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n t r o o C l T e t e o s t m e e r R Do you have problems with your infrared remote controls? Are their batteries dead or is it just that some of the buttons are not working? These and other questions involving remote controls can be readily answered with this handy tester. By LEO SIMPSON Everyone loves their remote controls, don’t they? Whether they are used to mute those irritating adverts on TV or to fast-forward through adverts on taped programs, they are a real boon. And of course, they are used on a multitude of other appliances these days so we are really lost and frustrated when they don’t work. It is at these times that remote controls are instantly con­ v erted from items of utmost convenience to items of extreme frustration. How do you test them? You can’t see the infrared beam that they are supposed to emit so you don’t know if they are functioning or not. Then again, they might be functioning as far as some of the buttons are concerned and others might be dead. How do you find out? On TV sets and other appliances which have an “acknowledge” LED, it is easy. Each time you press a button on the TV’s remote control, the “acknowledge” LED flashes and you are instantly assured that all is well. But the “acknowledge” LED most likely doesn’t work when other remote controls are pointed at it, so there’s no help there. Some remotes also have a telltale red LED and thus they provide a good indication that they are working; most don’t. If you have a camcorder or video camera you can generally use it to check whether your remote is working. Just point it directly at the camera and you will see the telltale flashes in the viewfinder or monitor while a button is pressed. How so? Because most video cameras will respond to infrared light. But while that is handy to know, it is not the most con­venient setup if you are plagued with a pesky remote control that just does not want to behave and do what it’s supposed to. These thoughts were prompted by my recent bout of wrestling with a cantankerous remote control. It had been becoming increas­ingly unreliaFebruary 1999  73 Fig.1: the circuit is based on an infrared detector module which drives the LED directly. ble over a period of a few months. The various users in the family responded by slapping it, pressing its buttons more fiercely and ultimately (shame) by saying unseemly words to it. None of these seemed to work as a cure. Coincidentally, the remote control tester to be described arrived in the SILICON CHIP offices and I pounced on it. The idea is simple. It has a membrane key on the small case. You press it and then simultaneously press a button on your suspect remote. If it is working a LED on the remote tester flashes brightly, in time with the data modulated onto the infrared carrier. This is far more convenient than aiming the suspect remote at your TV. The circuit of the remote control tester is shown in Fig.1. It consists simply of a 9V battery, a pushbutton switch, a LED and an infrared receiver module, M1. This infrared receiver module is contained in a compact tinplate case which houses a tiny PC board. This mounts an infrared This is how the PC board looks when all the parts are installed. detector diode, a surface mount preamplifier chip and number of other surface mount compon­ents. The module would normally be mounted behind a window in the front panel of a TV, VCR, CD player or whatever and would normal­ly drive decoder circuitry. In this case, we don’t need any decoding. Instead, we want the tester to respond when any button on any IR remote control is pressed. That it does and it lights the LED on its front panel for as long as any button on the remote handpiece is pressed. The module has inbuilt current limiting so it can drive the red LED directly, without resistors or any other components being required. Building it The circuit of Fig.1 is so simple that you really don’t need a PC board to build it but one is available as part of a kit from Oatley Electronics. The kit comprises a surplus PC board, a 9V battery snap connector, a high brightness red LED, the in­frared receiver chip, a membrane switch and a small plastic case measuring 123 x 36 x 23mm. The PC board measures 60 x 30mm and has been designed for a more complex circuit so there are a lot of vacant component positions. The photos show how the PC board is wired and how it sits in the case. Fig.2 shows the wiring layout. Putting it together will only take a few minutes but you do have to be careful with the polarity of the infrared detector, the LED and of course, the battery wires. The infrared detector module straddles one end of the PC board and lugs on the tinplate case are soldered to adjacent copper pads on the PC board. The positive battery wire passes through a hole in the PC board and is then wired directly to pin 2 on the module. The LED is wired directly across pins 1 & 2 on the module as well. The negative lead from the battery is wired to the membrane switch and then to pin 3 on the module. When you have the unit complete, connect the battery and press the membrane switch. The LED should flash once. Then if you aim an infrared remote control at it and press a button, the LED should flash for as long as the buttons are pressed. Remember though, you also need to keep the membrane switch on the tester pressed. Fixing remote controls Well, once you have an infrared tester you will certainly be able to work out whether your remotes are working or not and whether some buttons are defective. But it is entirely another matter to fix them. Let me tell you the story of the remote control that start­ed this story. Well, the tester indicated that the remote was indeed malfunctioning and the TV was OK. But where was the fault because one or two of the 74  Silicon Chip The PC board assembly sits at the top end of the case, with the battery occupying the other end. Take care to ensure correct battery polarity – the negative lead goes to the switch. buttons would work some of the time? The first step was to check the batteries, two AA cells being used in this case. They were around 1.4V each and although not fresh out of the carton, they certainly should have been good enough to run the circuit. Most remotes will run quite happily with cells that are down to 1.2V and some will work with a lot less. Mind you, the batteries are often not the problem but corrosion of the battery terminals can be quite obvious when you take the trouble to look. This can be most easily cleaned off using a Scotch-Brite or similar scouring pad. Don’t use steel wool as it is difficult, if not impossible, to ensure that there are no strands of it left to cause problems later. While there was some corrosion on the battery terminals of this cantankerous remote, that was not the problem. It still would not work reliably. There was nothing for it but to pull it apart. This involved removing one screw on the back and then prising the case carefully apart. That revealed a long narrow PC board with just one surface-mount IC, the infrared LED and the contact patterns underneath each rubber button. There were no other components. Older remotes can be expected to have quite a few compon­ents on the board and sometimes the fault can be a fractured component or a broken solder connection. This happens because remote controls are often dropped or sat upon. In the case of this remote the problem turned out to be blindingly obvious. Not only had quite a lot of food residue worked its way inside the case around the buttons and along the joins in the case but the PC board itself was wet! A sticky liquid was held between the rubber button sheet Fig.2: this is the wiring layout of the remote control tester. It uses a surplus PC board which fits into a small plastic case. and the PC board. No doubt someone had spilt drink over it at some stage. Drink residues, especially beer and cola, can be surpris­ingly hard to remove in this situation and since the PC board was largely bare in this case I decided to clean it up using kitchen detergent, thoroughly rinsed off with clean water. I was sorely tempted to dunk the whole PC board into the washing-up detergent but thought better of it. I also cleaned the rubber keyboard membrane but this job must be done carefully because it easy to inadvertently remove the resistive coating on the back of each button. It is this resistive coating which completes the circuit for each button and activates the remote control. Having carefully rinsed off all the detergent from the PC board and Where To Buy The Kit The complete kit for the remote control tester is avail­ able from Oatley Electronics for just $5.95, not including the 9V battery. They also have the infrared detectors available at $2 each or 10 for $15. Oatley Electronics’ phone number is (02) 9584 3563; fax (02) 9584 3561. the keyboard membrane, the drink residue appeared to be completely removed but it turned out not to be the whole cure. While it worked better when it was reassembled, it still would occasionally refuse to respond when some of the buttons were pressed. And even more irritating, sometimes none of the buttons would work! OK, I then cleaned the board and the button membrane again, this time using methylated spirits. This turned out to be effective and the remote control then worked reliably – for a whole week! At the end of that time, the most used button just fell out! As you might expect, some more unseem­ly words were uttered. Several times! There is no way that the missing button could be stuck back into place and since it was the one used to mute the commercials, the whole situation was rather frustrating. But wait! There is a solution. I will replace the missing button with a PC mount snap action switch. They’re available from Jaycar, Dick Smith Elec­tronics and Altronics, in various colours for a dollar or so. Yes, I will have to ream out the button opening in the case but I’m going to fix this remote, come hell or SC high water! February 1999  75