Avatar for JonBray


Member since Dec 2019 • Last active Apr 2020
  • 1 conversations

Vet(erinary surgeon) and Amateur programmer

Most recent activity

  • in Bangle.js
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    Thanks. I'm not sure comparing BPM values would work as the variability is fairly slight, and would be masked by reading multiple pulses in a row.

    Going to carry on playing with my puck for a bit, but pretty sure I know what my next watch is going to be :-)

  • in Bangle.js
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    Apparently the variability between inter-heartbeat frequency is quite a good indicator of stress.

    Do you know if its possible to access the data to this degree, or is it a matter of asking the heartbeat sensor for a heart rate and getting an answer?

    (You'd need a kind of OnPulse watcher!)

  • in Interfacing
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    That's OK - the puck.js is battery powered so doesn't have any external power supply.

    I don't think I need to be worried about current from the puck going through my body - even if I made the electrodes sharp enough to penetrate skin in two points (which I think brings body resistance down to about 500 ohms) we're still only talking 6.6mA from a 3.3v battery.

    Your point about static is appreciated (I must admit I've been very lax about the way I handle arduinos, compared to the paranoia with which I handle the insides of PCs!)

    Does touching the ground pin first do anything in this situation (ie when there is no proper route to earth?) Or are you talking about touching a "proper" earth such as a nearby radiator pipe before attaching the device?

  • in Interfacing
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    Thanks for your help everybody. Using D1 seems to work fine - although now, rather than using the grove device, I've also found this project:


    ...which also seems to work fine on 3.3V and has the advantage of being so simple that one can solder all the components into the cable (the insulation is drying as we speak, but had it working fine with the puck.js via breadboard!).

    With 3.3v I make the maximum draw through the resistors to be 0.016 mA. Maximum draw through the skin (assuming 1kOhm when wet) is 3.3mA, so very low power.

  • in Puck.js, Pixl.js and MDBT42
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    Thanks - and yes, that's the correct GSR device. I've got no shortage on pins I can use for this (as there isn't going to be anything else connected to the espruino). I was planning on using the Puck BTW.

    Yes, my vision started to blur a little when investigating skin capacitance too! I guess all I really need is for a reliably measurable change in capacitance as the skin gets sweatier - it doesn't need to be linear, it just needs a cut-off point where it sends an alert. So I think I'll try that first in the interests of reducing the number of components available to stick into my poor patient zero!

    Thanks again to both of you! I'll let you know what works.

  • in Puck.js, Pixl.js and MDBT42
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    Thanks; that makes sense and its handy to know the max current; I've posted on the Seeedstudio board as well so hopefully they will come back with the max current drain. I hadn't thought of using multiple pins; good idea.

    And I had no idea that it was important to set the pins to input before powering off, so glad I asked here before continuing!

    Just checking, do I do that with something like:

    pinMode("D1", "output");
    pinMode("D1", "input_pulldown");

    as per the Digital Dice tutorial? Specifically, should it be input_pulldown or input_pullup (Sorry, I'm sure you were clear in line 4 of your answer to someone with a bit more electronics knowledge than I have!)?



  • in Puck.js, Pixl.js and MDBT42
    Avatar for JonBray

    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? :-)