Espressoman007 wrote:Hm, there are several clips on YouTube where people use those load cells in projects, and it doesn't look complicated. There are projects about making DIY scales, and they need materials that you've mentioned, but also a few were far more simple. Just with reading weight, nothing else.

I was just talking about displaying the weight. A load cell outputs a voltage that has to be read and interpreted. You need some simple electronics (or you can buy a prefab board like Jeff mentioned) between the cell and a microprocessor. The processor reads the voltage, averages out noise, drives a display, and checks buttons to see if one has been pressed. It's not hard to understand but there are a lot of details.

If you open up an inexpensive pocket scale you'll most likely find a load cell, display, buttons, and one black box that contains the processor and electronics.

Hey, thanks for replying. I actually didn't notice this thread, so good to catch up on some ideas.

I do have a embedded electronics background and have worked with Arduinos and sensors in the past. With that being said, never worked with load cells. I can see a few challenges with this one though. Mainly how to mount a load cell that is small enough and second one is how to make sure that the reading is not impacted by the tray touching the sides of the machine.

I have some ideas, but none of them simple and I'm a bit short on time. I have an extra scale I might try taking apart to take apart and do a POC before I take on another hobby x

I bought a second copy of my coffee scale last year (500gx0.01g). This morning I took out the calipers and measured it. The load cell beam is 6.0mm thick. Mounted to the thin weighing platform it is 9.5mm. From ground to platform it stands 16.5mm tall.






The AA batteries (10.2mm) add to the overall height. If they were moved to the side or replaced with a coin battery and the load cell was bolted to a very thin base I think the working height could be as little as 11mm. But it would take some effort to repackage the buttons and display so that it is practical to use.

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There are ridges on the aluminum base of my machine (a Cafelat Robot) that I have never had any use for whatsoever. Frequently they bug me as things catch on them. I could file them down and gain an extra 1.2mm of clearance. It would mar the finish though and I'd feel compelled to polish it. That would be a lot of effort for 1mm. A better approach might be to replace the entire base with one that has a recessed area for the scale. That actually wouldn't be all that difficult to do. One guy who posted a couple of years ago replaced his Robot base with one that had an integral scale he made himself with a load cell.

Of course that wouldn't be as straightforward with other machines.

wojtowip wrote:
I have some ideas, but none of them simple and I'm a bit short on time. I have an extra scale I might try taking apart to take apart and do a POC before I take on another hobby x

Hey, it's great you responded. I don't have any background in electronics, besides soldering few diodes in TV or making simple things with batteries and bulbs, connecting electrical outlets, etc. So, basically none. But I have a vast experience in being creative, that's my calling in life actually. And I am always willing to make an effort in crazy little fun projects like this.
I remembered that you mentioned making something with sensors. Then I searched for anything and that short search led me to load cells, I also found strain gauges.

What kind of sensors you had in mind?
Please stay on this project until we finish it...hahaha

Cheers!

Being able to hack some things together is a skill for sure.

I actually ended up ordering a couple things to play around with last night after this thread. Had some wheels spinning in my head.

Order this load cell set: MakerHawk Digital Load Cell Weight Sensor HX711 AD Converter Breakout Module 5KG Portable Electronic Kitchen Scale for Arduino Scale https://www.amazon.com/dp/B07GQPV6C4/re ... JDCJY040ZM

And force sensor FORCE SENSING RESISTOR,1.5 INCH SQUARE,1oz-22LBS,2 LEADS,0.1 INCH SPACING https://www.amazon.com/dp/B00B887DBC/re ... UTF8&psc=1

I don't have high expectations for the force sensor, but was curious just how well it measures, considering how cheap it is.

I found some very low profile pressure sensors that could work, but I haven't seen any place to purchase them or how much they cost. Might need to reach out to manufacture if they sell small samples, though I doubt it. https://www.smdsensors.com/products/typ ... load-cell/

I already have some small Arduino boards and displays, so I'm set up to try a few things out once these get here.

Thanks for pushing me to actually try this out instead of just think about it.

jpender wrote:I bought a second copy of my coffee scale last year (500gx0.01g). This morning I took out the calipers and measured it. The load cell beam is 6.0mm thick. Mounted to the thin weighing platform it is 9.5mm. From ground to platform it stands 16.5mm tall.

image

image


The AA batteries (10.2mm) add to the overall height. If they were moved to the side or replaced with a coin battery and the load cell was bolted to a very thin base I think the working height could be as little as 11mm. But it would take some effort to repackage the buttons and display so that it is practical to use.

-----
There are ridges on the aluminum base of my machine (a Cafelat Robot) that I have never had any use for whatsoever. Frequently they bug me as things catch on them. I could file them down and gain an extra 1.2mm of clearance. It would mar the finish though and I'd feel compelled to polish it. That would be a lot of effort for 1mm. A better approach might be to replace the entire base with one that has a recessed area for the scale. That actually wouldn't be all that difficult to do. One guy who posted a couple of years ago replaced his Robot base with one that had an integral scale he made himself with a load cell.

Of course that wouldn't be as straightforward with other machines.

Yup, exactly what I had in mind. I can't remove Strietman's base, that would be sacrilege, lol, but I can make a new platform for load cells or try to adapt everything. It would be similar to building a ship in a bottle. But, this could be doable. I also had another thing in mind. That scale from the link you sent me could be pulled through the base of CT2 (its height is 16.7 mm from the front) and placed inside the base and not on the base. But that would be the same thing as this teared apart scale.
Thanks for showing inside of the scale, it's probably cheaper to buy a scale with all the elements than buy separate pieces.

Cheers!

wojtowip wrote:Being able to hack some things together is a skill for sure.

I actually ended up ordering a couple things to play around with last night after this thread. Had some wheels spinning in my head.

Order this load cell set: MakerHawk Digital Load Cell Weight Sensor HX711 AD Converter Breakout Module 5KG Portable Electronic Kitchen Scale for Arduino Scale https://www.amazon.com/dp/B07GQPV6C4/re ... JDCJY040ZM

And force sensor FORCE SENSING RESISTOR,1.5 INCH SQUARE,1oz-22LBS,2 LEADS,0.1 INCH SPACING https://www.amazon.com/dp/B00B887DBC/re ... UTF8&psc=1

I don't have high expectations for the force sensor, but was curious just how well it measures, considering how cheap it is.

I found some very low profile pressure sensors that could work, but I haven't seen any place to purchase them or how much they cost. Might need to reach out to manufacture if they sell small samples, though I doubt it. https://www.smdsensors.com/products/typ ... load-cell/

I already have some small Arduino boards and displays, so I'm set up to try a few things out once these get here.

Thanks for pushing me to actually try this out instead of just think about it.

Thank you once again for joining! You gave me an idea...and I am glad you've been pushed. One brain is good, but two or three together even better! Can't wait to see what's going to come out of it, I smell something great!

Cheers!

Jeff wrote:Watch linearity and repeatability on sensors. Even with 500 g FS, 0.05 g (for believable 0.1 g increments) is 0.01%

Yeah, my understanding is that those flat force sensors are pretty much worthless for weighing with reasonable precision. The one linked above from amazon is sold by Pololu. Pololu sells a lot of really nice hobbyist stuff. I love their tiny voltage regulators. Anyway, that force sensor has a range up to 2kg and a repeatability of ±2%.

They'd be a dream if they worked better. Maybe there's a tradeoff between deflection and precision. Part of the height budget for the scale I dissembled is an allowance for deflection. For that scale it is about 1mm.