How to interface Current Transformer ( 30:5 ) into 16F877 PIC

[fromdawest]

I want to make a simple ammeter circuit using PIC16F877 . To measure the current I'm using a simple CURRENT TRANSFORMER ( 30:5 A ) . So what i want is to, get this current transformer output and make it the input to the PIC IC ( to it's ADC ), and then to drive a small LCD to show the current value .

So I want to know how to interface a CURRENT TRANSFORMER with the pic 16f877 in proteus . I tried but even i cant find the current transformer element in proteus 7.x .

Please help .

[kam]

you will use a shunt resistor. Connect the resistor to the output of the transformer. Then you measure the voltage across the resistor. Ohms law will give you the current.

[cheerio]

i bet you want to measure AC... so you have to rectify the shunt signal without losses. check this out: http://sound.westhost.com/appnotes/an001.htm

[kam]

hmmmm i've never thought of this diode trick... But why the diode is at the output instead of the input? The result would be the same, right? Am i missing something here?

[cheerio]

let's assume that we have a signal of 100mv and you put the diode at the input... problem isn't it?

[kam]

let's assume that we have a signal of 100mv and you put the diode at the input... problem isn't it?

Sure, but the op-amp is a buffer, not amplifier, so the problem stands for both situations (diode at input or output).

hmmmm i wonder....

Now that i think of it again, the 0.7V of the output diode will be compensated by the op-amp... 1V input will cause the opamp to output 1.7 in order to have same + and -...
I knew that it was a good idea....