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Life, lawns & the Woofer Stopper Your Woofer Stopper in the May 1993 issue gives me renewed hope and I certainly intend obtaining one. However, my main trou­ ble with “mutts” and “moggies” is their nocturnal fouling of lawns and gardens. Some time ago I installed a passive IR floodlight unit primarily as a safety device, but find that it readily detects and to some extent scares animals bent on messing up the place. This in combination with a slightly modified Woofer Stopper should completely overcome the problem. My thoughts are: (1) since the flood unit has an adjustable timer (a few seconds to 15 minutes), it should be possible to delete the out, the amplifier has been loaded with a total of about 60W in speak­ers (to the 100V line outputs). Something that seems odd with the design in that you say the amplifier output should be loaded with an output transformer that presents a 4Ω load, but on checking the data in the Altron­ics catalog, the wiring configuration you suggest gives a 16Ω load. Could this be the problem? (D. W., East Gresford, NSW). • We think the most likely reason why the output resistors are burning out is that the 4.3µH inductor in parallel with those resistors is open circuit. That would explain why it takes an hour or two for the resistors to fail and also why your amplifier does not appear to be delivering full power. You can easily check whether the inductor is open circuit (or not properly soldered into circuit) by measuring across the three paralleled 12Ω resistors with your multimeter. The reading should be zero ohms but if it reads four ohms, then the inductor is open circuit. You are not the first person to be confused by the data in the Altronics catalog. The data is incorrect. The transformer should be connected as indicated in the circuit on page 28 of the December 1988 issue; ie, with 94  Silicon Chip Woofer Stopper timing function and switch it on/off with the floodlights; (2) Power a small PSU from the 240V at the lamps (easily accessible) to provide a suitable common DC supply for the modified circuitry. The flood unit is rated 300W maximum – I use two 100W lamps. There must be many garden enthusiasts who would appreciate such a gadget. Would you please consider publishing a modified circuit and description of such a unit? (A. B., Chittaway Bay, NSW). • There is no reason why the system would not work (technical­ly) but whether it would stop dogs defacing your lawn we do not know. If the idea receives sufficient reader interest, we shall consider a version along the lines you suggest. primary windings in series and the secondary windings in series. That connection “reflects” a load of close to 4Ω to the amplifier’s output and allows it to deliver maximum power. Building the FM subcarrier adaptor I wish to build the FM Radio Receiver described in the November 1992 issue of SILICON CHIP. In doing so, I wish to add on a subcarrier adaptor circuit detailed recently in another electronics magazine. This will allow me to receive the increas­ing number of ACS (known as SCA in the USA) transmissions being piggy-backed onto the FM broadcasts in our capital cities, in the subcarrier range of 67-92kHz. However, I have a slight problem in that the adaptor cir­cuit I have states that it should be connected to the FM receiv­er’s detector output, straight after the discriminator but before any filtering and obviously before the stereo decoder. The arti­cle further suggests that this point could be found (in the event that you lack a circuit diagram for the radio) by looking for audio signals in the high frequency range around 50kHz near the discriminator IC or coil, with a level of around a 100mV or so. It doesn’t seem to matter whether this signal has some DC present as it is AC coupled at the input of the adaptor. This sounds fine if you happen to have a CRO but I don’t and I also don’t want to go out and buy your circuit and the adaptor only to find that it will not work. Can you suggest the ideal point to get these signals for the adaptor on the FM Receiver you de­scribed in the November article? Having described my problem, you might like to know that the adaptor in question requires a fair amount of basic construc­tion and I am not aware of any kit resellers that intend to sell this kit complete. This brings up another point. Would SILICON CHIP be interested in producing a full ACS FM receiver in a future issue? An FM receiver along the lines of the November 1992 circuit, modified so that it could receive ACS or normal FM broadcasts at the flick of a switch, would be great. What would the readers think of this? I believe that you produced a sub­ carrier adaptor back in January 1988 but I don’t have the article and besides no-one that I am aware of produces the kits. I’ve also heard that it requires a slight modification to its twin-T filter circuit capacitors in order to receive signals such as the BBC, etc. Wouldn’t it be great to combine an FM receiver and the adaptor all in one? (P. F., Camberwell, Vic). • The FM Receiver described in our November 1992 can be used as a source for the SCA adaptor, as you suggest. Just take the output directly from pin 2 of IC1. The SCA adaptor we described in January 1988 is no longer available in kit form but the parts are readily available, including the PC board. It is quite simple to modify it to suit the BBC signals. All you have to do is change the capacitors in the twin-T filter from 0.0022µF to 0.0015µF. No other changes to the circuit should be necessary. Notes & errata Nicad Cell Discharger, May 1993: transistor Q2 is incor­rectly labelled on the circuit diagram (Fig.1) as a BC328. It should be a BC338 NPN type, as shown in the parts list. The parts list should also be amended to show 1 x 2.7kΩ resistor and 2 x 1.5kΩ (not 1 x SC 1.5kΩ) resistors.