Digital Scale Strain Gauge Weight Sensor

We took a $20 digital scale from Target and hooked it up to an amplifier and a microcontroller. This video outlines taking apart the scale, wiring it to the amplifier, and the code, as well as an overview of the concepts behind strain gauges and Wheatstone bridges. There's a demo of two live scale apps written in Python near the end of the video.

For the source code or more information about our microcontroller kits, go to http://www.nerdkits.com/videos/weighs...

• Category

  Science & Technology

[nerdkits]

Using the bridge approach means that most of the external coupling influences will be common mode and will be canceled by the instrumentation amplifier. If you really get down to it, all you want to look at is the signal at the alternating drive frequency itself, so you could put a narrow bandpass filter around that frequency for the best noise rejection. But a simple low-pass filter set at about 5 to 10x the alternating frequency should be OK while allowing the signal to have time to settle.

[nerdkits]

We use two pins of the microcontroller to drive the bridge. These pins alternate between being +5V/GND and GND/+5V. So effectively, it looks like a 10V peak-to-peak square wave of AC voltage. This technique helps reduce the noise because electronic components tend to have significantly more noise at lower frequencies, which is called 1/f noise, as well as DC offsets. Hope that helps!

[3l3CTR0maniac]

How fast are you alternating these pins ?

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[aryan gupta]

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[janardanist]

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[zaincbs]

How much is the CAPACITOR VALUE

[mpatelrajkot]

btscale@gamil.com 

[mpatelrajkot]

sir i am mfg for electronic weighing scale in rajkot (india), my reqment is weighing card for class 1 or 2 (200000 counts) weighing scale with .56 inch7segment led in6 digit pls hepl me

[PistonPackingPete]

Very nice tutorial. Thank you.

(For chiquiviveros, the LM 741 op amp is generally regarded as obsolete, so there are better parts for the price. The TL081 is slightly newer and somewhat better. "The AD620 is a low cost, high accuracy instrumentation amplifier that requires only one external resistor to set gains of 1 to 10,000")

[TheGerardo74080]

hey dude do you know where can i see how its made an electronico weighing