Load Cell- Validate and test

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(2 hr) Design and carry out tests to validate that the part will be suitable for the application you have planned.

• Compare accuracy and precision to pressure sensor
• Test if load cell can differentiate between different amounts of food

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Gain is set to 128, corresponding to a full-scale differential input voltage of ±20mV https://www.digikey.com/htmldatasheets/production/1836471/0/0/1/hx711.html

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On power up, default selection is channel A with 128 gain.

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Test using actual dog food weights

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About 300 grams of food per day for average dog (weighs between 6 kg – 20kg).

https://www.little-chompers.co.uk/dog-feeding-guide/

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The load cell was compared to a force sensitive resistor to determine which part is more suitable for our application. The force sensitive resistor was connected in series to a 43 kiloohm resistor, with a MCP3004 ADC used to read the values. As seen in Figure 8 and Figure 9, the MCP3004 returns a moderate value when pushed. According to Little Chompers Pet Food, a adult dog that weighs between 6-20 kg needs between 110-320 grams of food (6). As a result, a 200 gram weight was used to test the sensors, as seen in Figure 10. The resulting output of this test can be seen in Figure 11. Even when the orientation of the weights were changed, as seen in Figure 12, the ADC reading remained 0. Because the force sensitive resistor is unable to detect the change in weights, the load cell is the part more suitable for our application.