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IR remote control for old TV I have recently put together an infrared remote and at­tached it to my old TV (with pushbutton channel selec­tion) as an on/off switch and channel changer. It is operating fine as it is but I am looking for a method of perhaps storing the last sent signal in some kind of a buffer to be retransmitted when the next button is pressed, thus turning of the previously selected channel. As it is, you have to turn off the channel you are on before selecting the new channel. I have used two Dick Smith Electronics 4-channel in­frared remote control kits (Cat. K-2810). I have used Channel 8 to operate the on/off relay, with the other seven outputs for the seven channel positions. Each of these outputs drives two 5V relays to switch the signals. These I have connected directly to the back of the original switch. These kits use the MC145026 9-bit trinary encoder IC for the transmitter and the MC145027 9-bit trinary decoder IC for the receiver. about two years ago and find that it works just fine. Now I’m about to install another one in a 1992 Renault 19. My concern is that a radiator expert on a motoring radio program raised the possibility (and he quoted actual occurrences) of elec­trolysis occurring with cars fitted with aluminium radiator cores. Apparently, a current of 50mA is enough to ruin a radiator in a short time. My knowledge of electronics is limited to soldering kits together. There- The signal is inverted and two 74HC74 dual D flipflops are used as latches or not, depending on the intended applica­tion. Could the VT outputs be utilised in some way for this purpose? Could you please suggest possible components and/or a circuit which may suit this application? (W. W., Murwillumbah, NSW). • We don’t understand why you have to turn off the presently selected channel when a new channel is selected. In any conven­ tional remote system, such as a hifi amplifier, it is not neces­sary to turn off individual program sources (eg, CD player) when another program source is selected. Of course, in an integrated system, sources are usually turned off when a new one is selected but it does not have to be done that way. Nor can we see any way of storing the last transmitted signal. Possibly a better way would be to have a logic selector system, perhaps using a counter (4017?) or shift register so that when a new count (data) was selected, the old one could naturally be de-selected. fore, I would appreciate it if you could clarify as to whether there is a possibility of electrolysis occurring with the coolant level alarm. I understand that all the late model cars are fitted with aluminium radiator cores. It would be great if you could show how to check if electrolysis is happen­ing, with a multimeter. Do aluminium radiator equipped cars have a sacrificial anode in the system? (J. B., Surrey Hills, Vic). • While there is a potential problem with electrolysis occur­ring in alumin- ium radiators, the sensor current used in our circuit is very small, at around 47 microamps. This is determined by the 100kΩ sense resistor and 4.7V supply. You can confirm this current by connecting your multimeter in series with the sensor lead. As far as we know, there is no sacrificial anode in car radiators. Inevitably though, the car’s aluminium head will perform the same function. Inverter for a scanner I have a 12VDC car battery and I wish to get 10VAC <at> 50Hz from it to power a VHF and UHF scanner drawing about 350mA. Have you published a circuit for such an inverter? (A. P., Gladstone, Qld). • The project most suitable to your application would be our 12V-to240VAC 40W inverter described in the February 1992 issue. You would have to use it with a 10VAC plugpack to drive your scanner. However, we wonder if the scanner does not already have a 12V DC input or failing that, does not actually run from 12V DC after the 10VAC is rectified. You may even be able to feed 12V DC into the 10VAC input, if it is followed by a bridge rectifier. It would be worthwhile investigating this point. Notes & Errata LED FUN, March 1999: we have been advised by Dick Smith Electronics that a batch of PIC12C508 microcontrollers have been found to latch into Mode 1 when Mode 3 is selected. The solution is to change all 2.2kΩ resistors in the circuit to 270Ω. All resistors in the supplied kits will now be 270Ω. SC WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. April 1999  93