Introduction: DIY LED Tachomter (RPM Gauge)

Picture of DIY LED Tachomter (RPM Gauge)
This is my LED project. An LED tachometer for my 1977 PEUGEOT 504.

Step 1: Building the Circuit

Picture of Building the Circuit

This is the circuit I used in my project. A simple one which costs me about 35 Egyptian Pounds for components (<6 US Dollars)

:::::::::::::::::::: List of components: ::::::::::::::::::::::::
Integrated Circuits:
1 x LM2917  This is the frequency to voltage converter you need to convert the signal from the car's ignition coil into voltage
2 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)

21 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 20 will be lit one by one as you increase the engine speed

1 x  1N4007
1 x  1N4148
1 x  Zener diode 12 Volts

1 x 220 Kohm Trimpot variable resistor (for calibration)
2 x 1 Kohm
3 x 10 Kohm
1 x 22 Kohm
1 x 2.2 Kohm
 1 x 470 ohm     (I forgot I have one :) So, I connected two 1Kohm in parallel, see photos)

Electrolytic Capacitors:
1 x 470 µFarad 25 Volts (µ = micro)
1 x 2.2  µF      16 Volts

Polypropylene Capacitors:
3 x 100 nF  (nano)
1 x 47 nF
 1 x 1 µF  (Instead,I used 8 x 100nF in parallel = 0.8 µF  :$ & it works) 

:::::::::::::::::: List of other things you need:  ::::::::::::::::::::::::
Soldering equipment
Digital multimeter
Circuit board
Aluminium heatsink
A lot of patience

Step 2: Testing the Circuit

Picture of Testing the Circuit
This is the circuit I've built. Tested on my car

Connections as follows:
 1- Power: red wire to car battery +12 volts. Later on, I connected it to the 12V accessory line in the fuse box. This line functions only when you turn the car key on.
 2- Ground: blue wire to car chassis (any metallic part of the car body)
 3- Signal: white wire to -ve terminal of the Ignition coil. Refer to your car manual in case you cannot identify the ignition coil, it may vary in shape from car to another. Be careful not to manipulate connections related to ignition coil especially when the engine is running. The function of this coil is to generate high voltage (30-50 Kilo Volts) & you are not supposed to recieve such sparks by mistake. It's better to wear gloves & remove the key from the car to be safe while making your connections.

This video is before calibration. I've made a visit to a friend of mine whose car with RPM gauge where I made my calibration

 Calibration was made later on my friends car with RPM gauge. I made the calibration through the 220kohm trimpot resistor so that every 3 LEDs = 1000 RPM

Step 3: Mounting to the Instrument Cluster

Picture of Mounting to the Instrument Cluster

First I needed to provide a place to put my project in. The best one was the old  -& non working- clock of my car. I simply removed it to find plenty of room for my circuit.

I cut my board to fit well, making a secondary circuit board for the 20 LEDs.

 I modified a simple RPM gauge design to print on a photo paper. I made 2 prints above each other, so that not so much backlight will pass through. I used a scalpel to cut the yellow "windows" in front of my LEDs from the first paper only, keeping the second one intact.

Step 4: Final Assembly

Picture of Final Assembly


Rahul Aryan (author)2017-10-15

hey, i followed your given circuit and made one such but i am using it in bike,then from where to get -ve of ignition coil

AlexA388 (author)2017-03-03

Anyone have the PCB designe for this?

NgôT11 (author)2017-01-11

Hi Abo!

Can you ask me where you conect the signal capble??

Thank u! My English is not good, maybe i wrote wrong something. I hope u understand me. :)

thaivg (author)2013-01-13

Dear abo_hosni,
Could tell me the value of resistor R6 and R7 if I use 5VDC power supply; and can I use IC 555 instead of LM 2917 to convert input signal to voltage?

sid555 (author)thaivg2016-09-26

that would we make your entire circut less reliable. the voltage drop would not be absorbed easily in 555. LM2917 regulates a potential of 9v and your source is 12v. so always LM2917 is prferable.

abhi1984 (author)2013-02-28

Hi Abo,

I dont even know if somebody is following this instructable anymore. I have a honda cbr 600 and my tach broke. I googled and found your blog. I am not educated in electronics but know how to follow instructions.
I followed your diagram (From Step 1) and the circuit is almost completed.
When I wanted to test it in real life I just realised that the ignition coils are mounted inline for each spark plug in my cbr and it is like impossible to get to the -ve terminal.

I wanted to ask, can we modify this circuit in any ways so that it can pick up the signal using induction i.e. by wounding a cable around the spark plug wire externally and not the actual signal from the ignition.

I think it became too long, but any help from anybody would be appreciated.


sid555 (author)abhi19842016-09-26

instead try connecting those terminals to battery and add a seperate key for the tach.. that would be simple!

kmunnery (author)2016-05-04

is it possible to adjust led intensity as the rpm increases, as I want this for my motor cycles light graphics to to be at max brightness at full speed and off under 1k.

zincjunyi (author)2016-03-07

i reallly intested to this project, but unfortunally im not good in electrical job, may i buy complete project with you ?by paypal or else?kindly to email me if possible to buy from

i will be wait for your reply thank you very much

EMANHIGOY (author)2016-03-06

May I ask what car did you use? Im planning to make this circuit for my car also

EMANHIGOY (author)EMANHIGOY2016-03-06

Oh i forgot to read the title sorry haha

lkeerthan (author)2015-06-29

Is the input the circuit pulsed dc or is AC?

vdhakane made it! (author)2014-07-14

we are from India .We are from College of Engineering Pune.We are part of TEAM NEMESIS RACING .We were designing led tachometer but we didn't know the ckt. After watching your project, we were familiar with IC LM3914.


baguiman (author)2014-04-02

Helo sir abo is it possible to replace LM2917 into LM2907 because there's no available IC in our area...?

toedrag (author)baguiman2014-07-02

Yes. The only difference is that the LM2917 has an internal Zener diode that clamps the device's internal Vcc to 7.56V, so if you wonder why your input voltage is 9V (from the 7809 regulator) but your output is less than that at the max frequency, it's probably due to the internal Zener of the LM2917.

The purpose of the Zener is to keep the Vcc of the device stable with transient power supply voltages. Since the 7809 will regulate the voltage to 9V, the internal zener of the 7809 really isn't needed.

Alternatively, you could use the LM2907, delete the 7809 regulator, and use a 12V Zener rated for maybe 2W, placing it in series between 12V and pins 8 & 9. You'd probably want another Zener for each of the LM3914 LED drivers as well. The main difference with this circuit vs the one shown is that you'd have the full 12V swing on the LM2917 output, which allows a greater voltage difference between the various RPM levels. But that also means the reference voltages on the LM3914 may need adjusting. The downside is that if the 12V supply on the car drops (like the case of a failed alternator or too much electrical load on the car's system), the circuit may not operate correctly. With the 7809 regulator in place, it would absorb the voltage drop, as long as it was above 9V.

x0220 (author)baguiman2014-05-10

yes, when you use the NTE cross reference chart for both, it points to the same NTE placement part.

abo_hosni (author)baguiman2014-04-02

Not really sure. You can download the PDF datasheets of both & compare to see weather it's possible to replace LM2917 with LM2907 & what changes should be made to the circuit

baguiman (author)abo_hosni2014-04-02

Thank you...

ARJOON (author)2014-04-13

circuit easy but putting them together on the vero seems to be quite a pain in the ass. maybe i'll try to design a compact pcb layout

proboost (author)2014-03-22

hi abo can you help im fairly new to this can you tell me what voltage the polypropylene capacitors need to be ?

cyclonite (author)2013-08-09

You know you can buy a digital Tach for $11 including postage ebay

jmoore59 (author)cyclonite2013-10-08

but its not a sweeping type, nor is it accurate.

abo_hosni (author)jmoore592013-10-21

nor with a custom fit, nor having a spirit

rk.snr.rajesh (author)2013-03-29

hi sir, I am working for FSAE. I need RPM meter for my FSAE car. Can you tell me what kind of input from that Ignition coil? Is that circuit is correct? make it sure. I tried many times. But it was not working. can u mail me exact circuit.

srpitu (author)rk.snr.rajesh2013-10-15

Do you Seriusly works for FSAE? The circuit works, not as perfect as it is showed in the video in my case, but it works. I dont know how the input signal is, but i guess that it is a square signal that increases in frecuency as the RPM increase.

rkrz (author)2013-07-12

9v or 5v ???... the picture and list says different 7809 in list and 7805 in picture? ??

srpitu (author)rkrz2013-10-15

It is a 9....where do you see a 5? i made this circuit todays and it works. Try it

srpitu (author)2013-10-15

This circuit works BUT need some adjust. I will take a look over the circuit and see how to impruve it because now it is almost working in my case. My issues could be caused by voltage provided for the coil and the power supply provided for the tachometer.

AS I SAID, this circuit works! check the solder joints that you did and if you are not so confortable with this, test it before put it.

Check the photo that i made today!!

CostaDill (author)2011-11-20

I am finaly done with this projekt but on my first test led 0 is on and all looks good but, when i start the car led 1 goes on and only change in brightnes when i change the RPM. Any idée whats wrong? I have 2 meter cable betwen the circuts and the Led´s, might that be the problem? Will appreciate any answer.

CostaDill (author)CostaDill2012-07-20

Now after some time. i started to look at this project again and i see that i have a 2,2Kohm Trimpot not 220Kohm. Ordered one and will se if this fix the problem.

CostaDill (author)CostaDill2012-07-25

Now the 220Kohm Trimpot is instelled but i when i calibrate it i only chose how many leds that turns on and no change when i start the car..

Anyone had this problem? Sound like the coil i giving wrong signal or that i can read the signal in some way?

jmoore59 (author)CostaDill2013-10-08

i am having this same problem, i know its been a while but what car were you trying it with? i have an 86 300zx and a 2000 civic that both do the same thing.

rkrz (author)2013-07-12

9v or 5v ???... the picture and list says different 7809 in list and 7805 in picture? ??

rkrz (author)2013-07-12

9v or 5v ???... the picture and list says different 7809 in list and 7805 in picture? ??

jmoore59 (author)2013-07-02

I made this circuit and it doesnt seem to be working. i plug it into the tach wire and it goes to one spot then stays there like the frequency is staying the same. it also looks like i used polyester caps instead of polypropylene, could this be why?

Bujholm (author)2013-05-28

built it, tested it - it works! as simple as that.

vijayapriya (author)2013-04-24

this schematic is wrong plz help me!!!!! see lm3914 two 2, 4, 8
tell me is it work?

cEcKo0 (author)2013-02-27

Hello, I want to ask does it works on Aprilia Scarabeo 50cc 2t 97? If it does work how to connect it? Thanks! :)

rkrz (author)2013-02-06

hey..broo.. i need to know that ... can i use this for my 12000 rpm motorcycle... if not please help me to alter this circuit...

thanks .. hav nic dae.. :)

thaivg (author)2013-01-14

I just completed Led drive part of this circuit, but I have a problem: I use 20 cm leads to connect from IC 3914 to LED, all LED are lit when no input. The data sheet of 3914 instruct to connect 2 microF from +Led lead to pin 2(-) of IC but it can not fix the problem. Pls help me.

naruto813 (author)2012-10-26

can this also be used on an electric wheelchair?

gkim12 (author)2012-10-20

do you have a step by step instructional of what you did? if so could you possibly email it to me?

bajadma (author)2012-10-20

If want adjust to 1LED = 800 RPM How do make
thank you

keegancdr (author)2012-09-11

would this project be easy to hook up to a single cylinder engine like a motorcycle engine? if so where would i hook it up?

Ortzinator (author)2012-08-12

I made a Mouser project with everything except the resistors and capacitors. Let me know if anything is incorrect.

bmkhan (author)2012-08-03

Dear aoa, you have done a great job. Thumb Up.... Dear you have mentioned in tachometer gauge that signal should be from the negative of coil that means its negative signal in your. But sir mine engine produce positive signal for RPM so how should i solve this problem. Please also provide me your email.

keegancdr (author)2012-07-25

hey so ive never really purchased components like what you have here for your parts list, where is the best place to buy these? thank you very much, and for a total cost of the project you said it was about 6 dollars USD?

keegancdr (author)keegancdr2012-07-25

could you message me on my account so i remember where to look back, thanks again!

ysaddam (author)2012-05-10

i cant read your diagram sir. can you please mail me a circuit diagram? thank you

ludwig.svensson (author)ysaddam2012-06-06

Struggled with this a long time myself :P

About This Instructable




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