# Help to convert sine wave to square wave

#### JLourenco

Joined Sep 27, 2012
3
Hello friends

I need one simply help, from you.

I would like to resused one old Tachometer from my car, but due to the fact of the car don´t have any sensor, I was thinking to use the alternator that it gives 210Hz at 750rpm it gives, for max rpm 5000rpm it gives 1290Hz. Amplitude is ~16V.
Now the tachometer accepted square wave whit 12V at maximum scale 7.000 rpm whit 233Hz, so for example the 3.100 rpm should be 103Hz: like the photo.

http://i236.photobucket.com/albums/ff166/PhantasticPhoto/img_3262_rs2.jpg

So my question, how can I make one simply wave converter whit frequency adapter, use the IC 741, but looks I can only have the same frequency?

Thanks,

JL

#### crutschow

Joined Mar 14, 2008
24,919
..............................

But as the RPM is not linear from your alternator, it will be giving the wrong value!
.......................
Not true. The alternator RPM is directly linear with the engine RPM (even though the alternator is going at a higher speed).

#### ErnieM

Joined Apr 24, 2011
8,041
So my question, how can I make one simply wave converter whit frequency adapter, use the IC 741, but looks I can only have the same frequency?
Any simple single transistor amp would work. It inverts the signal but that should not be an issue here.

(Sorry I don't have a nice figure handy to paste but probably someone else will in the next 5 minutes.)

#### THE_RB

Joined Feb 11, 2008
5,438
What is "whit"? Is that some silly ghetto slang for "with"?

Do you want to do frequency conversion? It sounds like it from trying to read your post.

If you need frequency conversion then it is a lot more complex than just trying to turn something into a square wave. There are lots of commercial speedo and tacho frequency converters on the market, probably about $80 to$90.

#### JLourenco

Joined Sep 27, 2012
3
Thanks guys,

For all your help, one question guys, if I use the 555 timer like Dodgydave say, can I adapted the frequency? what component should be variable?

Yes I supposed the frequency is linear on the alternator also the voltage is all the same 16V.

Sorry guys I now that I have see that Automotive projects are forbiden, but I suppose, If I am wrong please acceptes my appologies, that the forbiden is to unlegal projects, like copy electronics keys, etc etc...that is not my problem I dont want to do nothing ilegal, just a simple project to convert sine wave to square wave (pulse wave) and speciality to adapted the frequency to put my old tachometer working...

#### JLourenco

Joined Sep 27, 2012
3
Sorry friend,

My native language is not english is portughese, sorry my mistakes.

BR

What is "whit"? Is that some silly ghetto slang for "with"?

Do you want to do frequency conversion? It sounds like it from trying to read your post.

If you need frequency conversion then it is a lot more complex than just trying to turn something into a square wave. There are lots of commercial speedo and tacho frequency converters on the market, probably about $80 to$90.

#### Dodgydave

Joined Jun 22, 2012
9,155
inside your revcounter there will be an adjustable resistor to set the dislay,so you can use the 555 timer.