# How to make a switch in a circuit?
**URL:** https://discourse.processing.org/t/how-to-make-a-switch-in-a-circuit/5603
**Category:** Coding Questions
**Created:** [November 16, 2018, 4:51pm UTC](https://discourse.processing.org/t/how-to-make-a-switch-in-a-circuit/5603 "2018-11-16T16:51:39Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@saotome](https://discourse.processing.org/u/saotome)
#### Post date: [November 16, 2018, 4:51pm UTC](https://discourse.processing.org/t/how-to-make-a-switch-in-a-circuit/5603/1 "2018-11-16T16:51:39Z")
Hello.
I have this "circuit!
> void setup() {
> size(600, 600);
> }
>
> void draw() {
> ellipse (300, 150, 40, 40);
> line (280, 150, 120, 150);
> line (120, 150, 120, 220);
> line (120, 220, 120, 290); //closed circuit
> line (120, 290, 120, 380);
> line (80, 220, 120, 270); // open circuit
> line (320, 150, 500, 150);
> line (500, 150, 500, 250);
> line (500, 250, 500, 380);
> line (500, 380, 350, 380);
> rect (250, 350, 100, 50);
> line (250, 380, 120, 380);
> ellipse (500, 250, 40, 40);
> line (270, 320, 325, 425);
> }
I need to know hot change the switch from open to close and viceversa using space key. How I can hide closed line by the open one and the opposite.
Thanks so much
---
### Author:  [@jb4x](https://discourse.processing.org/u/jb4x)
#### Post date: [November 16, 2018, 4:56pm UTC](https://discourse.processing.org/t/how-to-make-a-switch-in-a-circuit/5603/2 "2018-11-16T16:56:50Z")
Hi,
You can add a boolean variable to keep track of the state of your circuit.
Don’t forget to clear the screen before drawing it with `background()`.
```auto
boolean isOpen;
void setup() {
size(600, 600);
isOpen = true;
}
void draw() {
background(200); // CLear the screen
ellipse (300, 150, 40, 40);
line (280, 150, 120, 150);
line (120, 150, 120, 220);
if (!isOpen) {
line (120, 220, 120, 290); //closed circuit
}
line (120, 290, 120, 380);
if (isOpen) {
line (80, 220, 120, 270); // open circuit
}
line (320, 150, 500, 150);
line (500, 150, 500, 250);
line (500, 250, 500, 380);
line (500, 380, 350, 380);
rect (250, 350, 100, 50);
line (250, 380, 120, 380);
ellipse (500, 250, 40, 40);
line (270, 320, 325, 425);
}
void mouseClicked() {
isOpen = !isOpen;
}
```
It is currently the mouse click that will open or close the circuit. It will be your homework to make it with the space bar.
---
### Author:  [@saotome](https://discourse.processing.org/u/saotome)
#### Post date: [November 16, 2018, 5:11pm UTC](https://discourse.processing.org/t/how-to-make-a-switch-in-a-circuit/5603/3 "2018-11-16T17:11:49Z")
Thanks so much for the example
---
### Author:  [@saotome](https://discourse.processing.org/u/saotome)
#### Post date: [November 17, 2018, 10:39am UTC](https://discourse.processing.org/t/how-to-make-a-switch-in-a-circuit/5603/4 "2018-11-17T10:39:56Z")
I’m an absoliute begginer and I have some difficulties, the goal of this class is when the circuit closes, bulb
> ellipse (500, 250, 40, 40);
Should “light on”, ie. it will filled with white, and when circuit opens bulb turns back black. I tried with fill but has been impossible.
Many thanks
---
### Author:  [@saotome](https://discourse.processing.org/u/saotome)
#### Post date: [November 17, 2018, 10:48am UTC](https://discourse.processing.org/t/how-to-make-a-switch-in-a-circuit/5603/5 "2018-11-17T10:48:47Z")
I have this sketch, maybe could be useful
> void setup() {
> Vpila = 10.0; // Battery voltage in volts
> Rl = 100.0; // Bulb resistance in Ohms
> Rv=500.0; // Initial variable resistance in Ohms
> DR=5.; // Incremental step of variable resistance in ohms
> color\_alpha= 0; // Initial transparency in zero
>
> start = false; // Closed switch
> }
> //
> // In draw() animations are implemented
> //
> void draw() {
> if (start) { // Close switch.
> I = Vpila/Req; // Intensity in the circuit, Ohm’s LawLlei
> color\_alpha = 255\*I/Imax; // Brightness is proportional to intensity using alpha transparency
> }
>
> //
> // For changing the value of variable resistance we use UP for increasing resistance
> //
> void keyPressed() { //
> if (key == CODED & keyCode == UP ) {
> Rv = Rv+DR;
> }
> }
>
> // Mouse click closes swith and simulation begins
> void mouseClicked() {
> start = true;
> }
> // End
---
### Author:  [@jb4x](https://discourse.processing.org/u/jb4x)
#### Post date: [November 17, 2018, 11:07am UTC](https://discourse.processing.org/t/how-to-make-a-switch-in-a-circuit/5603/6 "2018-11-17T11:07:32Z")
Well, you actually wrote what you should do.
If the circuit is open: fill it black else fill it white.
You already have all you need in the previous code. You just need to add that if statement:
```auto
boolean isOpen;
void setup() {
size(600, 600);
isOpen = true;
}
void draw() {
background(200); // CLear the screen
fill(255);
ellipse (300, 150, 40, 40);
line (280, 150, 120, 150);
line (120, 150, 120, 220);
line (120, 290, 120, 380);
if (isOpen) {
line (80, 220, 120, 270); // open circuit
} else {
line (120, 220, 120, 290); //closed circuit
}
line (320, 150, 500, 150);
line (500, 150, 500, 250);
line (500, 250, 500, 380);
line (500, 380, 350, 380);
rect (250, 350, 100, 50);
line (250, 380, 120, 380);
if (isOpen) {
fill(0);
} else {
fill(255);
}
ellipse (500, 250, 40, 40);
line (270, 320, 325, 425);
}
void mouseClicked() {
isOpen = !isOpen;
}
```