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Sat 2019.12.28
'I've got a GSR from Seeedstudio which needs 3.3V to power it - can I do this from one of the digital IOs'
I personally don't like driving external chips/modules using the micro itself, as all those electrons need to flow somewhwere and therefore like to cook (shorten the life expectancy somewhat - but by how much might be unknown) the micro with dissipated heat when driven by those pins. I like to keep things extremely cool, and dissipate heat with buck converters or voltage regulators. As @allObjects has successfully done, it would be possible, but with at least two I/O pins under the following assumptions:
As no datasheet link for the GSR was provided, I took the first five star Google response and ended with this:
https://www.seeedstudio.com/Grove-GSR-sensor-p-1614.html.html
So, if that is the device/module, then at least 20mA will be required (at least by the LM324 as no module datasheet is available)
'Kudos for inventing this extremely cool bit of kit BTW'
Which Espruino board was intended to be used?
'Alternatively, am I right in thinking that skin capacitance varies with moisture in the same way that resistance does?'
Curiosity started me searching, but realized to find the definitive answer will take me too far down this rabbit hole. Short answer - yes but too many factors to consider
See Fig 2a
https://www.sciencedirect.com/science/article/pii/S0006349598740081
https://core.ac.uk/download/pdf/82613398.pdf
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2763825/
"The skin acts like an electrical device such as a capacitor in that it allows more current to flow if a voltage is changing rapidly"
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Robin
I'm also looking at doing a health app of sorts - turns out that quite a lot of people with type 1 diabetes get very sweaty when they're having a hypoglycaemic episode. So I'm looking to create a galvanic skin response reader (with DroidScript android app to do the alerting).
I've got a GSR from Seeedstudio which needs 3.3V to power it - can I do this from one of the digital IOs (which means I can turn it off when not reading to save power?)
Alternatively, am I right in thinking that skin capacitance varies with moisture in the same way that resistance does? IOW can I dispense with the separate GSR altogether and just use capsense?
The other part of this project (unfortunately the end-user I have in mind has deteriorating eyesight) is a simple bit of code (actually running on the Android) which counts the number of consecutive button presses and then performs tasks based on this (so 1 click is open google assistant, 2 clicks is say time, 4 clicks to phone a particular number, 5 clicks is get GPS location and send an email with a link to that location on google maps etc)
Kudos for inventing this extremely cool bit of kit BTW - my first attempts faltered when I realised how awkward it was going to be to put arduino plus bluetooth breakount plus GSR plus battery back in wearable form that was technophobe-friendly!
Has anyone done a 3D design for a star-trek communicator badge yet? :-)