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I want to know what could I use to have a stable 5V excitation voltage for my load cell(wheatstone bridge) which I could also use to have a stable 5V reference voltage for my arduino adc. Would a LM7805(positive voltage regulator) could be applicable for this or I need to use a precision programmable reference like a TL431?

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Virtually "any old voltage" will do if the "any old voltage" is used for both bridge excitation AND ADC reference voltage. Basically you will get no errors theoretically. This is called a ratiometric measurement.

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  • \$\begingroup\$ Good one! +1 for you. :-) \$\endgroup\$ – EM Fields Dec 21 '14 at 19:47
  • \$\begingroup\$ so it would be more applicable if i use the same amount of voltage for both bridge excitation and ref voltage? because I have a 12V voltage source and i am planning to use it to my bridge and will regulate it to 5V for my adc \$\endgroup\$ – Rhonald Rei Pahayac Dec 22 '14 at 15:24
  • \$\begingroup\$ Use precisely the same voltage reference indeed - share the node between bridge and ADC reference - any filters you add, make them common to both bridge and reference. If you do this then you needn't worry about drift because it'll have no effect. I see you may have "accepted" the answer you understood rather than the best answer!!! \$\endgroup\$ – Andy aka Dec 22 '14 at 16:53

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