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Electronic Building Blocks By Julian Edgar Quick and easy construction Great results on a low budget Long-distance Remote Control Ideal for triggering outside lighting, this remote control features a mains power relay and can switch high loads. It can reliably operate in difficult conditions over a 300m range – and further than that when in direct line of sight. T his project came about because I couldn’t find anything off the shelf that satisfied my requirements – not at a reasonable price, anyway. So, what did I want? I wanted to switch some powerful outside lights – but there was a problem. The lights are at the entrance gate of the block next door, where one day we will build a house. I wanted to be able to switch the lights from our existing house, and then in the future, from the new house. The obvious answer was to use a remote control – then the lights could be turned on and off from anywhere, now and in the future. But the first problem was range. The remote control’s receiver was to be mounted in a mains power meter box – that where’s the power for the lights was being sourced. But that box is about 80m from our existing house, and about 100m from where the new house will go. And cheap remote controls typically don’t work over anywhere near that range – especially when the receiver is located inside a metal box! The second problem was switching the mains power. While many cheap remote-control modules claim to have mains-rated relays, the ‘10A at 240V’ relay inscription doesn’t mean much when the PCB tracks and terminals are completely inappropriate for such mains connections. So, the answer was to assemble my own system – quite easy and, especially if you already have some parts like a mains power relay and box, cheap as well. Remote control receiver and transmitter Fig.1. The remote-control receiver module (bottom) triggers a mains-rated relay (middle). An override switch (top) allows the output to be switched even if the remote control isn’t working. Note that all the wiring in the upper box is mains wiring and must be suitably rated and insulated. While most remote-control modules have a quite limited range, there are others available that are much better in this respect. Typically, these are dubbed ‘long range’ or ‘long distance’. The one I bought on eBay was called ‘Garage Door LongDistance DC12V/24V RF Wireless Remote Control Switch System12V 433MHz’. It cost £14 delivered. Do also check Amazon. Frustratingly, at the time of writing this, I cannot find an identical unit for sale, so here are some hints in making your selection. First, the unit should be sold specifically as a long-range remote control. (But take with a large grain of salt the stated operating distances – some units that appear to be identical have quoted maximum distances that vary from 300m to 1000m.) Second, the Fig.2. The long-distance remote control uses a low-cost transmitter should have receiver module, a mains-power relay – and not much else. an extendable antenna Also fitted here is a manual override switch and connections for and be quite a lot larger power and an external antenna. The power cable uses a pre- than the typical ‘key fob’ wired plug-and-socket combination (the socket is shown here). style of remote control. Practical Electronics | November | 2023 65 Mains in Mains out E E N N L L Override switch Mains wiring Mains relay Low-voltage supply V– (0V) V+ (12V) NC C NO Receiver module Other parts Fig.3. When selecting a suitable long-range remote-control module and transmitter, ensure the transmitter is larger than a typical ‘key fob’ style remote and has an extendable antenna. The receiver also needs to have a relay output, and you should be able to configure it to have a latching function – that is, one press of the remote turns the relay on, and another press turns it off. Finally, pick an operating voltage that, preferably, suits a surplus plugpack (‘wall wart’) that you may have in your spare parts drawer. Note that I used a single-channel remote control system, but multichannel systems are a similar price, so think about whether having multiple channels (now or in the future) might be useful. The other main part that you will need is a mains power relay that’s rated for the current you are switching. In my case, I am operating two 300W lamps, with a third to be potentially added in the future. With my local (measured) 240V supply voltage, that’s a little under 4A total. I selected a 5A (at 250V) relay from my parts box – it turned out to be a double-pole, double-throw (DPDT) design. Relays with mains-voltage ratings up to 10A are quite common; above that you may need to go for a mains power ‘contactor’ of the sort often used when turning on and off heavy electrical machinery. Don’t forget to select a relay that uses a coil voltage that matches the remote-control receiver’s operating voltage – in my case, 12V. Many relays aren’t designed to accept screw or similar terminals. An easy way to overcome this problem is to select a relay that plugs into a screw terminal base. The base also typically has holes for mounting, allowing both easy wiring connections to the relay and for it to be securely mounted. You will also need an enclosure to allow the parts to be mounted and kept away from inquisitive fingers. But rather than go through each minor part one by one, let’s look instead at how the system was assembled. Building it The box I used was a good-quality plastic enclosure about 130 x 130 x 40mm. A clamshell design, it had two removable plastic end panels. On the inside of one end panel I mounted the 5A relay and its plug-in base. Since it was a DPDT unit, I decided to switch both the live and neutral connections. On the other end panel I mounted a mains-rated 10A switch. This switch Fig.4. This shows the terminal blocks for the mains power in/out connections and associated cable entrance holes. These terminal blocks make connections in the field quite easy. 66 is optional. I fitted it so that the lights could still be manually operated if the remote control were to fail (eg, the transmitter was temporarily mislaid, had a flat battery or simply broke). I used a double-pole single-throw (DPST) switch so that again I could switch both live and neutral feeds. Two holes were also drilled in this end panel. One was for the power supply cable from the plugpack and the other for a BNC antenna socket (more on this socket in a moment). On the floor of the enclosure I mounted, using plastic stand-offs, the remote-control receiver. Also mounted on the floor of the enclosure were two three-terminal connecting blocks – one for the mains inlet and the other for the outlet to the lights. Adjacent to these terminal blocks, holes were drilled to admit these cables. The holes were placed in the bottom of the box because the box was to be mounted flush against the power board panel within the meter box – these cables come through this mounting panel. The standard receiver antenna for this module (and most others) is a short length of coiled wire. Impressively, I tested the remote module with this standard antenna and found it worked at up to 100m range – even with the receiver inside the metal meter box. However, obviously such RF shielding is not ideal and so I added the antenna socket to allow an external antenna to be fitted. The shield wire of the socket is connected to the negative power terminal of the board (when accessing the receiver connections is near impossible, it’s a little hard to work out the best approach). The coiled antenna was cut off short and the remaining end of this wire soldered to the centre pin of the BNC socket. The antenna itself consists of a 270mm long piece of stainless-steel wire. I Fig.5. This remote-control module has a configurable link (arrowed). With the link in one position the relay engages when the remotecontrol button is pressed; in the other position the relay latches with one button press and unlatches with the next press. For applications like mine you want the latter system. The PCB button adjacent to the link is a ‘learning’ button, allowing the system to be used with multiple remotes. On the far right is the manual override switch that directly switches the mains power to the outlet. Note that its terminals have been insulated – no mains wiring should be exposed. Practical Electronics | November | 2023 Fig.6. Here you can see the power cable (top) and BNC antenna connection (bottom). It’s a little hard to see, but the original ‘coiled wire’ antenna has been cut short and soldered to the centre pin of the BNC connector. Since this receiver is to be mounted in a metal box, an external antenna adds noticeable range. used TIG welding wire, but a stainlesssteel bicycle wheel spoke could also be used. Using pliers, one end of the wire was wound around a suitable diameter mandrel (a long screw held in a bench vice) and then a right-angle bend placed in the wire. This approach allowed the antenna to be easily attached by a screw and washers to a threaded porcelain insulator. (The insulator came from parts I inherited from my father, so it’s perhaps 70 or 80 years old – it gives me a good feeling to re-use old bits and pieces) Connection to the antenna is via an eye terminal that fits under the antenna mounting screw. I used a short length of 50Ω coaxial cable to connect the antenna to the BNC connector. If you wished, it would be easy to trial different antenna lengths and connection methods. Simply powerup the receiver module, position an assistant with a mobile phone so that they can see the module, and then try triggering it from greater and greater distances while staying in phone contact with the assistant. I did exactly that and found that with the described antenna, I could achieve reliable operation at over 300m range – and that was with the receiver located inside a house, and with a large steel shed blocking line of sight. After that it was just a case of installing the receiver module in the mains power meter box and making the connections. Fig.7. The new external antenna was made from a short length of stainless-steel wire mounted to a porcelain insulator. Outcome It’s not a complex project or even one that takes much time to assemble. But it works well. It didn’t cost a great deal but achieved the outcome I wanted. And isn’t that what we want with our electronics projects? The two 300W entrance lights. They light-up literally thousands of square metres – and with the remote control, they can be switched from up to 100m away. You may be wondering at the power rating of these lights – 300W each!? Hasn’t his guy heard of LED lights? What must it cost to run these! Well, it’s an interesting story – and worth a brief excursion.The lighting units shown above are high-quality commercial metal-halide lights, as used in large parks and gardens. They are made with cast alloy housings and polished stainless-steel reflectors – disassembled, you can see their quality throughout. Practical Electronics | November | 2023 Once, they would have been worth perhaps £200 each – but we got them from the shop at the local rubbish tip (recycling centre) for just £5 each. And they were brand new! Obviously, a local government authority swapped all their new parkland lights to LEDs and decided these lights were worthless. Of course, metal halide lights will use a lot more energy than LEDs to run, but when they’ll be on only occasionally (and usually for short periods), the total cost will be fine – especially considering the immense amount of light they produce. 67