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By BEN DOUCHKOV ❋ Circuit uses a microcontroller IC ❋ Features toggle & momentary outputs ❋ Works with any TV or VCR infrared remote control Build an intelligent IR remote controller This simple project allows you to add infrared remote control functions to your favourite equipment. It works with almost any TV, VCR or universal remote control. The idea for this project first occurred many years ago when the author owned an old colour TV that was not remote con­trolled. One feature that was really missed was a remote on/off control but that problem can be easily overcome using this in­frared receiver. It’s based on a 68HC705 micro­con­ troller and can be used to remotely switch appliances such as old TV sets, or to perform a range of remote control functions in other equipment. A few applications that come to mind include amplifier power control, speaker mute functions, model trains, 16  Silicon Chip controlling small motors, robot control, and lighting control. To make it as versatile as possible, the receiver features toggled DPDT relay outputs and two open collector (ie, transistor switched) outputs (designated output 1 & output 2). These outputs are controlled by the channel 1 and channel 2 buttons on the transmitter. The channel 1 button controls the relay outputs, while the channel 2 button toggles output 1. The other open collector output (output 2) is either held low while ever the channel 2 button is pressed (repetitive code transmitter) or briefly pulsed low each time this button is pressed (one-shot code transmitter). Output 1 could thus be used for power switching via a relay or solenoid, while output 2 could be applied to user-controlled functions; eg, slide projector advance or focus motor control. Note: some remote control transmitters only send the code once when a button is pressed and held down, while others will continuously send the code while ever the button is held down. There were two important goals set in developing this pro­ject: (1) it had to be inexpensive; and (2) it had to work with virtually any common TV, VCR or universal IR remote control transmitter. It also had to be flexible so that it could be used in a number of different applications and configurations. A circuit based on a single chip microcontroller was the natural choice and also offers the chance to 5 +5V R1 150k 8 IN+ D1 TFK186  4 F0 R11 10k 1 VCC C4 .01 R3 4.7k GND 6 5 C2 4.7 C1 0.47 3 OUT 2 C1 +5V R4-R8 3 C3 220pF 8 7 6 X2 4 2 F1 4 AC1 +DC D3-D6 4x1N4004 IN C9 1000 3 AC2 IRD 0V PA1 PB5 PA2 IC2 68HC705J2 PB0 OUT IC3 7805 GND PA4 PB2 PA5 PB3 PA6 PA7 PB4 5x10k OSC1 +5V OSC2 R16 R15 1k VIEWED FROM BELOW A K B Q3 BC337 A 17 4 16 3 15 2 14 1 TP 2 C 4 3 E AUX1 AUX2 AUX3 0V 13 12 11 GND 10 C6 22pF +DC +5V 4 5 1 B C R12 1k 18 RELAY 1 D2 1N914  R9 10M C8 4.7 +DC E 2 XTAL1 4MHz C7 22pF I GO PA3 PB1 1 1 0V VCC PA0 5 +DC RESET +5V 19 C5 4.7 7 INCD LED1 9 20 IC1 UPC1490 R2 10  R10 10k C1 NC1 C2 D8 1N4004 D7 1N4004 X1 R14 1k Q2 BC337 B NC2 R13 1k C E Q1 BC337 B +DC OUT C10 .01 2 OUTPUT 1 TOGGLE 3 OUTPUT 2 MOMENTARY C E 1 K +5V OUT 0V INFRARED REMOTE CONTROL Fig.1: signals from the IR transmitter are picked up by photodiode D1 & fed to IR preamplifier stage IC1. The signal from IC1 is then fed to IC2, a 68HC705J2 microcontroller with programmed ROM tables. Its outputs drive Q3 to toggle relay 1, while Q1 & Q2 provide toggle & momentary open collector outputs. tackle more complex applica­tions at a later date. The ability to use an existing TV or VCR remote control transmitter means that you do not have to buy another one. It also means that quite a number of different codes have to be recognised by the microcontroller. This is achieved by using code tables that reside within the microcontroller’s ROM. The ROM codes that were selected for each remote control are for channel 1 and channel 2. With the current version of the software, 10 different transmitter groups (five TV and five VCR) are recognised. Each of these groups covers a number of different manufacturers and models, which means that a wide range of trans­mitters can be used. Unfortunately, not all the popular manufacturers and models can fit within the limited amount of ROM available and so, for this reason, a general purpose learning mode is also included. This mode allows one remote control code to be learned when the project powers up or is reset. The learnt code is stored in RAM and is lost when power is removed. Note that, due to the limited amount of RAM within the microcontroller used, only one code can be learned and so the same button is used to control all three outputs simultaneously. Thus, if the receiver is using a learned code, pressing the transmitter button will toggle the onboard relay, toggle output 1 and either pulse output 2 or acti­vate output 2 for as long as the code is received. Although not guaranteed to work with all transmitters, this mode does allow the use of a lot of remote control transmitters that would otherwise be March 1994  17 XTAL 1 R16 C1 NC1 NC2 +5V R8 10k R7 10k R6 10k R5 10k R4 10k RELAY 1 C2 22pF 10M 1 0V 10k 1k 10k 4.7k IC2 68HC705J2 X1 4.7uF 1k 1k .01 IC3 7805 X2 150k 4.7uF F1 1k AC1 1 D2 AC2 +DC OUT 0V 0V AUX3 AUX2 AUX1 +5V OUT 22pF 1000uF A LED1 K Q1 0V OUTPUT 1 OUTPUT 2 Q2 +5V OUT +DC OUT .01 D8 D7 10  Q3 D3-D6 0.47uF 220pF 4.7uF D1 IC1 UPC1490 K A Fig.2: install the parts on the PC board exactly as shown here & be sure to use a socket for the 68HC705J2 microcontroller (IC2). Pin 1 of IC1 can be identified by the adjacent dot in its plastic body. Note that although shown here & in Fig.1, the auxiliary outputs are unused in this version of the project. unsupported. It also allows the user to customise the code to which the unit responds. Circuit description The circuit can be broken down into three blocks: a power supply stage, an infrared preamplifier stage, and the microcon­ troller stage. Fig.1 shows the details. The power supply consists of fullwave rectifier D3-D6, filter capacitor C9 and 5V regulator IC3. Because the project may be incorporated into a piece of equipment, an onboard fuse (F1) is also included. This fuse is nominally rated at 0.75A but can be changed to suit the external circuit being powered via the receiver. The power supply screw terminals (X2) provide easy termina­tion for the input power (AC1 and AC2). These terminals can accept either 9-20VAC or 12-30VDC (the polarity does not matter). In addition, the output from the bridge rectifier is fed to a +DC terminal and this could be useful for powering external circuits. The infrared preamplifier (IC1 – UPC1490) was selected for its ability to operate from 5V and because no external inductor is necessary. However, the key to any infrared receiver is the quality of the infrared detector (D1) and, after a number of experiments, it was found that a BPW90 photodiode gave good per­formance. Unfortunately, it appears that this photodiode is no longer manufactured and so an equivalent unit from Tele­funken, the TFK186, was used. In operation, D1 picks up the infrared pulses from the transmitter and applies the resulting current pulses to pin 8 (IN+) of IC1. R2 and C1 set the initial gain and low frequency Specifications Range ���������������������������8-15 metres (depending on transmitter used). Power supply �����������������12-30V DC or 9-20VAC. Outputs �������������������������DPDT relay contacts; two open collector outputs; 1 indicator LED. Codes (preset mode) �����Channel 1 toggles the DPDT relay; channel 2 toggles open collector output 1 and either pulses open collector output 2 low or holds this output low for as long as the button is pressed. Learned mode ���������������A single button toggles the DPDT relay, toggles open collector output 1, and either pulses open collector output 2 low or holds this output low for as long as the button is pressed. 18  Silicon Chip roll-off for the input amplifier inside IC1, while R1 sets the bandpass filter. These components were selected to provide a wide bandpass. C2 is the detector capacitor, while C3 is the inte­grating capacitor. These were selected to provide maximum sen­ sitivity but the receiver can be detuned if necessary by changing C3. The output from IC1 appears at pin 2. This is an open collec­tor output and so requires a pull-up resistor (R3). C4 provides additional pulse filtering. Microcontroller IC1 drives the PB5 (pin 3) input of IC2, an MC68HC705J2 micro­controller from the 68HC05 family. This device uses CMOS technol­ogy and has 2064 bytes of program space and 112 bytes of static RAM. The “J2” also has 13 input/output pins and an inbuilt timer. Resistors R4-R8 on lines PB0-PB4 are used to select the desired ROM code and are connected to either the 0V or 5V rails, depending on the transmitter – see Table 1. This means that the input port lines (PB0-PB4) are either pulled to 0V or 5V. A DIP switch could have been used here but as the configuration will probably be permanent, the cost of the switch was saved by using only resistors. It is worthwhile mentioning several important control lines for the microcontroller. These are the oscillator, reset and IRQ (interrupt request) lines. C5 provides the power-on reset pulse by holding pin 20 low for a brief period after power is applied. During this period, the oscillator starts and this operates at 4MHz as set by crystal XTAL1 between pins 1 and 2. When the receiver is switched on, the software goes through its reset routines. One of these routines is designed to flash an on-board LED (LED 1) four times each time power is applied. If the receiver has been con­figured for one of the ROM codes, the microcontroller will then sit in the main program loop, waiting for infrared pulse signals from the transmitter. When a valid signal is received, LED 1 pulses on and off in sympathy with the pulse code. This feature is useful for testing the range of the receiv­er. If the Learning mode has been selected, the microcon­ troller will sit in a program loop after power-up looking for the infrared code to be learned. Some codes are easier for the Mount the relay separately from the PC board if you intend using it to switch mains voltages. Alternatively, you can leave the relay on the board & use it to control a slave relay. TABLE 1: Mode Selection Transmitters Type Learning mode (only one code) Setting R8 R7 R6 R5 R4 0 0V 0V 0V 0V 0V mains appliances, mount the relay off the board or use it to control an external slave 240VAC-rated relay. Resistor R16 is used to limit the current through the relay coil when the output voltage from the bridge rectifier (D3-D6) is higher than 12V DC. This rectified voltage is measured across C9. The nominal coil current is 45mA so the value of R16 is calculat­ed using the formula R16 = (VDC - 12)/0.045. Table 2 shows a range of suitable resistor values. Outputs PA5 and PA6 drive transistors Q1 and Q2 and these respectively provide the toggled and momentary open-collector outputs (output 1 and output 2). Each output is used by connect­ing the load between the collector of the transistor and either the +5V rail or the +DC rail, depending on the application; eg, a relay could be connected between Q1’s collector and the +DC rail exactly as shown for relay 1 and Q3 (don’t forget the current limiting resistor for voltages greater than 12V - see Table 2). Diodes D7 and D8 are there to protect Q1 and Q2 from any high back- EMF voltages that may be generated by inductive loads. Note that Q1 and Q2 have a maximum current rating of 1A. Akai, Goldstar, Magnavox, Marantz, AWA/Mitsubishi, NEC, Samsung TV 1 0V 0V 0V 0V 5V Marantz, AWA/Mitsubishi TV 2 0V 0V 0V 5V 0V GE, Panasonic TV 3 0V 0V 0V 5V 5V Panasonic TV 4 0V 0V 5V 0V 0V Sony TV 5 0V 0V 5V 0V 5V Construction Hitachi, Pioneer, RCA, Toshiba VCR 6 0V 0V 5V 5V 0V Sony Beta, Zenith Beta VCR 7 0V 0V 5V 5V 5V Canon, GE, Magnavox, Memorex, Panasonic, Realistic VCR 8 0V 5V 0V 0V 0V Realistic, Sharp VCR 9 0V 5V 0V 0V 5V AWA/Mitsubishi VCR 10 0V 5V 0V 5V 0V The construction is straightforward since all the parts are mounted on a small PC board (code IRJ201, 105 x 58mm). Fig.2 shows the parts layout. No particular order need be followed when installing the parts on the PC board, although it’s best to leave the larger parts until last. Take care when installing the semiconductors and electrolytic capacitors, since these parts are all polarity conscious. The crystal (XTAL1) can be installed either way around; its leads should be bent through 90° so that it will lie flat against the PC board. IC1 can be soldered directly to the PC board, while IC2 should be mounted using a 20-pin IC socket. Pin 1 of IC1 can be identified by the small adjacent dot in the plastic body of the device. The cathode (K) of the photodiode (D1) can be identified by the bevelled edge along one corner (see the pinout diagram on Fig.1) The five 10kΩ resistors (R4-R8) on pins 4-8 of IC2 must be installed so that they select the required ROM code for your transmitter. As mentioned re­ceiver to learn than others, so several attempts may be necessary to teach the receiver the desired code. Outputs The PA7 output from IC2 toggles high or low on each succes­sive press of the channel 1 transmitter button and this output drives NPN transistor Q3. Q3 in turn switches relay 1 on or off to open or close the two sets of contacts. Relay 1 is ideally suited to switching low voltage circuits such as loudspeaker lines and 12V power supply rails. The relay contacts are rated at 240VAC 5A but, due to the close proximity of the contacts to the rest of the circuit, it is not recommended that the relay be used for directly switching mains appliances. If you do wish to switch 240VAC TABLE 2 Voltage Across C9 R16 12V Link 18V 120W 0.5W 24V 270W 1W 27V 330W 1W 30V 390W 1W March 1994  19 PARTS LIST 1 IRJ201 PC board 1 20-pin IC socket (for IC2) 4 plastic PC board standoffs 2 4-way screw terminals 2 2AG fuseclips 1 2AG 0.75A fuse (F1) 1 FBR621D012 12V relay 1 4MHz crystal (XTAL1) Semiconductors 1 uPC1490 IR amplifier IC (IC1) 1 68HC705J2 programmed microcontroller (IC2) 1 78055 5V regulator (IC3) 3 BC337 NPN transistors (Q1,Q2,Q3) 1 TFK186 infrared photodiode (D1) 1 1N914 silicon diode (D2) 6 1N4004 silicon diodes (D3-D8) 1 5mm red LED (LED1) Capacitors 1 1000µF 35VW electrolytic (C9) 3 4.7µF 16VW electrolytic (C2,C5,C8) 1 0.47µF 16VW electrolytic (C1) 2 0.01µF monolithic (C4,C10) 1 220pF ceramic (C3) 2 22pF ceramic (C6,C7) Resistors (0.25W, 5%) 1 10MΩ (R9) 1 150kΩ (R1) 7 10kΩ (R4 -R8, R10-R11) 1 4.7kΩ (R3) 4 1kΩ (R12-R15) 1 10Ω (R2) 1 R16 – 0.5W or 1W (see text & Table 2) Miscellaneous Two LEDs plus two 1kΩ resistors for testing open collector outputs; plastic case; red plastic window. Take care when installing the infrared photodiode (D1). It must be oriented so that its bevelled top edge goes towards diode D7 (see Fig.1 for case outline). The two large LEDs were installed temporarily to test the open collector outputs. previously, each resistor can be con­ nected to either the 0V rail or to the +5V rail. Table 1 shows the codes for a range of TV and VCR transmitters. By way of example, let’s assume that you have a Sony TV remote control. In that case, you would use setting 5; ie, R4 & R6 connect to the +5V rail, while R5, R7 & R8 go to the 0V rail. Similarly, if you have a Sharp VCR remote control, then setting 9 is the one to use (ie, R4 & R7 to +5V and R5, R6 & R8 to 0V). R16 must be selected so that when relay 1 is on, only 12V DC is applied across its coil. It should be left off the PC board for the time being. Testing Once the board assembly is completed, go back over your work carefully and check that all parts are correctly Where to buy the kit Parts for this project are available from Benetron Pty Ltd, PO Box 43, Quakers Hill, NSW 2763. Phone (02) 963 3868. Prices are as follows: (1). PC board plus all on-board components (includes programmed microcontroller but does not include case or power supply) .....................$55 (2). Preprogrammed infrared transmitter ...............................................$40 (3). Programmable infrared transmitter (controls up to eight receiv­ers; does not come pre-programmed) ..........................................................$55 Please add $5 p&p for receiver only or $10 p&p for receiver plus transmitter. Payment can be made via cheque, money order or credit card. Note: copyright of the PC board and the ROM code in the microcon­troller is retained by Benetron Pty Ltd. 20  Silicon Chip oriented. This done, connect a power supply to the AC1 and AC2 terminals. Either a 9-20VAC supply or a 12-30V DC supply can be used. It doesn’t matter which way around you connect a DC supply to these terminals because of the presence of bridge rectifier. Switch on and check that LED 1 flashes four times as the unit powers up. The LED will now probably continue flashing in a random fashion due to stray infrared signals from various sources (eg, fluorescent lights). This is quite normal and does not interfere with the operation of the unit. The next step is to measure the DC voltage across the 1000µF capacitor (C9). Resistor R16 can now be selected from Table 2 and installed on the PC board (switch the power off first). Re-apply power and check that the relay toggles each time you press the channel 1 button on the transmitter. If it does, then the unit is probably fully functional but you will need to wire up some LED indicators to verify the two open collector outputs (output 1 & output 2). This can be done by connecting a LED and a series 1kΩ resistor between each output and the +5V rail (LED anode to +5V). This done, check that the LED connected to output 1 toggles each time the channel 2 button is pressed. Depending on the remote control, the LED on output 2 should either flash briefly each time the channel 2 button Setting Up A Universal Transmitter If you purchase the Bondwell preprogrammed universal trans­mitter, it will have to be correctly set up before it can be used with the receiver. This involves programming an appropriate 2-digit code to match a particular TV set or VCR into the unit, as set out in the manual. Once this has been done, it’s then simply a matter of choosing the appropriate connection for resistors R4-R8 from Table 1. Alternatively, you can use a programmable transmitter (ie, one which learns its codes from existing TV and VCR transmitters). A suitable unit is available from the author that can control up to eight separate receivers. is pressed or remain on for as long as the button is held down. Troubleshooting Check the following points if the unit appears to power up correctly but fails to operate: (1). If the channel 1 and channel 2 keys don’t work, then try the other keys. The reason for doing this is that different manufac­ turers use similar codes but with different key assignments on their transmitters. (2). Some manufacturers use a number of different codes so, if the receiver doesn’t work with a particular transmitter, try another setting from Table 1. (3). If all else fails and you cannot find a ROM code for a transmitter, try the Learning mode. Remember, however, that the learnt code is stored in RAM and is lost if the power is switch­ ed off, as mentioned previously. Note that, due to the limited amount of RAM available, some of the longer codes that are used will not be sampled completely and the receiver may respond to other codes that match the limited sample stored. Keep other light sources to a minimum during the learn­ ing process and position the trans­ mitter close to the receiver so that it swamps out any interference from such sources. It’s surprising just how much 50Hz and 100Hz pickup there can be from mains-powered lighting! If you do strike problems here, a red window placed in front of the photodiode (D1) can help filter out some of the unwanted infrared signals. Failing that, the best procedure is to tempo­rarily disconnect the indicator LED and teach the unit the code in the dark. It’s simply a matter of pointing the transmitter at the photodiode and pressing the channel 1 and channel 2 buttons in turn. Performance If you don’t wish to use an exiting TV or VCR remote control, this Bondwell universal remote control can be used instead. It comes preprogrammed with a range of transmitter codes. The exact range is difficult to specify, as this will depend on the transmitter output. Generally, you can expect a range of about eight metres and this is what was achieved by the prototype when combined with a Bondwell universal transmitter. Installing the unit in a plastic case with a red plastic window in front of the photodiode reduced the range to about seven metres. Some transmitters, however, will give a range of up to about 15 metres, although it is necessary to earth the 0V rail to reduce interference from unwanted sources to achieve this figure. In some cases, this can be done by connecting the 0V rail to the earth rail of the equipment SC being controlled. March 1994  21