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By JIM ROWE IR Remote Checker Do your remote controls often fail? Is it due to dead batteries, poor contacts under the switch buttons or a more serious fault? How would you know if it was working anyway? Here is the answer – a Remote Control Checker. It lets you very easily check whether an infrared (IR) remote control is sending out a code when each of its buttons is pressed, so you can avoid opening the thing up for cleaning or repair if it “ain’t really broke”. 34  Silicon Chip N OWADAYS, JUST ABOUT every item of home entertainment gear has its own remote control, so you can control its operation without ever having to get up from your easy chair – if you don’t want to, that is. Most homes have plenty of remotes but in most cases their reliability isn’t wonderful. Probably that’s because they have to take quite a lot of physical pounding: easily dropped, squashed, kicked, trodden on, splashed with drink and otherwise abused. When a remote fails completely, it’s usually just a matter of replacing the battery and away it goes again for another year or two. But what about when replacing the battery doesn’t fix it or one or two of the buttons seem to have stopped working? Then it can get a bit tricky and you want to be sure the siliconchip.com.au Fig.1: the complete circuit for the IR Remote Checker. Infrared pulses from the remote are picked up by sensor receiver IRR1 and fed to gate IC1a. IC1a then drives gates IC1b & IC1c which in turn activate the piezo transducer and LED1. fault is in the remote rather than in the equipment it’s supposed to control. Unfortunately most of the remotes made in the last few years don’t seem to be made for easy access to the insides, without damaging the case. They’re clipped together using a series of tiny lugs, moulded into the inside edges of the case top and bottom. The lugs can be hard to find from the outside and even harder to unclip without breaking one or more of them. So you don’t want to open up a remote unless it’s absolutely necessary. The little IR Remote Checker described here is designed to help in such cases, letting you quickly find out whether or not any suspect buttons are sending out codes from the remote’s IR LED. This will let you decide whether the fault is in the remote or in the equipment itself. You simply point the remote’s invisible output beam at the Checker’s sensor window and then press the various buttons. If the sensor picks up any codes, it gives you immediate confirmation by flashing a visible LED and sounding a small piezo beeper. The Checker can be operated from an internal 9V battery or an external DC siliconchip.com.au plugpack power supply. As a bonus, it also provides an electrical copy of the control code pulses received from the remote, so you can feed them to a scope or logic analyser for further analysis. This would also make the Checker a handy tool for anyone developing custom remote controls. The Checker uses only a handful of low-cost parts, all mounted on a small PC board which fits into a UB-3 size jiffy box. You should be able to assemble it in a couple of hours, especially if you build it from a kit. How it works Fig.1 shows the circuit diagram of the IR Remote Checker. The infrared pulse trains from the remote are picked up by sensor/receiver IRR1, which strips them from their supersonic carrier signal (usually about 38kHz) and provides them as negative-going electrical pulses from its output pin 1. We feed these pulses to pin 1 of gate IC1a, used here as an inverting buffer. The output of IC1a then drives one input each of two further gates, IC1c and IC1b. IC1c is also used as an inverter, to drive transistor Q1. Q1 is then used to switch current to LED1, so it flashes for the duration of each code pulse. IC1b is used as an oscillator which is gated on by the pulses from IC1a. The oscillator’s frequency is dependent on the 22nF capacitor and the total feedback resistance, so trimpot VR1 allows it to be adjusted over a reasonable range. The output from the oscillator is used to drive transistor Q2, which in turn drives the piezo transducer with a 5V peak-to-peak waveform. The 4.7kΩ resistor across the transducer is used to provide a DC load for the transistor, and also to discharge the piezo transducer’s capacitance between pulses. The idea of having trimpot VR1 is so that you can adjust the oscillator’s frequency to match the transducer’s resonant frequency, for maximum “beep” output. IC1’s fourth gate (IC1d) is used as another inverting buffer, driven directly from the output of IRR1. The output of this inverter is then fed to output socket CON1 via a series 4.7kΩ resistor, to provide the IR Remote Checker’s output pulses so they can be measured by an oscilloscope. All of the IR Remote Checker’s January 2005  35 Fig.2: install the parts on the PC board as shown here, taking care to ensure that all polarised go in the right way around. Note the mounting details for IRR1 and the 470µF electrolytic capacitor. circuitry operates from 5V DC and draws very little current even when responding to IR pulses. The 5V supply is provided by regulator REG1, a low-power 78L05 device. The raw input for REG1 is controlled by power switch S1 and comes from the internal 9V battery or from an external 9V DC plugpack. Diode D1 ensures that the circuitry can’t be damaged if the plugpack polarity is reversed. Construction Apart from the 9V battery, all of the components used in the Checker are mounted on a small PC board measuring 112 x 57mm and coded 04101051. The component overlay diagram is shown in Fig.2. The board is designed to fit inside a standard UB-3 size utility box (130 x 67 x 34mm) and mounts on the rear of the box lid using four 15mm x M3 tapped spacers with eight M3 x 6mm long screws (4 x countersink head). The 9V battery is held in the bottom of the box using a length of gaffer tape. Both external connectors are accessed by holes in the end of the box, when it’s assembled. You should be able to see the location and orientation of all the components on the PC board from the internal photos and the overlay diagram of Fig.2. Note that the piezo transducer is attached to the top of the board near the centre, using M2 machine screws and nuts. Begin the board assembly by fitting This view of the fully-assembled PC board shows just how easy the unit is to build. The sockets mount directly on the board, so the only external wiring is to the 9V battery. 36  Silicon Chip the two connectors to the end. Then fit the four PC terminal pins, two of which go on the far end of the board for the battery lead connections. The other two go near the centre, for the piezo transducer leads. Next, fit toggle switch S1, which mounts with its connection lugs passing down through the matching slots in the board as far as they’ll go, before soldering underneath. After this, fit trimpot VR1, near the battery terminal pins. The resistors come next; all fit horizontally. Diode D1 fits in the same way just behind CON2, with its banded cathode end towards switch S1. Now fit the capacitors. These all mount in the usual vertical fashion except for the largest 470µF electro, which is fitted lying on its side, with its leads bent down at 90° about 2mm from the body. Make sure you bend them the right way, so the positive lead ends up closer to switch S1 as shown. Watch the polarity of the other electrolytics too, as they are all polarised. Regulator REG1 and the two transistors are fitted next, with all three having their leads cranked outwards to mate with the board holes. That done, fit the IR sensor device. As shown in the photos and diagrams, this mounts with all three leads bent carefully downwards by 90°, about 2.5mm from the body. The very ends of the leads are then passed down through the matching board holes and soldered, so the sensor ends up facing directly upwards and with the top of siliconchip.com.au Parts List 1 PC board, code 04101051, 112 x 57mm 1 plastic utility box, 130 x 67 x 34mm (UB-3) 1 mini toggle switch, SPDT (S1) 1 PC-mount RCA socket (CON1) 1 PC-mount 2.5mm DC socket (CON2) 1 9V battery, 216 type 1 9V battery snap lead 1 piezo transducer, 30mm dia. x 5mm high 4 PC board terminal pins, 1mm diameter 4 M3 x 15mm tapped spacers 4 M3 x 6mm machine screws, csk head 4 M3 x 6mm machine screws, round head 2 M2 x 10mm machine screws, round head 2 M2 nuts with star lockwashers 1 10kΩ mini horizontal trimpot (VR1) Semiconductors 1 IR receiver, RPM1738 or IS1U60 (IRR1) 1 4093B quad Schmitt NAND gate (IC1) 1 78L05 low power +5V regulator (REG1) 2 PN200 PNP transistors (Q1, Q2) 1 3mm red LED (LED1) 1 1N4004 power diode (D1) The PC board is secured to the lid of the case using 15mm tapped spacers and M3 screws. Note that a prototype board is shown here (the wire link is not necessary on the final version). its hemispherical lens 15.5mm above the board. Next fit the IC, making sure that it’s mounted the correct way around as shown in Fig.2. Because it’s a CMOS device, make sure you use an earthed soldering iron and earth yourself when you solder its pins to their pads, to avoid damage due to static discharge. Mounting the piezo device Now cut the two leads of the piezo transducer to about 50mm long, assuming you’ve already mounted the transducer itself to the board in the right position using the M2 screws and nuts. Then bare about 4mm of wire on the end of both leads, and carefully solder them to the two PC terminal pins just to the left of the 470µF electrolytic cap. Note that the red positive lead should connect to the pin nearest to the 4.7kΩ resistor. The LED can also be fitted at this stage but not with both leads soldered. Solder only one lead to its pad with a bare minimum of solder, so it will be held in place temporarily until final positioning when the board is attached to the box lid. The last step at this stage is to solder the battery snap leads to the terminal pins on the end of the board, making sure that the red positive lead solders to the upper pin near IRR1. Capacitors 1 470µF 16V PC electrolytic 1 100µF 10V PC electrolytic 1 47µF 10V PC electrolytic 1 100nF (0.1µF) multilayer monolithic (code 100n or 104) 1 22nF (.022µF) MKT polyester (code 22n or 223) Resistors (0.25W 1%) 2 10kΩ 1 220Ω 3 4.7kΩ 1 47Ω Table 1: Resistor Colour Codes o o o o o siliconchip.com.au No.    2   3   1   1 Value 10kΩ 4.7kΩ 220Ω 47Ω 4-Band Code (1%) brown black orange brown yellow violet red brown red red brown brown yellow violet black brown 5-Band Code (1%) brown black black red brown yellow violet black brown brown red red black black brown yellow violet black gold brown January 2005  37 Fig.3: this full-size artwork can be photocopied onto an adhesive label and covered with clear “Contact” film for a professional finish. end of the box as well, for the access holes for CON1 and CON2. Remove any burrs which are left on the inside and outside of all holes in the box and lid, to make a tidy job. Once the lid has been prepared, attach the four board mounting spacers to the rear of it using the four countersunk-head M3 screws. Tighten these up quite firmly, so the top of each screw head is flush with the top surface of the lid itself. This will then allow you to stick on a front panel, made by photocopying the artwork (Fig.3) we’ve provided onto an adhesivebacked label. With the front panel attached, you can cover it with a piece of clear “Contact” or similar adhesive film for protection. It’s then just a matter of neatly cutting out holes in this double-layer panel escutcheon using a sharp hobby knife, to match the holes already cut in the lid underneath. Mounting the PC board Fig.4: check your PC board against this full-size etching pattern before installing any of the parts. Now prepare the box lid, by cutting the various holes in it, as shown in the drilling diagram of Fig.5. Note that the four outermost 3mm holes should be countersunk to allow for the heads of the board mounting spacer screws. While you’re preparing the box lid you can also cut the two holes in the The PC board assembly is mounted on four 15mm-long tapped M3 spacers behind the front panel, with the threaded ferrule of switch S1 passing through a matching 6.5mm hole. Check that IRR1’s lens just touches the rear of the front panel and that it is in line with its 6.5mm “viewing” hole. Once everything is in position, fasten the board to the spacers using four round-head M3 screws. Now you can unsolder the temporary joint holding the LED in place on the board. This will allow you to slide it forward until its body just passes through the 3.5mm hole in the box lid/front panel immediately above. Fig.5: this diagram shows the drilling details for the case lid and for the end panel of the base. 38  Silicon Chip siliconchip.com.au That done, you can solder both leads to their board pads permanently. Trim off any excess leads which may be left. Checkout time Your IR Remote Checker should now be complete, apart from fitting it into the box and screwing it all together using the lid attachment screws. Before you do this, connect a 9V battery to the snap lead (or plug the output of a 9V DC plugpack into CON2, if you prefer). That done, turn on switch S1, and you should notice a very brief flash of light from LED1 before it goes dark again. Now bring an IR remote control (one that you know is working!) within a couple of metres of the IR Remote Checker, pointing it roughly at the IR sensor “window”. Then try pressing any of the buttons on the remote and you should be rewarded with a series of flashes from LED1 and simultaneous beeps from the piezo transducer. The pattern of flashes and beeps may change with the various buttons or they may all seem very similar – it depends on the coding used by the remote control concerned. But you should get a series of flashes and beeps when each button is pressed, if the remote is working correctly. So if this is what you get, all that’s left to do is the final assembly of the IR Remote Checker. Fit the 9V battery into the bottom of the box using a length of gaffer tape to hold it down, then manoeuvre the lid/ PC board assembly into position by sliding the RCA connector (CON1) into its matching 11mm hole before swinging the assembly down into position. Fit the four small self-tapping screws supplied with the box to hold it all together and finally fit the soft plastic bungs into each screw recess. Your IR Remote Checker will then be complete and ready for use. Finally, you might want to adjust trimpot VR1 using a small screwdriver, with its shank passing down through the “Beep Freq Adjust” hole in the front panel. As explained previously, this sets the Checker’s oscillator frequency to match the resonant frequency of the piezo transducer, to give the loudest and clearest beeps. This adjustment can be done at any time and is basically a matter of taste. Troubleshooting Of course, if you are NOT rewarded with any flashes and beeps when you send IR codes to the Checker from a known good remote, you must have a fault in the Checker itself. In this case, you’ll have to unscrew the PC board assembly from the box lid and start searching for the fault. You may have fitted one of the polarised components (diode D1, electrolytic caps, transistors Q1 or Q2, LED1, REG1, IRR1 or IC1) the wrong way around, or accidentally left a component lead unsoldered. Or perhaps you’ve left a solder bridge shorting between two pads or tracks on the board, when you were soldering one of the component leads. It’s really just a matter of searching for whatever your SC fault happens to be and then fixing it. siliconchip.com.au Silicon Chip Binders $12.95 REAL VALUE A T PLUS P& P H S ILICON C HIP logo printed in gold-coloured lettering on spine & cover H Buy five and get them postage free! Available only in Australia. Buy five & get them postage free! Just fill in the handy order form in this issue; or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. Silicon Chip Publications, PO Box 139, Collaroy 2097 January 2005  39