremely simple. example for future people has been attached...

from what ive read around, my car will put about 5v of a/c voltage at around 60 mph.. and just at .5v around 1-3 mph.. so i hope i can tune the input signal with the potentiometer to work with this level of voltage

aflexo (author)2010-11-25


how did you made this one so accurate?

abo_hosni (author)aflexo2010-11-30

You can make the design you want with exact dimensions using Adobe PhotoShop. I used it to create 10x15cm prints

aflexo (author)abo_hosni2010-12-01

Oh thanks, but I meant - after Photoshop. Is it a print on some plastic or painting? Or is it paper? It looks like film or plastic because of gloss.

abo_hosni (author)aflexo2010-12-02

It's regular glossy photopaper, not plastic
Later, I used matte photopaper

aflexo (author)abo_hosni2010-12-02

Thank you.

Broom (author)2010-11-21

Missing: how you made the photopaper display cover. It's also missing from the list of steps at the beginning, and from the list of materials needed.

rickharris (author)2010-11-06
I think in the UK anyway you would need to be able to show calibration date if the police feel the urge to ask.

How did you calibrate it?

abo_hosni (author)rickharris2010-11-06

I used my cellphone (Samsung G810) to get the car speed by GPS, then calibration was done by changing the 47K ohm potentiometer value using a scerw while the car is moving & comparing the read speed to the speed I get from GPS

Broom (author)abo_hosni2010-11-21

Could also be done by a partner in a following car, calibrating off of their spedo. Then you'd only need two cellphones.

Brilliant 'ible!

anikhila67 (author)2010-11-13

good funda....

wacco (author)2010-11-12

i think you could actually hook the signal up to the ignition coil...(if you have one)

since there will be a differential in voltage..

that's what i seen on the normal car using an aftermarket tachometer or speedo meter.

correct me if i'm wrong.. :D

soundmotor (author)2010-11-12

Superb! I learned a great deal from this, thank you.

Vahmp (author)2010-11-11

Great instructable!
Just one question...
Who would I be able to adapt this idea/strutable to a motorcycles front wheel speed cable set-up? Also, a techo system for the motorcycle would help...

I'm not that apt at eletronics, but can follow intructions very well. lol
Here's my e-mail, lord_vahmp@
Any help would be greatly appreciated!

Thanks in advance.


abo_hosni (author)Vahmp2010-11-11

It depends on the design & space you have. You can attach the sensor to the speed cable away from the front wheel

askjerry (author)2010-11-11

Nicely done!

I have a laser engraver... and if I were doing this project, I would get reverse engravable plastic, engrave the red/orange band, then paint. Engrave the numbers and paint white, then engrave the LED bars. The result would be a nice looking plastic panel.

If anyone ever needs that done there are several places that can do it, or you can contact me and send the artwork. (If you drop ship the plastic to me it would only cost you the actual engrave time and shipping.)

Great idea... I may copy your circuit and use it for a wind-speed indicator or other projects needing a bar-graph display. Again... nicely done!


abo_hosni (author)askjerry2010-11-11

Great idea! Would be nice for anyone wanting a professional looking dashboard.
Thanks for your help

Exiumind (author)2010-11-11

Great work, by the way, where are you from?

abo_hosni (author)Exiumind2010-11-11

Egypt :)

jakdedert (author)2010-11-09

I guess you have no plans to add some circuitry to give you mileage? (You didn't have it anyway, since the original speedo was wonky.) Also, did you make some attempt to waterproof the sensor motor, since it is mounted beneath the car? If so, how?

abo_hosni (author)jakdedert2010-11-09

I may go for a digital odometerr when I get familiar with PICs.

About waterproofing, I filled the gaps between the stepper motor & the transmission body using epoxy glue. This is good for fixation & waterproof, too. The motor has small venting slits (through the black part) that I think not a major issue. moreover, the place where it's mounted is difficult to get water whilst on the road.
It's easy to wrap it in a plastic bag when cleaning the car with water.
I think waterproofing is not a big issue.

shad0w88 (author)2010-11-06

Looks Really Good!, I've been thinking about making a Digital Speedometer for my bike for sometime now. And you went and posted something very well suited to my requirements for converting a cable driven speedo, Good Job Man. I've thought about using a dc motor, a five wire stepper motor, an IR Transponder and looked up using a hall effect sensor or reed switch. Hall effect sensors and reed switches have been widely used to get the speed but I'm not sure about their accuracy.

Could a 12v dc motor be used for this somehow? or a Five wire stepper motor?

And Why not connect the Motor to the Speedo Cable(If it's not broken) rather than Directly, so it's all in one place?

abo_hosni (author)shad0w882010-11-09

hall effect sensors are good in this purpose. But I didn't use any.

12V dc motor is good, too.
When you rotate the shaft, it produces AC & not DC. In fact, The LM3914 works with AC well. I didn't add AC-DC converter.

If you need DC from AC, add a simple diode bridge to your input signal, cheap & easy

My speedo wire was wobbly especially at low speeds. I preferred to get the movement directly from the transmission

hivoltage (author)2010-11-08

This is an awesome idea! loved the led tachometer as well. I'm thinking about doing the same thing in my car, but isn't your odometer driven from the speedometer cable as well?

abo_hosni (author)hivoltage2010-11-09

Yes it was. It wasn't working in the past 5-6 years by the way :D

Timothy.Mehlhorn (author)2010-11-08

How does it look during the day?

The tachometer looks fine during day being more distant from light & the photopaper used is more thin

The speedo needs more dimming during light. I'm planning to:
1- change the design
2- print on a thinner photopaper
3- add seven segment display too, this is definitely going to make it better during day

penzer (author)2010-11-06

nice work doctor
guess who ?

abo_hosni (author)penzer2010-11-06

any clues?

atombomb1945 (author)2010-11-05

So, is this giving you a speed based on the voltage created by the motor spinning?

abo_hosni (author)atombomb19452010-11-05


About This Instructable




More by abo_hosni:Using a stepper motor as automtive speed sensorTransform a trimmer potentiometer into a multiposition rotary switchDigital multimeter for your car
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