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apps: heart: Initial heart rate detection

The algorithm is fairly crude and the GUI is pretty simple but, if you stay
still for 10 seconds, there's a good chance of an accurate pulse
reading.

Of course if you jog on the spot for ten seconds it more likely to
calculate how many steps per minutes you are performing!

Signed-off-by: Daniel Thompson <daniel@redfelineninja.org.uk>
This commit is contained in:
Daniel Thompson 2020-06-24 21:20:18 +01:00
parent b1faec667d
commit e6811bb693

View file

@ -2,6 +2,7 @@
# Copyright (C) 2020 Daniel Thompson # Copyright (C) 2020 Daniel Thompson
import wasp import wasp
import array
import machine import machine
class Biquad(): class Biquad():
@ -26,7 +27,7 @@ class Biquad():
class PTAGC(): class PTAGC():
"""Peak Tracking Automatic Gain Control """Peak Tracking Automatic Gain Control
In order for the correlation checks to work correctly we must In order for the correlation checks to work correctly we must
aggressively reject spikes caused by fast DC steps. Setting a aggressively reject spikes caused by fast DC steps. Setting a
threshold based on the median is very effective at killing threshold based on the median is very effective at killing
@ -39,7 +40,7 @@ class PTAGC():
self._boost = 1 / decay self._boost = 1 / decay
self._threshold = threshold self._threshold = threshold
def step(self, spl): def step(self, spl):
# peak tracking # peak tracking
peak = self._peak peak = self._peak
if abs(spl) > peak: if abs(spl) > peak:
@ -52,12 +53,62 @@ class PTAGC():
threshold = self._threshold threshold = self._threshold
if spl > (peak * threshold) or spl < (peak * -threshold): if spl > (peak * threshold) or spl < (peak * -threshold):
return 0 return 0
# booster # booster
spl = 100 * spl / (2 * peak) spl = 100 * spl / (2 * peak)
return spl return spl
def _compare(d1, d2, count, shift):
e = 0
for i in range(count):
d = d1[i] - d2[i]
e += d*d
return e
def compare(d, shift):
return _compare(d[shift:], d[:-shift], len(d)-shift, shift)
def trough(d, mn, mx):
z2 = compare(d, mn-2)
z1 = compare(d, mn-1)
for i in range(mn, mx+1):
z = compare(d, i)
if z2 > z1 and z1 < z:
return i
z2 = z1
z1 = z
return -1
def get_hrs(d):
din = memoryview(d)
# Search initially from ~210 to 30 bpm
t0 = trough(din, 7, 48)
if t0 < 0:
return None
# Check the second cycle ...
t1 = t0 * 2
t1 = trough(din, t1 - 5, t1 + 5)
if t1 < 0:
return None
# ... and the third
t2 = (t1 * 3) // 2
t2 = trough(din, t2 - 5, t2 + 4)
if t2 < 0:
return None
# If we can find a fourth cycle then use that for the extra
# precision otherwise report whatever we've found
t3 = (t2 * 4) // 3
t3 = trough(din, t3 - 4, t3 + 4)
if t3 < 0:
return (60 * 24 * 3) // t2
return (60 * 24 * 4) // t3
class HeartApp(): class HeartApp():
"""Heart Rate Sensing application. """Heart Rate Sensing application.
@ -74,13 +125,15 @@ class HeartApp():
draw.fill() draw.fill()
draw.string('PPG graph', 0, 6, width=240) draw.string('PPG graph', 0, 6, width=240)
self._hpf = Biquad(0.87518309, -1.75036618, 0.87518309, -1.73472577, 0.7660066) self._hpf = Biquad(0.87033078, -1.74066156, 0.87033078, -1.72377617, 0.75754694)
self._agc = PTAGC(20, 0.971, 2) self._agc = PTAGC(20, 0.971, 2)
self._lpf = Biquad(0.10873253, 0.21746505, 0.10873253, -0.76462555, 0.19955565) self._lpf = Biquad(0.11595249, 0.23190498, 0.11595249, -0.72168143, 0.18549138)
self._x = 0 self._x = 0
self._offset = wasp.watch.hrs.read_hrs() self._offset = wasp.watch.hrs.read_hrs()
self._hrdata = array.array('b')
wasp.system.request_tick(1000 // 8) wasp.system.request_tick(1000 // 8)
def background(self): def background(self):
@ -89,13 +142,22 @@ class HeartApp():
del self._agc del self._agc
del self._lpf del self._lpf
def _tick(self, ticks): def _subtick(self, ticks):
"""Notify the application that its periodic tick is due.""" """Notify the application that its periodic tick is due."""
draw = wasp.watch.drawable
spl = wasp.watch.hrs.read_hrs() spl = wasp.watch.hrs.read_hrs()
spl -= self._offset spl -= self._offset
spl = self._hpf.step(spl) spl = self._hpf.step(spl)
spl = self._agc.step(spl) spl = self._agc.step(spl)
spl = self._lpf.step(spl) spl = self._lpf.step(spl)
spl = int(spl)
self._hrdata.append(spl)
if len(self._hrdata) >= 240:
draw.string('{} bpm'.format(get_hrs(self._hrdata)), 0, 6, width=240)
del self._hrdata
self._hrdata = array.array('b')
color = 0xffc0 color = 0xffc0
@ -104,14 +166,11 @@ class HeartApp():
color = 0xffff color = 0xffff
if spl > 104 or spl < -104: if spl > 104 or spl < -104:
spl = 0 spl = 0
spl = int(spl) + 104 spl += 104
x = self._x x = self._x
draw = wasp.watch.drawable
draw.fill(0, x, 32, 1, 208-spl) draw.fill(0, x, 32, 1, 208-spl)
draw.fill(color, x, 239-spl, 1, spl) draw.fill(color, x, 239-spl, 1, spl)
x += 2 x += 2
if x >= 240: if x >= 240:
x = 0 x = 0
@ -124,16 +183,16 @@ class HeartApp():
""" """
t = machine.Timer(id=1, period=8000000) t = machine.Timer(id=1, period=8000000)
t.start() t.start()
self._tick(1) self._subtick(1)
wasp.system.keep_awake() wasp.system.keep_awake()
while t.time() < 41666: while t.time() < 41666:
pass pass
self._tick(1) self._subtick(1)
while t.time() < 83332: while t.time() < 83332:
pass pass
self._tick(1) self._subtick(1)
t.stop() t.stop()
del t del t