I am trying to build a ball sorter. There are two types of ball I need to sort; one made of acetal the other nylon. Both are 20mm in diameter. I don't have the balls to hand but I need this built beforehand. I've calculated the acetal ball to weigh approximately 5.8g and the nylon ball to weigh 4.6g. The way my machine will work is the balls will come in along a channel and be fed one at a time via an aperture (piece of card + servo). The fed ball will land on a scale, be weighed and push into its respective container.
I figured I could do this with a load cell, two servos and an Arduino. I looked online in case someone had already done it before and sure enough there were a few applicable projects out there. After reading through one of them I got the parts I needed.
- Oomlout ARDX kit with Arduino UNO
- 1kg digital jewellers scale with 0.1g accuracy off eBay
- BurrBrown INA125P amplifier
To start with I followed the guide by Christian here and ended up with this: http://imgur.com/a/tfskO#0 This worked to an extent but required a 500g mass to produce a noticeable reading. I read the guides/blogs again and changed the gain resistor from 10 ohms to 560 ohms (the next highest I had was 2.2 kilo-ohms), added analogReference(INTERNAL) to my code and averaged a sample of 50 before printing to the serial monitor. Now I could detect 5g changes.
Next instead of using the 5v on the Arduino I used the scale's own excitation power (close enough to be 2 volts) instead (it also meant I could see the weight on the scale too). This brought down the readings from around 140 to 60 on the serial monitor but still no improvement in the resolution. I need at least 1g accuracy (0.1g would be excellent) which I haven't been able to achieve. From what I understand I need to adjust my reference voltage and my gain resistance to get the accuracy I need. This is where I need your help because although I can take apart, fix and improve all things mechanical my knowledge of electrical principles is pretty much ends with Kirchhoff’s and Ohms Laws. I am technically minded so don't worry too much about me not understanding explanations and requests for more information.
[u]Links to what I have looked at (the hw2sw.com stuff seems to be the most useful/rich):[/u] http://cerulean.dk/words/?page_id=42 http://www.elane.net/index.php?go=loadcell_amplifier# https://sites.google.com/site/vitorrosamd/load-cell-arduino-interface http://www.hw2sw.com/2011/10/20/weight-sensors-and-arduino/ http://www.hw2sw.com/2011/10/27/liquid-filling-machine-part-4/ http://www.hw2sw.com/filling-machine/
[u]Notes and images:[/u] http://imgur.com/a/tfskO#4