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digital weighing scale question

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Thunderhorse312

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wheatstone bridge resistor values = 750 ohms
excitation voltage = 5 volts

Hi! I'm trying to build a digital weighing scale(see figure above) and integrating it to a micrococontroller but i was having problems with the output voltage on pin 6. I amplified the signal from the wheatstone bridge by 150 and was expecting to find 0 volts on pin 6 on the event that the bridge has no pressure on it. However, by the time i measured the output voltage on pin 6 without load i was a value of 2.214 volts minimum load and a voltage of 4.11 maximum load. Somebody told me that the output voltage must be zero is this supposed to be right?
 

Your output will be centered around 2.5V (that's what the reference input does). The fact that you're seeing 2.2 volts may be due to unbalance in the bridge.
 

barry said:
Your output will be centered around 2.5V (that's what the reference input does). The fact that you're seeing 2.2 volts may be due to unbalance in the bridge.
Click to expand...

I see.. by 'unbalanced' what do you mean? are the resistance values of the resistors unbalanced?
 

For the unloaded state, it is assumed that the ratio of the two resistors on the left side of the bridge is the same as the ratio of the two resistors on the right side. (This means that the voltage at the two sense outputs of the bridge is the same). If those ratios are NOT the same, the bridge is unbalanced.
 

barry said:
For the unloaded state, it is assumed that the ratio of the two resistors on the left side of the bridge is the same as the ratio of the two resistors on the right side. (This means that the voltage at the two sense outputs of the bridge is the same). If those ratios are NOT the same, the bridge is unbalanced.
Click to expand...

I see.. is the output that i am receiving correct? the 2.2 Volts because of the reference voltage connected to pin 5..
 

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