トランジスタ技術2014年10月号第6章のソフトウェア
Information
tg_201410s6_Plethysmographs トランジスタ技術 2014年 10月号 第6章のソフトウェア
Program for Section 6 in October. 2014 issue of the Transistor Gijutsu
(Japanese electronics magazine)
概要
このプログラムは、
- 脈波データ取得(A-Dサンプリング、ハイパスフィルタ)
- 脈拍数の算出(パルス検出、LEDおよび同期音出力、移動平均処理)
を行うPulseRateクラスと、それらをUSBシリアル通信でホストへ送信するmain関数で構成されています。
PulseRate.h, PulseRate.cpp
- A-Dサンプリング - 100 SPS
- ハイパスフィルタ - 遮断周波数0.1Hz、1次バターワースフィルタ
- パルス検出 - 脈波を微分処理、5point移動平均して速度脈波を求め、
それを包絡線検波した波形を、速度脈波が再び超える点をパルス開始とする - LED、同期音出力 - パルス同期LED(10ms)、圧電サウンダ出力(1kHz、10ms)
- 移動平均処理 - 直近5拍分の平均値を脈波として算出
main.cpp
- PulseRateクラスのインスタンスを生成
- 処理開始メソッドを実行
- メインループ - ポーリングにより、脈波データ、脈拍数データの完了フラグが返されたら、
USBシリアル通信経由で、ホストへ送信する
シリアル通信フォーマット
- 4byte固定長パケット方式
- 脈波データパケット、脈拍数データパケットの2種類
脈波データパケット | 脈拍数データパケット | |
0x00 | パケットヘッダ(固定値0xAA) | パケットヘッダ(固定値0xAA) |
0x01 | 波形番号(0 - 99繰り返し) | 脈拍数ID(固定値0xBB) |
0x02, 0x03 | 脈波データ(singed, 2byte) | 脈拍数データ(20 - 300, 2byte) |
Description
This contains PulseRate class and main function.
PulseRate class:
- Acquiring pulse waveform (A-D sampling, high pass filter)
- Calculate pulse rate (Detecting pulse, Sync. LED and buzzer, moving averaging)
Main function:
- Send pulse waveform and rate to host via USB serial class.
PulseRate.h, PulseRate.cpp
- A-D sampling - 100 SPS
- High pass filter - Cut off frequency 0.1Hz, first order butterworth
- Detecting pulse - Calculating velocity pulse waveform by derivation and moving averaging (5point).
Moreover, calculating threshold waveform like envelope demodulator.
Detecting point the velocity waveform pass over the threshold waveform as starting pulse. - Sync. LED, buzzer - Synchronous pulse LED(10ms), piezo sounder(1kHz, 10ms)
- Moving averaging - Calculating pulse rate averaging the previous 5 pulse.
main.cpp
- Generating an instance of PulseRate class
- Executing start procedure method
- Main loop - sending pulse waveform data and pulse rate data via USB serial interface when detecting ready in return value.
Packet format for USB serial interface
- Packet size: 4 bytes(fixed)
- Two types of packets, pulse waveform packet and pulse rate packet
Pulse waveform packet | Pulse rate packet | |
0x00 | Packet header (0xAA (fixed))) | Packet header (0xAA (fixed)) |
0x01 | Sampling number (0 - 99) | Pulse rate ID (0xBB (fixed)) |
0x02, 0x03 | Pulse waveform data (singed, 2byte) | Pulse rate data (20 - 300, 2byte) |
PulseRate.cpp
- Committer:
- t_tatsuoka
- Date:
- 2014-09-11
- Revision:
- 0:f0c12790aadb
File content as of revision 0:f0c12790aadb:
/** * @file PulseRate.cpp * @brief Calculate pulse waveform and pulse rate * @date 2014.08.08 * @version 1.0.0 */ #include "PulseRate.h" /** Constructor * @param sensor Pin for A/D converter * @param sync_led Pin for synchronous LED * @param beep Pin for piezo sounder */ PulseRate::PulseRate(PinName sensor, PinName sync_led, PinName beep) : _sensor(sensor), _sync_led(sync_led), _beep(beep) { _sync_led = LED_OFF; _val = 0; _wave_flag = false; _pr_flag = false; _sampling_num = 0; _mv_idx = 0; _beep.period(1.0/BEEP_FREQ); } /** Start interval timer */ void PulseRate::start_sampling() { _sampling.attach(this, &PulseRate::interval_timer, SAMPLING_RATE); } /** Get waveform data * @param &num Sampling number * @param &wave_val Waveform value * @retval true Ready for data * @retval false Not ready */ bool PulseRate::get_wave(uint32_t &num, int32_t &wave_val) { if(_wave_flag) { _wave_flag = false; num = _sampling_num; wave_val = _val; return true; } else { return false; } } /** Gat pulse rate * @param &pr Pulse rate * @retval true Ready for data * @retval false Not ready */ bool PulseRate::get_pr_val(uint32_t &pr) { if(_pr_flag) { _pr_flag = false; pr = _pr; return true; } else { return false; } } /** Interval timer */ void PulseRate::interval_timer() { /* Pulse waveform */ _val = ((int32_t)(_sensor.read_u16()) - AD_OFFSET); /* Get AD value */ _val = hpf(_val); /* High pass filter (Comment out if not necessary) */ _sampling_num = (_sampling_num + 1) % SPL_NUM; /* Update sampling number */ _wave_flag = true; /* Set ready flag for pulse waveform */ /* Pulse rate */ if(detect_peak(_val)) { /* If detecting pulse */ calc_pr(); /* Calculate pulse rate including flag set */ } /* Control LED and Beep */ if(_pr_flag) { _sync_led = LED_ON; _beep.write(BEEP_LOUD); } else { _sync_led = LED_OFF; _beep.write(0); } } /** Fixed point high pass filter * @param val Input value * @return Output value * * A/D value of mbed is Q6 format. * Please shift in advance if necessary. */ int32_t PulseRate::hpf(int32_t val) { int32_t reg, ret_val; int64_t temp_val; temp_val = (int64_t)COEF_AH * (int64_t)_reg_hpf; reg = val + (int32_t)(temp_val >> 30); ret_val = reg - _reg_hpf; temp_val = (int64_t)COEF_BH * (int64_t)ret_val; ret_val = (int32_t)(temp_val >> 30); _reg_hpf = reg; return ret_val; } /** Detect pulse peak * @param &val Waveform data value * @retval true Detected pulse peak * @retval false No detection */ bool PulseRate::detect_peak(int32_t val) { int i; bool retVal = false; /* Calculate differential of input value */ _mv_buf[_mv_idx] = val - _prev_val; _prev_val = val; _mv_idx = (_mv_idx + 1) % MV_LENGTH; /* Calculate moving averaging */ _detect_val = 0; for(i=0; i<MV_LENGTH; i++) { _detect_val += _mv_buf[i]; } _detect_val = _detect_val / MV_LENGTH; /* Calculate exponential decline for threshold line */ _threshold_val = (int32_t)((double)_prev_th_val * TH_COEF); if(_detect_val >= _threshold_val) { /* If exceeding threshold */ if(_prev_dt_val < _prev_th_val){ /* If previous value is under threshold and over ignore value */ if((_detect_val > PEAK_MIN) && (_pr_counter >= PR_INT_MIN)) { /* Detecting peak!!! */ retVal = true; } } /* Previous threshold value is set to input value */ _prev_th_val = _detect_val; } else { /* Previous threshold value is set to decline value */ _prev_th_val = _threshold_val; } /* Update previous input value */ _prev_dt_val = _detect_val; /* Increment pulse rate counter */ _pr_counter++; return retVal; } /** Calculate pulse rate */ void PulseRate::calc_pr() { int i; /* If pulse rate counter is within maximum value */ if(_pr_counter <= PR_INT_MAX) { /* Calculate moving averaging */ _pr_buf[_pr_idx] = _pr_counter; _pr_idx = (_pr_idx + 1) % PR_LENGTH; _pr = 0; for(i=0; i<PR_LENGTH; i++) { _pr += _pr_buf[i]; } /* Set pulse rate value */ _pr = PR_1MIN_SPL * PR_LENGTH / _pr; } else { /* Pulse rate is set to invalid value */ _pr = 0; } _pr_counter = 0; /* Set pulse rate flag */ _pr_flag = true; }