ECE 110/120 Honors Lab Section : Week 4 (Oct 18--Oct 24)

The benefit of Transistors

by Jianqiao Xiao

     Last week, we faced the problem that the duty cycle of the LED was not well controlled and the entire circuit seems to be unstable. With our attempt with the transistor, the problem has been solved. The instability is located in the double usage of inverter with no intermediate regulation. A small variation in voltage at the beginning is highly likely to cause a big difference in current flowing into the second inverter. With that going through the capacitor, the final current going into LED has extreme variation, causing the instability.

    Transistor, turning the analog signals into digital ones, actually prevents the instability from happening. I added two transistors in the circuit--between the output of the first inverter and the input of the second inverter and between the output of the second inverter and the LED light. This design was proved effective since I was able to make each duty cycle equal and stable. The schematic is shown below.

The actual experimental circuits are shown below

We requested the TAs to order the pressure sensor we found useful and we have not received it. 

By Kausik Venkat and Yupeng Yang