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• Unfortunately, the maximum rate is determined by the TFDS4500 module, which you correctly state at 115.2kbps. We may publish something faster in the future (MIR and/or FIR) but we can’t give any guarantees. If you’re keen to upgrade soon, you might consider a commercial solution. Microgram Computers often advertise IR add-ons – check them out at www.mgram.com.au Ammeter has stopped working I recently constructed the 80A Automotive Ammeter from the June 2002 issue and it was working well. However, it now fails to give any correct indication of current levels. When I attempted to re-calibrate the unit at the ‘zero’ current level, the ‘CAL’ LEDs light but on removal of the shorting plug, the indication goes to ‘OL’. Attempts to calibrate at other levels bring either totally erroneous (high) readings or the ‘OL’ indication again. The ammeter is an important part of my domestic solar sys­tem. I gather it should work satisfactorily in this situation? (R. T., Darbys Falls, NSW). • Perhaps there is a short in the Hall effect wiring or the Hall sensor is not working. Check that the Hall effect unit is receiving its 5V supply and that its output is around 2.5V. Alternatively, there may be a problem with the LM358 and associated components. Check its supply and that the output is a varying voltage, indicating that the conversion process is work­ing. Operating the turbo timer from 24V Is it possible to operate the turbo timer (SILICON CHIP, November 1998) on 24V DC. If so, what mods do I need to make? (G. S., via email). • It is possible to operate the turbo timer from 24V. Change the 33Ω resis- tor to ZD1 to a 680Ω 1 W resistor and change ZD1 to a 15V 1 W zener. Also, change the 10kΩ resistor connecting between ground and the 1.8kΩ resistor to 1kΩ. Also the relays will need a series resistor with the 12V relay coil to limit the voltage across their coils. Measure the coil resistance in ohms and use a 5W resistor of the same value in series SC with the coils. Notes & Errata Whistle & Point Cable Tracer, October 2002: the pinout diagram for the C8050 package (circuit, page 54) is incorrect. The C8050 collector & emitter pins are reversed with respect to common general-purpose TO-92 transistors like the BC549. 5A Speed Control, October 2002: the 100nF capacitor shown on the PC board diagram on page 17 should be 47nF to agree with the circuit on the same page. Note also that the pinout diagram for the MCR100 on the circuit is wrong with regard to the Anode and Gate pins. The gate is the centre pin of the package as it is with the C103B however the A and K pins are swapped. 40W Fluorescent Inverter, September 2002: due to tolerance varia­tions within the L6574 (IC3), it is recommended that the maximum current delivered to the fluorescent tube be adjusted using a trimpot. The 100kΩ resistor connecting between pin 2 of IC3 and the top of the dimming potentiometer (VR1) should be replaced with a 50kΩ trimpot and www.siliconchip.com.au series 82kΩ resistor. The 1.2Ω resistor between the source of Q4 and ground should be changed to 2.2Ω to allow the full dimming range available from VR1. Using the current measuring setup of Fig.8, the trimpot should be adjusted for the 370mV, corresponding to 3.7A when the dimming pot (VR1) is turned fully clockwise. Note that this adjustment should be made after the inverter has been running for some time and is fully warmed up. Once adjusted, the trimpot and 82kΩ resistor can be swapped for a single resistor that is the same value as the total series combination. When testing the current (using the setup of Fig.8), it is important not to have the 0.1Ω 5W resistor in series with the supply for any appreciable length of time as the current drawn will begin to increase. To prevent this, short out the 0.1Ω resistor (with a clip lead) when not making the measurement. Remove the clip lead briefly to make the current measurement. In addition, use heavy gauge wire rated at 7.5A or more to connect the inverter to the 12V battery. The lower cost MTP3055E Mos­ fets can be substituted for the STP­60NE06 devices used for Q1 and Q2. The Dick Smith Electronics D-5375 ferrite core is also suitable for L2 and requires 100 turns of wire (50 turns on each half) instead of the 84 total shown in Fig.6. 4-Channel UHF Remote Control, July 2002: the circuit diagram on page 20 is incorrect. On the PC board overlay diagram, the col­ lectors of all four transistors (Q1Q4) connect first to 2.2kΩ resistors, then to their respective LEDs. However, the resistors and LEDs are swapped on the circuit diagram. MP3 Jukebox, September/October 2001: since publication of this project, version 2 of the Winamp software has been superseded by version 3. Unfortunately, Winamp version 3 is not suitable for use with the MP3 Jukebox. However, the last release of version 2 (v2.8.1) can be downloaded from http://classic. SC winamp.com December 2002  93