The MCUTracer which appeared in the August and September 2004 issues of AudioXpress was built with the idea in mind that the reader could copy out the schematic and PCB drawing and have a working unit that could generate the characteristic curves of vacuum tubes.  We have had a number of inquiries from audio amateurs and ham radio operators looking for a prefab board.  (I had generated the original boards with Ultiboard and Multisim and etched them in my small workshop.)  Before jumping right in and ordering boards from my proto-shop I decided that it would be a good idea to isolate the MCUTracer from its host computer.  I decided that the Basic Stamp-II Processor could be dispensed with in favor of the much less expensive PIC 16F84 from Microchip.  For those who don't want to bother programming the device I have preprogrammed micro-controllers for sale at the Tech-DIY.COM webstore. LINK.  While I haven't encountered any problems with my original MCUTracer, in the interest of protecting potential users' laptops and PC's I thought that it would be a good idea to separate the high voltage analog side of the board from the serial port with several optocouplers.

To power the newly designed MCUTracer we built a low noise, high frequency power supply.  My original intention was to use an off-line switcher based upon the slew-controlled power controller chips from Linear Technology.  To keep this a DIY project, however, I decided that it would be more convenient to use a wall wart to drive a 45kHz power sine-wave oscillator for a small torroidal transformer, with separate windings for the digital and analog sections of the power supply.  The power supply delivers +/- 6 volts for the operational amplifiers and analog-to-digital converter, and +5 volts for the microcontroller and RS232 interface chip. 

Amplifier Section

 
The OUTPUTs from the PIC are enabled with a signal to OPT-01 (the top optocoupler).  This allows the other optocouplers to hibernate when their service is not needed.  sent to a transistor which turns on the LED within the 4N28 optocouplers.