DIY: Build your own computer-based compression tester for $68 (or $100).
Thread Starter
What am I doing here?
Joined: Mar 2006
Posts: 3,606
Likes: 652
From: 2017 Miata RF Launch Edition
Hah yeah Arduino memory is hilarious. I was going to say take a raspberry pi, if you have no power constraints. Then you can run whatever you want. You can even put it in a gameboy case. Or an Arduino Méga, that should give you the 0-5v inputs you want and 256k?
As far a sample frequency, I think you need to sample far faster. 5hz works if you catch the peak exactly. The peak duration is tiny, like 5ms, so you need to sample at 200hz+ to confidently catch the max of each one.
You can use the old derivative method to find peaks. Anywhere where the slope is 0 is either a min or a max. Throw away the mins and you're set.
As for when to start recording, record the last x samples continuously, so the problem becomes detecting stops. This should be easier, you're just looking where X time has passed without peaks. The first few peaks are garbage anyway, the starter doesn't reach full speed until after a few revolutions.
As far a sample frequency, I think you need to sample far faster. 5hz works if you catch the peak exactly. The peak duration is tiny, like 5ms, so you need to sample at 200hz+ to confidently catch the max of each one.
You can use the old derivative method to find peaks. Anywhere where the slope is 0 is either a min or a max. Throw away the mins and you're set.
As for when to start recording, record the last x samples continuously, so the problem becomes detecting stops. This should be easier, you're just looking where X time has passed without peaks. The first few peaks are garbage anyway, the starter doesn't reach full speed until after a few revolutions.
I wasn't saying that I was going to sample at 5Hz, just that it was roughly the frequency of the peaks. I'm hoping the 48 MHz processor will be fast enough for our desired sample rate.
It's looking like the derivative method might be the conceptually easiest way. I think I can calculate the slope for X number of samples and watch for it to change from positive to negative.
Adding in a watchdog function to see if the pulses start/stop shouldn't be too hard. (famous last words)
I was never really an electronics or programming guy but I seem to be drifting that direction more and more.
Thread Starter
What am I doing here?
Joined: Mar 2006
Posts: 3,606
Likes: 652
From: 2017 Miata RF Launch Edition
Okay, I got some help brainstorming on /r/arduino and have a plan. Now I just need the time to actually write the code...
I'm playing around with CircuitMaker and will probably use that to host the project. I'm going to start a new thread when I get further along since this is a distinct project from what came before.
I'm playing around with CircuitMaker and will probably use that to host the project. I'm going to start a new thread when I get further along since this is a distinct project from what came before.
I realized I never posted the excel sheet I use with this tool to handle conversions, rpm, etc.
Here it is!
I did have to replace the pressure transducer because the original stopped transducing.
Here it is!
I did have to replace the pressure transducer because the original stopped transducing.
///// Upscale Zoom-Zoom
Joined: Nov 2009
Posts: 1,593
Likes: 190
From: Massachusetts
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