Fullscreen HTML5Med Res (??MB)HTML4

Ideal for remote control of practically anything you like and with a range of more than 200m, this wireless transmitter and receiver pair use pre-built UHF modules that make it easy to construct and use. 433MHz UHF Remote Switch by John Clarke Features • • • • • • • 80  Silicon Chip Range over 200m (tested using Jaycar UHF modules) Receiver has momentary or toggle output Adjustable momentary period Receiver can drive a 12V relay Transmitter draws no standby current from 9V battery Transmit and receive indication Up to five receivers can be used in the same vicinity siliconchip.com.au A cheap garage door controller is just one use for our UHF Remote Switch. If your brand-name garage door remote control is broken or lost, you’ll be able to build this whole project – transmitter AND receiver – for much less than the cost of replacing the original remote! T here are quite a few 433MHz 434.790MHz band, at a level of 25mW. pair. The best part about them is that transmitter and receiver mod- Classified as Low Interference Poten- they are pre-assembled and aligned – ules around these days. Rela- tial Devices (LIPD), they are widely you don’t even need a multimeter to tively inexpensive, they are ideal for used for sending wireless data in get them going! As LIPD devices, they have no legal remote control applications as well as industrial, medical and for scientific protection against interference from their more usual tasks, wireless data purposes. However, these days you are more other LIPD devices on the same or links. While the majority offer only fairly short range (tens of metres), some likely to find them in wireless consum- similar frequencies. The trade-off is er applications such as door openers, that they are one of the few radio frecan work over a 200m+ range. quency transmitters that can be used Even tens of metres range is a con- doorbells and weather stations. We have used these devices in the without a licence. siderable improvement over infrared transmitter and receiver pairs that not past for various wireless applications, only have limited range (<10m) and including the Water Tank Level Meter ASK featured in SILICON CHIP between NoThe 433MHz modules send data by usually don’t work well in sunlight but vember 2007 and January 2008. a method known as Amplitude Shift more importantly, have strictly line-ofBoth Jaycar and Altronics sell a Keying or ASK. This simply means sight reception. A wall, a filing cabinet, version of the transmitter and receiver that to send data, the transmitter sends even a vase of flowers can stop infrared bursts of 433MHz signal. When dead – just like your TV/video the transmitter is sending the infrared remote control. SECURITY NOTE 433MHz signal, the data is a ‘1’ On the other hand, UHF modWhile this UHF Remote Switch has protection and when the transmitter is off ules can operate where there against unauthorised access via its “identity” and not sending 433MHz signal is no line-of-sight between the the data is a ‘0’. The receiver retransmitter and receiver. They’ll settings, there is little to prevent someone with sponds to the transmitted signal even work through (most!) a similar transmitter stepping through these by producing a high output when walls, although walls with inidentities if the basic operation is known. the data sent is a ‘1’ and a low terior aluminised insulation or Therefore it should not be placed in locations output when the data sent is a ‘0’. similar will cause them grief. where security could be compromised It may seem easy to use the Commonly known as 433MHz – eg, used on a garage door opener where the UHF transmitter/receiver moddata transceivers, they opergarage gives access to the rest of the home. ules just to do simple switching, ate on the 433.050MHz to siliconchip.com.au January 2009  81 How not to use the UHF transmitter and receiver modules +5V +5V S1 CLOSED S1 OPEN 10k S1 OPEN DATA +5V 0V (NOISE) S1 Fig.1a 433MHz TRANSMITTER 433MHz RECEIVER +5V +5V S1 CLOSED S1 OPEN S1 DATA S1 OPEN +5V 0V 10k Fig.1b 433MHz TRANSMITTER 433MHz RECEIVER The two alternative arrangements for connecting a switch (S1) to activate the transmitter are shown in Fig.1a and 1b. With S1 open, the transmitter will be sending 433MHz signal to the receiver and the receiver output will be set constantly high. When S1 is closed, the transmitter will be off and the receiver will pickup random noise shown as a series of irregular high and low signal. Fig.1b has S1 connected so that the transmitter only sends 433MHz signal when closed to produce a high output at the receiver. When S1 is open the transmitter is off and the receiver outputs random noise. by simply connecting them as shown in Fig.1a. This is where the transmitter is set to continuously send a signal with the data input held at 5V. The receiver then responds by outputting a high. It follows that the data output from the receiver would go low when the transmitter ceases transmitting its signal. The alternative arrangement with the transmitter off with S1 open is shown in Fig.1b. In this case the output from the receiver would go high when S1 is closed. However, nei- ther of these arrangements will work. The reason is that the data rate must be a minimum of 300 bits per second and a maximum of 10k bits per second. So for slow speed use where the switch remains open or closed for longer that the minimum rate, there are problems. The first problem is that with no signal sent by the transmitter, the receiver outputs a continuous stream of noise. This is seen as random high and low signal at the receiver output. The reason for this effect is that the receiver has automatic gain control (AGC). In the absence of 433MHz signal the receiver increases its amplification (or gain) until it begins to receive signal. If there is no 433MHz signal, the gain will become so high that the receiver just detects noise. This noise is then what is applied to the receiver output. When there is a 433MHz signal transmitted, the receiver gain is reduced so that the signal is received correctly without detecting the background noise. The AGC action is designed to work if the 433MHz signal is modulated (switched on and off) at the correct 300Hz to 10kHz range. The second problem is that the receiver will respond to any 433MHz signal that occurs in its range. So if your next-door neighbour’s garage door is being activated using a 433MHz remote control, then the receiver will also provide an output. So some form of encoding is needed so that the receiver will only work in conjunction with its transmitter and not from another transmitted signal. As a consequence, UHF modules cannot be used without some form of signal conditioning. For transmission, the signal needs to be processed so that a signal with the correct bit rate is sent to the transmitter module. For reception, the signal needs to be processed to ignore the noise from the receiver module in the absence of signal and to only respond to a valid transmission. The complexity of the signal conditioning means that a microcontroller is almost a prerequisite and we chose an 8-pin PIC12F675-I/P device for both the transmitter and receiver. Using the microcontroller also allows extra features such as the Inside the two cases – the receiver in its utility box at left with a long-wire antenna (all of 170mm!) and the transmitter with its coil antenna, fitted into a remote control case. The battery compartment is on the other side of the case. 82  Silicon Chip siliconchip.com.au LK4 D1 1N4004 + A K K ZD1 16V 1W 9–12V – REG1 78L05 Q1 BC327 10 E 10 F 16V B A ANTENNA +5V OUT IN C GND 10 F 16V 100nF 100nF 470 1k 1k +5V + 1 POWER OFF: LK1 IN POWER ON: LK3, LK4, LK5 IN EXTERNAL D2 1N4148 A K C S1 10k LK3 Q2 BC337 LK1 SC UHF REMOTE SWITCH 3 22k 10k 2009 TP1 IDENTITY VR1 10k B E 5 7 Presentation Both the transmitter and receiver are quite flexible in their presentation. We elected to fit the transmitter into a handheld remote control case which also houses the 9V battery in a separate battery compartment. A pushbutton switch is used to start transmission of signal. However, the transmitter could be housed in a smaller plastic case or even in no case at all, ie, just as a PC board, depending on the application (eg, behind the dashboard of your car with just the pushbutton seen on the dash). Similarly, the receiver may be housed in a small plastic case or perhaps inside a garage door remote controller case. Even if the case was metal, which would normally stop the signal, the antenna wire could emerge through a suitable hole. The receiver PC board has input terminals for power and two output terminals that can drive a 100mA load such as a relay coil. The relay contacts can drive low voltage items as motors siliconchip.com.au A IC1 12F675-I/P AN3 10k GP0 GP5 Lk2 IN: RETRANSMIT A A A ANT GND TRANSMIT  LED1 K 2 C B Vss 8 Fig.2: the transmitter section of the UHF Remote Switch sends a burst of 433MHz signal when its pushbutton is pressed and/or an external source triggers it. The microprocessor ensures that the receiver knows which transmitter sent the signal. ability to have momentary or toggle output, an adjustable momentary delay and you can also have up to five different transmitter and receiver pairs working in the same vicinity without interfering with one another. DATA Vdd MCLR 6 GP2 GP1 LK2 TRANSMITTER 4 TX1 433MHz TRANSMIT MODULE LK5 Q3 BC337 433MHz Tx MODULE ANT Vcc DATA GND E TP GND D2 D1 ZD1 K K BC327, BC337 LED K A 78L05 B E GND C IN OUT K and lamps. A LED indicates when the output is on. This receiver includes link options for momentary or toggle output and an adjustable momentary delay adjustment. Both transmitter and receiver include an identity control that sets one of five possible identities. The identity of the transmitter and the receiver must be the same for the receiver to respond to the transmitter. Transmitter circuit Fig.2 shows the transmitter circuit. As previously stated, it is based on a PIC microcontroller (IC1) and a 433MHz transmitter module. The PIC12F675-I/P microcontroller includes an internal oscillator and up to five general-purpose input/outputs (GPIO). Four of these GPIOs can be used as analog-to-digital inputs. The circuit is designed to run from a power supply between 7V and 12V with very low power drain, suiting battery use. Normally, we would assume a 9V battery would be used but it could be wired into a vehicle’s 12V supply. Absolutely no power is drawn when the transmitter is in its standby state – that is, when the transmit switch has not been pressed. When the transmit switch is pressed the power drawn is less than 20mA and this is only for a short period while the switch is held closed and the unit is transmitting. Power is applied to the circuit via diode D1 and a 10Ω resistor to the emitter of transistor Q1. The diode provides reverse polarity protection (essential when used with a 9V battery) while the 10Ω resistor in conjunction with the 16V zener diode (ZD1) protects against transient voltages. Transient voltages are not likely when used with a battery supply but the protection is included should the circuit be powered from an automotive 12V supply. One form of transmitter mounting is inside a handheld case, complete with a 9V battery as shown here. January 2009  83 +11.4V REG1 78L05 10 K ZD1 16V 1W 0V IN K A 100 F 16V +5V OUT GND 100 F 16V 470 100nF 1k LED1 IDENTITY VR1 10k GND 5 DATA VR2 10k MOMENTARY DELAY AN3 IC1 PIC12F675-I/P GP1 GP2 TP2 7 GP5 AN0 UHF REMOTE SWITCH 84  Silicon Chip LK1 OUT: MOMENTARY LK1 IN: TOGGLE 2 433MHz Rx MODULE Vss RECEIVER LK1 8 D1,D2 Fig.3: the receiver is also based on a PIC12F675-I/P chip, which interprets the data signal from the 433MHz receiver module. If all is OK, it turns on Q1 which can control a relay or otherwise switch an external device. Pressing switch S1 connects the base of transistor Q1 to ground via the 1kΩ resistor. This allows current to flow from the emitter to base and so the transistor switches on. Power is then connected to the input of regulator REG1. REG1 supplies 5V to IC1 and the UHF transmitter TX1. Pressing S1 is not the only way to trigger the transmitter – other methods are available to suit many different applications. For example, connecting the two “External” inputs together will turn transistor Q2 on, having the same effect as if switch S1 is closed. A further alternative is to apply a voltage (as low as 1.8V) to the anode of D2 to trigger Q2. The input current at 1.8V is 60μA. With power now connected to IC1, the program begins to run and the GP2 output at pin 5 goes to 5V. This high output drives the base of transistor Q2 via the 10kΩ resistor and link LK1, so the transistor switches on. Power to the circuit is now maintained even if the switch is released. IC1 now reads the voltage applied to its AN3 input from trimpot VR1, connected across the 5V supply. Voltage from this trimpot is divided up into five equal divisions where each division represents its own identity: 0-1V = identity 1, 1-2V = identity 2, Q1 BC337 ANT GND GND Vcc SC C B E TP GND 2009 1k 6 A ZD1 A BC337 LED K K 2-3V = identity 3, 3-4V = identity 4 and 4-5V = identity 5. The identity is sent as part of the code in the transmission. As noted previously, the receiver must be set to the same identity as the transmitter before it will respond to the signal. For Identity 1 the sent code has the value of 8. Identity 2 has the code 16, Identity 3 is 32 and 64 and 128 for Identities 4 and 5. The microprocessor looks for these values in the signal and matches them with values it has stored as part of the program. 78L05 GND B K A E C IN OUT Signal from IC1’s GP1 output drives both the DATA input of the UHF transmitter and the base of transistor Q3 via a 10kΩ resistor. Q3 powers the LED via a 470Ω resistor and this LED flashes as signal is sent to the transmitter module. Initially, GP1 is set high for 50ms. This sends a burst of 433MHz signal from the transmitter and sets up the UHF receiver so that it is ready to receive data without producing noise. GP1 then goes low for 1ms before going high again for 16ms. The 16ms allows the receiver to lock DASHED LINE IS UTILITY BOX SIZED PC BOARD REG1 LK4 10 F Q3 Q1 10 TO 9V BATTERY SNAP D1 470 10 F LK2 TP1 VR1 LK5 1P T 10k ZD1 GPTTP GND 100nF LED1 100nF LK1 22k 433MHz RX MODULE K 10k ANT OUTPUT A MCLR 10k Vcc 3 Vdd D2 1N4004  4 1 TP1 IC1 12F675 100nF K A Vcc DATA DATA GND A TI MS NART F HU +12V 1k D1 1N4004 LK3 D2 1k GND DATA Vcc ANT 433MHz EXTERNAL 4148 10k Tx S1 Q2 19010 151 MODULE 7 TURNS OF 0.5mm ENAMELLED COPPER WIRE (WOUND ON 6mm FORMER [eg, DRILL BIT]) siliconchip.com.au onto the data rate of the transmitter. The data rate between the transmitter and receiver needs to be locked because we are using the internal oscillators of the microcontrollers rather than crystal oscillators. The 2% accuracy of the oscillators can affect whether the data is received correctly. After the 16ms burst of 433MHz is a 1ms low. This is followed by an 8-bit encode value, an 8-bit on/off signal and an 8-bit stop value. The receiver must receive all bits correctly before it will act upon the signal. The 8-bit on/off signal has the value 120 and the stop bit value is 240. When transmission is completed, output GP2 goes low (to 0V), switching off Q2. If switch S1 is also open then power is removed from the circuit, as Q1 would also be switched off. Setting the links As an alternative to having power switched on only during transmission of the signal, you can have power permanently connected to IC1 and the transmitter module. This may be required if you power the unit from an existing 5V supply or if you want to use the 5V supply from REG1 to power another circuit that requires permanent power. A change of jumper links is all that is required to make the changes. Swap the link for LK1 to LK3 and fit links to both LK4 and LK5. If using an existing 5V supply, REG1 is not necessary and can be omitted: simply connect +5V to what was REG1’s “out” position. Link LK5 signals to the IC1 microcontroller that the power arrangement is different and transmission is not required when power is connected. The transmission in this case is initiated by a closure of S1 or a signal at the external input. This is detected by IC1 as a low-going level at the GP2 input. Link LK2 is used to set repeat transmission at a nominal 200ms rate. The idea of this option is to allow the receiver to provide an output while ever the transmission is being sent and to cease the output when the signal stops. Receiver circuit The receiver circuit, shown in Fig.3, also uses a PIC12F675-I/P microcontroller which works in conjunction with the 433MHz receiver module controller. The circuit is powered from a 12V supply. It’s much the same as the transmitter: diode D1 protects from reverse polarity connection while the 10Ω resistor and zener diode ZD1 prevent any transient voltages from reaching the 5V regulator, REG1. This supplies power to both the microcontroller IC1 and the 433MHz wireless receiver module. Overall current consumption is around 7mA with the LED off and 14mA with the LED on. More current is required from the supply if a relay is connected to the output. REG1 includes two 100μF bypass capacitors, one at its input and the other at its output. Both IC1 and the 433MHz module have their supply decoupled by a 100nF capacitor close to the supply pins for each. IC1 has two analog inputs (AN0 and AN3) to monitor the voltage set Fig.4 (opposite) is the component overlay for the full-sized transmitter PC board, which matches the photo above. siliconchip.com.au by VR1 and VR2. The voltages at each input are converted to a digital value within IC1. VR1 sets the identity and this is adjusted to match the identity of the transmitter. VR2 sets the timeout period of the output when it is set for momentary action. Data from the UHF receiver module is monitored by the GP2 input of IC1. When it receives a signal it compares the values embedded in the code with the identity value set by VR1 and for the correct on/off and stop bit codes. If the values are correct it sends its GP1 output high, which turns on transistor Q1. With Q1’s collector now low, LED1 is connected virtually across the 5V supply (via its 470Ω current-limiting resistor), so the LED lights. Q1’s collector is connected to one of the output terminals. This can be used as an output itself for any device capable of being switched by a low (<1V) level or it can drive a 12V relay connected across the output terminals. Diode D2 protects Q1 from the voltage spike likely when the relay switches off. The output can be either momentary or toggled, as selected using link LK1. When LK1 is out, operation is momentary and Q1 is initially turned on only when it receives a valid transmission from the transmitter. It stays turned on for a period set by trimpot VR2. Timeout periods can be set from 0.2s through to about 50s. If the transmitter is set to retransmit then Q1 can be held on for as long as the transmitter switch is held. The timeout needs Here’s the mini version, intended for mounting in a utility box. It doesn’t have the spiral wire antenna; instead a 170mm length of hookup wire is soldered to the antenna pin (lower left of the green UHF module). January 2009  85 100 F Q1 10 1P T OUTPUT CON2 100nF DATA Vcc GND DATA TPG D2 VR2 1k GP T ZD1 LED1 TP2 433MHz Rx MODULE Vcc GND GND ANT 0V 470 2P T LK1 TP1 VR1 100nF 1k CON1 +12V A 100 F IC1 12F675 D1 REVIE CER F HU REG1 29010151 170mm LENGTH OF HOOKUP WIRE Fig.5 (above) is the receiver PC board. Make sure you get the edge-mounted UHF module around the right way. It’s just visible in this picture at left, along with the antenna, a 170mm length of hookup wire. to be set long enough that Q1 does not momentarily switch off between each retransmission of signal from the transmitter. Q1 switches off when the transmitter switch is released and after the timeout period. Construction We’ll start with the transmitter which, as we mentioned before, is designed to fit into either a small remote control case measuring 135 x 70 x 24mm or into a 83 x 54 x 31mm utility box. The PC board, coded 15101091 measures 85 x 63mm. An alternative outline, measuring 79 x 48mm for the utility box version, is also shown. Fig.4 shows the parts layout. Begin by checking the PC board for shorted tracks or breaks in the copper. Also, check the hole sizes. The corner mounting holes should be 3mm in diameter, as should the two holes to anchor the battery snap leads. Now work can begin with the assem- bly. Install the link and resistors first. The table overleaf shows the resistor colour codes but it is a good idea to also check each value using a digital multimeter before soldering it onto the PC board. Next, install the PC stakes for the test points and antenna connection, followed by the jumper header pins. Capacitors can now be installed, making sure the electrolytic capacitors are oriented as shown on the overlay. The ceramic capacitor is located near to the transmitter module When soldering in diodes D1and D2 and zener diode ZD1, take care to orient them as shown. Likewise the 8-pin IC socket – it is oriented with its notch as shown on the overlay. Q1 (BC327), Q2 and Q3 (BC337) and REG1 (78L05) also must be installed the right way around – and in the right positions (the transistors all look the same!). LED1, as well as being the right way around, must sit up higher than the transistors so that it can be seen This shot gives a better idea of how the 433MHz UHF receiver module is mounted. Note the capacitor in front of the chip on the module – it is the 100nF ceramic disk. 86  Silicon Chip through its hole in the case. The top of the LED should be 15mm above the PC board. The last components to mount before the UHF transmitter module are trimpot VR1, the two-way screw terminals and switch S1. Note that the switch must be installed with its flat side toward the edge of the PC board. The UHF transmitter module is mounted horizontally on the PC board and its leads will have to be bent over at 90° before inserting into the PC board holes. Make sure the transmitter is oriented correctly before bending the leads. The pin-outs for the module are screen printed on its PC board. As you can see from the photos and diagrams, the transmitter antenna is a small coil, made by winding seven turns of 0.5mm enamelled copper wire around a 6mm (1/4”) drill bit. Each end of the wire should be stripped of its insulation and soldered to the antenna PC stake at one end and the PC board pad at the other. If you have cut down the PC board to suit the smaller (utility) case, then an alternative antenna can be made using a 170mm length of insulated hookup wire attached to the antenna PC stake. The 9V battery leads pass through one of the battery compartment holes in the hand-held remote case before being looped through the holes in the PC board and into the screw terminals. A cable tie secures the wires in position. The PC board is secured to the case with four M3 screws that screw into the integral support bushes of the case. Receiver All receiver components mount on a second PC board, coded 15101092 and measuring 79 x 48mm. It can be housed in a plastic utility box that measures 83 x 54 x 31mm (the same size as the alternative transmitter case). The PC board doesn’t have any mounting holes – it is designed to clip into the horizontal slots in the side guides of the box. Fig.5 shows the parts layout. Again, begin by checking the PC board for shorted tracks or breaks in the copper and before soldering any components in, check that the PC board clips neatly into the box as shown. It may require a little filing to narrow the PC board for a good fit without bowing out the side of the box. Construction is similar to the transsiliconchip.com.au Parts List – UHF Remote Switch TRANSMITTER 1 PC board coded 15101091, 85 x 63mm 1 remote control case 135 x 70 x 24mm (Jaycar HB-5610, Altronics H 0290* or equivalent) 1 433MHz wireless transmitter module (TX1) (Jaycar ZW-3100, Altronics Z 6900 or equivalent) 2 2-way PC mount screw terminals with 5.04mm pin spacing (CON1,CON2) 1 DIP8 IC socket 1 9V battery 1 9V battery snap connector 1 SPST PC board mount snap action switch (S1) 3 2-way pin header with 2.54mm pin spacings 1 3-way pin header with 2.54mm pin spacings 4 jumper plugs 1 100mm cable tie 4 M3 x 6mm screws 2 PC stakes 1 170mm length of 0.5mm enamelled copper wire 1 20mm length of 0.7mm tinned copper wire Semiconductors 1 PIC12F675-I/P microcontroller programmed with 1510109A.hex (IC1) 1 78L05 low power 5V regulator (REG1) 1 BC327 PNP transistor (Q1) 2 BC337 NPN transistors (Q2,Q3) 1 1N4004 1A diode (D1) 1 1N4148 switching diode (D2) 1 16V 1W zener diode (ZD1) 1 3mm green LED (LED1) mitter: install the link, resistors (use the colour code table and/or digital multimeter to confirm values), capacitors, PC stakes, jumper header pins, IC socket and finally the semiconductors. Once again, make sure any polarised components (eg, electrolytic capacitors and semiconductors) are soldered in the right way around. As with the transmitter, the LED should be mounted so its top is 15mm above the PC board surface Trimpots VR1 and VR2 can be installed along with the two-way screw terminals. Unlike the transmitter, the UHF receiver module is mounted vertically on the PC board – make sure siliconchip.com.au Semiconductors 1 PIC12F675-I/P microcontroller programmed with 1510109B.hex (IC1) 1 78L05 low power 5V regulator (REG1) 1 BC337 NPN transistor (Q1) 2 1N4004 1A diodes (D1,D2) 1 16V 1W zener diode (ZD1) 1 3mm green LED (LED1) Capacitors 2 100μF 16VWPC electrolytic 1 100nF MKT polyester (code 104 or 100n) 1 100nF ceramic (code 104 or 100n) Resistors (0.25W, 1%) 2 1kΩ 1 470Ω 1 10Ω 2 10kΩ horizontal trimpots (Code 103) (VR1,VR2) Capacitors 2 10μF 16V PC electrolytic 1 100nF MKT polyester (code 104 or 100n) 1 100nF ceramic (code 104 or 100n) Resistors (0.25W, 1%) 1 22kΩ 3 10kΩ 2 1kΩ 1 470Ω 1 10kΩ horizontal trimpots (VR1) RECEIVER 1 PC board coded 15101092, 79 x 48mm 1 plastic utility box 83 x 54 x 31mm 1 433MHz wireless receiver module (RC1) (Jaycar ZW-3102, Altronics Z 6905 or equivalent) 2 2-way PC mount screw terminals with 5.04mm pin spacing (CON1,CON2) 1 DIP8 IC socket 1 2-way pin header with 2.54mm pin spacings 1 jumper plug 4 PC stakes 1 170mm length of light duty hookup wire 1 20mm length of 0.7mm tinned copper wire (* Altronics case is narrower and longer – 182 x 65 x 28mm; the PC board may need to be shaped) 1 10Ω the receiver is oriented correctly. The pin-outs for the module are screen printed on its PC board. The receiver antenna is simply a 170mm length of insulated hookup wire, with a 2mm bared end soldered to the antenna PC stake. With the exception of the ICs, which will be placed after testing, that completes assembly. Before moving on to the testing stage, thoroughly check both transmitter and receiver boards RESISTOR COLOUR CODES No. r 1 r 3 r 4 r 2 r 2 Value 22kΩ 10kΩ 1kΩ 470Ω 10Ω 4-Band Code (1%) red red orange brown brown black orange brown brown black red brown yellow violet brown brown brown black black brown 5-Band Code (1%) red red black red brown brown black black red brown brown black black brown brown yellow violet black black brown brown black black gold brown January 2009  87 Testing Set your multimeter to a low DC voltage (6-10V or thereabouts) and connect the 9V battery to the transmitter. Connect the probes to pin 1 and pin 8 of the IC socket. Press S1 and check that the multimeter reads somewhere between 4.75V and 5.25V. If there is no voltage, check the battery, battery connections and also that Q1 and Q2 are indeed in the right way around and in the right places. Check the receiver in a similar way (except there is no S1 to press!). Again, the voltage across pins 1 and 8 of the IC socket should be between 4.75V and 5.25V when 12V DC is connected to the power input terminals. If the voltages in both these checks are incorrect, disconnect power and trace through the circuit until you find the error or problem. Kit suppliers tell us that 90% of problems in project construction are poor soldering while the other 20% are incorrect component placement or polarity. If the voltages are correct, switch off power and insert the microcontrollers for both transmitter and receiver into their sockets – dare we say it – the right way around! First, the transmitter PC board: insert jumper LK1 and adjust VR1 fully anticlockwise. Reapply power and check that the transmitter flashes its transmit LED when S1 is pressed. So far so good. Now apply power to the receiver and press S1 on the transmitter again. The receiver LED should light for around 200ms (ie, a brief flash). Note that the receiver will not work if it is too close to the transmitter (the transmitter is overloading the receiver). You need to have the transmitter and receiver apart by about 1m before it will work reliably. Close up operation is possible if the receiver antenna is disconnected. You can test the momentary delay by rotating VR2 to mid setting. The LED should light for around 5 seconds. Note that the delay values from VR2 are not linear with respect to rotation so you can select closer spaced delays at the lower periods. Values that can be selected are ap88  Silicon Chip Fig.6: here’s how to switch a RELAY low voltage load with a relay. NORMALLY CLOSED – The relay coil should be rated COMMON at 12V and the contacts NORMALLY OPEN MOTOR rated to suit the load. OR LAMP If using as a garage TO OUTPUT door opener contTERMINALS roller, the NO and common relay terminals would be connected in CONNECTING A RELAY AND LOAD parallel with the existing (low voltage) pushbutton switch. + for component misplacement (or polarity) and bad or missing solder joints. If you are satisfied that all is well, move on! proximately 200ms, 400ms, 600ms, 800ms, 1s, 1.2s, 1.4s, 1.6s, 1.8s, 2.0s, 2.2s, 2.4s, 3s, 4s, 5s, 6s, 8s, 10s, 12s, 15s, 18s, 21s, 25s, 27s, 30s, 32s, 35s, 38s, 41s, 44s and 50s. These values are spaced about 156mV apart as measured at TP2. The two lowest 156mV settings will only give the 200ms period because trimpots are not very easy to set much below 200mV at the fully anticlockwise end. The upper end adjustment may not access the 41 and 44s position depending on the trimpot linearity. If you want the output to toggle where the output alternates between on or off for each transmission, insert the jumper plug for LK1. The momentary delay has no effect for this setting. Identity If you are using more than one UHF transmitter and receiver pair, or if you receive a valid signal from a neighbour’s transmitter, then you may wish to have a separate identity. This will prevent another transmitter from operating the receiver. Remember, however, that each transmitter and receiver pair must have the same identity in order to work together. There are five possible identities, selected using trimpot VR1 in both the transmitter and receiver. The easiest selections are Identity 1 where VR1 is set fully anticlockwise, Identity 3 where VR1 is to set midposition and Identity 5 where VR1 is set fully clockwise. Positioning of VR1 for Identity 2 is mid way between fully anticlockwise and mid setting while Identity 4 is between mid setting and fully clockwise. Further options for the transmitter include ‘retransmit’ using link LK5. This sets the transmitter to continue repeating a transmission while S1 is closed or while the external trigger is applied. This will keep the receiver output activated provided that the + LOW VOLTAGE SUPPLY – momentary delay is sufficient to prevent LED1 dropping out between transmissions. The setting is ideal if you want the receiver to ‘follow’ the closure of S1. Finally, the transmitter includes supply options where the circuit can be continuously powered. To do this swap the jumper LK1 into LK3. Also insert LK4 and LK5. Note that for this arrangement, transistor Q1 and its 1kΩ base resistor are not required and can be left off the PC board. Connecting a relay A 12V relay can be driven via the output terminals of the receiver, provided the receiver is powered by a 12V supply with a 100mA or higher current capability. The contacts can be used to drive a load as shown in Fig.6. For general 12V-24V use, with loads up to about 3A for a motor and 10A for a lamp, a standard 12V horn relay could be used. These are available from Jaycar – SY-4068 for a single pole changeover (SPDT) version or SY-4070 for the double pole (DPDT) version. Altronics sell a similar SPDT horn relay, S-4335A. These relays are rated at 30A. Higher rated relays are also available, such as the 60A-rated Altronics S-4339 and the similar Jaycar SY-4074. If using as a garage door controller, most openers have a “local” lowvoltage pushbutton switch. The relay contacts would simply wire in parallel with this switch and the receiver set to “momentary” mode. Note that the relay is not recommended to drive mains appliances unless you are proficient with using mains wiring. A mains-rated relay is obviously required. The contacts of the relay must be rated for the load and, of course, any 240V wiring must be adequately isolated. Switching motors will require a higher rated contact than the stated running current because start-up currents are much higher. SC siliconchip.com.au