Hello, I want to integrate Core module with HX711 24bit ADC to build a battery-powered weight scale.
I was thinking about using Mini Battery Module, is it a good idea?
Won’t TPS61099 boost IC introduce unwanted noise on analog power rail? Or do you suggest completely different approach?
Thank you for all your work and support.
Honza
Hi,
Mini battery module is using step-up, which usually makes higher ripple than step-down. Is there possibility to use regular Battery Module which has step-down TPS62745? Do you have size-constraints?
Are you using some breakout board or designing your own board with HX711? By adding some filtering or LDO with low Iq that will change 3V from Core Module to let’s say 2.8V (since HX711 has 2.7-5V) could solve that. You’ll just add some series resistor PD_SCK so the higher 3V from Core will not back-power the ADC with protection diodes.
Now I noticed, that the chip has some linear regulator. So adding another LDO might not be needed, just some filtering maybe.
I also asked my colleagues, they have a lot of experience with practical usage of 24bit ADCs and load cells. However they use them on our CHESTER, but let’s see.
I’ll let you know when I get more info from them.
Do you have size-constraints?
Yes, I’d like to fit it into a specific box with the strain gauge to have it portable and not bulky. I can measure the dimensions when I get back home. So CR2032 or 2xAAA baterries would be ideal and I think that’s also what most of the commercial kitchen scale use. Do you think it’s doable?
Are you using some breakout board or designing your own board with HX711?
My plan is to design my own board, I think https://cdn.sparkfun.com/assets/f/5/5/b/c/SparkFun_HX711_Load_Cell.pdf is a good start, but maybe improve the filtering. Currently I use shielded module from China.
I’ll let you know when I get more info from them.
Thank you very much, I’d be very grateful for any tips or general info.
So I have some tips from my colleagues.
One of our customers shared kitchen scale project with the exact chip.
Together with Adastra labs we manufacture different retail sensors that use matrix switches in the shopping shelves or by measuring weight. Smart Shelf / Adastra
In our first prototypes we started woth HX711 but it did not was precies enough. They says 24 bits, but the range was really lower. Our final design is using ADS122C04 from TI.
My guess is that you will first try that combination of HX711 and Core Module powered over USB, it uses LDO when powered from USB so you can test chipr and see how many bits you can actually get. Then try power it with (Mini)Battery Module (with disconnected USB, because USB has priority over batteries) and see how what precision you get.
Even if you tell me the range and precision of your load cells, I cannot tell how it will behave, it needs to be tested if the chip itself meets your requirements.
For our CHESTER we have module X3 which has two ADS122C04 chips for two load cells. But this module is not opensource and no public documentation was written, no TOWER support in SDK. It is all in our heads. So there might be possibility you can buy few of these modules from us (we manufactured them in load cell configuration last weeks), we can give you schematics, but we are really busy with bigger projects, so we won’t be able to give you much support unless your project expects big sales.
Here is schematics of X3 in WEIGHT SCALE configuration. The power to the load cells are enabled by transistors Q1A/B.
Some info about our X modules is here. It has 2.54mm castellated edges. 23 x 25.4mm dimensions.
We have Maxi base module in the TOWER, that has footprint for X modules. But this is not solution for your final product since you need small footprint.
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