Calling all mathemeticians

[ThermalRunaway]

Hi everyone, I've got a relatively simple maths problem which is causing me some hassle. Simple that is, to anyone who's any good at maths!

I'm trying to remember how to rearrange equations. Now, I can do basic stuff no problem but the equation I'm trying to rearrange is a little more complex. I'm trying to extract "t" from the following equation:

V= Vpk x sin(2pie F t) where pie is the maths constant (couldn't find the correct symbol on my keyboard)

It's pretty obvious that V/Vpk = sin(2pie F t) but I'm not sure how to get t out of the rest of the equation. Any ideas?

I'd appreciate the answer if someone knows but I'd also really appreciate the technique so I can answer similar problems myself in the future.

Brian[/url][/quote]

 

[JimB]

Starting from V/Vp = sin(2.Pi.f.t)

InvSin (V/Vp) = 2.pi.f.t

t = (1/(2.pi.f)). InvSin(V/Vp)

Where InvSin is the inverse sine function, usually pronounced as "sine to the minus 1".
I dont see an easy way to do superscripts, or I would have written Sin-1 (if you see what I mean!).

JimB

 

[Styx]

that is why "arcsin" has a use, although I prefer Sin^-1

 

[ThermalRunaway]

Yep that makes sense to me. I've been out shopping with the gf and I was thinking that you could simply use sin-1 to get rid of the sin. The rearranging is easy once the sin function has been removed

Thanks for the reply both

Brian

 

[ThermalRunaway]

Just checked it and it works too. Incase you're interested, I'm using a PIC micro to detect the zero crossing point of the domestic mains. I'm using that equation to calculate how long it takes for the Pic Micro to detect the zero crossing point on the falling and rising edge, given that a schmitt trigger is used as the input buffer (4V and above is logic 1, 1V and below logic 0).

With that in mind, I've worked out that the pic micro will generate an interrupt 37uS after the zero crossing point has occured on the rising edge and 9.4uS after the zero crossing point has occured on the falling edge.

Thanks again both

Brian

 

[kinjalgp]

With that in mind, I've worked out that the pic micro will generate an interrupt 37uS after the zero crossing point has occured on the rising edge and 9.4uS after the zero crossing point has occured on the falling edge.
Brian

That should be 9.4uS "BEFORE" the zero-crossing since the schmitt trigger would detect any voltage below 1V as logic zero. This means when input ac voltage reaches below 1V, interrupt occurs and that would be well before the actual zero crossing.

 

[ThermalRunaway]

Yes that's right - my mistake

Brian