# Smart Weighing Machine

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#### razzmatazz87

##### New Member
Hello everyone,

I have planned to build a weighing machine which can input the reading into computer and store it for monitoring purposes.

Honestly, this is my first time building such machine. So, i would like some assistance from you guys. Can you list out appropriate sensor(s) to sense the load from user.

Is it suitable to use potentiometer as load sensor. What are its advantages and disadvantages.

Thank you.

#### georgetwo

##### Member
variable resistor would have been good but will need complex construction. if you can lay your hands on a length of resistance wire. it will give more precise result than variable resistors.

#### razzmatazz87

##### New Member
ok..but I have observed that strain sensor is hard to extent for huge amount of force applied...for example..lets say my weight is 75 kg..if i want to measure my weight using strain gauge, maybe i got nothing because 750N is not sufficient to make the strain gauge extent for 1%...

#### blueroomelectronics

##### Well-Known Member
Look up Wheatstone bridge

#### razzmatazz87

##### New Member
Ermm....would you care to explain??
I kind a newbie here

by the way, i have 1 question in my mind. If i use multiple strain gauge to measure human weight? ive heard that strain gauge can hardly strain 1% and it cannot return to normal state is it? Hence making it not suitable for my project. Correct me if im wrong ok?

#### ericgibbs

##### Well-Known Member
Ermm....would you care to explain??
I kind a newbie here

by the way, i have 1 question in my mind. If i use multiple strain gauge to measure human weight? i`ve heard that strain gauge can hardly strain 1% and it cannot return to normal state is it? Hence making it not suitable for my project. Correct me if im wrong ok?
hi,
You purchase the strain gauge elements that give say 10mV/Volt at the maximum expected weight.
You would not use a load cell rated for say 10,000Kg to weigh a maximum of 1Kg.

There are also 'semiconductor' strain gauge elements which produce a higher output voltage than the simple resistive elements.

You have to decide the weight range and accuracy before designing the load cell.

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