Hi Guys
I'm not really an electronics person but a mechanical engineer looking to build a DIY Strain gauge data logging kit. I want to mount several strain gauges on a machine during operation to log small displacements over time.
From what I can see ill need arduino UNO R3, SD card adaptor, amp and strain gauges.
I'm hoping to find a tutorial showing me how to do it. Does anyone know of any?
Thanks
look for HX711 libraries, tutorials and/or examples.
HX711 is a cheap specialized ADC IC for load cells.
I've made a reasonable accurate (4+ significant decimal digits) 4 platform scale that weighs small glass vials before and after filling and calculates the net (product) weight. The load cells are driven to full Arduino voltage in the +ve direction, the output is amplified (Av ~ 300) and read, and then the drive voltage is reversed, again reading the the amplified output. This effectively doubles the drive voltage, and removes any DC offset errors from the amplifier. Each load cell is read 32 X in each direction in a burst. The reading rate is determined by the time to do 256 analogRead() (~30 milliseconds for the whole burst of 256 readings). The +ve drive results for for each cell are added (unsigned integer required), as are the -ve results and, at the end of the burst, the two are subtracted.
The drive is a single FET H-bridge that drives all 4 load cells together. The H-bridge must saturate fully or a weight error results. The supply voltage is also measured and used to scale the readings to a the values they would have had had the drive voltage been exactly 5.0000 (or whatever).
The software calculates (in a calibrate mode) a scale factor for each load cell and stores it in EEPROM, and that scale factor, plus a little arithmetic, produces a result in grams.
In this application, the weight data is sent as a string to a Mac which logs the weights.