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Mini Projects #004 – by Tim Blythman SILICON CHIP Wired Infrared Remote Extender IR (infrared) remote controls have been around for about 50 years, with TV being one of the first major applications. They are used in many fields, so components and modules for IR remote control systems are widely available. Here’s how to use them to build an IR remote control extender. S ometimes an IR remote doesn’t have enough ‘reach’, especially if the receiving device is in another room, around a corner or blocked by furniture. The Wired IR Extender is a simple fix for that problem; it can easily be built with just a few components. Rather than transmitting the binary ones and zeroes of IR codes as the presence or lack of an IR signal, the IR beam is modulated (turned on and off) at around 38kHz and further encoded to simplify reception and error checking. The modulation helps to make IR signals immune to interference from things like sunlight and fluorescent tubes, since they do not modulate their IR output near 38kHz. A simple design Thanks to the technology packed into modern electronics modules, we can create the Wired IR Extender with a couple of simple modules and a few other bits and pieces. The main components are the IR Receiver Module and an IR LED Module. While it might appear that we could simply connect one to the other, the IR Receiver Module demodulates the 38kHz IR carrier, but the IR LED Module has no internal means of reapplying the modulation. So we need some extra circuitry to add back the necessary modulation. Fig.1 shows the resulting circuit. The 100μF and 100nF bypass capacitors help to reject noise on the 5V supply rail and keep its voltage stable. The IR Receiver Module contains the parts in the box on the left. The part labelled IR1 could be substituted by a separate component like Jaycar’s ZD1952 IR receiver. The output (at the S pin) usually sits near 5V, but when an IR signal around 38kHz is detected, this pin goes low, lighting up the LED on the The Wired IR Extender is built on a small prototyping board, which can easily be put into a small Jiffy box for permanent use. You can run two wires (eg, a figure-8 cable) to situate the Transmitter Module wherever it needs to be. siliconchip.com.au May 2024  65 220Ω 10kΩ The lines drawn on top of the board 2 x 1kΩ module. That is called an activelow output. The 555 timer based circuit turns the active low signal from the IR Receiver Module into a 38kHz modulated active-high signal that can drive the Infrared Transmitter Module, which consists of nothing more than an IR LED (similar to Jaycar ZD1945) on a PCB. NPN transistor Q1 and its two resistors (1kW & 10kW) form an inverter that turns the active low signal into an active high signal. With no IR signal falling on the IR Receiver Module, current flows into Q1’s base, turning it on. When Q1 is on, it conducts current into its collector (C) and out of its emitter (E). The voltage at the collector is therefore low. If an IR signal is received, the S pin goes to 0V and no current flows into the base of Q1, so Q1’s collector voltage can rise to 5V due to current flowing through the 10kW resistor. That allows the 555 to oscillate and deliver a 38kHz-­ modulated signal to the IR LED. The inverted signal from Q1’s collector goes to IC1’s RESET pin (RS, pin 4), so IC1’s output (O, pin 3) is low whenever there is no IR signal. However, when RESET is high, the 555 timer can operate. Its output will be mirror the copper tracks on the underside. 10nF output producing a 38kHz square wave. This signal is applied to the IR LED as long as the IR Receiver 100nF Module receives a signal. Note that when there is no sig100μ 100 μF nal, current through LED1 must flow through both 1kW resistors. When a signal is detected and the S pin is near ground, current only needs to flow through one of the resistors. So you will see the LED’s brightness increase as a signal is received. high after the TRIGGER (Tr) pin goes below 1/3 of the supply voltage, then Construction switches low when the THRESHOLD We built our prototype on a bread(Th) pin goes above 2/3 of the supply board pattern prototyping PCB and voltage. recommend you do the same, as we The TRIGGER (pin 2) and THRESH- found that using a breadboard added OLD (pin 6) inputs are joined, and stray capacitance. Some of this stray the 10nF capacitor is kept discharged capacitance appears in parallel with when RESET is low by the 1kW resis- the 10nF capacitor, slowing down tor. So the 555’s output goes high as the oscillator. That means it may not soon as RESET goes high. work, although we found that many The 10nF capacitor charges up from devices were not too fussy about the the OUTPUT through the 1kW resis- exact frequency. tor until the voltage on it (and thus To help you place and wire up the the TRIGGER and THRESHOLD pins) components, closely examine the reaches 2/3 of the 5V supply. The out- prototype photos; solder the compoput goes low and the 10nF capacitor nents and wires in place as shown. To discharges until the 1/3 supply voltage make it easier to see where the coppoint is reached. per tracks go on the underside of the The cycle continues, with the 555’s PCB, we have drawn lines on the top Pin 1 Fig.1: the two boxes correspond to the modules; they could be replaced by the separate parts in each box. The Receiver Module demodulates the incoming IR signal. Q1 and IC1 add back the modulation before resending the signal via the Transmitter Module. 66 Silicon Chip Australia's electronics magazine siliconchip.com.au Silicon Chip PDFs on USB Scope 1: the blue trace is the voltage at the Receiver’s S pin, while the green trace is the voltage at IC1’s pins 2 and 6 (across the 10nF timing capacitor). The red trace is the voltage across the Transmitter LED, while the yellow trace is the signal from another Receiver Module that is not connected to the circuit. and + and – symbols on the two supply rails. Note that pin 1 of the 555 is near the 100nF capacitor (towards the bottom in both photos). We used stiff wire to join the modules to the PCB. You can use longer wires (or jumper wires) to place the Transmitter further from the Receiver. We recommend using short wires for the Receiver and longer wires for the Transmitter, especially since there are only two wires to the Transmitter. You could use a socket for the IC rather than soldering it directly to the board. Take care with the orientation of the transistor. Its pin 1 (collector) is connected on the same row as IC1’s pin 4, with the Q1’s flat edge facing away from the middle. The white wire in the photo loops over the top of IC1, from its pin 6 to pin 2; add it last. Testing Solder the Transmitter and Receiver modules, but leave off the S wire for the Receiver (yellow in the photos). This allows IC1 to run and the Transmitter will produce a signal continuously, so you can aim the Transmitter at the Receiver to test them both. Apply 5V to the + rail and connect supply GND (0V) to the – rail. The LED on the Receiver module should light up. If you wave your hand between the Transmitter and Receiver, the LED should flicker as the signal changes. If you don’t see this, use an oscilloscope, multimeter or frequency counter to check the frequency at either end of the 220W resistor. Scope 1 shows some of the waveforms you should see. Once the circuit is working, hook up the last wire and deploy the Extender. Don’t aim the Transmitter at the Receiver in use; otherwise, it will be SC confused by its own signal! ¯ A treasure trove of Silicon Chip magazines on a 32GB custom-made USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. ¯ Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). Parts List – Wired IR Remote Extender (JMP004) 1 breadboard-pattern prototyping circuit board [Jaycar HP9570] 1 555 timer IC, DIP-8 (IC1) [Jaycar ZL3555] 1 8-pin DIL IC socket (optional; for IC1) [Jaycar PI6500] 1 IR Transmitter Module [Jaycar XC4426] 1 IR Receiver Module [Jaycar XC4427] 1 BC548 NPN transistor, TO-92 [Jaycar ZT2154] Assorted solid-core wire [Jaycar PB8850] 1 5V DC supply 1 100μF 16V electrolytic capacitor [Jaycar RE6130] 1 100nF 100V MKT capacitor [Jaycar RM7125] 1 10nF 100V MKT capacitor [Jaycar RM7065] 1 10kW 1/2W 1% metal film resistor [Jaycar RR0596] 2 1kW 1/2W 1% metal film resistor [Jaycar RR0572] 1 220W 1/2W 1% metal film resistor [Jaycar RR0556] siliconchip.com.au Australia's electronics magazine EACH BLOCK OF ISSUES COSTS $100 NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 OR PAY $500 FOR ALL SIX (+ POST) WWW.SILICONCHIP.COM. AU/SHOP/DIGITAL_PDFS May 2024  67