Need help to understand how circuit functions__please!

[Sceadwian]

It depends on the exact micro controller you're using Misch, as Gayan said all you need on many micros is a 1 meg resistor, the I/O lines of many modern micros have built in clamp diodes, you just have to limit the current through them, which is what the resistor does, the diodes are connected to the VCC and GND rails. You could use a pair of Schotky diodes if you want to be safe. If you're not sure how to connect them another user here may be able to post a quick schematic for y ou or I can do it when I get home (nothing to do it with here)

 

[kchriste]

I would suggest, better use an oscilloscope to probe at points of interest.

Don't do this without an isolation transformer on the "project side"! If you don't use a isolation transformer, the ground lead on the scope probe can vaporize in a shower of sparks.

 

[Gayan Soyza]

I just guess he is going to send data through AC power lines.So you can plug your control circuit (TX) to any power outlet & send data through power lines & the receiver can plug to any power outlet & receive the data through power lines.He needs a burst of 120Khz frequency.

 

[mbarazeen]

if he is going to transmit data why is it required for zero crossing? he can simply use multiplexing of different frequencies coded for a data set with AC line. this injection can be done easily using a signal transformer and few capacitors.

 

[mischa]

i need to do exactly what gayan soyza said. In order to put the pulse out i need to know when the zero crossing of the ac signal is. Seeadwin and Gayan, I agree with the both of you on the part about just using a a 1M resistor to limit the current. The output of which will be connected to RB0 of the pic16f877 since this is the external interrupts source. But thats where i get stuck. what would my software look like for the Zero crossing detector in c? Please help. I need some major help.

 

[Gayan Soyza]

Initialization
*Make RB0 as an input pin (turn off internal pull-ups)
*Turn on External Interrupts INTE (Start from rising edge first)
*Turn on GIE

Main
*Wait until ZX interrupt occurs
*When ZX occurs it will goto ISR now Load the Timer (Delayed angle) & turn on the timer interrupts, (Delayed angle must between 1ms-9mS to make sure you are not crossing ZX boundaries)
*invert the ZX edge
*return from the ISR
*Wait until Timer interrupt occurs.
*When Timer interrupt it will goto ISR & fire the triac or make a 120Khz burst(a known time length).
*Turn off Timer & return from ISR until next ZX occurs.

To send data through AC lines you need to define a protocol from your 120Khz burst frequency. This you have to define. We don’t know.

Something like.
If you divide the waveform you get four quadrants. Apply four bursts in all four quadrants after a known time after each burst & ZX. This way you get a 4 bit value.
Like wise you can make your own data frame by combining 2 or three cycles, so you can insert start bit, data bits & an end bits as well.

 

[mischa]

Hey Gayan. I actually got the whole thing working earlier today but thank you so much dude. Have you by any chance used the Labcentre electronics Proteus simulation package? I am having an error with it and need to pick someone's brain regarding it. Please let me know.