Analog configuration on the puck.js?

Here you go:

var ll = require("NRF52LL");
// source of events - compare D31 against vref/2
var comp = ll.lpcomp({pin:D31,vref:8});
// A place to recieve events - a counter
var ctr = ll.timer(3,{type:"counter"});
// Set up and enable PPI
ll.ppiEnable(0, comp.eCross, ctr.tCount);
/* This function triggers a Task by hand to 'capture' the counter's value. It can then clear it and read back the relevant `cc` register */
function getCtr() {
  poke32(ctr.tCapture[0],1);
  poke32(ctr.tClear,1); // reset it
  return peek32(ctr.cc[0]);
}

// Every 10 seconds, wake and print out the number of crosses
setInterval(function() {
  print(getCtr());
}, 10000);

It configures hardware to count crosses using the comparator:

• You have to use pins with analog inputs - check the pinout page for the board you're using for info
  
• The voltage reference is in 16ths - so vref:8 is a half of VCC. You can also use another analog pin as a reference - proper docs in http://www.espruino.com/NRF52LL
  
• They are 32 bit counters, so you've got no issue with the counter overflowing
  
• It seems pretty low power - drawing around 100uA
  
  

Hope that helps!