[chbot] Data filter

Marshland Engineering marshland at marshland.co.nz
Tue May 11 23:11:29 BST 2021

This is one of those projects where you learn what is required while doing the

Make sure you have had you coffee fix before reading on !!   

This is version 2 of my dyno both hardware and software. The old version was a
bought package that used a freq to voltage converter and then an A to D
converter for the input to the PC but the resolution was very poor and I had
to do a lot of fiddling with higher power bikes to get reasonable data.  

My idea with this version is to get as high a resolution as I can, however,
what this has highlighted is, how many samples do you need for an A4 page size
graph, and what kind of resolution do I need?

Here is my data with my current parameters.


If you have some time to spare, here is my logic and happy for it to be picked
to pieces. 

The drum speed goes from 45 to 65 kph over 4 seconds. Or 12.5 to 18 m/s. I'm
sampling at 30 hz

Over the time period, I take 120 samples. That should be enough for an A4. 
The average rate of change of each sample is 0.17 kph or 47 mm/s. If I take
the 0.17m over the average speed range of 55, it is
1/330 or 0.3 %. That is quite optimistic for dyno, but it where I'm starting. 

Each timing period from the drum represents 200mm on the surface and the
ATMEGA can count up to 65535 clock cycles in this period.  My resolution with
the ATMEGA is therefore  0.003 mm per clock cycle.  

I think I have enough resolution for what I want. 

One of the problems is that the wheel to drum, engine speed changes etc are
not exactly linear. I believe this is where the noise is from, however, the
data below the noise is valid.  

I can improve the plots by fewer samples, ie getting a bigger rate of change
between samples but then my resolution will decrease. Maybe 30 hz is too high
and 0.3 % too optimistic. 

If not, what filters can I use to smooth the data ? I've looked at a lot of
them but creating the maths code to use them is a bit beyond my scope at the
moment.  I'm using Delphi and I cant find any Components for smoothing. 

The best I found was taking 10 samples, deleting the max and min and averaging
the rest. If I did that a second time with the result, it wasn't that bad but
still looking for a better solution. 

Cheers Wallace 

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