Dual PSU (Part 1)
Our dual channel workshop power supply unit has multiple output options (switched and variable), PIC16F877 monitoring of both current and voltage, LCD display and of course, current limiting control on one channel. Everything you need to power up your workshop projects! 18V/36V/±18V up to 1A/ 350mA (see text).

In November 2001 issue (P. 799) we published a correction as follows: Page 890, Fig. 10 should be amended as follows: Link 24 to A11 (not A9); Link 25 to A12 (not A5); Link 26 to A5 (not A12) and Link 27 to A9 (not A11). Note that having the links incorrectly connected as above will not damage the PIC. Ignore the statement saying B14 no connection. Resistors R43 to R46 should read R35 to R38 (10k).

FREE Christmas Supplement
Twinkling Star - Christmas Bubble - Festive Fader - PICtogram

Our free supplement of extra projects -- LED twinklers and lamp flashers -- is sure to be a big hit at every Christmas party!

In the January 2001 issue (P. 31), corrections were made as follows: Page 8 circuit diagram, Fig. 3. The unconnected lead from the mains input "live" should run horizontally across the circuit tolink up with the unconnected lead running down to thejunction of R8/ MT2. Thep.c.b. is correct.
Also, thevalues of capacitors C3 and C6 on the circuit diagram shouldbe 1µF multi-layer ceramic. The parts list is correct. Although not listed in their catalogue, we understood that Farnell (www.farnell.com) stock the transformer Dagnell D3607 3VA p.c.b. type (# 330-3809).

The Schmitt Trigger (2)
Continuing our in-depth designer's guide at the most versatile trigger, detection and shaping circuit. This month we look at op.amp and comparator circuits.