Transient Response of a Capacitor With Flea-Scope

In today's mini tutorial we will be exploring the transient response of a capacitor. This topic is covered pretty extensively in circuits 1 and utilizes differential equation techniques to solve, but today we'll just be creating the signal using some simple components and gain some intuition.

Pre-Requisites: Flea-Scope: Getting Started (Instructable created by me), Completion of ECE102

Flea-scope, Arduino, Transistor, Resistor, Capacitor, Jumper Wires, Bread Board

If a constant voltage is applied across a capacitor with no voltage initially across it we can expect the voltage to look like the general function below over time.

This program will act as an impulse signal which allows us to see how a capacitor will respond when a constant voltage is applied to it.

The impulse signal goes to the pin on the transistor that essentially opens the “gate” that allows current to flow.

● Connect a digital pin of an Arduino

to the left most pin of the transistor

● Connect 3.3V to the right most pin

of transistor

● Connect middle pin with resistor

then long leg of capacitor then

short leg of capacitor to ground

● Reference image to the right

● Orange Wire = Ground

● Red Wire = 3.3V

● Set up Flea Scope and connect to

Webpage

● Attach a wire to the SCOPE & GND

pins of the fleascope PCB and

connect the SCOPE wire in the

same row as the long capacitor leg

and the GND wire in the the short

leg row as seen in the image

● Observe the signal...

Your signal should look similar to the one above, though you may notice that even though the Arduino has not output high to the transistor the voltage reading is starting above zero. Do some research why could this be? Regardless we can still tell when the Arduino write high to the transistor because of the exponential rise of the voltage signal.

Is there a way to view signal over larger period of time?

Going to secs/div on the top left of the web page allows you to view the signal over larger intervals of time. This allows you to see the periodic charging and discharging of the capacitor. Change the delays in the pulse program and see what happens to the signal.