PC Boards for most Silicon Chip (plus EA & ETI) projects can be obtained from RCS Radio, Sydney.
Phone (02) 9738 0330. Fax (02) 9738 0334. Email sales@rcsradio.com.au or visit www.rcsradio.com.au

Capacitance Adapter for DMMs, November 1987:
to give more range of calibration adjustment, change trimpot VR1 to 200k & the associated 120k resistor reduced to 47k. (03/88)

24V to 12V Converter for Trucks, December 1987:
the wiring diagram on page 31 shows the 100μF capacitor (associated with D9) incorrectly polarised. The circuit diagram on page 30 is correct.

To provide crowbar overvoltage protection in the event of a circuit mishap, connect a 15V 5W or 20W zener diode across the 13.6V output. The zener’s anode should connect to the positive output terminal. If the output voltage exceeds 15V the zener will conduct heavily and blow the fuse. The zener may also fuse and become short-circuit.

 Note: Jaycar Electronics can supply a 15V 5W zener diode, type 1N5352B, which would be suitable for this application. (03/88)

24V to 12V Converter for Trucks, December 1987:
the 4.7k load resistor connected to the output side of L1 is incorrectly shown as 47k on the wiring diagram on page 31. The circuit diagram on page 30 is correct. (08/88)

Passive IR Movement Detector, December 1987:
the PCB layout connects the relay, D3 & R18 to +5V instead of to +12V (as shown on the circuit diagram). To fix this problem, isolate these components from the +5V rail by cutting the copper track at two locations. The isolated section should then be connected to the +12V rail using an insulated wire link. Finally, the isolated section should be bypassed by connecting an insulated wire link between the +5V output of IC6 & the track to pin 7 of IC5. 

Readers should also note that capacitor C6 (22μF) is shown connected with reverse polarity on the overlay diagram (the circuit is correct). In addition, the polarity of C14 (100μF) is not marked on the overlay. Be sure to connect the positive side of the capacitor to +12V.  Full details of the above modifications are supplied with the kit sold by Oatley Electronics. (06/88)

Digital Fundamentals, December 1987:
Fig.6 on page 92 has been reproduced incorrectly.  The type down the left-hand edge of the diagram should read INPUT A, INPUT B, INPUT C and OUTPUT D. In addition, the second last paragraph on page 92 should read as follows: “At times t1 through t8 the three inputs are never high at the same time. However, beginning at time t8 and ending at time t9 the three inputs are all high so that output D goes high.” (01/88)