How to implement a zero crossing

Hi, i need to create and S-Function that is a zero-crossing detector of a sinusoidal wave with of a specific amplitude (let's say 120). This zero crossing must creat a positive ramp as well.

How can i create it?

PS: I know that in simulink i already have this function but i can't use it because it is for school purpose.

[dpb]

Since "... it is for school purpose." what purpose would it serve for us to provide a solution other than for you to not do the work yourself?

At least show what you've attempted and where you have a *specific* Matlab/Simulink question on syntax or such; not "do my work for me"...

[Jucimar Carpe]

Hi, actually i need to build and AC/DC converter, since i 'm working with thyristor i need to activate the thyristior in a speciffic alpha angle. This alpha angle is achieved after a zero crossing the it has a ramp function. The simulink/simscape has a functioj already implemented that is calls pulse generator, i need to build one like this function basically.

[dpb]

See above...

[Jucimar Carpe]

sorry i didnt get it the point...

[dpb]

The point is it is your homework problem, not ours...we (the community, that is) generally don't supply solutions to such without the poster at least showing have made an effort to solve the problem first...such demonstration would include posting the work you've done to date; where you got stuck and (best practice) a specific question on the actual coding using Matlab rather than just "do it for me".