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fuiru 01/08/2018
I was able to get this working very quickly, but the values coming from the HX711, with no load on the bar, kept drifting very significantly. After a long troubleshooting session, I found out that the HX711 print has a major design flaw. They forgot to connect the AGND pin of the HX711 to GND, so it's just floating in the air, explaining the drifting. This can be fixed by soldering a wire between the GND pin on one connector and the E- pin on the other side. I found the exact same board on a different site with a picture of the schematics. This confirms that AGND is not connected to GND. See attached picture. It's also important to note that the print is designed to be supplied with 5V, even though the HX711 is specified to work down to 2.6V. The internal voltage regulator on the HX711 is configured with R12 and R13 to produce 4.2V across the sensor (E+ and E-). Considering the drop across the transistor, the supply voltage needs to be about 4.5V (or up to 5.5V), otherwise the regulator can't do its job. If a 3.3V supply is provided, the resistors can be changed accordingly. If you use it as is on 3.3V, be aware that the built-in regulator will not be able to do its job, so any ripple on the supply voltage will influence the measurement.
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  • Banggood Dear customer, Thank you for your order and before even attempting to explain the reasons leading to this unintended mistake, we would like to sincerely apologize to you. In our attempt to serve you better and retain you as one of our valuable customers, please contact our customer service representatives by this link: http://www.banggood.com/Contact-Us_hi111 We would highly appreciate if you could send us all the information listed here below: 1.Some photos of the shipping label, which can be found on the external side of the package; 2.The SKU number of the products you received. You can find this information on the label placed on the item itself; 3.Some photos or video to show the entity of the problem; 4.The order number and the product ID. Looking for your kindly reply. Have a nice day. Best regards, Banggood team

    24/05/2024
  • fuiru I no longer have the packaging and shipping label. Photos of the product don't help either. I'm just trying to help other customers fix the problem with the HX711 PCB included in this bundle. You can verify if the HX711 board has a problem by using a multimeter to measure the resistance between GND and E-. Those should be connected (see HX711 datasheet). The other board on Banggood (p1039638) is designed well and has this connection.

    Reply 09/08/2018
  • CoilWinder Very useful to know, thank you! I knew I read this some months or maybe a year ago. My google (and duckduckgo) searching this site didn't help, but I finally found your comment again :)

    Reply 14/01/2020
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