Post ABf2ceEsZWI9ldwKmG by yuki@lgbt.io
 (DIR) More posts by yuki@lgbt.io
 (DIR) Post #ABf2ceEsZWI9ldwKmG by yuki@lgbt.io
       2021-09-23T15:36:04Z
       
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       Today while I was exercising I reminded my hands from the sensor handle for around a minute. When I put them back, it took a while to reveal my pulse. It slowly began to raise from 0 to 130bpm.After thinking it for a while, I realized why: The bpm counter uses an analog to digital converter, and it's calibrated to a certain voltage.Everytime my heart beats, it amplifies theelectrical pulse and feeds it to a small charge capacitor so that the voltage between its terminals can remain relatively stable; then the ADC measures the voltage and gives you the pulse in bpm.Much simpler circuitry than I had imagined.Ingenious! 🤓#electronics
       
 (DIR) Post #ABf2cejMkAg7ICCgIS by sullybiker@sully.site
       2021-09-23T18:08:21Z
       
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       @yuki I have two, a chest strap (conductive) and my fitbit (uses an LED array on the skin). The chest strap does this weird thing where for about five minutes (before you perspire enough to get good conductivity) it underreads by exactly half.
       
 (DIR) Post #ABf2cfzM4D3vC4gxrE by yuki@lgbt.io
       2021-09-23T18:04:27Z
       
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       Errata: reminded -> removed
       
 (DIR) Post #ABf2iE24v5diE8bzrU by sullybiker@sully.site
       2021-09-23T18:09:24Z
       
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       @yuki The wrist one gets similar numbers but fitbit do not provide an open API for non google shit so my bike head unit can't read it, hence the chest strap...