1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
|
# SPDX-License-Identifier: LGPL-3.0-or-later
# Copyright (C) 2020 Daniel Thompson
import wasp
import array
import machine
class Biquad():
"""Direct Form II Biquad Filter"""
def __init__(self, b0, b1, b2, a1, a2):
self._coeff = (b0, b1, b2, a1, a2)
self._v1 = 0
self._v2 = 0
def step(self, x):
c = self._coeff
v1 = self._v1
v2 = self._v2
v = x - (c[3] * v1) - (c[4] * v2)
y = (c[0] * v) + (c[1] * v1) + (c[2] * v2)
self._v2 = v1
self._v1 = v
return y
class PTAGC():
"""Peak Tracking Automatic Gain Control
In order for the correlation checks to work correctly we must
aggressively reject spikes caused by fast DC steps. Setting a
threshold based on the median is very effective at killing
spikes but needs an extra 1k for sample storage which isn't
really plausible for a microcontroller.
"""
def __init__(self, start, decay, threshold):
self._peak = start
self._decay = decay
self._boost = 1 / decay
self._threshold = threshold
def step(self, spl):
# peak tracking
peak = self._peak
if abs(spl) > peak:
peak *= self._boost
else:
peak *= self._decay
self._peak = peak
# rejection filter (clipper)
threshold = self._threshold
if spl > (peak * threshold) or spl < (peak * -threshold):
return 0
# booster
spl = 100 * spl / (2 * peak)
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():
"""Heart Rate Sensing application.
"""
NAME = 'Heart'
def foreground(self):
"""Activate the application."""
wasp.watch.hrs.enable()
# There is no delay after the enable because the redraw should
# take long enough it is not needed
draw = wasp.watch.drawable
draw.fill()
draw.string('PPG graph', 0, 6, width=240)
self._hpf = Biquad(0.87033078, -1.74066156, 0.87033078, -1.72377617, 0.75754694)
self._agc = PTAGC(20, 0.971, 2)
self._lpf = Biquad(0.11595249, 0.23190498, 0.11595249, -0.72168143, 0.18549138)
self._x = 0
self._offset = wasp.watch.hrs.read_hrs()
self._hrdata = array.array('b')
wasp.system.request_tick(1000 // 8)
def background(self):
wasp.watch.hrs.disable()
del self._hpf
del self._agc
del self._lpf
def _subtick(self, ticks):
"""Notify the application that its periodic tick is due."""
draw = wasp.watch.drawable
spl = wasp.watch.hrs.read_hrs()
spl -= self._offset
spl = self._hpf.step(spl)
spl = self._agc.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
# If the maths goes wrong lets show it in the chart!
if spl > 100 or spl < -100:
color = 0xffff
if spl > 104 or spl < -104:
spl = 0
spl += 104
x = self._x
draw.fill(0, x, 32, 1, 208-spl)
draw.fill(color, x, 239-spl, 1, spl)
x += 2
if x >= 240:
x = 0
self._x = x
def tick(self, ticks):
"""This is an outrageous hack but, at present, the RTC can only
wake us up every 125ms so we implement sub-ticks using a regular
timer to ensure we can read the sensor at 24Hz.
"""
t = machine.Timer(id=1, period=8000000)
t.start()
self._subtick(1)
wasp.system.keep_awake()
while t.time() < 41666:
pass
self._subtick(1)
while t.time() < 83332:
pass
self._subtick(1)
t.stop()
del t
|
