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Member #114323

Member Since: January 9, 2010

Country: United States

  • SparkFun’s tutorials directly contributed to my successfully earning my MSEE after graduating 16 years ago with a BSME. And while I was in school, I heard many students express the opinion that the SparkFun tutorials were more valuable than the class lectures (for some topics). Keep it up!

  • Just a note for others: If you are planning on using these for a custom cape, and you need clearance above the ethernet jack, these are too short for a reliable connection. Samtec makes a version of this with a 14mm pin length that works well.

  • Diagonal bracing will fix most of your wobble problems. Just put the bracing in the same plane as the direction of the wobble you want to control.

    Here’s an example, from which you can extrapolate: http://www.howtospecialist.com/finishes/furniture/simple-desk-plans/

  • Like others here, I’m working on an arduino based data-logging scale. I’ve been reading up on load sensors and the sparkfun ADC tutorial, https://learn.sparkfun.com/tutorials/analog-to-digital-conversion to understand this. I thought I might post what I’ve learned and try to get feedback on the pitfalls, especially for the benefit of absolute beginners, like myself. I also found this to be informative: http://www.aandd.jp/products/weighing/loadcell/introduction/pdf/6-1.pdf

    First off, the 10 bit ADC on board the Arduino means that the maximum resolution from the Arduino is 110lbs/1024 (10 bits) = 0.107 lbs/4.88mV per step. If you need higher resolution, you’ll need a separate ADC. Also note that this is different from the accuracy of the sensor.

    Second, at full load, 110 lbs, with 5V excitation voltage, this sensor outputs 5mV. This means that without an amplifier, your arduino will probably read the analog pin as nearly zero, even at full load. As I understand it, you need a gain of 1,000 V/mv or 120 dB to amplify the voltage such that 0lbs = 0V and 110 lbs = 5V. Have I got that right?

    Third, the comprehensive error in this sensor is .05mv/V or .25mV for a 5V excitation circuit, this translates into an error of 5.5 lbs.

    Finally, from my reading, it looks like the voltage may vary on the arduino analog pins, so you need to be cautious with your calculations that when you convert the proportion to a weight that your proportion uses the correct reference voltage. Can someone point me to a reference for that?