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By JIM ROWE & MAURO GRASSI Power up your PC’s peripherals automatically with this . . . USB-Sensing Mains Power Switch Do you have to manually switch your PC’s peripherals on (and later off again) each time you boot your PC? If so, this project will make life a lot easier. It monitors your PC’s USB port and automatically turns all that other gear on and off as required. M ANY EARLY PCs had an IEC-type 240V outlet socket on the back of the box that was switched by the PC’s own on/off switch. This allowed you to automatically switch power to the computer’s monitor, printer and other peripherals when the PC itself 26  Silicon Chip was switched on or off. All you had to do was plug a power distribution board into this outlet and then plug the peripherals into this board. The power switch on the front of the PC then controlled everything – all very neat and convenient. Unfortunately, this handy switched power outlet disappeared when the PC manufacturers changed over to software-controlled power supplies. So with most newer PCs, you’re now forced to use a power distribution board with its own master power siliconchip.com.au switch, if you want to control all your peripherals with a single switch. Of course, that means you have to remember to manually switch on the peripherals when you switch on your PC and vice versa. And that can be a real nuisance. If you forget to turn the peripherals on, the computer won’t recognise the monitor or any USB peripherals when it boots and may have to be restarted. Apart from that, having to manually switch everything on and off at the wall socket can be a real nuisance. Not only that, it can also be impractical if the wall socket is inaccessible because it’s hidden behind a desk or some other piece of furniture. That’s where this USB Sensing Power Switch comes in. It connects to one of your PC’s USB ports and when it detects activity on that port, it automatically switches mains power through to a socket on its front panel. By connecting a powerboard to this socket, you can automatically switch all your peripherals (including your monitor) on when the PC itself is switched on and then off again when the PC is powered down. This not only relieves you of having to manually switch gear on and off but also means that the wall socket can be left on. Life ain’t easy At first glance, the circuitry required to do the job should be quite simple – just monitor the USB port’s +5V line and use it to turn a transistor on when the PC is switched on. This transistor could then turn on a relay to switch the mains power through to the outlet socket each time the PC was switched on. Unfortunately, it’s not that easy in practice, unless you use a laptop (more on this later). The reason is very simple – most desktop PCs maintain +5V standby power on their USB ports even when they are powered down. And that would mean that our USB Sensing Power Switch would never switch off if we simply sensed the +5V USB rail. In fact, the only way to “kill” the +5V standby power on the USB ports is to switch the PC off at the wall socket (or at the back of the computer itself), hardly the most convenient solution. So why do desktop PCs do this? Well, there are a couple of reasons. First, by maintaining power to the siliconchip.com.au POWER DISTRIBUTION BOARD FOR PERIPHERALS USB OUT USB IN MONITOR PC USB SWITCH (USB KEYBOARD CABLE) USB EXTENSION CABLE USB KEYBOARD Fig.1: how the unit is used. All peripherals plus the monitor are plugged into the power distribution board. Note that a USB keyboard or mouse must be connected to the USB Switch if you are using a desktop PC. USB ports, it allows the computer to be booted simply by double-clicking a USB mouse or by typing a password into a USB keyboard. This is set up in the PC’s BIOS (eg, “Power On By Mouse” or “Power On By Keyboard”) and is a very convenient way of starting the machine if the computer is tucked away under a desk. Second, it allows you to recharge the batteries in a range of devices via a USB port, even when the computer is off. These devices include MP3 players, iPods, some GPS units and cordless keyboard/mouse receiving stations. number of laptops indicate that powering them via a mains adaptor makes no difference either – the USB ports are still powered down when the machine is switched off. For laptops then, simply monitoring the +5V USB line is valid and our circuit has an option to do just this. That means that laptops are easy to cater for. A few desktop machines also have a jumper option on the motherboard to disable USB standby power. However, most don’t so we need to use some other method to determine when the machine is switched on. Laptops are different The answer for desktop machines is to monitor the D- data line of the USB port instead. To do this, however, we must have a USB device plugged into the USB port that the PC recognises, typically a mouse or keyboard. By contrast, laptop computers do shut down the standby power to their USB ports when they are powered down. Presumably, this is done to conserve the battery. Our tests on a Monitoring a data line The USB input and output sockets are accessed via cutouts in one end of the case. The connection to the PC is via a standard type A to type B cable. January 2009  27 mains on by default after the polling signal is detected and by then using a timer to turn it off a set period after the polling signal ceases. In the case of the USB Sensing Power Switch, this delay period can be set anywhere between 33s and 67s but can easily be extended if your computer is slow to boot. Note that using the delay circuit also means that the peripherals remain powered up for a brief period after the computer is turned off. So if the delay period is 40s, for example, the peripherals will remain on for 40s after shut down. Loop through sensing Fig.2: this scope grab shows the polling signals with a full-speed USB device connected to the USB Sensing Power Switch. The green trace is the signal on the D- line of the USB port while the yellow trace is the signal at the collector of transistor Q1. The polling frequency is 1kHz, as specified in the USB standard. The reason for this is that when a recognised device is plugged in, the USB host (ie, in the PC) regularly “polls” that USB port for activity. This polling signal takes place at a 1kHz rate (ie, 1ms frames) for low-speed and full-speed devices and has an amplitude of 3.3V. By contrast, high-speed USB devices use a differential 8kHz polling signal that has an amplitude of just 0.3V. This type of device can not be used with this project – only low-speed and full-speed devices can be used. Fig.2 shows the USB polling signal with a full-speed USB device connected. This signal appears shortly after the machine is switched on. What happens then depends on whether you have USB mouse (and/or keyboard) support enabled in the system BIOS. If it isn’t enabled, then the polling signal almost immediately ceases again and stays off during the boot period until well into the Windows splash screen, at which point Windows loads its own driver. When that happens, the polling signal reappears and remains on until the machine is powered down again. However, the polling gap during bootup can typically be 30-40 seconds long or more, depending on how long it 28  Silicon Chip takes Windows to load its driver. Alternatively, if USB mouse (or keyboard) support is enabled in the BIOS, the polling signal remains present as the machine boots and only briefly ceases towards the end of the splash screen as the Windows driver takes over. So, in this case, the polling signal is almost continuous from switch on. By detecting the polling signal on the D- line, we can thus reliably detect when a desktop PC has been switched on. But what about the gap in the polling signal that occurs during boot-up, particularly if USB mouse/keyboard support is not enabled in the BIOS? Unless precautions are taken, the peripheral devices would power up shortly after the PC was switched on, only to almost immediately switch off again when the polling signal ceased. They would then remain off until the Windows driver loaded for the particular device that was plugged into the USB port. For a plug and play monitor, that could be a real problem – if it isn’t turned on, Windows can not recognise it and so loads a default low-resolution desktop. Fortunately, this problem is easily solved by designing a circuit that re- Fig.1 shows how the unit is used with a desktop computer. Basically, it uses “loop through” sensing via two USB ports (one for USB in and one for USB out). As already mentioned, you must have a USB mouse or keyboard (or some other low-speed or full-speed USB device) plugged in. You can not use a high-speed device and that includes most USB flash drives and disk drives (the USB device itself will work but the USB Sensing Power Switch won’t). Alternatively, for a laptop, all you need to do is connect the unit to a USB port on the computer and configure it to monitor the +5V rail. In this case, you don’t have to have a peripheral connected to the USB Out socket but you can if you wish. What’s more, you can connect any type of USB device you want, including high-speed devices – they will all function normally. By the way, which ever method you use to monitor the USB port, this unit will also power down your peripherals if the PC goes into hibernation. It will then automatically turn them back on again when the machine comes out of hibernation. Earlier unit Before going further, we should mention that this unit supersedes the USB-Controlled Power Switch described in November 2004. That earlier unit was built into a modified power board and used an optocoupler to provide isolation and a Triac to switch the mains power. However, some readers have found that the Triac fails under certain circumstances. Because of the confined space inside the powerboard, the total loading on the unit was specified as siliconchip.com.au N E WARNING: COMPONENTS & WIRING IN SHADED AREA ARE AT 240V MAINS POTENTIAL WHEN THE CIRCUIT IS OPERATING. CONTACT MAY BE LETHAL! SLOW BLOW F1 10A A GPO E S1 T1 12.6V/2VA D1–D4 K 12.6V * FOR SY-4042 RELAY (20A) USE 47  5W FOR SY-4040 RELAY (30A) 6.3V 240V RLY1 20A AC CONTACTS A A K +17V 68  5W A K 0V K 470 F 25V A * 100 F 25V D5 K A A K +5V (FROM USB) 10 F 16V VR1 500k 1k 3.3k IC1 555 2 Q3 BC337 4 10 12 4 11 22k S D Q IC2b CLK 1 100 F LL Q R B 10k C Q1 BC549 E USB IN CON3 1 2 3 4 9 2 8 3 D S 14 Vcc 5 Q IC2a CLK R 13 150pF 10k 1k E 3 6 JP1 JP2 2.2k C 8 7 Q Vss 1 7 A 2.2k 6 C Q2 B 2009 POWER  LED2 K BC337 E 22k IC2: 74LS74 TO TRIGGER FROM USB DATA: LEAVE OUT JP1 & JP2 TO TRIGGER FROM USB +5V RAIL: INSTALL JP1 ONLY USB OUT CON4 V+ 1 2 3 4 D– D+ 0V BC337, BC549 LEDS SC  ACTIVE  LED1 2.2k 220 F 16V 1k B 470k 1k N A 240V INPUT USB SENSING POWER SWITCH D1–D5: 1N4004 A K K A B E C Fig.3: the circuit can be triggered either from the +5V USB line (JP1 in) or from the D- data line (JP1 out) using transistor Q1 and dual D-type flipflop IC2. When triggering occurs, Q2 turns on and this turns on relay RLY1 to switch mains power through to the GPO. Q3 and its associated parts form the reset circuit for IC2, while 555 timer IC1 switches the unit off after a preset time if no data is detected on the D- line. 700W maximum and it’s possible that this rating was being exceeded in some cases. By contrast, this new project uses a relay with 20A AC contacts to switch the mains, which means that the outlet is rated at a full 2300W. The relay also completely eliminates the problem of Triac failure. In addition, because it is built into its own enclosure, this new unit is easier to build than the earlier version, since you don’t have to doctor a powerboard. Finally, the earlier unit monitored the +5V USB line only. It’s suitable for use with laptops but is limited to those desktop machines in which the USB standby power can be disabled siliconchip.com.au or where the PC itself is switched off at the wall. How it works OK, let’s see how the unit works. Fig.3 shows the circuit details and as you can see, there’s not a lot to it. The first thing to note is that the electronic switching circuitry must be electrically isolated from the mains, so there’s no risk of 240V AC getting back into the computer via its USB port. That’s done by using a transformer in the power supply plus a relay to switch the mains through to the GPO. As shown, a pair of standard USB sockets, CON3 and CON4, allow the unit to be connected between the PC and an external peripheral using standard USB cables. All of the USB connections go “straight through”, so the added circuitry is essentially “transparent” as far as USB communication is concerned. Let’s start by considering the simplest configuration, in which the unit is used to monitor the USB 5V (V+) rail (ie, it’s being used with a laptop). In this case, jumper JP1 is installed and IC1, IC2a, IC2b and transistors Q1 & Q3 are effectively bypassed and have no role in the circuit’s operation. When the laptop is powered up, +5V DC appears on pin 1 of each of its USB ports. We simply “steal” a couple of milliamps from this convenient January 2009  29 Parts List 1 PC board, code 10101091, 151 x 109mm 1 IP65 ABS sealed polycarbonate enclosure with clear lid, 171 x 121 x 55mm (Jaycar HB-6248 or equivalent) 1 2851 12.6V 150mA (2VA) mains transformer 1 chassis-mount 12V coil SPST relay with 20A contacts (Jaycar SY-4042) 2 PC-mount 2-way terminal blocks (CON1,CON2) 1 PC-mount Type B USB connector (CON3) 1 PC-mount Type A USB connector (CON4) 1 snap-fit fused male IEC connector with switch 1 M205 10A slow-blow fuse 1 10A flush-mounting mains outlet socket with side wire entry 1 300mm length of 10A brown mains wire 1 150mm length of 10A blue mains wire 1 150mm length of 10A green/ yellow mains wire 12 Nylon cable ties 4 M3 x 6mm machine screws 2 M3 x 10mm machine screws 2 M4 x 10mm machine screws, pan head 2 M3 hex nuts 3 M3 star lockwashers 2 M4 hex nuts 2 M4 star lockwashers 2 M4 flat washers 4 M3 x 10mm Nylon screws, pan head source of 5V DC and use this to turn on transistor Q2 via a 2.2kΩ resistor and jumper JP1. Q2 in turn switches on relay RLY1. As a result, RLY1 closes its contacts (which are in the Active line) and so power is switched through from the mains input socket to the GPO (general purpose outlet). In addition, Q2 turns on LED1 (green) to indicate that the relay is on. Conversely, if the laptop is turned off, the +5V DC disappears from USB pin 1 and this removes the forward bias on Q2 (its base is pulled down to ground via the 22kΩ resistor). Q2 therefore stops conducting, turning 30  Silicon Chip 8 M3 hex Nylon nuts 2 6.4mm insulated spade connectors for 1mm2 wire 7 4.8mm insulated spade connectors for 1mm2 wire 1 4.8mm insulated piggyback spade connector for 1mm2 wire 1 5.3mm ID eyelet terminal for 1mm2 wire 1 72 x 38 x 1mm sheet steel or aluminium (for IEC connector mounting plate) 1 3-pin header 1 jumper link 1 500kΩ miniature horizontal mount trimpot (VR1) 1 14-pin machined IC socket 1 8-pin machined IC socket Semiconductors 1 555 timer (IC1) 1 74LS74 dual D-type flipflop (IC2) 1 BC549 NPN transistor (Q1) 2 BC337 NPN transistor (Q2,Q3) 1 5mm green LED (LED1) 1 5mm red LED (LED2) 5 1N4004 1A diodes (D1-D5) Capacitors 1 470μF 25V PC electrolytic 1 220μF 16V PC electrolytic 2 100μF 25V LL PC electrolytic 1 10μF 16V electrolytic 1 150pF ceramic Resistors (0.25W, 1%) 1 470kΩ 3 2.2kΩ 2 22kΩ 2 1kΩ 2 10kΩ 1 68Ω 5W 1 3.3kΩ off the relay (and LED1) and in turn switching off the power to the GPO. Simple. Monitoring the D- line Now let’s consider the more complicated case, where we monitor the “D-” data line (ie, the unit is to be used with a desktop machine). In this case, JP1 is left open so that the unit can not be triggered by the +5V USB line. Instead, IC1, IC2a, IC2b and transistors Q1 & Q3 now come into play and transistor Q2 is driven from the Q-bar output of D-type flipflop IC2a. It works like this: normally, when the PC is off, the pin 6 Q-bar output of D-type flipflop IC2a is low and transistor Q2 and the relay are off. However, if the PC is turned on, transistor Q1 is rapidly pulsed on and off by the polling signal that appears on the D- line. Q1 inverts this polling signal and applies a train of brief low-going pulses to the reset pins (13 & 1) of IC2b & IC2a. As a result, IC2b & IC2a are reset, thus forcing their Q outputs low and their Q-bar outputs high. This turns on transistor Q2 via a 2.2kΩ resistor at pin 6 of IC2a and activates the relay which now remains on. IC1 is a 555 timer which is wired to operate in astable mode. It is also reset each time Q1 is briefly pulsed on by the timing signal (ie, pin 4 is pulled low). This sends pins 3 & 7 of IC1 low and discharges the 100μF timing capacitor on pins 2 & 6 via the 1kΩ resistor. After the first brief reset pulse, Q1 turns off for a period of 1ms and so pin 3 of IC1 switches high for 1ms and clocks IC2b. Because IC2b’s Q-bar output is connected to its D input, its outputs immediately toggle, with Q now going high and its Q-bar output switching low (ie, a rising-edge clock signal transfers the logic state on its D input through to its Q output). This has no effect on IC2a though, since the flipflops only respond to high-going clock pulses. At the end of this 1ms period, Q1 is pulsed on again by the polling signal and IC1, IC2b & IC2a are again reset. As a result, both Q2 and the relay remain on while ever polling pulses are present. No polling signal Now let’s see what happens if the polling signal ceases. When that happens, IC1’s pin 3 output immediately switches high and clocks IC2b, sending its Q-bar output low. At the same time, IC1’s 100μF timing capacitor begins charging towards the supply rail via trimpot VR1 and the 470kΩ and 1kΩ resistors. The timing period for IC1 can be set anywhere from 33-67s, depending on the setting of VR1. If another polling pulse occurs within this timing period, then the circuit is reset and the relay remains on. However, if no polling pulse is detected (ie, the PC has been powered down), the timing capacitor continues to charge until it reaches 2/3Vcc. At this point, pin 3 switches low and the 100μF timing capacitor siliconchip.com.au This view shows the fully completed prototype. Be sure to build it into the specified plastic case to ensure safety. quickly discharges into pin 7 via the 1kΩ resistor. When the voltage on the timing capacitor discharges to 1/3Vcc, pin 3 switches high again and the 100μF capacitor begins recharging. This highgoing output from IC1 clocks IC2b again, sending its Q-bar output (pin 8) high. This in turn clocks IC2a and switches its Q-bar output low. As a result, both Q2 and the relay switch off, as does LED1. Further clock pulses from IC1 now have no further effect on IC2a. That’s because its D input (pin 2) is tied high and any further clock pulses simply transfer this logic high to its Q output and so Q-bar remains low. In effect, IC1 functions as a missing pulse detector. If the polling signal is absent for longer than its timing period, it applies two clock pulses to IC2b – one almost immediately and the other at the end of the timing period. IC2b simply prevents this first clock pulse from reaching IC2a and turning off the relay prematurely. Transistor Q3 and its associated parts form a power-on reset circuit for IC2b & IC2a. This might seem siliconchip.com.au rather complicated for a reset circuit but is necessary to give a long time constant (about 0.7s). This prevents the USB reset pulse which appears on the D- line almost immediately after power is applied from falsely triggering the unit (ie, before the computer is turned on). Note that we originally used a simple RC reset network here but were forced to use the more complicated circuit when we discovered this problem. This accounts for some of the differences between the unit shown in the photos and the final version. Power supply All the circuitry involving IC1, IC2, Q1 & Q3 is powered directly from a +5V rail which is derived from the USB port. By contrast, the relay circuit (including transistor Q2 and LED1) is powered from a 12V rail. This 12V rail is derived from a simple power supply based on mains transformer T1. Its 12.6V AC secondary is rectified using bridge rectifier D1-D4, the output of which is then filtered by a 470μF electrolytic capacitor. This supply provides about 17V DC, so a 68Ω 5W dropping resistor is used to reduce the effective relay voltage to around 12V when it’s energised. The specified relay draws about 75mA. Note that it is also possible to use a similar relay (Jaycar SY-4040) with contacts capable of switching 30A What Happens During Hibernation? O NE FEATURE of this device is that it will power down the peripherals plugged into it if the computer goes into hibernation. That’s because all data activity ceases on the USB data line during hibernation and because laptop machines power down their USB ports. This allows you to save power while the computer hibernates which is worthwhile over long periods. The peripherals will automatically start up again when the machine comes out of hibernation. January 2009  31 JUMPER OPTIONS: (1): TO TRIGGER FROM USB DATA (D- LINE), LEAVE JP1 & JP2 OPEN (2): TO TRIGGER FROM USB +5V RAIL, INSTALL JUMPER JP1 ONLY 2 2 10k 470k IC1 555 2 GM & Q3 1k 2.2k 1 4 2 3 22k Q2 MAINS WIRING CONNECTORS: 1: 6.4mm INSULATED SPADE CONNECTORS 2: 4.8mm INSULATED SPADE CONNECTORS 3: 4.8mm PIGGYBACK SPADE CONNECTOR BC337 220 F 2 RLY1 IEC MAINS CONNECTOR WITH SWITCH AND FUSE (REAR VIEW) CON3 100 F IC2 74LS74 1 (ACTIVE: BROWN) 1 22k USB IN 3 Q1 1k 3.3k D5 3 2 150pF 10k K 4004 DO NOT LED1 SHORT JP1 & JP2 AT THE SAME TIME M3 x 10mm SCREW WITH LOCK WASHER & NUT JP2 JP1 4 BC549 10 F A 2.2k HCTIWS REWOP 2 VR1 500k K GNISNES BSU 2 1k A LED2 9002 C CON4 4004 D1-D4 USB OUT CON1 2.2k 19010101 4004 SECONDARY (NEUTRAL: BLUE) 4004 2851 N PRIMARY A 4004 100 F T1 1k GPO (REAR VIEW) E 470 F SEE DETAIL DIAGRAM 68  5W (EARTH: GRN/YELLOW) 1 CON2 BC337 2 M4 x 10mm SCREWS WITH FLAT & LOCK WASHERS, NUTS NOTE: ALL WIRING TO THE IEC CONNECTOR, THE GPO AND THE OUTPUT CONTACTS ON THE RELAY (1) MUST BE RUN USING 240VAC CABLE Fig.4: follow this parts layout and wiring diagram to build the unit. Note that all wiring to the GPO, IEC connector and relay contacts must be run using mains rated cable and this wiring must be secured using cable ties (see photos) AC. However this relay needs 100mA of energising current, so if it’s used the dropping resistor value must be reduced to 47Ω. There is no real advantage in using the higher rated relay however, as the IEC mains input connector is only rated for 10A. In any case, it’s very unlikely that the current drain of the peripherals connected to your PC will total 10A – which corresponds to 2300W. So the 20A relay we’re using is already overkill. Diode D5 is connected across the relay coil to protect transistor Q2 from the back-EMF voltage that’s generated by the relay’s coil when it switches off. LED1 (green) indicates when the relay is on and mains power is present at the GPO, while LED2 (red) indicates when mains power is applied to the unit. Finally, switch S1 (which is integral with the IEC socket) allows you to manually turn off the mains power. 32  Silicon Chip This is handy if you want to boot the computer but you don’t want to power up certain peripherals, such as a printer or external disk drive. Construction All of the parts used in the project are housed in a sturdy polycarbonate enclosure (171 x 121 x 55mm) with a clear lid and a neoprene lid-sealing gasket. Note that you must use the specified plastic case for safety reasons – do not use a metal case. As shown in the photos, the IEC mains input connector (with inbuilt switch S1 and fuse F1) mounts on one end of the enclosure, while the 3-pin GPO socket mounts in the lid. Everything else is mounted on a PC board coded 10101091. This board measures 151 x 109mm and has corner cut-outs at one end to allow it to sit on the base of the box. Fig.4 shows the parts layout and CRIMP EYELET M3 NUT STAR WASHERS TRANSFORMER MOUNTING FOOT PC BOARD M3 x 10mm SCREW Fig.5: an M3 x 10mm screw & nut, two M3 star washers and a crimp eyelet are used to secure the earth wire to the transformer frame. wiring. All the low-voltage circuitry is mounted at the righthand end of the board and there are square cutouts in the end of the case to provide access to the USB connectors. The indicator LEDs are viewed through the transparent lid of the enclosure. Two-way terminal blocks CON1 and CON2 are used to terminate the connections from the secondary winding of T1 and the coil of RLY1, respectively. By contrast, one of T1’s siliconchip.com.au primary leads and the relay contacts are connected to the mains wiring via insulated spade connectors. Begin the assembly by installing the six wire links on the PC board, then install the resistors. Table 1 shows the resistor colour codes but you should also check each one using a digital multimeter before soldering it to the board. The 68Ω 5W resistor should be mounted with its square-section ceramic body spaced up about 3mm from the board, so that the air can circulate beneath it (you can use a cardboard spacer to do this). Diodes D1-D5 can go in next, followed by the three transistors (Q1-Q3). Be sure to use the correct transistor at each location. Q1 must be a BC549, while Q2 & Q3 are BC337s. Note that the transistors and diodes are all polarised, so be sure to install them with the correct orientation. Follow these parts with the two ICs. We used good-quality machined IC sockets on the prototype but you can solder these devices directly to the PC board if you wish. Be sure to orientate these devices as shown on Fig.4 (the dot or notch on each device is at the pin 1 end). The electrolytic capacitors are next on the list, again taking care with their orientation. Once they are in, install the 150pF capacitor and the two LEDs (flat side as shown). You can either mount the LEDs close to the board or leave their leads reasonably long so that they will later sit close to lid of the case for improved visibility. The 3-pin header can now be soldered in place, followed by screw terminal connectors CON1 & CON2 and the two USB connectors (CON3 & CON4). Be sure to install CON1 & CON2 with their entry holes Inside the completed prototype – note how the mains wiring is firmly secured using cable ties, as are the leads to the transformer secondary and relay coil. Note also that the PC board used in this prototype version differs in several respects from the final version shown in Fig.4. Table 1: Resistor Colour Codes o o o o o o o o siliconchip.com.au No.   1   2   2   1   3   2   1 Value 470kΩ 22kΩ 10kΩ 3.3kΩ 2.2kΩ 1kΩ 68Ω 5W 4-Band Code (1%) yellow violet yellow brown red red orange brown brown black orange brown orange orange red brown red red red brown brown black red brown not applicable 5-Band Code (1%) yellow violet black orange brown red red black red brown brown black black red brown orange orange black brown brown red red black brown brown brown black black brown brown not applicable January 2009  33 (RIGHT-HAND END OF BOX) 31 10.5 15 8 CUTOUT FOR TYPE A USB CONNECTOR 15.5 CL CUTOUT FOR TYPE B USB CONNECTOR 11 12 (BOX LID) 14 (LEFT-HAND END OF BOX) 10 A 5.5 27 47 10 A 13.5 A 5 18 50 A A CUTOUT FOR IEC CONNECTOR 6 30 5 A HOLES A: 3.0mm DIAMETER CORNER RADIUS 2.5 A 18 CL 72 25 IEC CONNECTOR MOUNTING PLATE: MATERIAL 1mm SHEET STEEL OR ALUMINIUM 5.5 A 26 6 40 18 38 33.5 16.75 10.9 4.5mm DIAM. 4.0 Fig.6: this diagram shows the cutout and drilling details for the GPO socket in the case lid, the access holes for the USB connectors (righthand end), the IEC connector (lefthand end) and the metal mounting plate for the IEC connector. A large cutout can be made by drilling a series of small holes around the inside perimeter, then knocking out the centre piece and carefully filing the job to a smooth finish. 34  Silicon Chip siliconchip.com.au NOTE CABLE TIES USED TO SECURE NEUTRAL & EARTH LEADS TO GPO This view inside the prototype unit shows how the mains wiring is installed and secured. It’s a good idea to fit two Nylon nuts to each Nylon screw that’s used to secure the IEC connector bracket, to firmly lock it into place. facing towards the transformer and relay. The board assembly can now be completed by installing transformer T1 and the relay. First, transformer T1 is mounted using two M3 x 10mm long screws with lockwashers and nuts. Note that the screw fitted to the transformer’s “rear” foot is fitted with an additional lockwasher, because this screw is also later used to attach the crimp eyelet of a mains (safety) earthing lead for the transformer frame. Note also that the enamel must be scraped off the transformer foot to ensure a good contact. Once the transformer has been mounted on the board, the white “centre tap” secondary wire can be cut short and fitted with a short length of heatshrink sleeving. The two yellow secondary leads go to CON1. Keep these two leads short and secure them together using a couple of cable ties. Relay RLY1 is mounted using two M4 x 10mm machine screws with flat washers, lockwashers and M4 nuts. Short leads fitted with 4.8mm insulated spade connectors at one end are then used to connect its coil siliconchip.com.au terminals to CON2. Once again, secure these leads together with cable ties, as shown in the photos. Preparing the enclosure Once the board assembly has been completed, it can be placed aside while you cut the various holes in the enclosure and its lid. The size and locations of all of these holes are shown in Fig.6. In summary, there are two small rectangular cutouts at one end of the case for access to USB connectors CON3 and CON4, plus a single large rectangular cutout at the other end for the IEC mains input connector. In addition, there are two holes in the lid to mount the GPO socket. The IEC fused male connector and switch is a snap-in type intended for use with a mounting plate thickness of about 1mm. Unfortunately, the specified IP65 box has a wall thickness of 3mm, so the IEC connector cannot be mounted directly to it. Instead, it is fitted to a 1mm-thick metal plate and this plate is secured to the inside of the box using four M3 x 10mm Nylon screws and eight Nylon nuts. As a result of this arrangement, the flange of the IEC socket is mounted flush with the surface of the box, giving a neat finish. As well as the box cut-outs, Fig.6 also shows the dimensions of the metal plate for the IEC connector. It should be made from 1mm thick sheet steel or aluminium. Having made the plate, the next step is to snap the IEC connector into it and then attach this assembly inside the enclosure using the four M3 x 10mm Nylon screws and nuts. It also a good idea to then install an additional Nylon nut on each mounting screw. These will firmly lock the first nuts into position and ensure that the assembly can not possibly come loose. That done, mount the PC board assembly inside the enclosure and secure it using four M3 x 6mm machine screws. These screws go into the integral threaded mounting bushes on the base of the box. The GPO outlet can now be fitted to the lid. That’s done by first unscrewing the centre screw holding the front plate to the rear moulding and then screwing the outlet back together with January 2009  35 nectors may have 6.4mm lugs and will require 6.4mm spade connectors. As shown in the photos, all this mains wiring must be neatly installed and secured using eight cable ties. This is necessary to make it impossible for any leads to come loose and make contact with the low-voltage components on the PC board. Note that the Neutral and Earth wires are also tied to the GPO socket using the holes in its moulding as anchor points (see photo). Additional cable ties are used to secure the leads to CON1 & CON2. Again, the idea is to ensure they cannot come loose and contact mains voltages. Initial checks The IEC connector is snap-fitted to a metal plate and this assembly is then secured to one end of the case using M3 x 10mm Nylon screws and nuts. the enclosure lid sandwiched between the two sections. Mains wiring The final assembly step is to install the mains wiring. This involves all wiring to the IEC input connector, the relay contacts and the GPO socket, plus the primary winding of T1. Note that all this wiring must use 250VAC 10A rated wire. Brown wires are used for the Active connections, blue for Neutral and green/yellow for the Earth wiring – see Fig.4. Fig.5 shows how the Earth lead is attached to the transformer mounting foot via a 5.3mm ID crimp eyelet terminal. All leads to the IEC connector and to the relay are terminated using insulated spade connectors. You must use a ratchet-driven crimp connector to fit these. Do not use a cheap automotivestyle crimp tool, as this will not give reliable connections. The Earth wire terminations, in particular, must be well made in the interests of safety. Fig.4 shows what type of spade connector to fit to each wire. Use 4.8mm spade connectors to the IEC connector as indicated. These spade connectors should all be fully insulated. If you are unable to obtain fully insulated 4.8mm connectors, then use non-insulated connectors but be sure to fully insulate each one using 6mm-diameter heatshrink tubing after its lead is crimped in place. Note that the connector at the terminal marked “3” on the IEC connector is a piggyback type. Again, it should be fully insulated using heatshrink tubing. Note also that some IEC con- Before doing anything else, use your multimeter (set to a low ohms range) to check between the earth pin of the IEC connector and the earth outlet of the GPO. You should get a reading of zero ohms here (this checks the integrity of the earth connection). Similarly, you should get a reading of zero ohms between the earth pin of the IEC connector and the transformer frame. Having verified the earth connection, fit the 10A fuse to the fuseholder in the IEC socket. Note that this fuse should be a slow-blow type. Testing It’s now time to test the unit. Here’s the step-by-step procedure: (1) Rotate trimpot VR1 fully anticlockwise (this sets the timing period to minimum). (2) If you are using a laptop, install jumper JP1 to trigger off the +5V USB rail. If you are using a desktop machine, leave JP1 out so that the unit triggers off the D- line. (3) Attach the lid to the case. This is important – we strongly advise against into MICROS OR PICS? 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Enabling USB mouse or USB keyboard support (depending on which device you have plugged into the USB Out port) will allow you to set VR1 to minimum (ie, to give the minimum delay period). Silicon Chip Binders REAL VALUE AT $13.95 PLUS P & LAPTOP COMPUTER: trigger from the USB +5V line. Install jumper JP1 and connect the device to the computer via a standard USB cable. Use of the USB Out socket is optional and you can plug in any device you wish. Note that plugging in a USB mouse or keyboard will introduce a switch-off delay (as set by VR1), unless you leave out IC2. connecting this unit to mains power without the lid in place, to eliminate the risk of electric shock. (4) Connect the unit to a mains power outlet, then switch on the mains out­ let and switch on the IEC connector’s switch (S1). The red LED should light to indicate that the power is on but nothing else should happen – ie, the relay and LED1 (green) should remain off. (6) Connect the unit to your computer using a standard USB type-A to type-B cable. If you are using a desktop computer, then connect your USB mouse or keyboard to the USB Out socket (CON4) as well. (7) Power up the computer. After a brief delay (no more than several seconds), you should hear a click as the relay operates and the green LED should light to indicate that mains power has been switched through to the GPO. (8) If you have a desktop computer, check the green LED as the computer boots. If it goes out and then comes back on again towards the end of the Windows splash screen, then the delay period is too short. To adjust the delay, first unplug the mains cord from the IEC connector, then open the lid and adjust trimpot VR1 slightly clockwise. Be sure to replace the lid before testing the unit again. Repeat this procedure if necessary, so that the green LED remains on while the computer boots. (9) Power down the computer. If you are using a laptop, the green LED should go out as soon as the machine shuts down. You should also hear a click as the relay switches off. Alternatively, if you are using a desktop machine, the green LED and relay should remain on for the delay period after the computer switches siliconchip.com.au P Points To Check (1) Be sure to use the specified ABS plastic case & note that Nylon screws must be used to secure the IEC connector plate to ensure safety. (2) Use mains-rated cable for all connections to the IEC socket, the GPO and the relay contacts. Secure this wiring using cable ties – see photos. (3) Use fully-insulated spade connectors to terminate the leads to the IEC connector and to the relay contacts. A ratchet-driven crimping tool is necessary to fit the spade connectors. (4) Do not touch any part of the 230VAC wiring while this device is plugged into the mains. Also, DO NOT attempt to build this device unless you know what you are doing and are familiar with high-voltage wiring. off. This period will be somewhere between about 33s and 67s, depending on the setting of VR1. Note: if your desktop computer is very slow to boot and 67s isn’t long enough, increase the value of the 470kΩ resistor in series with VR1. Alternatively, enable USB mouse or USB keyboard support in the system BIOS, depending on which device you have plugged into CON4. If this all checks out, your USBSensing Power Switch is working and can be put into service. All you have to do is plug a power distribution board into the GPO on the top of the enclosure and then plug your peripherals into this distribution board. Don’t forget to connect a USB mouse or keyboard to the unit if you are triggering the unit from the D- line of the USB port. That’s it. Your peripherals will now be automatically turned on and off SC with the computer. These binders will protect your copies of SILICON CHIP. They feature heavy-board covers & are made from a dis­tinctive 2-tone green vinyl. They hold 12 issues & will look great on your bookshelf. H 80mm internal width H SILICON CHIP logo printed in gold-coloured lettering on spine & cover H Buy five and get them postage free! Price: $A13.95 plus $A7 p&p per order. Available only in Aust. Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or call (02) 9939 3295; or fax (02) 9939 2648 & quote your credit card number. Use this handy form Enclosed is my cheque/money order for $________ or please debit my  Visa    Mastercard Card No: _________________________________ Card Expiry Date ____/____ Signature ________________________ Name ____________________________ Address__________________________ __________________ P/code_______ January 2009  37