LCD Current Meter

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ian McLean" <ianmm-at-optusnet-dot-com.au> 

Hi Coilers,

I have been checking the archives, and found a recent thread on current
transformers that probably answers my questions regarding this, but thought
it a good idea to check with the list now before commencing, in case someone
has found a cleverer way to do this.

I want to have an LCD panel on my Tesla Coil control panel to show both AC
voltage and current draw.  The voltage bit is easy enough - Rectify output
of variac, filter cap, and voltage divider consisting of two resistors, and
feed that to the A/D input of a PIC chip.  For safety however, I will
probably use an op-amp as a voltage follower after the resistor divider to
clip the output to 5V max to protect the A/D input of the PIC chip.

The current reading is what I searched the archives for.  Could someone
confirm I have the right idea here ?  Using a 50A:5A CT, put the primary of
the CT in series with the hot wire of the mains input, put a burden resistor
(high wattage, small resistance) across the secondary of the CT, and use the
voltage drop across this resistor as an input into an op-amp wired as a
differential amplify, to amplify the voltage drop to a range of 0-5V, and
use this for the A/D input to the PIC.  I believe I don't need to rectify
the secondary output of the CT - an average current reading will do, and is
easy enough by averaging results in firmware on the PIC.  The A/D conversion
and LCD display stuff is easy (done lots of PIC stuff before).

Will this work ?

Rgs
Ian