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By JOHN CLARKE Switch on your PC and your peripherals will come on as well. Switch on your amplifier and all your hifi gear will come on too. Switch on your TV and the rest of your home theatre system will power up as well. That’s the beauty of this “PowerUp” unit. 32  Silicon iliconCChip hip www.siliconchip.com.au siliconchip.com.au Fig.1: the PowerUp works by detecting the current flow through the master mains outlet and then switching power to slave outlet. Y OU CAN ALSO USE PowerUp in your workshop. Switch on your router or bench saw and the vacuum cleaner will suck away the sawdust straightaway. Doubtless there are other applications to save you switching on numerous other items of equipment when you want to get straight into work or play. The PowerUp connects to the main unit such as an amplifier and switches on power to the remaining units whenever the main unit is switched on. This saves having to power up the other units separately. PowerUp is a small box with two mains outlets, one for the master appliance and the other to run the slave appliances. This second outlet would provide power to a multi-way power-board for the remaining appliances. When the master appliance is switch­ed on, the other appliances will be powered up also. PowerUp works by detecting the current flow through the master mains outlet and then switching power to slave outlet. The general scheme is shown in the block diagram of Fig.1. The cur­rent detector is a toroidal coil combined with a Hall effect de­vice. sistor and 1µF capaci­tor which rolls off frequencies above 159Hz. The filtered output is then AC-coupled to pin 3 of op amp IC1a. Pin 3 is biased at +5V via the 100kΩ resistor from the +5V rail. Op amp IC1a is set for a gain of 471 using the 470kΩ feed­back resistor from pin 1 to pin 2 and the series 1kΩ and 10µF capacitor to the +5V rail. The 10µF capacitor rolls off frequen­cies below 16Hz. Frequencies above 154Hz are rolled off by the 2.2nF capacitor across the 470kΩ feedback resistor between pins 1 & 2. Op amp IC1b is wired as a precision half-wave rectifier by virtue of diodes D5 and D6 which are connected within the feed­back loop. The rectified signal at D5’s anode is filtered with a 100kΩ resistor and 10µF capacitor so that the result is a DC voltage proportional to the signal from the Hall sensor. IC2a is half an LM393 dual comparator wired as a Schmitt trigger. It monitors the filtered DC signal at pin 6 and compares it to the threshold voltage at pin 5. Pin 5 is connected to the 5V rail via a 4.7kΩ resistor and also to trimpot VR1 across the 5V rail. A 1MΩ positive feedback resistor to pin 7 applies hys­teresis. Hysteresis means that the pin 5 voltage is at a different level, depending on whether the output at pin 7 is high or low. When pin 7 is low, pin 5 is pulled a few millivolts lower via the 1MΩ resistor and if pin 7 is high, pin 5 is pulled a few millivolts higher. Circuit description The full circuit is shown in Fig.2. Besides the Hall effect device, it uses just two ICs and a relay. The Hall sensor is placed in a slot (air gap) in a toroidal core. The master outlet current flows through the toroidal coil and generates a corre­sponding AC signal from the Hall sensor (HS1). Its output is filtered with a 1kΩ resiliconchip.com.au This is the view inside the prototype. The toroidal coil on the PC board operates at mains potential and is protected by a Prespahn insulation cover (see text). July 2003  33 34  Silicon Chip siliconchip.com.au Fig.2: the complete circuit diagram. IC1a amplifies the signal from the Hall sensor and feeds it to precision rectifier stage IC1b. IC1b’s output is then fed to Schmitt trigger stage IC2a which drives Q1 and the relay to switch in the slave GPO. In this oscillogram, the top trace shows the Hall effect signal when connected to a 60W mains load. This is amplified to 8.9V peak-to-peak by IC1a (lower trace). This ensures that small variations in DC input voltage to pin 6 do not cause the output to oscillate high and low. Trimpot VR1 sets the trigger threshold for IC2a. This is normally set at around mid-position. Setting it slightly towards the 5V supply will trigger the Schmitt at small signal levels from IC1, while setting it towards the 0V rail will mean that the signal needs to be greater before IC2a’s output will go high. When pin 7 of IC2a does go high, it drives transistor Q1 to turn on relay RLY1 which then applies 240VAC to the slave GPO socket. The 3.3V zener diode in Q1’s emitter to ground connection reduces the voltage applied to the relay to around 12V rather than above 15V. Power for the circuit comes from a 12.6V transformer. It drives a bridge rectifier (D1-D4) and a 100µF capacitor to provide about 16V DC. This supplies IC2 and the relay. IC1 is powered from +12V, derived using a series 820Ω resistor and 12V zener diode (ZD1). The Hall effect sensor is fed with 5V from a 78L05 regulator (REG1) and this also provides the input reference for IC1a, IC1b and IC2a. IC2b is not used. Mains power indication Both GPO sockets have a neon indicator wired across them to indicate when power is present. Neon 2, across Active and Neutral for the slave GPO outlet, lights when the relay contacts are closed. The relay contacts are shunted with a 1nF 3kV capacitor which prevents contact arcing when power is removed. The capaci­tor also siliconchip.com.au IC1a’s output (lower trace) is rectified by IC1b (top trace). This rectified signal is filtered and fed to the Schmitt trigger to control the relay. allows a small amount of current to flow when the relay is open and this is sufficient to dimly light Neon 2 even though it has two 1.2MΩ resistors connected across it. In practice though, this is not a problem because Neon 2 lights quite brightly when it should; ie, when power is available at the salve GPO socket. Construction The PowerUP circuit is built on PC board measuring 79 x 140mm (coded 10107031). It is housed in a plastic case measuring 165 x 85 x 55mm, with two chassis-mount GPO (general purpose) sockets on the lid. Note that you must use a plastic case for this project and there must be no exposed metal parts that pass through to the live wiring area inside. DO NOT use a metal case for this project – that would be too dangerous. You can begin assembly by checking the PC board against the published pattern of Fig.6. There should not be any shorts or breaks bet­ween tracks. If there are, repair these as necessary. Next, insert and solder the PC pins and the resistors. Use Table 2 as a guide to the colour codes for the resistors. Note that the two 1.2MΩ resistors must be high-voltage Philips VR25 types or equivalents. Do not substitute for these. Next, insert and solder in the zener diodes, diodes and trimpot VR1, taking care with the positioning of ZD1 and ZD2. The ICs can be installed next, taking care with their orientation. The LM393 is placed adjacent to Q1. When installing transistor Q1 and the 78L05 regulator, take care that you don’t get them confused; they look the same! The capacitors can be installed next. Table 1 shows the codes on the MKT and ceramic types. Make sure that the leads of the 3kV ceramic capacitor are covered with 5mm long insulating WARNING: MAINS VOLTAGES! Note that this circuit is connected to the 240VAC mains supply and is potentially lethal. While most of the electronics circuitry is isolated from the mains, it is possible that you could make contact with a live part. In particular, note that inductor L1, the two 1.2MΩ resistors, the 1nF 3kV capacitor, the relay contacts and the Neon indicators all operate at 240VAC. Do not apply power to this circuit unless it is fully enclosed in a plastic case and DO NOT TOUCH ANY PART OF THE CIRCUIT when it is plugged into a mains outlet. Always remove the plug from the mains before working on the circuit or making any adjustments. Finally, do not build this project unless you are completely familiar with mains wiring practices and techniques. July 2003  35 BIND ALL MAINS WIRING TO THE PC BOARD & TO THE MAINS SOCKETS WITH CABLE TIES WARNING: LETHAL VOLTAGES ARE PRESENT ON THE PC BOARD (INCLUDING INDUCTOR L1) Fig.3: follow this wiring diagram exactly to build the PowerUp. In particular, take care to ensure that all parts are oriented correctly and that the mains wiring is installed in a professional manner. sleeving, before inserting it into the PC board. The electrolytic capacitors must be oriented with the polarity as shown, except for the two non-polarised (NP) types which can be mounted either way around. The relay is mounted next. We have provided for different relays (as specified in the parts list). Making the toroidal inductor As noted above, the toroid inductor 36  Silicon Chip (L1) is slotted to take the Hall sensor. Cutting a 2mm slot in a ferrite toroid is almost impossible because the material is so brittle but the specified powdered iron toroid is quite easy to cut with a hacksaw. Clamp the toroid lightly in a vice; if you over-tighten the vice, it is likely to crack the core. After you have cut through one side of the toroid, you will need to enlarge the slot to about 2mm with a small file. Just make it suf- ficiently wide so that the Hall sensor can easily slide into the slot. Now wind 42 turns of 1mm dia­meter enamelled copper wire onto the toroid and strip the insulation from the wire ends. That done, place this assembly in position on the PC board with the slot directly over the position for the Hall sensor. Finally, solder the wires in position and secure the inductor with cable ties. You can now insert and solder in siliconchip.com.au Parts List Table 1: Capacitor Codes Value 100nF 2.2nF 1nF µF Code EIA Code IEC Code 0.1µF 100n 104 (.0022µF) 2n2 222 (.001µF) 1n0 102 the Hall sensor, taking care with its orientation. The correct position is with the sensor body centrally located in the toroid slot. Working on the case The first step here is to drill out and file the hole in the end of the case for the cordgrip grommet. This hole must be a tight fit to make sure that it securely anchors the mains cord. Next, mark out and drill the front panel for the mains out­lets, switch, Neon indicators and fuse holder. The cutting tem­plate for the GPO sockets is shown in Fig.5. You can then fit the front panel label (if available), the GPO sockets, the Neon bezels, the switch and the fuseholder. Note that the fuseholder must be a safety type, as specified in the parts list. Do not use a standard fusehold-er. The PC board can now be mounted in position using the screws supplied with the case. Once it’s in, you can complete the wiring as shown in Fig.3. Note that all mains wiring must be run in 7.5A 250VAC-wire. The earth connections are soldered or crimped to the solder lugs using green/yellow mains wire and secured to the transformer case using an M3 x 10mm metal screw, nut and star washer. Make sure the transformer case is indeed earthed by measur­ ing with a multimeter for a low ohm reading between earth and the transformer metal body. It may be necessary to scrape the lacquer coating off the 1 PC board, code 10107031, 79 x 140mm 1 plastic case, 165 x 85 x 55mm (Altronics Cat. H-0306) 2 chassis-mount GPO sockets (Altronics Cat. P-8241 or equivalent) 1 12.6V 150mA mains transformer (Altronics Cat. M-2851L or equivalent) 1 10A 250VAC SPST (or SPDT) relay (Altronics Cat. S-4250A, S-4170A or equivalent) 1 6A SPST 250VAC mini mains rocker switch 2 250VAC Neon indicators (Altronics Cat. S-4016 or equivalent) 1 M205 panel-mount safety fuse holder (F1) (Altronics Cat. S-5992, Jaycar Cat. SZ-2028) 1 M205 10A fuse 1 7.5A mains cord and moulded 3-pin plug 1 ring type crimp lug for 1.52.5mm diameter wire 1 70 x 70 piece of Prespahn insulating material 1 powdered iron toroidal core 33mm OD x 20 ID x 10mm (Neosid 17-742-22; Jaycar LO-1244; L1) 1 50kΩ horizontal trimpot (coded 503) (VR1) 2 M3 x 10mm screws 2 M3 nuts 2 3mm star washers 1 2m length of 1mm enamelled copper wire 1 400mm length of 7.5A brown 250VAC-rated wire 1 400mm length of 7.5A blue 250VAC-rated wire 10 100mm long cable ties 10 PC stakes 1 80mm length of 3mm diameter heatshrink sleeving for mains to PC stake connections 1 40mm length of 6mm diameter heatshrink sleeving for switch terminals 1 100mm length of 13mm diameter heatshrink sleeving for fuseholder and Neon indicators Semiconductors 1 LM358 dual op amp (IC1) 1 LM393 dual comparator (IC2) 1 UGN3503 Hall sensor (HS1) 1 78L05 3-terminal regulator (REG1) 1 BC338 NPN transistor (Q1) 1 12V 1W zener diode (ZD1) 1 3.3V 1W zener diode (ZD2) 5 1N4004 1A diodes (D1-D4,D7) 2 1N914 diodes (D5,D6) Capacitors 1 1000µF 25V electrolytic 3 10µF 16V electrolytic 1 10µF 50V NP (non-polarised) electrolytic 1 1µF 16V electrolytic 1 1µF 50V NP (non-polarised) electrolytic 2 100nF (0.1µF) MKT polyester 1 2.2nF (.0022µF) MKT polyester 1 1nF (.001µF) 3kV ceramic Resistors (1%, 0.25W) 2 1.2MΩ Philips VR25 (don’t substitute) 1 1MΩ 4 4.7kΩ 1 470kΩ 2 1kΩ 3 100kΩ 1 820Ω 2 10kΩ Table 2: Resistor Colour Codes o No. o  2 o  1 o  1 o  3 o  2 o  4 o  2 o  1 siliconchip.com.au Value 1.2MΩ (VR25) 1MΩ 470kΩ 100kΩ 10kΩ 4.7kΩ 1kΩ 820Ω 4-Band Code (1%) brown red green yellow brown black green brown yellow violet yellow brown brown black yellow brown brown black orange brown yellow violet red brown brown black red brown grey red brown brown 5-Band Code (1%) N/A brown black black yellow brown yellow violet black orange brown brown black black orange brown brown black black red brown yellow violet black brown brown brown black black brown brown grey red black black brown July 2003  37 Fig.4: this diagram shows how to make the Prespahn insulation cover that fits over coil L1. Fig.6: this full-size front-panel artwork can be used to mark the mounting positions for the fuseholder and the Power switch. Specifications Power level to switch slave GPO ............................. 1-25W adjustable Maximum load (master and slave GPO)....... 6A or 1440W (set by S1) Standby current........................................................................ 18.5mA Fig.5: use this template to mark the cutouts and mounting holes for the two GPOs. Fig.7: check your PC board against this full size etching pattern before installing any of the parts. 38  Silicon Chip siliconchip.com.au Silicon Chip Binders REAL VALUE AT $14.95 PLUS P & P These binders will protect your copies of S ILICON CHIP. They feature heavy-board covers & are made from a dis­ tinctive 2-tone green vinyl. They hold 12 issues & will look great on your bookshelf. H 80mm internal width Use mains rated cable for all mains connections and bind the wires with cable ties to prevent them coming adrift. Note that all exposed mains connections should be covered with heatshrink tubing. transformer mounting foot to allow a good con­tact. Secure the other side of the transformer using an M3 x 10mm screw, star washer and nut. Use heatshrink sleeving over any bare terminals. You should also tie the wires with cable ties to prevent them breaking and coming loose from their terminations. Make sure that the mains cord is securely anchored to the case with the cord grip grommet. Covering inductor L1 Inductor L1 has 240VAC flowing through it and to improve safety, this is covered with a Prespahn cover folded from a 70 x 70mm square piece of the material. Cut out 15mm squares on each corner and fold down. Fig.4 shows the details. The cover sits over the toroid inductor and its connections to the PC board. This can be secured to the PC board with some silicone sealant. Adjusting VR1 Trimpot VR1 is initially set to the midpoint. Once that’s done, fit the lid, plug in the appliance to be used as the master (computer, stereo amplifier or whatever) and apply power. siliconchip.com.au Now turn on the master appliance. If Neon 2 does not light, you will need to disconnect the power and adjust VR1 – ie, turn it clockwise by a small amount. Note: this should be done with the PowerUp’s power cord disconnected from the mains wall socket (see warning panel). You then redo the test and repeat the procedure again, as necessary. VR1 is adjusted correctly when Neon 2 is on when the master appliance is switched on and off when the master appliance is switched off. If the Neon is always alight, adjust VR1 further anticlockwise. Troubleshooting If the circuit does not work, switch off power and unplug the unit from the mains. Then check your work for correct wiring and parts placement. You can check the supply voltages for each IC using mains-rated probes on your multimeter but take care not to touch any part of the circuit with your hands. IC1 should have 12V between pins 4 & 8, while IC2 should have about 15V or 16V between pins 4 & 8. The output from REG1 should SC be 5V. H SILICON CHIP logo printed in gold-coloured lettering on spine & cover H Buy five and get them postage free! Price: $A14.95 plus $A10.00 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_______ July 2003  39