Open Spirometry Network » hardware http://openspirometry.org Open-source, low-cost, web-guided spirometry Thu, 17 Dec 2009 21:38:38 +0000 en hourly 1 http://wordpress.org/?v=3.0.1 Implementing the ZMD signal conditioner http://openspirometry.org/2009/04/implementing-the-zmd-signal-conditioner/ http://openspirometry.org/2009/04/implementing-the-zmd-signal-conditioner/#comments Mon, 13 Apr 2009 05:39:22 +0000 admin http://openspirometry.org/?p=115 Last week we met with David Van Sickle and David Hubanks of ZMD America, Inc. – which has a Madison office – to discuss the possibility of utilizing one of ZMD’s signal conditioners in the spirometer circuitry. David H drew our attention to one in particular (the 31014), which costs only around $2.

There are numerous benefits to using a signal conditioner, including the ability to control the amplification of the sensor using software instead of physical op-amps, minimizing the components on and the size of our circuit board. The signal conditioners can also be calibrated to allow correction for sensor offset and temperature effects. Finally, the signal conditioner incorporates an A/D converter, allowing the output signal to be transmitted in the digital formats of either I2C or SPI. The 31014 signal conditioner produced by ZMD is specially designed for resistive bridge sensors, such as our differential pressure sensor.

The BME design team met with Eric Hoffman and Isaac Wiedmann of ZMD to learn how to connect the 31014 to our existing pressure sensor and how to use the various features of the chip. Isaac also demonstrated a personal project of his that uses a differential pressure sensor to calculate the velocity of a fluid flow through a tube. In his design, a flexible plastic tube has a small constriction where the second pressure is measured, causing a larger differential pressure between the inputs. The team connected this portion of his project to their pressure sensor and expired through the tube. The ZMD software collected the output, and the data was graphed on an Excel worksheet.

Flow-time figure

Flow-time figure

We’ll add technical details to the long neglected hardware section of the wiki soon. Many thanks to David H, Eric, and Isaac.

In the meantime, we’re turning our focus to the construction of the spirometer body. Once manufactured, we will attach sensor circuitry and correlate the signal output with known air flow rates. After correlation, the spirometer will be able to measure air flows through the tube in units of L/s. The team will then create software that will use this data to calculate air flow vs. volume graphs and important measurements such as FEV1 and FVC.

The team will be giving a poster presentation on May 1st in the UW-Madison Engineering Centers Building from 12-2PM. Please come say hello and check out their prototype; you’ll also be able to check out all the other great student design projects underway this semester.

- J Glynn

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