Automatic weighing machine

Question

Hi friends

For my high school project.

I want to build a automatic weighing machine which shows the avarage of every 20 weights it weighed and calculate the standard diviation of each weight with avarage weight.

I want It should show the data on a display .

I am working with microprocessor and load cell with calibration system and a step-down circuit to have 5 voltage.

Can you help me

I am a beginner.

Is it possible to feed such program in microprocessor/controller ?

to choose which microprocessor would be good to burn the avarage calculation program in to it?.

Should I use Ardino to do the job ?

fmilburn · Answer

This is an ideal task for microcontrollers and there are many that could do it including the Arduino. An Arduino has some advantages for a beginner in that there are lots of code examples on the internet and in your case it will work with 5V easily. There are shields made especially for the Arduino to use with load cells, e.g. https://learn.sparkfun.com/tutorials/load-cell-amplifier-hx711-breakout-hookup-guide?_ga=2.71342740.681789251.1539186257… Good luck with your project.... Frank

dougw · Answer

As Frank points out, your project could be performed entirely with an arduino. Here is another tutorial:

https://www.robotshop.com/community/blog/show/interfacing-a-load-cell-with-an-arduino-board

Another approach would be to use the arduino to read a load cell as these tutorials show and then send the readings to a PC to do the averaging and standard deviation calculations in Excel. It depends whether you find it easier to program an Excel macro to read in data and do the math or to program the arduino to do the math and display the results.

This sounds like a pretty ambitious high school project. It will be impressive if you get it working. Good luck. And ask more questions if there is anything tripping you up.

michaelkellett · Answer

Doug's suggestion is a good one to get started. I had a quick look at this board. It's very hard to find a schematic (none in the downloadable documentation) but they do almost admit what parts they use. AD8426 diff amplifier and unnamed buffer amplifiers with Arduino 10 bit ADC. It's pretty cheap ($20) but limited. Don't expect to get better resolution than 1 part in 500 (and with a cheap load cell it will be worse because the offset can be quite large) so the weighing range will be limited. If you can live with those limitations it's about as simple a way of doing it as you'll find. To put it in perspective, I'm working on a weighing project for a customer and it uses Microchip MCP6V64 chopper amplifiers with an ADS131A02 24 bit ADC. The Microchip amplifier is cheaper than the AD8426 but does need two additional precision resistors - still works out cheaper for much better performance. This system gives a resolution of better than 1:50000. There are reasons that real weighing systems go this far, and one of them is that pretty much every weighing scale you see in a shop uses zero tracking - so that slow drift of the zero load error can be cancelled out as the scale is working. If they didn't do that they would be forever having to re-zero the scale. To make zero tracking work you need a resolution of about e/10 (e is legal metrology jargon for the smallest displayed division on your scale.) If you go for the Robotshop board and they give you a schematic then post it here and we can advise you of any simple tweaks or pitfalls. What will you be weighing in your project ? MK

michaelkellett · Answer

Good call Frank ! I've not seen that chip before (or used it) but it's spec (although not quite complete) looks pretty good. I would think it a much better bet for Shaik than the Robotshop one. The Sparkfun support, and the price, are is no bad thing either. MK

fmilburn · Answer

The SparkFun board is $10. Schematic is here . Elecrow appears to sell something similar for $1.98. They also have the schematic and datasheet for the HX711. I have not used either.

Automatic weighing machine

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