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Pulse Oximetry on the MSP430. Overview and Introduction What is Pulse Oximetry? Signal Characteristics Filtering Requirements MSP430 Features MSP430 Timing.

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Presentation on theme: "Pulse Oximetry on the MSP430. Overview and Introduction What is Pulse Oximetry? Signal Characteristics Filtering Requirements MSP430 Features MSP430 Timing."— Presentation transcript:

1 Pulse Oximetry on the MSP430

2 Overview and Introduction What is Pulse Oximetry? Signal Characteristics Filtering Requirements MSP430 Features MSP430 Timing SHARC comparison

3 Pulse Oximetry

4 Signal Characteristics Will detect a maximum heart rate of 200 BPM, which is 3.3 BPS Needs to sample at least double that (Nyquist), but 5-10 times ideally Will sample the signal at 32 Hz

5 Filtering Requirements - LPF at 3.3 Hz sampled at 32 Hz (16 tap, 32 tap, 1000 tap)

6 Filtering Requirements

7 MSP430 Features Higher End MSP430s have certain features that can make FIR filters significantly faster

8 MSP430 Timing Analysis With DMA setup it’s about 7 cycles / tap With no DMA setup it’s about 28 cycles / tap Tap SizeCPU Speed (Mhz)CPU Usage % % % % % % % % % % % % Tap SizeCPU Speed (Mhz)CPU Usage % % % % % % % % % % % %

9 MSP430 Timing Analysis We can slow down the clock to save power Tap SizeDMACPU Speed for 50% usage 32YES19.84kHz 32NO57.34kHz 50YES26.24kHz 50NO89.60kHz 100YES46.72kHz 100NO179.2kHz 1000YES467.2kHz 1000NO1.792Mhz

10 SHARC Comparison SHARC has a lot more features to make FIR quick (SIMD, parallel instructions, dm/pm, etc) When optimized the SHARC can do 0.5 cycles / FIR tap This is around 14 times faster than the fastest MSP430 setup In class we sample at 48 kHz. If we were to use an MSP430 with a 16 Mhz clock speed with 50% utilization, we could only use a 23 tap FIR. Obviously the MSP430 would not be suitable for our labs, but works well in this aplication

11 Conclusion MSP430 is an adequate solution for pulse oximetry due to it’s low sampling rate The clock speed can be lowered quite a bit to save power May be able to get by with a lower end MSP430 Chip, but there will be power trade offs Questions?

12 References Jeff Bachiochi, “Light to Frequency Conversion – TSL230R-Based Pulse Oximeter”, Circuit Cellar, Issue 173 & 174, Kripasagar Venkat, Efficient Multiplication and Division Using MSP430, (Texas Instruments, 2006), Kripasagar Venkat, Efficient MSP430 Code Synthesis for an FIR filter, (Texas Instruments, 2007), Murugavel Raju, Digital FIR Design Using the MSP430F16x (Texas Instruments, 2004), “Pulse Oximetry”, last modified September 10 th 2002, Texas Instruments, The MSP430 Hardware Multiplier, (Texas Instruments, 1999), Vincent Chan, Steve Underwood, A Single-Chip Pulseoximeter Design Using the MSP430, (Texas Instruments, 2012),


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