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Remote Control Extender For VCRs There's no need to buy a second VCR for the bedroom. This simple project will allow you to operate your VCR using its remote control from any room in the house. By JOHN CLARKE & GREG SWAIN Many families now have two colour TV sets, one usually located in the living room with a VCR and the other in one of the bedrooms. While it's easy to link both TV sets to the VCR (via a splitter), controlling the VCR when you want to watch a video in bed is a problem. Until now, the only way to control the VCR has been for you to get out of bed and go into the living room so that the remote control can be . operated. That's a real nuisance, especially if you want to fast forward over adverts or access any of the VCR's other controls. But now that problem has been solved with our new Infrared Remote Control Extender. It will let you control the VCR from your bedroom using the existing remote control. Basically, the project consists of a receiver that picks up the signal from your remote control. This signal is then converted to an electrical signal and sent down a VCR. Fig.1 shows the basic scheme. Of course, the extender is not only limited to VCRs - it can relay any IR-transmitted signal. Typically, the extender sits next to your TV set and will have a range of 10-15 metres, depending on the output from your remote control. The unit uses inexpensive parts, does not require any special shielding, and is easy to build and install. How it works Refer now to Fig.2 which shows the circuit schematic. There are just two ICs involved, plus a Darlington transistor, a photodiode, an infrared LED and a few other bits. ICl is a Plessey SL486 Infrared Remote Control Preamplifier which is specifically designed for processing received infrared control signals. This device features a differential photodiode input to re- The circuit is housed in a plastic case which is smaller than the remote control. A LED at one end flashes when you activate the remote control to indicate that the signal is being received. 2-wire cable to an infrared LED located near the VCR in the living room. Thus, when you operate your remote control, the IR LED in the living room flashes with the correct code sequence and activates the 24 SILICON CHIP duce noise pickup and an automatic gain control circuit for improved operation in noisy environments. It also incorporates two gyrator circuits and these allow the device to operate in high ambient light conditions. ROOM 2 ~-□ SECONO TV \\ MAIN TV Pulse extender a VCR REMOTE ,_.CONTROL ROOM 1 Fig.1: a typical set-up. The IR extender picks up infrared light from the VCR's remote control and converts it to an electrical signal. This signal is then sent down a 2-wire cable and drives an IR LED located in the same room as the VCR. The incoming IR signals from the remote control are picked up by photodiode D1 (BPW50). This is connected across the differential inputs of IC1 which converts the IR pulses to electrical pulses. These pulses are then amplified and filtered by ICl, with the output pulse train appearing at pin 9. In operation, pin 9 is normally at ground potential but swings high each time a pulse is received from the remote control transmitter. The capacitors on pins 2, 3, 5, 6 and 15 of IC1 roll off the frequency to control the gain of the first three amplifier stages. Schmitt trigger inverters IC2a and IC2b square up the signal from IC1 and drive paralleled inverter stages IC2c, IC2d and IC2e. These in turn drive the base of Darlington transistor Ql via a lkO resistor. Each time a pulse of infrared light is received, Ql turns on and pulses the infrared LED (IRLED 1) via a 4.70 resistor. responses of the gyrator and gain stages below 2kHz. This filters out any 100Hz and 50Hz signals which are generated by mains powered lights and picked up by the photodiode. If this was not done, these noise signals would seriously degrade the receiver's sensitivity and reduce its effective range. Automatic gain control (AGC) is provided by an internal peak detector which measures the output at pin 9. A 0.15µ,F capacitor on pin 8 filters the output of the peak detector and the resultin~ signal is used LED 1 and its associated circuit provide a visible indication that a signal has been received. LED 1 cannot be directly driven by Q1 because this transistor is only pulsed on for very short periods of time. To overcome this problem, a simple pulse extender circuit is used. Each time Ql turns on, the .033µ,F capacitor on pin 3 of IC2f charges via D2. When it reaches a critical level, pin 4 of IC2f switches low and LED 1 turns on. The 100kn resistor discharges the .033µ,F capacitor when the pulses from Q1 cease. Thus, depending on the code from the transmitter, LED 1 will flicker on and off but at a much slower rate than the pulse frequency applied to IRLED 1. Power for the circuit is derived from a 9V DC plugpack which feeds a 7808 3-terminal regular. This provides a fixed + 8V supply rail which is filtered by a 470µ,F capacitor. A 470 resistor and 22µ,F capacitor provide further supply .....--------41.,..._---.........,._______,470W J ~ - - - -.....- - - - - - > - - - - - - - - - - - - - - + 8 V 6.8 16VW 47 _ 16VW + + 470 + 10VW! .0047 _ .033 RECEIVER ACKNOWLEDGE LED1 RED . IC2b 74C14 , 40106 A a, B0682 IC1 SL486 01 BPW50 RECEIVER AMPLIFIER PULSE SQUARER ANO DRIVER .,. +v-------11.........., +BV 9V DC PLUG-PACK -+ m""' ~PLASTIC TRANSMITTER EICl8 IR REMOTE CONTROL EXTENDER r lR LIGHT ACTIVE SIDE K A Fig.2: each time an IR light pulse is received, pin 9 of IC1 switches high. This then drives Ql and IRLED 1 via Schmitt trigger inverters IC2a-IC2e. · SEPTEMBER1990 25 CAPACITOR CODES Value 0.15µF .033µF .015µF .0047µF 56pF LED 1 and Dl are both mounted at full lead length and then bent over so that they fit into holes in the end of the case. It is also necessary to bend the 7808 regulator over slightly to clear the lid. line decoupling for !Cl to prevent false triggering. Construction Most of the parts are mounted on a small PC board coded SC 15108901 (50 x 44mm). Fig.3 shows the parts layout diagram. Begin the assembly by installing PC stakes at points 1 and 2 and at the plus and minus terminals for the power supply leads. Next, install the wire link, followed by the resistors and capacitors. Note that the 470µF capacitor is laid on its side and its leads bent at right angles to pass through the holes on the PCB. Take care with the polarity of the electrolytic capacitors. Diode D2 and the two !Cs can now be mounted. Check the orientation of the two !Cs carefully, as they face in opposite directions. The infrared LED (IRLED 1) is mounted at the end of the 2-wire cable. It can be mounted in a small case or taped in some inconspicuous location near the VCR. The next step is to mount Ql and the 7808 regulator. Push these components down into the board as far as they will comfortably go before soldering their leads. Ql is installed with its metal face towards the 470µF capacitor while the metal IEC Code 100n 33n 15n 4n7 56p EIA Code 154 333 153 472 56 tab of the 7808 goes towards the adjacent lOµF capacitor (see pinout diagrams on Fig.2}. Bend the 7808 over slightly so that its tab does not later foul the lid of the case. LED 1 and Dl are mounted with full length leads so that they can later be bent over to protrude through the side of the project box. Be sure to orient these devices correctly. In each case, the anode (A) lead is the longer of the two. The completed PCB can now be fitted inside the case and used as a template for marking the mounting hole positions. Drill these holes to accept the mounting screws (3mm), then temporarily mount the board in the case on 6mm standoffs and mark out the holes for LED 1 and Dl. Once this has been done, remove the board and drill the hole for LED 1, plus additional holes in the other end of the case to accept the power socket and the rubber grommet. To make the cutout for Dl, first drill a pilot hole, then use a needlepoint file to square up the hole so that the photodiode fits neatly into it. All that remains now is the final assembly. Refit the PCB, install the socket and grommet, and complete the external wiring as shown in Fig.3. You will have to bend the leads of LED 1 and Dl so that these components fit the holes drilled in the case (see photograph). Before soldering the power supply leads to the PCB, it is a good idea TABLE 1: RESISTOR COLOUR CODES □ □ □ □ □ □ 26 No 1 1 1 1 1 SILICON CHIP Value 100k0 1k0 4700 470 4.70 4-Band Code (5%) brown black yellow gold brown black red gold yellow violet brown gold yellow violet black gold yellow violet gold gold 5-Band Code (1%) brown black black orange brown brown black black brown brown yellow violet black black brown yellow violet black gold brown yellow violet black silver brown PARTS LIST 1 ,, l~~K 2---:-0 - - A t TO IRLED1 \ CQY89 RUBBER GROMMET Fig.3: here's how to wire up the IR extender. Take care with component orientation and note that the two ICs face in opposite directions. Check the polarity of the power supply leads using a multimeter before soldering them to the PC board. Testing This view shows how the photodiode (Dt) and the acknowledge LED (LED 1) are mounted. Make the holes so that both components are a tight fit. to connect the plugpack supply and check their polarity with a multimeter. Once you have identified the leads, they can then be soldered to the PC board. The IR LED is connected to the receiver via a long length of light-duty speaker cable. This LED can be either mounted in a separate small case or taped tn some inconspicuous location near the VCR. To test the circuit, apply power and check for + 8V on pin 14 of ICZ. If this is OK, activate the remote control and check that the acknowledge LED flickers. You should be able to do this out to a range of about 10 metres, depending on your remote control. Make sure that light from IRLED 1 cannot reach the receiver during this test procedure, otherwise the receiver will be desensitised. The unit can now be tested with your VCR. You should be able to get a range of at least 4 metres between the VCR and IRLED 1, although this will depend on the sensitivity of the VCR's IR receiver. If need be, the range can be increased by adding a second IR LED in series with IRLED 1. Finally, keep the receiver away from the TV set. If you place it too close, line flyback pulses from the TV can find their way into the receiver's circuitry and degrade the sensitivity. ~ 1 1 4 4 4 plastic case, 54 x 83 x 30mm PCB, code SC15108901, 50 x 44mm front panel label, 80 x 50mm 6mm ID rubber grommet 6mm PCB standoffs screws & nuts for standoffs small rubber feet Semiconductors 1 SL486 IR preamplifier (IC1) 1 40106, 7 4C14 hex CMOS Schmitt trigger (IC2) 1 B0682 PNP Darlington transistor (01) 1 7808 3-terminal 8V regulator 1 BPW50 or equivalent IR photodiode (D1) 1 1 N914, 1 N4148 signal diode (D2) 1 CQY89, LD271 IR LED (IRLED 1) 1 5mm red LED (LED 1 ) Capacitors 1 4 70µF 1 OVW PC electrolytic 1 4 7 µF 16VW PC electrolytic 1 22µF 16VW PC electrolytic 1 1 OµF 25VW PC electrolytic 1 6.8µF 16VW PC electrolytic 1 0.15µF metallised polyester 2 .033µF metallised polyester 1 .015µF metallised polyester 1 .004 7µF metallised polyester 1 56pF ceramic Resistors (0.25W, 5%) 1 1 OOkO 1 470 1 1k0 1 4.70 1 4700 Miscellaneous Twin wire for IR LED, small plastic box for IR LED if required, solder, etc. F Figs.4 & 5: here are actual size artworks for the PC board and the front panel. _:J SEPTEMBER 1990 27