Erik - / Mbed 2 deprecated Si114x_HelloWorld

Example code to create a heartbeat sensor using the Si1146 on Silicon Lab's Biometrics expansion board for the Wonder Gecko

Dependencies:   EFM32_SegmentLCD Si114x mbed

main.cpp@1:b2b2924c3c48, 2015-08-25 (annotated)

Committer:
Sissors
Date:
Tue Aug 25 19:30:13 2015 +0000
Revision:
1:b2b2924c3c48
Parent:
0:f3705ec14cf0 
Improved heartbeat algorithmes.

Who changed what in which revision?

UserRevisionLine numberNew contents of line
Sissors 0:f3705ec14cf0 1 /*
Sissors 0:f3705ec14cf0 2 Heart rate example for the SiLabs biometrics board using the Si1146
Sissors 0:f3705ec14cf0 3
Sissors 0:f3705ec14cf0 4 Since their own example code is all hidden behind precompiled libraries, here an
Sissors 0:f3705ec14cf0 5 example which is actually useful :D. Take into account this is an example, I just screwed
Sissors 0:f3705ec14cf0 6 around a bit and observed some output waveforms to make it work reasonable, there are
Sissors 0:f3705ec14cf0 7 for sure better ways to implement this.
Sissors 0:f3705ec14cf0 8
Sissors 0:f3705ec14cf0 9 User manual:
Sissors 0:f3705ec14cf0 10 If the Gecko symbol turns on on the LCD it is connected to the sensor
Sissors 0:f3705ec14cf0 11 Place your finger on the sensor. In the biometrics board manual it is explained how,
Sissors 0:f3705ec14cf0 12 but you can also try until it works properly. You don't want to use the extreme tip of your
Sissors 0:f3705ec14cf0 13 finger, but a bit further back.
Sissors 0:f3705ec14cf0 14 The battery indicator will flash briefly when a beat is detected.
Sissors 0:f3705ec14cf0 15
Sissors 0:f3705ec14cf0 16 Every beat it re-calculates your heartbeat using the time of the previous beat, since no
Sissors 0:f3705ec14cf0 17 filtering happens here, it can jump around a bit, but this should be limitted.
Sissors 0:f3705ec14cf0 18
Sissors 0:f3705ec14cf0 19 And just to be sure since we can never overestimate human stupidity: This is not a medical tool...
Sissors 0:f3705ec14cf0 20
Sissors 0:f3705ec14cf0 21
Sissors 0:f3705ec14cf0 22 Todo:
Sissors 0:f3705ec14cf0 23 1. Get rid of my hardcoded value used as threshold
Sissors 0:f3705ec14cf0 24 2. Measure PO2
Sissors 0:f3705ec14cf0 25 */
Sissors 0:f3705ec14cf0 26
Sissors 0:f3705ec14cf0 27
Sissors 0:f3705ec14cf0 28 #include "mbed.h"
Sissors 0:f3705ec14cf0 29 #include "Si114x.h"
Sissors 0:f3705ec14cf0 30 #include "EFM32_SegmentLCD.h"
Sissors 0:f3705ec14cf0 31
Sissors 0:f3705ec14cf0 32
Sissors 0:f3705ec14cf0 33 DigitalOut myled(LED1);
Sissors 0:f3705ec14cf0 34 silabs::EFM32_SegmentLCD segmentDisplay;
Sissors 0:f3705ec14cf0 35
Sissors 0:f3705ec14cf0 36
Sissors 0:f3705ec14cf0 37 int main() {
Sissors 0:f3705ec14cf0 38 segmentDisplay.AllOff();
Sissors 0:f3705ec14cf0 39 Si114x sensor(PD6, PD7);
Sissors 0:f3705ec14cf0 40 while(sensor.verifyConnection() != 1);
Sissors 0:f3705ec14cf0 41 segmentDisplay.Symbol(LCD_SYMBOL_GECKO, 1);
Sissors 0:f3705ec14cf0 42
Sissors 0:f3705ec14cf0 43 int curval;
Sissors 0:f3705ec14cf0 44 int prevval = 0;
Sissors 0:f3705ec14cf0 45 int mvingavg[3] = {0};
Sissors 0:f3705ec14cf0 46 int sum;
Sissors 0:f3705ec14cf0 47 int prevtime = 0;
Sissors 0:f3705ec14cf0 48 int timesincelast;
Sissors 1:b2b2924c3c48 49 float abssum;
Sissors 1:b2b2924c3c48 50 float abssum_iir = 0.0f;
Sissors 0:f3705ec14cf0 51
Sissors 0:f3705ec14cf0 52 Timer timey;
Sissors 0:f3705ec14cf0 53 timey.start();
Sissors 0:f3705ec14cf0 54 while(1) {
Sissors 0:f3705ec14cf0 55 curval=sensor.getProximity(2); //We use visible light, seems to work alot better than IR
Sissors 0:f3705ec14cf0 56
Sissors 0:f3705ec14cf0 57 //Three times moving average of the diff of the output
Sissors 0:f3705ec14cf0 58 mvingavg[2] = mvingavg[1];
Sissors 0:f3705ec14cf0 59 mvingavg[1] = mvingavg[0];
Sissors 0:f3705ec14cf0 60 mvingavg[0] = curval - prevval;
Sissors 0:f3705ec14cf0 61 sum = mvingavg[2] + mvingavg[1] + mvingavg[0];
Sissors 0:f3705ec14cf0 62
Sissors 1:b2b2924c3c48 63 //Float val for abs(sum) to calculate threshold dynamically
Sissors 1:b2b2924c3c48 64 abssum = (float)abs(sum);
Sissors 1:b2b2924c3c48 65 abssum_iir = abssum_iir * 0.99f + abssum * 0.01f;
Sissors 1:b2b2924c3c48 66
Sissors 1:b2b2924c3c48 67 //Now we know the 'average' absolute 'noise' ( plus some part of the heartbeat)
Sissors 1:b2b2924c3c48 68 //We multiply this by four (yes randomly chosen) and use it as threshold for heartbeat
Sissors 1:b2b2924c3c48 69 //Possibly this is too much if you are really excited, but haven't been excited enough to check this
Sissors 1:b2b2924c3c48 70 if (sum < (int)(-4.0f * abssum_iir)) {
Sissors 0:f3705ec14cf0 71 segmentDisplay.Battery(4);
Sissors 0:f3705ec14cf0 72 timesincelast = timey.read_ms() - prevtime;
Sissors 0:f3705ec14cf0 73 if (timesincelast > 250) {
Sissors 0:f3705ec14cf0 74 uint32_t hearthrate = 60000 / timesincelast;
Sissors 0:f3705ec14cf0 75 segmentDisplay.Number(hearthrate);
Sissors 0:f3705ec14cf0 76 prevtime = timey.read_ms();
Sissors 0:f3705ec14cf0 77 }
Sissors 0:f3705ec14cf0 78 }
Sissors 0:f3705ec14cf0 79 else {
Sissors 0:f3705ec14cf0 80 segmentDisplay.Battery(0);
Sissors 0:f3705ec14cf0 81 }
Sissors 0:f3705ec14cf0 82
Sissors 0:f3705ec14cf0 83 prevval = curval;
Sissors 0:f3705ec14cf0 84
Sissors 0:f3705ec14cf0 85 }
Sissors 0:f3705ec14cf0 86
Sissors 0:f3705ec14cf0 87 }