Change R1 from 20k to 11.5k and AVDD becomes 3.0 V, which is obviously 300 mV below the input 3.3 V and it also meets the dropout spec, and the HX711 should work just fine and give you reasonable conversion results. But, obviously with a 3.3 V VCC, there's no way this will work, so you need to adjust the feedback resistors on the board to something that is acceptable. With a 5 V VCC, the drop-out spec is easily met. So do the math, and AVDD with the resistor values on the board is 4.3 V. (Also, as commenter Member #461211 points out below, the data sheet is wrong - the denominator should be R2, not R1, and the SparkFun schematic reflects that.)ġ00 mV is the dropout spec for the HX711's regulator. This voltage should be designed with a minimum of 100mV below VSUP voltage." The output voltage is equal to VAVDD=VBG*(R1+R2)/ R1 (Fig. There is a statement: "When using internal analog supply regulator, the dropout voltage of the regulator depends on the external transistor used. So there is no reason why you can't use single 3.3 V supply for both VCC and VDD with this board. If you read the HX711 data sheet, you'll see that it specs a range of 2.7 V to 5.5 V for DVDD and VSUP. Note: Special thanks to Bodge for supplying the Library for the HX711! Please keep in mind that some load cells might have slight variations in color coding. The YLW pin acts as an optional input that is not hooked up to the strain gauge but is utilized to ground and shield against outside EMI (electromagnetic interference). Each color corresponds to the conventional color coding of load cells: These are commonly colored RED, BLK, WHT, GRN and YLW. Load cells use a four-wire Wheatstone bridge configuration to connect to the HX711. Check the hookup guide below for more information. Any microcontroller’s GPIO pins should work, and numerous libraries have been written, making it easy to read data from the HX711. The HX711 uses a two-wire interface (Clock and Data) for communication. It has all the features of the HX711 but with additional library support, a true I2C interface, and no soldering required! Need even more? Checkout the SparkFun Qwiic Scale. This version of the SparkFun Load Cell Amplifier features a few changes that you specifically asked for! We have separated the analog and digital supply, as well as added a 3.3uH inductor and a 0.1uF filter capacitor for digital supply. This can be handy for creating your own industrial scale, process control or simple presence detection. By connecting the amplifier to your microcontroller you will be able to read the changes in the resistance of the load cell, and with some calibration you’ll be able to get very accurate weight measurements. The SparkFun Load Cell Amplifier is a small breakout board for the HX711 IC that allows you to easily read load cells to measure weight.
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