Scales and design - Page 5

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Espressoman007 (original poster)

#41: Post by Espressoman007 (original poster) »

I also found this:
http://www.youtube.com/watch?v=ex_WrPool_E
https://gerelectronics.com/product/yocto-bridge/

Pretty neat, and simple...and according to them, it works flawlessly. Not cheap though. Also they have WiFi module too...but that would raise the price even more. The only tricky thing would be how to install the load cell inside the base. Why these load cell aluminium blocks aren't thinner? I saw that measurements on some 12.7 mm.
https://gerelectronics.com/product/yoct ... reless-sr/

Cheers!

wojtowip
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#42: Post by wojtowip »

So I actually found a tear down of the Brewista II https://www.ifixit.com/Guide/Brewista+S ... bly/144334

I happen to have one on hand I'm not using, might be a good donner for a load cell. It's pretty low profile looking at it. Will try and use the 5kg load cel today that's 12.7mm thick to see how it goes, but the Brewista one looks like it's half the height of what I have. If I can attach it directly to the base of the Strietman, that would make for a fairly low profile built in scale. Though would require me to drill two holes in the platform. Wish I had a drill press and a workshop for something like this.
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jpender

#43: Post by jpender »

Espressoman007 wrote:Why these load cell aluminium blocks aren't thinner? I saw that measurements on some 12.7 mm.
You can buy thinner load cells. The one in my $20 pocket scale is 6mm thick. The one in the Brewista scale looks very similar. And thinner ones are available but quite a bit more expensive. The details of load cell design might be interesting. I wonder if a thinner one that is non-linear but can be corrected for in firmware is possible.

I'm not going to try make my own load cell though. I don't even want to make my own scale. But I might hack my extra scale to make it thinner.

wojtowip
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#44: Post by wojtowip »

So I started playing around with hooking up my Arduino to the scale. Got the display to work with a ATTiny85 module to work (but couldn't fit the scale and display drivers on the ATTiny85 :(, will probably need to see if I can get a smaller version of the scale code running to fit, I thin I was less than 500 bytes over the memory limit).

So I grabbed my trusty Arduino Uno, and I can get a reliable display reading and scale reading all at once. Works pretty well and is relatively stable. I can actually measure adding 0.1grams to the scale, though it's probably more accurate to 0.2grams with this particular load cell/amplifier combo. I could have also damaged the amplifier here, since I reversed the power connection the first time and it got kind of hot, oops :|.
Anyway, since this is mostly running, next steps:
1. Trim down the plexus glass platform to fit inside the CT2, already have a plan how to cut it out for testing this.
2. Order smaller load cells. I have 750g load cells from AliExpress on order. Should be here be December :(.

The smaller load cells are half the height of the current one, so with some plexiglass platform I'm calculating about 10-12mm total for the scale and display will be somewhere on the side. Seems like this might actually happen.
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jpender

#45: Post by jpender »

Nice job. How tall is it?

I thought at first you were saying you somehow got the FSR device to work to 0.1g precision. That would have been something!

wojtowip
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#46: Post by wojtowip » replying to jpender »

This one is huge, but I can get it down to about 18mm too tall, but will be able to fit it in the base. I'll try to hack it this week.

Once I get the new sensor I'll be down to about 10-12mm in height and very tiny foot print, so looking forward to that sensor. I've actually stayed up a bit longer and got nice smoothing working with it and get a timer going as well. Now all I need to do is build it for the smaller board.

I wish I got the force sensor to work, but I either got a dud or they are just this bad. Mine keeps on drifting with weight on it :(.
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jpender

#47: Post by jpender »

Why are piecing together load cell, display, processor, and firmware instead of hacking an existing scale? Is it just for the fun of it? Or is it because you want to add functionality?

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wojtowip
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#48: Post by wojtowip »

For the fun of it more or less. Maybe it's easier to break down a scale, but haven't had a chance to play with Arduinos in a while. Seemed like the logical choice at the time :).

Nothing like a rush of seeing a physical reading from something you hacked together.
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jpender

#49: Post by jpender »

It is geeky fun. I use an Arduino based widget every morning when I pull shots. It tells me the water temperature and the shot time and stores the data on an SD card if I want.

Is the scale code home brewed or did you find it somewhere?

wojtowip
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#50: Post by wojtowip »

I'm using HX711 amplifier and a library to communicate with it. Still working out firmware to get a steady reading and figure out how to do tearing and calibration on boot. I'll post the code on GitHub once I'm happy with it.

Now all I need is a 3d printer to make a case for the electronics :). Who knew I could combine so many hobbies together.
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