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Long-range 16-channel remote control system Based on pre-built UHF transmitter and receiver modules, this versatile 16-channel remote control is very easy to build and requires no alignment. It has a range of up to 1.5km and you can program it to function just the way you want. By JEFF MONEGAL R EMOTE CONTROL SYSTEMS are hardly new but before you write this one off as just another variation, take a look at the features panel. It’s got a lot more features than other standard “run of the mill” remote control projects. Among other things, these features include a 4-digit combi­nation lock to prevent unauthorised use, extra long range (up to 1.5km), 16 independent channels and programmable channel 70  Silicon Chip func­tions. There are also two modes of operation: Mode 1 and Mode 2. Two pre-built UHF modules make this unit really easy to build. The transmitter module is designated the TX434 and uses a SAW resonator to lock the transmission frequency to 433.92MHz. This module is truly tiny, measuring just 20mm long x 8mm wide. It has a data rate of 1200pbs (maximum), a frequency toler­ance of 175kHz and operates from a 3-9V DC supply. It also has seven external connections and is installed “surface-mount” style on the back of the transmitter PC board. At the other end of the link is the complementary RX434 UHF receiver module. This is a full superheterodyne UHF receiver that measures just 44 x 15mm. It is crystal-locked to 433.92MHz, has a sensitivity of 115dBm, operates from a 5V DC supply and has eight external connections (four at either end) which are brought out to pin headers. It is installed directly on the receiver PC board. Both UHF modules are supplied pre-aligned, which means that you don’t have to make any adjustments after assembly. Channel functions Because we’ve got 16 channels to play with, we’ve divided them up into several groups and given them different functions for Mode 1 operwww.siliconchip.com.au Fig.1: the transmitter uses trinary encoder IC1 to feed a coded data stream to a 433MHz transmitter module. The code depends on which pins ((10-14) of IC1 are pulled high by switches PB0-PB16 and the D1-D23 diode matrix. ation. What’s more, you can program the channels at will thanks to a PIC microcontroller that’s buried in the receiver circuit. OK, let’s take a closer look at these channel groupings: Channels 0-5: these channels can be set up for either momentary or toggle operation. When the unit is powered up for the first time, the dewww.siliconchip.com.au fault for all channels is toggle mode. Pressing any of the 0-5 buttons will then change the output state of the associated channel. To change modes, the operator simply holds the required channel button down for more than two seconds (2s), after which a beep will be heard and the button can be released. If the channel was in toggle mode, it will now be in momentary mode and vice versa. It’s as easy as that! Pressing the button again for 2s will swap the modes back again. All changes to the various modes are stored in an EEPROM, so if power is lost and then restored, the channels will all come up with all modes set as last programmed. Note that when a channel is set to momentary mode, its output line goes November 2003  71 Main Features • • • • • • • • 16 channels – see text for channel functions. Up to 1.5km range or further in some cases. 4-digit combination lock with fully reprogrammable code. Two modes of operation – full featured or standard toggle/momen­tary. Back up fail-safe code in case user code is lost or forgotten. Fail-safe code is different for each kit sold. Program boots up in “Locked” mode – system unusable if stolen. All codes, times and modes stored in EEPROM and reloaded at power on. high for 1s and then low again when the corre­sponding transmitter button is pressed and released. Channels 6 & 7: these are non-programmable channels where the outputs go high when their buttons are pressed and remain high while ever the buttons are pressed. These channels could be useful for dimming lights or controlling music volume via suitable interface circuitry. Channels 8-11: these channels all have programmable timers at­tached. Channels 8 & 9 are programmable from 1-255s. Their out­puts go high when activated, then go low again 1-255s later (ie, after the programmed interval). During the last 10 seconds, an inbuilt speaker in the receiver “beeps” every second. Channels 10 & 11 work the same way but their delay times are programmable from 1-255 minutes. Once activated, the speaker “beeps” every minute on channel 10, while channel 11 is totally silent (eg, so that it could control a bedroom fan via a suiable interface) except when first activated. Channels 12 & 13: the outputs of these channels go high when their respective buttons are pressed and remain high until an external event pulls the inputs to these channels low. These channels can also be turned off by simply pressing their respec­ tive buttons on the keypad again. Channels 14 & 15: these channels are programmable from 1-255 minutes. When their buttons are pressed, their outputs remain low but subsequently go high for 1s at the end of their programmed times. Pressing a channel button during the time period simply cancels the end result and the output remains low. Mode 2 In Mode 2, as selected by an onboard link, all channels are the same as channels 0-5 above – ie, all channels are have either momentary or toggle operation. Each individual channel output changes state with each press of its corresponding button on the transmitter. Note, however, that the transmitter button has to first be released before the operation takes place. In other words, to change a channel, you must first press its transmitter button and then release it again. The reason for this will be explained later. As before, a channel output goes high for 1s (when the button is released) and then low again when configured for momentary operation. Stopping unauthorised use A 4-digit combination lock is in- Where To Buy Parts A complete kit of parts for this project (Cat. K192) is available from Oatley Electronics, PO Box 89, Oatley, NSW 2223. Phone (02) 9584 3563. Prices are as follows: Transmitter (K192A): includes PC board, parts, case & keypad label .. $39 Receiver (K192B): includes PC board plus all parts (no case) .............. $69 Postage and packing is $6 and all prices include GST. Note: the PC board copyrights for this design are retained by Oatley Elec­tronics. 72  Silicon Chip cluded so that each time the system is turned on, it comes up in “locked” mode. This means that unless you enter this user code (to unlock the receiver), the unit cannot be used. But what happens if you forget your user code? In that case, the system also has a fail-safe code which, when activated, reprograms the user code to the default of 10-10-10-10. When this is done, the user should immediately program another 4-digit user code into the receiver. The failsafe code is different for every unit that’s sold. It is supplied with the kit and should be kept secret by the owner. How it works Fig.1 shows the circuit details for the 16-Channel UHF Remote Control Transmitter. Apart from the UHF transmitter modu­ le, the only other component of any real note is the SM5023RF trinary encoder (IC1). In addition, there are 16 pushbutton switches, an associated diode matrix (D1-D23), a transistor (Q1), five resis­ tors and a LED. Trinary encoder IC1 has eight coding inputs which can either be individually tied high, low or left open circuit (O/C) to give a unique security code. This gives one of 6561 possible combina­tions but it’s really a bit more complicated than that, as we shall see. In order for the receiver to acknowledge the transmitter, its trinary decoder (IC2) must have the same connections as the encoder (IC1) – ie, the corresponding pins on the encoder (IC1) and the decoder (IC1 on Fig.2) must be connected in the same way (either high, low or open circuit). OK, let’s take a closer look at the transmitter circuit. There are 16 pushbutton switches (PB0-PB16) and when any of these is pressed, one or more of the inputs to IC1 (either pin 10, 11, 12 or 13) is pulled high – either directly or via two or more of the diodes in the switch matrix. The exception here is PB0 which turns on transistor Q1 via a 10kΩ resistor. As with pins 1-8 of IC1, pins 10-13 also function as coding inputs. So when a button is pressed, its corresponding coding inputs are set to logic 1 and the code sequence from IC1 is altered. For example, pressing PB3 pulls pins 10 & 11 high via D2 & D1 respecwww.siliconchip.com.au Fig.2: the coded transmitter signal is picked up by UHF receiver module RX1 and fed to trinary decoder IC1. This decodes the data into 4-bit BCD and drives PIC microcontroller IC2. IC2 processes this BCD data and drives two shift registers (IC3 & IC4). tively. Similarly, pressing PB11 pulls pin 10 high via D14, pin 11 high via D13 & D11 and pin 13 high via D13 & D12. As a result, IC1 transmits one of 16 coding sequences, depending on which button is pressed – thus allowing us to dis­tinguish between the channels. At the same time, pressing any of the switches also turns on NPN transistor Q1 via a 10kΩ base resistor. This in turn pulls the Transmit Enable pin (pin 14) of IC1 low and so the coded data stream appears at pin 17 of IC1 and gates the UHF transmitter module. www.siliconchip.com.au And that’s all there is to the transmitter, apart from a 2.2MΩ timing resistor between pins 15 & 16 of IC1 and a 22nF decoupling capacitor on the supply line. The unit can be run from any suitable 3-9V DC supply (eg, a 9V battery). Receiver circuit At the receiver end, the coded transmission is picked up by the UHF receiver module. This signal is then demodulated and the resulting data stream fed out via pin 2 to pin 14 of IC1, an SM5035RF-M4 trinary decoder. IC1 decodes this data stream into 4-bit BCD. When a valid transmission is received, the decoder places the data on its output pins (pins 10-13), then switches its valid data line, pin 17, high. IC2 detects this valid data signal (at pin 2) and then goes to work processing the BCD data (on pins 6-9) according to its internal software program. Depending on the mode that the microcontroller is currently operating in and the data it receives, this gives the channel functions described above. The 470kΩ resistor between pins November 2003  73 Fig.3: follow this parts layout diagram to assemble the transmitter PC board. Note that all the parts, except for the pushbutton switches, are installed on the copper side of the PC board – see photo. 15 & 16 sets IC1’s internal oscillator (so that it matches the oscillator in the encoder), while the associated 100nF capacitor provides supply line decou­pling. Shift registers Because microcontroller IC2 does not have 16 output pins that we can use, the channel data is sent out in serial form to shift registers IC3 & IC4. Basically, IC3 & IC4 function as “port expanders”, since we don’t have enough output ports on the micro­ controller. They decode the incoming data stream applied to their pin 7 inputs and switch their outputs high or low in response this data. Channels 0-7 are collectively termed “Bank A”, while chan­nels 8-15 make up “Bank B”. The data for all channels is sent to both shift registers at the same time but only pin 18 of the microcontroller is clocked (to clock IC3) when Bank A data is being shifted. Similarly, the microcontroller only provides clock signals from pin 1 when Bank B data is being shifted. As stated above, channels 12 and 13 require negative going inputs (ie, from some external source) to turn them off once they have been activated. This is done by pulling pins 11 & 12 of IC2 low via diodes D5 & D6 and their series 1kΩ resistors. LEDs 3 & 4 are used as status indicators while changing security codes. During normal operation, pins 11 & 12 of IC2 function as inputs and the LEDs turn on to indicate incoming low inputs. Conversely, during programming, pins 11 & 12 function as outputs which turn on the status LEDs. LED1 is the “locked” status indicator LED and is driven by pin 3 of IC2 via a 2.7kΩ resistor. This LED lights when power is first applied (pin 3 low), indicating that the receiver must first be unlocked before it can be used. Installing the optional Mode Select link pulls pin 4 of IC2 low and switches the operation to Mode 2. Normally (ie, for Mode 1 operation), this pin is held high via a 10kΩ pullup resistor. The 47kΩ resistor and its associated 470nF capacitors reset the two shift registers (IC3 & IC4) when power is applied. Clock signals for IC2 are provided by a 3.58MHz crystal oscillator based on X1. The two associated 22pF capacitors pro­vide the correct loading for the crystal, to ensure that the oscillator starts reliably. Pushbutton switch S1 is used for system programming. It pulls pin 10 of the microcontroller low so that new programming values can be entered and stored in the PIC’s EEPROM. Finally, pin 13 of IC2 drives the base of transistor Q1 via a 4.7kΩ resistor. This transistor in turn drives a small loud­speaker which is used as a “beeper” (mainly during programming). Power supply The receiver circuit is powered from a 6V AC plugpack sup­ply. Its output is rectified using bridge rectifier BR1 and filtered by a 1000μF capacitor before being fed to regulator REG1. The +5V output from REG1 is filtered using 100nF and 10μF capacitors and powers all the circuitry. It also lights power indicator LED2 via a 1kΩ resistor. The 2.7kΩ resistor across the supply ensures that the filter capacitors quickly discharge when the power is switched off. Table 2: Capacitor Codes Value 470nF 100nF 22nF 22pF μF Code EIA Code IEC Code 0.47μF 474 470n 0.1μF 104 100n 0.022μF 223 22n   22 22p Table 1: Resistor Colour Codes         No. 1 1 1 7 3 1 21 74  Silicon Chip Value 2.2MΩ 270kΩ 47kΩ 10kΩ 4.7kΩ 2.7kΩ 1kΩ 4-Band Code (1%) red red green brown red violet yellow brown yellow violet orange brown brown black orange brown yellow violet red brown red violet red brown brown black red brown 5-Band Code (1%) red red black yellow brown red violet black orange brown yellow violet black red brown brown black black red brown yellow violet black brown brown red violet black brown brown brown black black brown brown www.siliconchip.com.au This view shows the assembled transmitter PC board, ready for installation in the case. This is necessary to ensure that the microcontroller resets correctly when the power is switched off and then on again within a relatively short period. Construction Construction can start with the transmitter assembly – see Fig.3. Note that all components except for the switches are mounted on the copper side of the PC board. The first step is to install the socket for IC1. This job is straightforward but make sure that you don’t inadvertently create any solder bridges between the IC pads and the adjacent parallel copper tracks. That done, you can install the UHF transmitter module. It’s just a matter of orienting the module so that its solder pads at either end line up with those on the PC board. Once you have the module correctly aligned, it can be held in position with a clothes peg (be careful not to damage the coil) while you solder the connections. The 16 pushbutton switches (PB0-PB15) are installed on the transmitter PC board in the conventional manner. www.siliconchip.com.au You will need good eyesight, a good light and a fine-tipped soldering iron for this job. If you have a magnifying glass or a Mag-Lite, then so much the better. It’s also best to lightly tack-solder a single connection at either end first, then check the module’s alignment before soldering the remaining connec­tions. Transistor Q1, the diodes, the resistors and the 22nF ca­pacitor can now all be installed on the copper side of the PC board. That done, the 16 This view shows the back of the case lid, after the switch membrane has been attached – see text. November 2003  75 Fig.4: install the parts on the receiver PC board as shown here but don't plug the ICs into their sockets until after the initial test procedure has been completed (see text). Parts List Transmitter 1 transmitter PC board, 78 x 50mm 1 TX434 433.92MHz UHF transmitter module 1 18-pin DIL IC socket 16 miniature pushbutton switches (PB0-PB15) 1 22nF MKT capacitor Semiconductors 1 SM5023RF trinary encoder (IC1) 1 C8050 NPN transistor (Q1) 23 1N914 diodes (D1-D23) 1 miniature red LED (LED1) Resistors (0.25W, 5%) 1 2.2MΩ 5 10kΩ Receiver 1 mini-speaker 1 receiver PC board, 126 x 64mm 1 miniature PC-mount pushbutton switch (S1) 1 RX434 433.92MHz UHF receiver module 1 2-way pin header 2 18-pin DIL IC sockets 2 16-pin DIL IC sockets 1 8-pin DIL IC socket 9 2-way PC-mount screw terminal blocks 1 3-way PC-mount screw terminal block 76  Silicon Chip Semiconductors 1 SM5035RF-M4 4-bit decoder (IC1) 1 PIC16F628-04 programmed microcontroller (IC2) 2 4015 dual 4-bit shift registers (IC3,IC4) 2 1N4148 signal diodes (D1,D2) 1 W04 bridge rectifier (BR1) 1 L4949 5V regulator (REG1) 1 C8050 NPN transistor (Q1) 2 5mm green LEDs (LED1, LED4) 1 5mm red LED (LED2) 1 5mm yellow LED (LED3) 16 5mm orange LEDs (LED5LED20) 1 3.579MHz crystal (X1) Capacitors 1 1000μF 16V electrolytic 1 10μF 16V electrolytic 1 470nF monolithic 2 100nF monolithic 2 22pF ceramic Resistors (0.25W, 5%) 1 270kΩ 3 4.7kΩ 1 47kΩ 1 2.7kΩ 2 10kΩ 21 1kΩ Footnote: a complete kit of parts for this design is available from Oatley Electronics – see panel for details. pushbutton switches can be installed from the other side of the board. They must all be oriented correctly but they only fit one way, so you can’t get them wrong. LED1 is installed by pushing it into a 3mm hole from the copper side of the PC board. It’s leads are then bent over and soldered to two pads on the PC board but make sure you get these the right way around – the anode (A) lead goes to the V+ input on the PC board. The LED can be secured in position using a small dab of epoxy adhesive. The transmitter board can bow be completed by fitting a 170mm-long insulated wire antenna at the “ANT” position. The two parallel tracks adjacent to pins 1-8 of IC1 let you set the transmission code – the inside track is at 0V, while the outside track is at +9V (note: it’s the opposite way around on the receiver). This makes it easy to tie the coding pins either high or low by creat­ing solder bridges between the pads and the tracks. Alternatively, you can also leave some of the pins open circuit (O/C). For the time beinsg, it’s best to leave pins 1-8 all O/C, so that there’s no confusion when it comes to testing. Transmitter housing The completed transmitter board is housed in a small plas­tic utility case and the pushbutton switches are activated by pressing a keypad membrane www.siliconchip.com.au The assembled receiver PC board is housed inside a cut-down plastic utility case as shown here. Note the mounting method for the mini-speaker – it’s secured to the tops of IC3 & IC4 using a few “blobs” of silicone sealant. that’s affixed to the top of the lid. The first job is to use the supplied template to mark out the 16 key positions on the lid. The keypad cutouts can then be made in the lid by drilling a series of small holes around the inside perimeter of each marked square, knocking out the centre pieces and filing for a smooth finish – see photo. That done, the keypad membrane can be trimmed to size and carefully affixed to the lid. It’s self-adhesive, so it’s just a matter of removing the backing paper before placing it in posi­tion. You then have to cut sixteen 6 x 7mm squares from the scrap piece of membrane material and stick them to the back of the membrane through each keypad hole. This is necessary to prevent the membrane from sticking to the buttons when the keys are pressed. The PC board sits on top of the corner pillars in the base of the case and is held in position when the lid is screwed down. Note that it will be necessary to remove about 3mm from the top of each pillar, so that they sit 4mm below the top edge of the box. In addition, the matching posts at the corners of the lid have to be filed down by about 1mm. The job is a bit fiddly and has to be done carefully so that the keypad www.siliconchip.com.au membrane just touches the tops of the switches when the lid is screwed down. Receiver assembly Now for the receiver assembly. Once again, this is straightforward and its just a matter of installing the parts on the board as shown in Fig.4 Begin by installing the wire links and resistors, then install, crystal X1, the capacitors, switch S1, the 2-pin header for LK1, the bridge rectifier (BR1) and the IC sockets. Take care to ensure that the transistor and bridge rectifier are correctly oriented. The Table 3: Default Values • • • • • • Channels 0-5 set for toggle outputs. Channel 8 time set at 10s; channel 9 set at 60s. Channel 11 time set at 10 minutes; channel 11 set at 60 minutes. Channels 14 & 15 set at 60 minutes each. The user code is set to 10-1010-10. In Mode 2, all channels are set for toggling outputs. same goes for the electrolytic capacitors but the crystal can go in either way. Next, you can install the 5mm LEDs, taking care to ensure they are all correctly oriented. They can be followed by the PC-mount screw terminal blocks. Leave all the ICs and the UHF receiver off the board for the time being. They are installed later, after you’ve performed a few basic tests. Regulator REG1 should be installed, however. Now for the smoke test – apply power and check that LED 2 lights. If it does, use your multimeter to measure the voltage at the output of REG1 – it should be 5V. This voltage should also be present on pin 14 of IC2’s socket. If all is correct, switch off and plug the ICs into their sockets taking care to ensure that each is correctly oriented and that the correct IC goes in each socket. That done, you can install the UHF receiver module (the round metal can for the SAW filter goes towards switch S1). Finally, complete the board assembly by installing a 173mm-long antenna lead and wiring up the mini speaker. The latter can be secured by using some silicone sealant to attach it to the tops of IC3 & IC4 – see photo. OK, now for a second smoke test. Make sure that the “Mode Select” link is removed, then apply power to the November 2003  77 System Programming: Step-By-Step Programming the unit is quite straightforward using the following step-by-step guide. Note that all programming is done with the Mode Select link removed – ie, programming is done with the receiver operating in mode 1. Changing the user code The user code is changed as follows: (1). Press and hold down the pushbutton switch S1 in the receiv­er. The “happy” sound will be heard. (2). Press button 1, 2 or 3 on the transmitter (any of these buttons will select the “code program mode”). A single tone is heard and the “change code” LED will come on. (3). Enter the old user code. If this is the first time that the code is being changed after building the unit, then the “old user code” is the default of 10-10-10-10. (4). Press the 12 key. If the user has entered the correct “old code”, the “happy” sound will be heard, the “change code” LED will go out and the “enter new code” LED will come on. Converse­ly, if an incorrect code was entered, the “sad” sound will be heard and all programming will be cancelled. The procedure must then be restarted after first releasing pushbutton switch S1. (5). Enter a new 4-digit code, then press key 12 to write the new code into the PIC’s EEPROM. The “happy” sound will be heard and the “enter new code” LED will go out. (6). Release pushbutton switch S1 to resume normal operation. Programming the channel times Channels 8-11 can be programmed with delay times as follows: (1). Press and hold down pushbutton switch S1. (2). Select the channel to be programmed by pressing its key on the transmitter. The speaker will give a series of beeps equal to the channel number. (3). Enter the required time in 78  Silicon Chip seconds for channels 8 & 9 and in minutes for channels 10 & 11. The maximum number that can be en­ tered is 255 and a beep will accompany each key press. (4). Release pushbutton switch S1 – the “happy” sound will be heard. As an example of setting channel 11 to 105 minutes, do this: (1). Press and hold pushbutton switch S1. (2). Press key 11 on the transmitter – 11 beeps will be heard. (3). Press key 1, 0 & 5 on the transmitter. A beep will follow each key press. (4). Release switch S1. The “happy” sound will be heard. That’s it – channel 11 is now set for 105 minutes. This time is also stored in the PIC’s EEPROM each time the unit is powered on. User code fail-safe The PIC program includes a facility to reload the default user code, in case the programmed user code is for­gotten. The procedure is as follows: (1). Install the Mode Select link so that the receiver is now operating in Mode 2. (2). Press and hold down pushbutton switch S1, then turn the power on. The “happy” sound will be heard followed by the “sad” sound. The change code LED and the new code LED will both come on (LEDs 3 & 4). (3). Enter the supplied fail-safe code, then press the Enter key (key 11). Provided the correct code has been entered, the system will now be reprogrammed with the default user code of 10-10-10-10. Conversely, if the entered fail-safe code is incorrect, the sad sound will be heard and you must re-enter the fail-safe code. Once the default code has been reprogrammed, the system operation will return to normal and you can then reprogram a new user code. Do not loose the fail-safe code that’s supplied when you purchase your kit. If you do, the unit will be rendered useless if you forget your user code. unit – you should immediately hear a 3-note sound. This is the “happy” sound and you will hear it a lot during the operation of this project. LED1 (the “locked” indicator) should come on as well. If it does, then the receiver is probably working correctly. If not, then you have a fault somewhere and you will need to go back over your work. The receiver board is housed in a plastic utility case, as shown in the photos. This involves cutting away a 103 x 24mm section from one side of the lid, to provide access to the indicator LEDs. In addition, a matching 103 x 17mm section is cut away from one side of the base, to provide access to the screw terminal blocks. The front of PC board rests on the lip of the cutout, while the back rests on top of the integral slots at the back of the case. These slots have to be trimmed, so that their tops sit 17mm below top of the base (ie, so that they line up with the lip of the cutout). Final testing At this stage you have connected power and the microcon­troller is waiting for the program to be unlocked. To do this, enter the default user code of 10-10-10-10 followed by the enter (11) key. You should be rewarded with the “happy” sound. The system is now ready for use with all programmable func­tions set to the defaults – see Table 3. Once the system has been unlocked, it can be easily locked again by pressing and holding either the 8, 9, 10 or 11 key for more than 3s. At the end of 3s, the Locked LED will come on and the “happy” sound will be heard. Note that because nothing happens when a key is first pressed (only when it is released), none of these channels will be affected provided the button is held down for more than 3s. Finally, once the unit is working correctly, you can code the pin 1-8 address lines. As indicated previously, you code each address pin by either leaving it O\C or by bridging it to the supply rail or to 0V. Just make sure that the transmitter and receiver codes match. Footnote: technical queries on this design can be directed to the author, Jeff Monegal. Jeff can also customise the PIC software if you wish to change the channel functions. His email address is: jmonegal<at>ozemail.com.au www.siliconchip.com.au