what does this cap do?

[daviddoria]

on the first circuit (2nd picture) on this website
https://www.eleinmec.com/article.asp?4

there is a capacitor straight from +v to 0v on the left of the circuit(220 uF)

what the heck is this for?

also, can i just connect pin 5 to ground? or do i have to run it through a tiny cap?

 

[Styx]

That big cap is the local de-coupling for that IC.
If it wasnt there and there was alot of things taking charge out of the DC it would upset the workings of that IC (since it would no longer be being supplied with a firm 5V dc)

If you look at the device spec it will tell you what the 5V tolerance is
That cap on pin 5 is the control voltage pin. it is used for PWM control

since it is not used in this application it is GND via a cap to ensure a firm GND and to short out and HF noise - you dont want any noise to trigger that pin.

I suggest you read ALL of that parts datasheet it will tell you all you need to know.

It is one thing to just copy a cct but you really need to know what the components are capable of