Fullscreen HTML5Med Res (??MB)HTML4

Advertising Index Ask SILICON CHIP . . . continued from page 94 has two read-out modes: percent gradient and degrees. In percent gradient mode, it will read 0-100 when rotated up to 45°, then just shows dashes above 45°. It sounds like your chip is in gradient mode. To switch modes, hold down the calibration button for at least five seconds after it is switched on. It should then be in degrees mode and you can re-calibrate as necessary. Capacitor discharge for points motors The circuit diagram for the Capacitor Discharge Unit (SILICON CHIP, March 2013) indicates that it is suitable for both AC and DC power supplies. The unit apparently half-wave rectifies an AC supply, increasing the RMS voltage to peak voltage, thereby almost doubling its power potential. By contrast, a DC current through the unit with no increase in voltage suffers voltage drops through the DOWNLOAD OUR CATALOG at www.iinet.net. WORLDWIDE ELECTRONIC COMPONENTS PO Box 631, Hillarys, WA 6923 Ph: (08) 9307 7305  Fax: (08) 9307 7309 Email: worcom<at>iinet.net.au transistor and two diodes, making its power potential less than that of the AC power supply. It seems to me that the unit is not intended to be used with a DC power source. (J. M., via email). •  There is no problem with using AC or DC. We referred your email to the designer, Jeff Monegal, and his reply is below. It should be remembered that although there is a silicon diode and the voltage drop across the transistor is in series between the power supply and the storage capacitors, there is very little current flow. In fact, forgetting leakage current through the capacitors, the only current flow is that though the LED – only around 9mA. This will mean very little voltage drop across the diode and transistor. When either pushbutton is pressed, Notes & Errata Digital Sound Effects Generator, September 2012: while the LM4889 was specified as an alternative to the LM4819 audio amplifier IC, we have discovered that the shutdown pin polarity of the LM4889 is opposite to that of the LM4819 (active low rather than active high). We recommend constructors stick with the LM4819. 1W LED Driver With Protection, Circuit Notebook, May 2013: the second and third paragraphs in the third 96  Silicon Chip column should say “With an open circuit, the voltage across the 220µF capacitor can become as high as the supply, damaging the LEDs should they be reconnected with this higher voltage present. With the protection circuit, a higher than normal voltage allows ZD1 to conduct, pulling pin 5 of IC2b higher than its inverting input. This occurs with about 1mA through ZD1 and 1V across each 1kΩ resistor. So there is about 10.2V across the 220µF capacitor”. Altronics....................... Loose Insert Embedded Logic Solutions.......... 91 Emona Instruments........................ 5 Grantronics................................... 95 Harbuch Electronics..................... 85 Hare & Forbes.......................... OBC HK Wentworth................................ 3 Instant PCBs................................ 95 Jaycar .............................. IFC,45-52 Keith Rippon ................................ 95 KitStop.......................................... 87 LED Sales.................................... 95 Low Energy Developments.......... 95 Microchip Technology................... 25 Mikroelektronika......................... IBC Ocean Controls............................ 12 Premier Batteries........................... 7 Quest Electronics......................... 95 Radio, TV & Hobbies DVD............ 87 RF Modules.................................. 96 Sesame Electronics..................... 95 Silicon Chip Binders..................... 84 Silicon Chip Online Shop........ 88-89 Silicon Chip Subscriptions........... 35 Syndetic Pty Ltd............................. 9 Tekmark Australia......................... 55 Tenrod Pty Ltd.............................. 11 Wiltronics................................. 23,44 Worldwide Elect. Components..... 96 the coil of the point motor sees all of the voltage across the capacitor(s) minus the voltage drop across the output diode. To say it seems that the CDU is meant for AC and not DC is incorrect because the CDU will work fine with DC. The Peco point motor we used operated well with a coil voltage of 12V DC. While it is true that a higher voltage will be available with AC power in, the point motor will operate fine with a DC voltage of around 15V or more. I set up a CDU and obtained the following results: •  15V DC gave 14.1V across the capacitors; •  13V AC gave 15.4V across the capacitors; and •  16.1V AC gave 18.9V across the capacitors. These figures were with no load connected to the output. The only load SC was the LED (9mA). siliconchip.com.au