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Both the receiver top and the transmitter (bottom) are based on pre-built UHF modules, so they are easy to assemble. Do you have an application for a multichannel UHF remote control? This one has long range, four inde­pendent channels and can be built in less than 30 minutes. T By GREG SWAIN HIS IS BY FAR the longestrange UHF link ever described in SILICON CHIP – over 1km according to Oatley Electronics (the project’s developers). It’s also by far the easiest to build, thanks to prebuilt UHF transmitter and receiver modules. There are lots of things you could use this 433MHz UHF remote control unit for. Both the transmitter and receiver are smaller than a match box, making it suitable as a hand-held remote control for alarm systems, gar­age doors and electric door strikers. It can 74  Silicon Chip also be used for controlling pumps and gates (eg, on a small farm) and for remote data collection. It all depends on the circuitry you “hang off” the four outputs on the receiver PC board. A feature of the transmitter is its four separate pushbut­ ton switches -–one for each channel. However, depending on your application, these could be removed and replaced with a cable carrying data from a PC or some other device capable of generating 5V logic signals. Note too that the transmitter will accept single or simultane­ous button presses, or even BCD data. So, by connecting a suit­able decoding chip to the receiver, you could control up to 16 separate outputs. For example, you could use a 4514 4-to-16 line decoder for controlling up to 16 outputs or a 4028 BCD-to-decimal decoder for controlling up to 10 outputs. Pre-built UHF modules The two pre-built UHF modules are what makes this unit so 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 ±75kHz 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. www.siliconchip.com.au 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 pre-built and pre-aligned, which means that you don’t have to make any adjustments after assembly. Circuit details Fig.1 shows the circuit details for the 4-Channel UHF Remote Control. Apart from the UHF modules, the only other components of any real note are the trinary encoding and decoding ICs (IC1 & IC2, re­spectively). These each have 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 this, 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 (IC2) must be connected in the same way (either high, low or open circuit). Let’s take a closer look now at the transmitter circuit. There are four pushbutton switches and when any of these is pressed, its corresponding input on trinary encoder IC1 (either pin 10, 11, 12 or 13) is pulled high. As with pins 1-8, these pins also function as coding inputs. So, when a button is pressed, its corresponding coding input is set to a logic “1” and the code sequence from IC1 is altered. As a result, the coding sequence from IC1 depends on which button(s) have been pressed, thus allowing us to distinguish between 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. And that’s all there is to the transmitwww.siliconchip.com.au Fig.1: the transmitter (top) uses trinary encoder IC1 to feed a coded data stream to a 433MHz transmitter module. The transmitted signal is then picked up by the receiver module and fed to trinary decoder IC2. ter, apart from a 2.2MΩ timing resistor (R5) between pins 15 & 16 of IC1 and a 22nF decoupling capacitor (C1). The unit can be run from any suitable 3-9V DC supply (eg, a 9V battery). Note: do not run the transmitter module from a higher supply voltage, otherwise the maximum permitted output level of 25mW may be exceeded. Receiver circuit At the receiver end, the coded UHF transmission is picked up by the RX434 UHF receiver module which then feeds the data stream to IC2, an SM5035RF-M4 trinary decoder. If a June 2003  75 It works like this: each time the clock input (CP1) of the 4013 goes high, its Q1 output (pin 1) will toggle (either low to high or high to low). As a result, the relay either latches on or releases. If you don’t want the latching function, just delete the 4013 and connect the relevant output from the SM5035RF-M4 trinary decoder direct to Q1’s 10kΩ base resistor. Construction Fig.2: this simple relay driver circuit can be connected to a receiver output and wired for either latching or momentary operation. valid data code sequence is received, pin 17 of IC2 goes high and lights LED2 via a 2.2kΩ current limiting resistor. At the same time, pins 10, 11, 12 and 13 will momentarily go high, depending on which transmitter button(s) were pressed. For example, if switch PB1 in the transmitter is pressed, then pin 13 of IC2 will momentarily go high. Similarly, if PB1 & PB3 are pressed simultaneously, then pins 13 and 11 of IC2 will go high, and so on. Resistor R7 (470kΩ) sets IC2’s internal oscillator so that it matches the oscillator in IC1, while capacitors C2C4 provide power supply decoupling. The circuit is powered from 9V DC, with regulator REG1 (L4949) providing a +5V rail to power the UHF receiver module and IC2. Momentary or latching? The trinary decoder specified in this unit is the SM5035RF-M4, which has four momentary outputs – ie, one or more of its outputs momentarily go high when valid data is received on its pin 14 input. In practice, each output goes high for as long as its corresponding transmitter button is held down. Alternatively, if you want latching outputs, the SM5035RF-L4 can be directly substituted for the “M4” version. This chip will latch its relevant output high if a button is pressed on the transmitter but note that if another button is subsequently pressed, this output will go low again. This means that if you want two latched outputs on at once, you have to press two buttons on the transmitter simultaneously. There’s just one further wrinkle here – Oatley Electronics do not currently stock the “L4” version of the trinary decoder. However, they do intend making it available in the near future. Alternatively, if you want a latching relay driver circuit, take a look at Fig.2. It’s pretty simple and just consists of a 4013 D-type flipflop (ie, one half of a dual package), a transis­tor, a diode, a relay, a couple of resistors and a capacitor. This photo shows how the pre-built UHF transmitter module is mounted on the back of the PC board. 76  Silicon Chip Both the transmitter and receiver are constructed on PC boards measuring just 48 x 29mm. Fig.3 shows the parts layout details. We suggest that you start with the transmitter assembly. The first thing to do here is to install the miniature UHF trans­mitter module. This mounts on the back of the PC board (in the position indicated by the screen printing on the top) – see Fig.3. 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 seven con­nections. 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. Once the UHF module has been mounted, the remaining parts can be installed. These include the four pushbutton switches (they only go in one way), transistor Q1, the capacitor and the resistors. Note that the resistors are all installed “end-on”. The pre-built UHF receiver module is installed on the receiver PC board via two integral 4-way pin headers. www.siliconchip.com.au Parts List Transmitter 1 PC board, 48 x 29mm 1 TX434 433.92MHz UHF transmitter module 1 18-pin DIL IC socket 4 miniature pushbutton switches (PB1-PB4) 1 22nF MKT capacitor 1 SM5023RF trinary encoder (IC1) 1 C8050 NPN transistor (Q1) Fig.3: install the parts on the transmitter and receiver PC boards as shown here. You will need a fine-tipped soldering iron to solder in the UHF transmitter module. It’s a good idea to check each resistor value using a digi­tal multimeter before installing it on the board. The IC socket can go in last. Note that its solder pads along one side sit between two parallel tinned copper tracks. These tracks are quite close to the IC pads, so be careful that you don’t get solder bridges between them at this stage. The two parallel tracks are there to let you set the trans­mission code – the outside track is at 0V while the other is at +9V (ie, the supply rail). This makes it easy to tie the coding pins (1-8) high or low by creating solder bridges between the pads and the tracks. Alternatively, you can also leave some pins open-circuit (O/C), as stated previously. For the time being, it’s best to leave pins 1-8 all O/C so that there’s no confusion when it comes to testing. You can code the unit later on, once it’s all working correctly. Finally, you can complete the transmitter module by plug­ging in IC1 (SM5023RF) and installing the supply leads and a 173mm-long antenna lead. Take care to ensure that IC1 is cor­rectly oriented – ie, with pin 1 towards the 22nF capacitor. Receiver assembly Now for the receiver assembly. This should only take you 10 minutes. Begin by installing the resistors and capacitors, then install LED1 and the two IC sockets. Take care with the orienta­tion of the electrolytic capacitors and the LED – the flat side on the rim of the LED (cathode) goes towards the 2.2kΩ resistor (R6). www.siliconchip.com.au Once all these parts are in, you can install the UHF re­ceiver module. This is installed with its SAW filter (in the round metal can) towards the L4949N regulator (REG1). Push the module down onto the boards as far as it will go before soldering its eight pins. Finally, complete the receiver module by installing the supply leads and the antenna lead (173mm). Testing Now for the smoke test! Check your work carefully, then connect a 9V DC supply to both modules and press each of the transmitter buttons in turn. If the project is working correctly, you should see LED1 on the receiver board light each time a button is pressed. If it doesn’t, disconnect power to both modules immediately and check that pins 1-8 on both IC1 & IC2 are all open cir­cuit (O/C). It’s important that both ICs have the same coding, otherwise the unit definitely won’t work. Check also for missed solder joints, solder bridges and incorrect component orienta­tion. If these checks fail to reveal anything, reapply power to the transmitter and check for +5V at the output of REG1 (pin 8). Finally, you can check Resistors (0.25W, 5%) 1 2.2MΩ 4 10kΩ Receiver 1 PC board, 48 x 29mm 1 RX434 433.92MHz UHF receiver module 1 18-pin DIL IC socket 1 8-pin DIL IC socket Semiconductors 1 SM5035RF-M4 trinary decoder (IC2) - see text 1 L4949 5V regulator (REG1) 1 red LED (LED1) Capacitors 1 100µF 16V electrolytic 1 10µF 16V electrolytic 1 22nF monolithic Resistors (0.25W, 5%) 1 470kΩ 1 2.2kΩ transistor Q1 in the transmitter by reap­ plying power and momentarily shorting pin 14 of IC1 to ground. If LED1 now lights, Q1 is probably faulty. Changing the code Assuming that the project is working correctly, you can now 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 adjacent +5V rail or to the 0V rail. Just be sure that the transmitter SC and receiver codes match. Where To Buy The Parts A complete kit of parts for this project is available from Oatley Electronics, PO Box 89, Oatley, NSW 2223. Phone (02) 9584 3563. Prices are as follows: Transmitter (includes PC board, UHF Tx module plus all parts) ............ $22 Receiver (includes PC board, UHF Rx module plus all parts) ............... $32 Postage and packing is $7 and all prices include GST. Note: the PC board copyright for this design is retained by Oatley Elec­tronics. June 2003  77