Capture the highest value of AIN? (track and hold)

MIOS programming (C)
1

What’s the best routine to capture the peak value from an analog in pin?

I’m working on a gesture-based instrument, in specific, a glove with a 3-axis accelerometer on it. It’s obviously impossible to maintain some kind of constant acceleration with one’s hand, so instead I want to choose a note based on how fast I move my hand along an axis.

That means taking the maximum (or minimum) AIN-reading each time it passes a threshold, like some kind of track-and-hold.

Here’s my first prototype, with an accelerometer, flex sensor and finger contacts using conductive thread:

This is just for testing, unlike my 2nd prototype below which has a proper glove, smaller case and TQFP (!) SMD PIC18F:

glovetest1.jpg
glovetest1.jpg1000×667 144 KB

glovetest1b.jpg
glovetest1b.jpg1000×667 160 KB

2

Nice work! :slight_smile:

I think that the a “deadband” algorithm would be sufficient, it’s already integrated into MIOS -> MIOS_AIN_DeadbandSet

You could also dynamically decrease the deadband if your application notices a fast movement, and set it to a higher value again if it stops.

The C implementation of the deadband can be found in the MIOS32 variant under: http://svnmios.midibox.org/filedetails.php?repname=svn.mios32&path=%2Ftrunk%2Fmios32%2FLPC17xx%2Fmios32_ain.c

This one even supports a “spike filter”, which could be helpful for your application as well! :slight_smile:

Best Regards, Thorsten.

3

Aha! That’s exactly what I needed. Thanks for those suggestions :)I’ll try them out tomorrow.