Idea for showing frequency or RPM as trace on am inexpensive scope

After watching one of Pico Automotive vids where Frank Massey showed the frequency of a MAF as a trace on the scope I realised that the most expensive Pico oscilloscpes and plot frequency ----really cool. It would be nice if more affordable scopes could do that as you could plot not just MAF frequency but RPM.
It occurred to me that old style electric analogue tachometers worked this way so I had a look around ebay low cost modules that convert frequency into a DC voltage . I have one ordered so it should an interesting experiment.

Subscribing to this for later. The Snap-On graphing meter will do this, but I've found that it can be glitchy at times. I've used it on a couple GM MAF sensors during a WOT snap, and saw drop-outs that caused me to needlessly replace a MAF sensor. :blush:

So far this idea has hit a dead end. I bought two modules to try it. The cheapest one eventually arrived and I found it works much too slowly to be of any use, the second one a more expensive type should respond much more quickly but so far I cannot get an output from it.

Hi Andy,

Sorry about resurrecting this old post, but is this still something you would be interested in pursuing?