HX-711 , Attiny804 weighing scale ,ASM , assembly

darth vader's picture
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HX711 weighing scale

0-5kg load cell 

Attiny 804 MCU

AS7 project with video and schematics attached

language - assembly

;prototype was 5kg Ali express loadcell with HX711 board costing 2-3 us$
;the load cell reading drifts even with slight change in temperature 40deg - 30deg is 12-15gm drift
;always re zero by pressing/shorting PA3 to ground for 1 -2 second with weighing tray empty for correct reading
;as current offset value of the sensor based on the ambient temperature is subtracted from sensor reading
;to get correct weight.

;to find out how much ADC count is 1 gm I placed car wheel balancing sticker weights which are available in 5gm increments and are fairly accurate

;I got 2000 counts increment on the raw ADC value for each 5 gram weight placed on the sensor. 2000adc count/5gm = 400adc count for 1 gm

;multiplying the RAW ADC COUNT - sensor offset with 1/400 gives the weight. (ACD - offset)x 1/400 = weight measured (1/400 = 0.0025)

; offset handling is automatically done on pressing the re-zero switch for 1 second , remove the weight from the sensor and press re zero switch to calibrate the sensor to zero.

;On doing the above the current ADC value without weight is stored in the SRAM for offset calculation. If abnormal values are displayed due to temperature drift always re zero.

;more modifications can be done on the code to print messages, disable underflow when sensor drifts etc which is not included

;finally thanks for the conversion & math code snippets taken from AVR freaks website.

;I have also posted another code named HX711_raw_data_reader that displays raw data from HX711 to LCD which can be used to find the raw ADC counts for a known weight

;which can be used to find the ADC count per 1 gram. 

;HX711.zip is full weighing scale code

;HX711_raw_data_reader is for finding the ADC counts for 1 gm on a new load cell, adc count calculated is used as divisor in HX711.zip program to run the weighing machine calculations


Darth vader