how to detect lower edge of sine wave at 100Hz..?

Hi all,

I need to start a timer after detecting every lower edge of a ac standerd sine wave of 50HZ.

I have changed these waves to fully rectified sinewave.

..............................*........*.......... ..........................*.......*..............
.....................*........................*... ..................*.....................*........
................*................................. .*...........*...............................*...
.............*.................................... ....*....*......................................*.
.. --->..*............................................*<---................................-->...*
...here........................................... .......here................................. here

can any one give me idea how to do this and if any one can share some sample code.

Regards

You can try to use "zero crossing" detector (shouldn't matter if the signal doesn't really cross 0V)..
Try this link:
**broken link removed**
Regards,
IanP

I have an idea but it must be tested.
u can use two opto_coupler in sinwave source to simulate your rectifier .IN positive half wave Q1 can turn on and Q2 off. and ...

if u use zero crossing u should talk into consideration that
--noise effect will be great (this may make the minimum value varies arounding the zero


i think first of all u have to
--1--convert this sine to square .
--2--lpf to remove noise.
--3--check signal to get the zero crossing point

it's a really funny sine wave!!! it looks more like a full rectified sine wave!
The idea of the zero cross detector is the best suitable for your porpouse, and the easiest to achive.
good luck

Keeping the sine wave in it's unrectified form and using a zero-crossing detector is certainly favourite.
Having said that, detecting the *exact* zero voltage is actually quite difficult, as all semiconductors have some kind of minimum threshold voltage (p-n junction or similar).
A lot depends on the precision required in your application - one method which comes to mind is to trigger using identical voltages on either side of the zero voltage point - using zeners or comparators - then simply divide the count between these trigger points to determine the exact moment of zero voltage, and use this as an counter offset.
If such precision isn't warranted, then use the largest voltage sinewave available, where semiconductor-induced zero-crossing errors will have minimum effect.

Colin