Looking for a Low Cost Frequency Counter Circuit?

So I was looking for a device that can measure the rpm of my car. There are some that I found on electronics hardware, but they’re quite expensive! So I did some research and lots of googling to find some ways and alternatives so I can have a device for my beloved mini copper.

What I wanted for my frequency counter is that, I wanted the device to be able to observe and oscillator’s accuracy, it can measure the mains frequency and can find out the rpm of a motor that is connected to an encoder. It’s typically and all-around frequency counters.

I did a lot of research and found this interesting tut about how to build your own frequency counter circuit. What I love about this DIY frequency counter is that the cost will be low.

The project we will be making is just a basic, low cost frequency counter circuit. The device can measure 16Hz to 100Hz signals with maximum amplitude of 15V.  The device’s sensitivity is high, with resolution of 0.01Hz as stated by the tutorial. The input signal can be a sine, a square or a triangle waveform.

I've also found this document by Wolfgang "Wolf" Büscher, Frequency counter with a PIC and minimum hardware, it's also a good alternative, but on a much higher price for the parts.

So now let’s get started and make our hands dirty.