about circuit questions

[aarviii]

is it possible to have a circuit using transistor as a switch that my input as a sensor is weight and output will be LED as light. and when i put the object to the sensor, the heavier object the more the LED will light? and one more question. what IC can i substitute to 3140?

 

[sherazi]

when you are using transistor as a switch your transistor acts as a switch- that means either it will be ON or OFF- so u cant do it

 

[myfaithnka]

All you need is a substance called pressure sensor and an opamp. Try an opamp non invertor. Make amplification some 10 time or 100.