利用“数字心率传感器(IC)”检测心跳信号- iOS
我刚刚购买了数字心率传感器： http://www.dealextreme .com/p/digital-heart-beat-rate-sensor-3-5mm-data-port-16009 我正在寻找如何制作适用于 iOS 的应用程序。
传感器有 3.5mm 插孔，我可以在 iOS 上使用音频框架检测信号。
您能给我一些如何开始检测心率信号的指导吗？
I just bought Digital heart beat rate sensor:
http://www.dealextreme.com/p/digital-heart-beat-rate-sensor-3-5mm-data-port-16009
And I'm looking how I can make application for iOS to work with.
Sensor has 3.5mm jack and I can detect signal with audio framework on iOS.
Can you give me some guidelines how to start with detecting these signals into heart beat rates?
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该传感器看起来很像我垃圾箱里的传感器。如果是这样，它会产生一个电压信号，该信号取决于其所压的皮肤施加在其上的压力。如果在压力点有强脉冲，我会在示波器上看到一个信号，该信号具有脉冲频率的分量：因此它的频率约为 1-2Hz。
这远低于音频范围，并且在大多数音频接口中，它会在到达 ADC 中的音频之前被过滤掉。我没有方便的 iPhone 来检查这一点，但如果音频输入确实让这样的频率通过，那将是糟糕的设计。乔布斯先生（RIP）并不赞成糟糕的设计！
其他频率也存在很多干扰：电源嗡嗡声（此处为 50Hz），以及较低频率的肌肉抽搐产生的杂散信号。
为了实现这一点，您需要某种信号调节。如果由我决定，我会使用一个高输入阻抗放大器，通带约为 0.1Hz - 10Hz，然后是一个电压频率转换器。这会给我一个音调，我可以在音频带中设置该音调，其频率向上和向下变化。随着传感器上的压力变化而下降。这将使我可以使用相当简单的频率检测软件来恢复压力波形，然后可以使用自相关或类似技术对其进行处理以恢复心跳频率。不过，DTMF 解码器并不是正确的工具。
当我玩弄传感器时，我确实发现它非常敏感，几乎对所有发生的事情都有反应，而且很难辨别出心跳。不过，您的传感器可能有所不同。
That sensor looks rather like one I have here in my junk box. If so, it generates a voltage signal which depends on the pressure exerted on it by the skin against which it is pressed. If there is a strong pulse at the point of pressure, I see a signal on an oscilloscope which has a component at the pulse rate: so it is at a frequency of around 1-2Hz.
This is WAY below the audio range, and in most audio interfaces would be filtered out before it ever got to the audio in ADC. I don't have a handy iPhone to check this on, but it would be bad design if the audio input did let such frequencies through. And Mr Jobs (R.I.P.) did not approve of bad design!
There is also a lot of interference at other frequencies: mains hum (50Hz here), and at lower frequencies spurious signals from muscle twitches.
To make this work, you would need some sort of signal conditioning. If it was up to me, I would use a high input impedance amplifier, with about a 0.1Hz - 10Hz passband, followed by a voltage to frequency converter. That would give me a tone, which i could set in the audio band, whose frequency varied up & down as the pressure on the sensor changes. That would let me use fairly simple frequency detection software to recover the pressure waveform, which could then be processed using autocorrelation or similar techniques to recover the heartbeat frequency. A DTMF decoder is not the right tool, though.
I did find when I played about with the senor that it was very touchy, responding to almost everything going, and it wouldn't be easy to pick out the heartbeat. Your sensor may be different, though.