So for those that dont know what corner weight scales are, they are 4 pads that go under each wheel of your car and they all connect up to a central unit that takes reading from each pad and provides and nice interface to show you the weight of your car as a total, as well as front to rear and side to side percentages and a few other bits and pieces. Below is pics i found on the web of a typical setup, these range from $1500-$3000 from what i've seen of a quick google search.
- commercial scales1.png (455.05 KiB) Viewed 11283 times
- commercial scales2.png (456.55 KiB) Viewed 11283 times
So the thought process started around having scales to help set up the four link in the FX properly, and i queried VL400 about could a load cell be connected to the data logger analog inputs to make a basic scale reader, i figured even just a basic display of 4 weights would be better than nothing.
He quickly pointed out that a nextion screen would be a cool option and connects easily to an arduino which has the capacity to take inputs from wheel pads and drive the screen over serial, so i started looking into all the bits, the arduino was easy, i bought one years ago to play, did the blinking LED on it to confirm i could actually program it and then never really used it.
I also purchased a 4.3 inch nextion screen from ebay, these are made in heaps of sizes and this one was about $80 delivered.
- nextion.jpg (68.99 KiB) Viewed 11283 times
So i setup the bits and got a pot connected to one of the analog inputs to simulate the 0-5v input i would get from a load cell.
I quickly got bored of waiting for parts to arrive from china so i started making the white screen with 4 numbers on it a bit prettier
- screen1.jpg (270.79 KiB) Viewed 11283 times
Most of the numbers above are simulated but gives you an idea of what the layout can look like with these nextion screens.
- screen2.jpg (251.74 KiB) Viewed 11283 times
I set it up so when you click on the first image it changes to the second screen
[youtube]
https://www.youtube.com/watch?v=ZwMBLqrJ7p8[/youtube]
One of the parts i had been waiting for was a load cell interface to connect between the load cell and the arduino, these finally arrived last friday.
- load cell amp.jpg (18.13 KiB) Viewed 11283 times
So i plan to use these load cells, as they are nice and flat and these are very similar to what you find in commercial units., so i will make a steel plate to go on each side of it and some sides so it looks half professional
- load cell1.jpg (28.91 KiB) Viewed 11283 times
- load cell2.jpg (35.72 KiB) Viewed 11283 times
I connected up one of the load cells and put it in the vice to see what sort of readings i could get from it, i am not actually sure what these numbers mean as the load cell is up to 500kg ... so maybe 5000grams or something.... anyways the fact i can get increments from it as i apply load was the main test really.
- load cell data.jpg (28.95 KiB) Viewed 11283 times
Its still very much in the R&D phase but the plan is to mount it all in a jaycar box or similar and have the option of either a battery pack or just a 240v plug pack to drive it all.
I will probably make a PCB to plug the arudino and all the amps into and get them all linked up and powered through one PCB and then have plugs on the size of the box for each wheel pad to connect to.
so far the running totall is roughly:
nextion screen $80
arduino with usb $30
4 x load cell amplifiers $11
4 x cantilever load cells $220
there will be some more cost with steel for the pad and probably a bit more to fit it all into a box, but im hoping it can be complete for under $500
one thing i really love about it is the nextion screen is so configurable, the sky is the limit really and its about the same size as my samsung phone and probably very similar picture quality so its pretty cool in that regard!
