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This simple device lets you operate your VCR using its remote control from another room in the house. It picks up the signal from the handpiece and sends it via a 2-wire cable to an IR LED located close to the VCR. Remote control extender for VCRs By RICK WALTERS have two or more TV sets which M are linked (via antenna cable) to a single VCR. The problem is, you can’t directly control the VCR from another room in the house. ANY HOUSEHOLDS NOW For example, you might want to watch a video on a second set in the bedroom but if you want to stop, fast forward or freeze-frame the action, you have to “walk” the remote control to the room where the VCR lives. Wouldn’t it be great if you could control the VCR directly from your bedroom? Well, the answer is you can – by building this simple Remote Control Extender circuit. It packs into a small plastic zippy case and should only take you half an hour to assemble. In use, the device sits on top of the remote TV set (or in some other convenient location in the room) and picks up the signals from the VCR’s remote control. It then converts these signals into electrical impulses and feeds them down a thin 2-wire cable to an IR (infrared) LED placed in front of the VCR. Because the IR pulses from this LED mimic the IR pulses from the remote control handpiece, the VCR responds in exactly the same fashion. It’s as though the handpiece was being operated in the same room as the VCR. Fig.1 shows the basic scheme. It’s been done before OK, we confess that the idea is not new – designs for remote control extenders have been published before. Our last unit was described in April 1994 and was very popular. However, the SL486 IR preamplifier IC used in that design is no longer available and so this circuit is now obsolete. July 1996  31 Fortunately, a new IC which can do the job has recently appeared. This device, from Dick Smith Electronics, carries a Z1954 type designation and is actually a complete IR receiver subsystem. An equivalent part, designated PIC12043, is available from Oatley Electronics. In both cases, the device comes in a TO-220 style package with an integrated plastic lens on one side. This lens sits in front of an integral IR receiver diode. As well, the device includes amplifier, limiter and bandpass filter stages, plus a demodulator. Its on-axis reception distance is quoted as eight metres but this will obviously depend on the intensity of the light output from the remote control. Circuit details Because so much circuitry is packed into the Z1954, the final circuit of the extender is much simpler than previous designs – see Fig.2. Apart from the Z1954, there’s just one low-cost CMOS IC, a transistor, an IR LED and a few sundry bits and pieces. Each time the VCR’s remote control is operated, it sends out bursts of pulsed IR radiation. These bursts are picked up by the IR photodiode inside IC1, converted to electrical signals and fed to the internal amplifier and filter stages. The demodulated output appears at pin 1 and is fed to pin 2 of NOR gate IC2a (note: this gate is actually wired in parallel with IC2d but Fig.1: the unit picks up infrared (IR) 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. wave oscillator stage based on NOR gates IC2b and IC2c. The output from this stage appears at pin 10 of IC2c and is fed to pin 3 of IC2a, where it is gated by the signal from IC1. The output from IC2a is depicted by the bottom waveform in Fig.3. This signal drives transistor Q1 via a 2.2kΩ resistor. Q1 in turn drives IRLED1 which is at the end of the 2-wire cable and is positioned where it can be “seen” by the sensor in the VCR. Because the signal drive to IRLED1 mimics the transmitted signal, the VCR will obey all the remote control functions. Trimpot VR1 allows the oscillator frequency to be adjusted to suit your VCR (or whatever piece of equipment you are control­ling). The frequency is usually not all that critical and will typically be somewhere around 30-40kHz. Power for the circuit is derived from a 9V DC plugpack supply via reverse-polarity protection diode D1. The resulting supply rail is filtered using a 470µF capacitor and regulated to 5.1V using ZD1 and a 470Ω resistor. Finally, an acknowledge Fig.2: the circuit is based on IC1 which is a complete IR receiver subsystem. When IR LED is connected in series light is received, IC1’s output switches high and low. This signal is applied to NOR with a 1kΩ resistor between gate IC2a,d and gates an oscillator signal generated by IC2b and IC2c. The gated the positive supply rail and signal then drives transistor Q1 which in turn drives infrared LED IRLED1. 32  Silicon Chip we’ll just talk about IC2a to simplify the circuit description). The top two waveforms in Fig.3 depict the transmitted signal and the signal at pin 1 of IC1. Note that the latter waveform has been stripped of the carrier and that it is inverted compared to the transmitted signal. Unfortunately, we don’t want to lose the carrier but we don’t have a choice with IC1. To overcome this, a suitable carri­er is regenerated using a square- lead will be the longer of the two. The IR sensor (IC1) should be installed so that it sits about 5mm above the board surface. The IR LED (IRLED1) is connected via a suitable length of figure-8 cable. This is wired as follows: (1) slide a 50mm length of 5mm-diameter heatshrink tubing over one end of the cable; (2) separate the leads at this end and slide a 30mm length of 2mm-diameter heatshrink tubing over each lead; (3) strip the ends of the leads and solder them to the LED. Con­nect the black trace lead to the cathode and the plain lead to the anode. (4) Push the 2mm heatshink tubing over each soldered joint and shrink it down using a hot-air gun. This done, cover both leads with the 5mm tubing and shrink it down as well. The other end of the cable goes to the jack plug. Connect the black trace lead to the centre pin – ie, to the tip terminal. The plain lead goes to the outer pin. Fig.3: this diagram show the waveforms at various points in the circuit. The output waveform is obtained by gating the middle two waveforms together using parallel NOR gates IC2a and IC2d. Testing Fig.4: install the parts on the PC board as shown in this diagram, taking care to ensure that all polarised parts are correctly oriented. the output of IC1. Normally, IC1’s output is high and LED 1 is off. When the remote control is operated, IC1’s output pulses low and LED 1 lights to indicate that the code is being received. Putting it together The circuit is built on a small PC board coded 15107961. This should be carefully checked for etching faults before you begin assembly. Fig.4 shows where the parts go. Fit the two wire links first, then the six resistors and the two diodes. This done, install the trimpot, transistor Q1, both jack sockets and the ca­ pacitors. Make sure that the diodes and the electrolytic capaci­ tors are correctly oriented. Next, install the acknowledge LED so that it sits about 12mm proud of the PC board. Again, make sure that the LED polari­ty is correct – the anode The unit can now be bench tested to check that it is work­ing properly. Before applying power, check that the centre pin on the 2.5mm power plug is positive. If it is, plug it into the power socket and plug the IRLED lead into the other socket. Now aim the remote control at the IR sensor, press a button and check that the acknowledge LED flashes. If it doesn’t, check the supply voltage to IC1 and IC2 (it should be 5.1V). If everything is OK so far, place the IR LED in front of the VCR and position the Remote Control Extender in another room. Operate the remote control and check to see if the VCR responds. If it doesn’t, hold down a button on the remote control and slowly adjust VR1 until it does. SILICON CHIP Fig.5: check your board carefully against this full-size etching pattern before mounting any of the parts. Fig.6 (right) shows the full-size front panel artwork. REMOTE CONTROL EXTENDER July 1996  33 PARTS LIST 1 PC board, code 15107961, 78 x 33mm 1 plastic utility case, 28 x 54 x 83mm 1 9V DC plugpack with 2.5mm plug 1 3.5mm PC-mounting socket 1 2.5mm PC-mounting socket 1 3.5mm line plug 2.5mm 1 50mm length 5mm-dia. heatshrink tubing 1 60mm length 2mm-dia heatshrink tubing 1 length of figure-8 light duty speaker cable to suit 1 10kΩ horizontal mount trimpot (VR1) The assembled PC board fits neatly inside a standard plastic case and is held in place by the collars of the jack sockets and by the acknowledge LED. Once the VCR operates, find the minimum and maximum trimpot settings and adjust it to the mean position. If it doesn’t work, go over the PC board carefully and check for missing or bad solder joints. You should also check that all polarised parts (ICs, transistor, LED, diodes and elec­ trolytic capacitors) have been correctly oriented and that all resistor values are correct. Once testing has been completed, the PC board can be in­stalled in the case. Note that you will have to drill four holes (two at each end) to accept the jack sockets, the acknowledge LED and the lens of IC1. The PC board is then pushed down into the case so that the collars of the sockets protrude through their respective holes. After that, it’s simply a matter of pushing the acknowledge LED into its hole and aligning the lens of IC1 with its hole, so that it can “see” the IR pulses from the remote control. Finally, if you find a plugpack sup- Semiconductors 1 IR subsystem (IC1); DSE Z1954 or Oatley Electronics PIC12043 1 74HC02 quad NOR gate (IC2) 1 BC548 NPN transistor (Q1) 1 1N4004 power diode (D1) 1 5.1V 400mW or 1W zener diode (ZD1) 1 IR LED, 940nm, Oatley 600D or equivalent (IRLED1) 1 5mm red LED Capacitors 1 470µF 16VW PC electrolytic 1 100µF 16VW PC electrolytic 1 680pF 100VW MKT polyester Resistors (0.25W, 1%) 1 100kΩ 1 1kΩ 1 8.2kΩ 1 470Ω 1 2.2kΩ 1 220Ω Top: the lens of the IR sensor (IC1) must be aligned with a hole in the end of the case, so that it can “see” the pulses from the remote control. Above is a close-up view of the IR LED. ply inconvenient, the unit can be run from a 9V battery. Its current consumption is around 8mA under quiescent conditions and around 25mA when puls­ing. Don’t forget to turn it off when you are finished as the battery will not last very long if the unit is left on SC continu­ously. RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 1 1 1 1 1 34  Silicon Chip Value 100kΩ 8.2kΩ 2.2kΩ 1kΩ 470Ω 220Ω 4-Band Code (1%) brown black yellow brown grey red red brown red red red brown brown black red brown yellow violet brown brown red red brown brown 5-Band Code (1%) brown black black orange brown grey red black brown brown red red black brown brown brown black black brown brown yellow violet black black brown red red black black brown