sense resistor coupling

[gehan_s]

hey all,

i have a 0R5 sense resistor in the neutral side of the AC mains. i need to isolate this input and feed it to a PIC microcontroller. how do i do this???? (there is about a maximum of 4A rms curent flowing through it)

thanks !!!!!!!!!!!!!!!

 

[Tahmid]

How about using a transformer across it?

You can use a transformer with a turns ratio of 1:1 just for isolating. Or you can amplify as well, by using turns ratio 1:2, 1:1.5, etc.

Remember to rectify the output of the transformer. And make sure the voltage isn't greater than 5V. So, choose turns ratio accordingly.

Hope this helps.
Tahmid.

 

[gehan_s]

thank you tahmid for your reply !!!!!

if i don't rectify the output but shift it so that the resultant will be a sin wave within 0 to 5V will that be ok ??? in this way i will be connecting one output lead of the transformer with the ground of the PIC i think that is not going to be a problem. one more thing since the input to the transformer is fairly low do i have to make the transformer myself because normally i have seen transformers rated as 230V 50Hz input.

thanks

 

[Tahmid]

As long as the signal to the PIC does not go below 0V and above 5V (some tolerance is allowed), it's okay. So, make sure that after you shift it the peak voltage of the sine wave is within 5V.

Use a transformer with a low voltage rating. You may have to make one yourself. See if you can find ready-made ones.

 

[picgak]

in this way i will be connecting one output lead of the transformer with the ground of the PIC i think that is not going to be a problem.
thanks

keep a zener also to ensure safety of pic

 

[Tahmid]

Yes, to protect from overvoltage, use a 4.7V or 5.1V zener at the input of the PIC.
Use an RC filter as well. And make sure you use sufficient filtering and decoupling.