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PC CONTROLLED Everyone, it seems, has an old computer, unused and unloved, gathering dust somewhere. Wouldn’t you like to do something useful with it, like controlling external devices? This project has both the hardware and software to do exactly that – and it will work on anything from a 386 up! Concept, hardware and software design by Trent Jackson Words by Ross Tester I goes. Just remember, though, that this nitially, this project was designed is a mains-powered and mains-conto turn a swimming pool filter trolling device and the circuit “floats” pump on and off at appropriate at full mains potential at all times. times. Sure, you can buy a pretty cheap mechanical or electronic timer There are certain practices and proto do that but with an old 486 lying cedures which must be followed for idle and the possibility – no, make your own safety and that of anyone else that probability – of controlling a lot using the device (not to mention the more than a pool pump, I thought, longevity of your computer!). Most of why not? all, be extremely cautious when testing As it turned out, the hardware to do or servicing the circuit with the cover the job is relatively simple and cheap – there are only about twenty components required FEATURES to give a pretty nifty circuit. build  Low cost, easy to The software, though, is a little more complicated – but as I tection  Fuse and surge pro have already done that part for ion you, all you need to do is build  Full optical isolat the control box, dust off that old ction  System enable fun computer, fire it up and load the itching software.  Efficient relay sw It uses the parallel (printer)  Precision timing port of just about any PC from, r events say, 386 vintage onwards. It op Control up to fou erates under good, old fashioned er settings  Save and open tim DOS (remember that?) – in fact, I wouldn’t recommend it being run under Windoze. off. To be absolutely safe, I’d suggest The hardware you do all your testing with a 12V battery powering it. At SILICON CHIP There is nothing too difficult to either we like our readers and want to keep comprehend or build as far as hardware all of them alive! We’ll show you how to hook in a 12V supply later on. Speaking of safety, the circuit features fuse and surge protection and has full electrical isolation (by means of an optocoupler) between the mains and the connection to your computer. Now, let’s look at the block diagram, Fig.1, in conjunction with the circuit diagram, Fig. 2. The first thing you will note is that there is no transformer. The 240V mains is applied via a 10A fuse (for protection against catastrophic failure) and a 275V varistor (to suppress any mains-borne spikes). A capacitor across the mains also assists in filtering out any noise. Next there is an AC current limiter consisting of a pair of parallel capacitors which together add up to about 1µF. From first principles, we know that series capacitors in an AC circuit offer resistance (or more correctly impedance) to current flow. This is expressed by the formula XC = 1/2π f C, where XC is in Ohms, f is the frequency in Hz and C is the THIS IS A MAINS-POWERED DEVICE AND THE CIRCUITRY IS LIVE (240V AC) WHILE EVER POWER IS CONNECTED, EVEN IF THERE IS NO OUTPUT VOLTAGE. DO NOT ATTEMPT TO BUILD THIS PROJECT IF YOU ARE NOT ENTIRELY FAMILIAR WITH MAINS WIRING PRACTICES AND CONSTRUCTION TECHNIQUES. 36  Silicon Chip www.siliconchip.com.au D MAINS SWITCH capacitance in farads. Therefore, at 50Hz, the two capacitors are going to present an impedance of about 3.2kΩ. From Ohm’s law (I=E/R), we can then deduce that the current will be limited to 240V/3200Ω or about 75mA. The 47Ω resistor following the series capacitors can be all but ignored for the purpose of this equation – its job is to limit the inrush current which would otherwise occur at switch-on. The four diodes (D1-D4) form a bridge rectifier across the 240V AC mains, resulting in a pulsating DC voltage output of about 340V (240 x 1.414). Zener diode ZD1 is connected as a shunt regulator across this supply, clamping it to around 12V DC. The two capacitors (C3 and C4) provide further smoothing, resulting in a relatively well-regulated 12V DC supply for the rest of the circuit. A red LED across the 12V supply shows that power is applied. So far, all we’ve looked at is the power supply – but there is not much else to it! Turning back to the other input, www.siliconchip.com.au that from the computer, we see that two pins, Data 1 and Strobe, of the parallel port, provide the signal drive for the switch. Under software control, when Data 1 goes high and the Strobe goes low, D5 and D6 are both forward biased, lighting the LED inside the optocoupler (the 180Ω series resistor limits current from the parallel port to safe levels). As you can see from this, there is no electrical connection whatsoever between the computer and this circuit. The optocoupler specified, SFH601-3, has been chosen because of its high isolation. Lower rated optocouplers should not be used. When the LED in the optocoupler lights, the transistor in the opto-coupler Fig.1: the block diagram of the PC-controlled mains switch shows that there is complete isolation between the mains and the PC. September 2001  37 PC CONTROLLED MAINS SWITCH WARNING: THE MAJORITY OF THIS CIRCUIT OPERATES AT 240VAC! N  E  LED2 1.2k ZD1 12V 5W E B C 1000F 25V BC548 0.1F SC 2001 LED1 POWER 1.2k ½OPTO1 SFH601-3  RLY1 10 D5 1N4007 E CONTACT WITH ANY PART OF THIS CIRCUIT WHILE CONNECTED TO THE 240VAC MAINS SUPPLY COULD KILL YOU! 240VAC OUTLET A RLY1 250VAC Q1 BC548 C B 4.7k 4 5 D1 - D4 4 x 1N4007 ½OPTO1 SFH601-3 1  2 PARALLEL PORT CONNECTOR PIN NUMBERS. *NUMBERS SHOWN INDICATE 0.1F 250VAC CLASS 'X2' 20 12 13 11 10 PORT TO PC *PARALLEL 1 3 100 D7 1N914 180 E 240VAC INPUT N D6 1N914 V1 V275LA20A 275VAC A F1 10A (MAX) 250VAC 100k ½ W 0.47F 250VAC CLASS 'X2' 0.47F 250VAC CLASS 'X2' 47 1W K A LED The software Fig. 2: the complete circuit diagram of the PC-Controlled Mains Switch. 38  Silicon Chip conducts. This transistor is connected in “Darlington” fashion to Q1 which is then turned on. Current flows from Q1’s collector to emitter, through a 10Ω resistor and then through the relay coil, pulling it in and closing the 240V active circuit. Therefore, whatever is connected turns on. At the same time, the green LED between Q1’s emitter and ground also turns on to give indication that 240V power is available. The reverse-biased diode across the relay coil doesn’t normally conduct. Its purpose is to protect Q1 when the optocoupler turns off and the relay de-energises. This can generate a quite high voltage pulse which might destroy Q1; when the relay de-energises the diode becomes forward biased, safely bleeding the pulse away. Finally, you will note that all 4-bit inputs to the PC parallel port are connected together and tied low, to pin 20. This is essential for the port to operate as we intended. Incidentally, the port must be operated in the “ECP” mode, which can normally be set up via the computer’s CMOS setup. ECP, by the way, stands for Enhanced Capabilities Port. If you don’t know how to do this, refer to your computer’s manual (or perhaps you shouldn’t be attempting this project!). The software, PCMS.EXE, does the vast majority of the “work” – my philosophy is minimum hardware and maximum software! It is written in Q-BASIC and a zipped version can be downloaded from the SILICON CHIP website. As mentioned before, this should be run in DOS mode. While I have run it under Windows, it occasionally gets upset and freezes. You shouldn’t have this problem under DOS. The software will run without the controller hardware plugged in, so you can get a feel for its operation and features. There is a scrolling message at the bottom of the screen which tells you which keys to press for which operations. It’s also designed to be very user-friendly – once you’ve used it a couple of times you will get the hang of it. The heart of the program is the timer settings box. When you first run the program it will load up null settings www.siliconchip.com.au back and type over. (The backspace key will delete characters in the files box). Files box You can save current timer settings in a file and recall it later – press the F4 key to save your current settings and F5 to open any presaved settings. System box The current time and date, read from your PC’s real time clock, are displayed in the top two boxes. You cannot change these – you must go into your PC’s time and date setting procedure (via CMOS setup) to do this. The Port Address can be changed to match the port address of your computer’s parallel port. The default is H378; some computers have theirs at H278 but pressing the F1 key will toggle through the various addresses possible. If you have a valid port address, the port data (immediately underneath) should read between H120 and H148. Note that the port mode must first be set to ECP (enhanced capabilities port) mode via your CMOS setup. The “Device Enable” box is not controlled by the timers; you have to set The completed PC board with its connections to power, to the mains outlet (GPO), the front panel LEDs and to the computer parallel port. There were some minor differences between this photo and the final version shown below. (0’s) for each of the four programmable events. are entered in the format MM-DD-YY (eg, 19th September 2001 would be 00-19-01); times are in 24 hour format (8.15pm would be 20:15). To modify any setting, use the arrow keys (keypad) to move the flashing cursor to the unit you want changed and enter the new setting of the null setting. The backspace key does not delete – move the cursor Timer Settings box There are two modes. MX is the normal mode and can handle both dates and times. DX is the alternate mode, used when you want an event to occur on a daily basis (so no date input is needed) Dates GPO (REAR VIEW) E A CASE CASE LO EL /Y EN RE (G L RA UT NE ) UE (BL CORD GRIP GROMMET www.siliconchip.com.au 180 SOLDER RESISTOR ACROSS V1 D6 1.2k 10 4.7k 1.2k 100k Q1 D5 F1 10A (MAX) 250VAC 1 * * 3 OPTO1 SFH601-3 1 PIN NUMBER ON *PC PARALLEL PORT CONNECTOR 0.1 F 250VAC 0.47 F 250VAC 0.47 F 250VAC 0.1 F D3 25V (BROWN) 1000 F TIVE D2 D7 1N 4148 + ZD1 AC 47 1W D4 Fig.3: follow this component overlay and wiring diagram when building the project. Build and test the PC board first – but don’t put in the 5W Zener (ZD1) until after testing. DATA CABLE ISOLATED SECTION 4 x 1N4007 D1 V1 E TH AR N 1N 4148 250VAC MAINS CABLE CORD GRIP GROMMET ) W A LED1 K A LED2 1N4007 K RLY1 10A / 250VAC September 2001  39 Here’s what the software, PCMS.EXE, looks like on the screen. You can set the on and off times for up to four events as well as change various parameters as described in the text. Download the software from www.siliconchip.com.au this manually with the F2 key in order to enable the hardware. Finally, the “Device Status” box should automatically come up with a “connected” message if your port is functioning correctly and the hardware is connected. If the software has detected errors (eg, no hardware connected or a port malfunction of some sort) it will read unknown. The big box underneath the System box is a visual indication that everything is working as it should: when the timer turns the hardware on, the box changes from red to green and the message changes from “AC POWER IS OFF” to, surprise surprise, “AC POWER IS ON”. If you don’t like the background colour, toggle the F6 key. There are 16 different colours and styles to choose from – there must be something there you’ll like! we specify nylon types – if a nut works its way loose inside the case and shorts out something, you or your PC could disappear in a puff of blue smoke. As usual, start by visually checking the PC board to ensure there are no etching or drilling defects. Then commence assembly with the lowest profile components – resistors, varistor and diodes (ensure the diodes are the right way around!). At this stage, don’t fit the Zener diode because it will get upset with our checking procedure later. Next are the smaller capacitors (watch the polarity on the electrolytics), the IC and transistor (ditto) and the fuse clips. Some fuse clips have little lugs on them which will stop a fuse being inserted if they are back-tofront: check yours by inserting a fuse before soldering. All that’s left now are the larger capacitors and the relay. Now we are ready to move on to the wiring which Construction Before we start, another word of warning. Please ensure that you follow the construction method to the letter – we have gone to a great deal of trouble to ensure that the design is safe and construction methods echo that safety. For example, do not substitute standard metal bolts and nuts where 40  Silicon Chip The PC board is secured to the case lid with four nylon screws, as shown here. Each screw has a nylon nut on the inside acting as a spacer before the PC board is seated and secured with another nylon nut. www.siliconchip.com.au is where you have to be particularly careful to make sure nothing is wrong. The basic premise is that the wires need to be only as long as necessary to reach and not long enough to short to something else if for some reason they come adrift. Before you do that, though, you should prepare the jiffy box for the external components and wiring. A 6mm hole is required at each end (for the mains cable and the computer cable), each with a rubber grommet. The bottom of the box is used as the top (the lid becomes the base) and in this you will need two 5mm holes for the LEDs, two 3mm holes for the power outlet mounting screws and finally a 30mm hole for the back of the power outlet to poke through. All labels should now be glued to the box and left to dry. While that’s happening, go over your PC board assembly once more to make sure everything’s where it should be. It will be much more difficult to check it later. Prepare the red and green LEDs by soldering a 100mm length of 4-way rainbow cable to their respective legs. Note which legs are the anode and the cathode (the anode lead is the longer) and then cut both legs very short – say 3mm – and solder the rainbow cable to them leaving as much as the cable intact as you can. Then wrap the soldered joints in insulation tape so that no exposed legs or wire are visible. If necessary, put a piece of tape between the legs to ensure they don’t short. If you’ve now forgotten which leg was which, the cathodes are the ones adjacent to the flat on the LEDs! Write down the colours of 4-way rainbow cable which go to each leg, and which colours go to which colour LED. Fit LED mounting collars over them and push them through the bottom of the box. Lock them in place with a dab of silicone sealant, super glue, 5-minute Araldite or other suitable adhesive. Refer to the wiring diagram for the mains wiring and follow it exactly. Again, only make the leads as long as you need to. Remove the outer insulation from the three-wire mains lead to a length of 175mm. Cut off 100mm and put it aside – you’ll need this as mains hookup wire. Push the wires of the mains lead through the appropriate www.siliconchip.com.au Parts List – PC Controlled Mains Switch 1 PC board, 101 x 57mm, coded 10109011 1 plastic case (Jaycar HB6013 or equivalent) 1 mini switched power outlet (GPO) (HPM 787 or equivalent) 2 cord-grip grommets to suit cables used 2 3AG fuse clips, PC mounting with protective cover 1 10A 3AG fuse 1 SPST relay, 12V coil (220Ω) with 10A 240V-rated contacts (Jaycar SY-4050 or equivalent) 1 piece insulating material to suit – Elephantide or plastic (see text) 5 mini cable ties 6 M3 x 10mm nylon screws 10 M3 nylon nuts 6 spring washers 100mm length 4-way rainbow cable (colours unimportant) 2m length 240V 10A mains lead with moulded 3-pin-plug 2m parallel printer cable (D-25 plug) (without Centronics plug) OR 2m length 2-core shielded cable and 1 D-25 male plug Semiconductors 1 SFH601-3 optocoupler (OPTO1) (DSE Z9023 – do not substitute) 1 BC548 NPN transistor (Q1) 1 12V 5W Zener diode (ZD1) 1 275VAC Varistor (V1) 5 1N4007 power diodes (D1-D5) 2 1N914 signal diodes (D6, D7) 1 5mm red LED (LED1) 1 5mm green LED (LED2) Capacitors 1 1000µF 25VW PC mounting electrolytic 2 0.47µF 250V AC X2-class polyester 1 0.1µF 250V AC X2-class polyester 1 0.1µF MKT polyester Resistors (0.25W, 1%) 1 4.7kΩ 2 1.2kΩ 1 180Ω hole from the outside. You’ll need to push through much further than the end of the insulation – at least another 50mm or so, to give you enough room to attach the power outlet. Take the Neutral (blue) and Earth (green yellow) wires through the large hole in the box to the outside. Remove 15mm of insulation from both. The only connection to the Earth terminal of the power outlet (labeled “E” or perhaps with green or green/ (Code 474 or 470n) (Code 104 or 100n) (Code 104 or 100n) 1 100Ω 1 10Ω 1 47Ω 1W yellow marking) is the Earth wire. Bend the bare wire back on itself, push it into the terminal and tighten the grub screw. Ensure there is no exposed wire (especially tiny strands of wire). Now take that blue length of mains wire you cut off before and strip 15mm of insulation from it. Tightly twist this and the blue wire coming out of the box together and insert them into the Neutral terminal of the power outlet Resistor Colour Codes       No. 1 2 1 1 1 1 Value 4.7kΩ 1.2kΩ 180Ω 100Ω 47Ω 10Ω 4-Band Code (1%) yellow purple red brown brown red red brown brown grey brown brown brown black brown brown yellow purple black brown brown black black brown 5-Band Code (1%) yellow purble black brown brown brown red black brown brown brown grey black black brown brown black black black brown yellow purple black gold brown brown black black gold brown September 2001  41 (labeled “N” or perhaps with blue or black marking) and tighten the grub screw. Ensure there is no exposed wire nor strands of wire. Now take that brown length of mains wire you cut off before and strip 15mm of insulation from it. Twist the strands together, fold them back on themselves and insert the wire into the Active terminal of the power outlet (labeled “A”, perhaps with red or brown marking). Tighten the grub screw and ensure there is no exposed wire nor strands of wire. Push the power outlet down onto the box and secure it in place with two 3mm x 10mm nylon bolts and nuts (don’t use metal ones!) and spring washers (which should be metal). Tighten completely and check that the power outlet will not move around at all. Fig.4: wiring the D-25 (parallel port) plug which connects to your computer. We’re not going to connect the mains wiring to the board yet – that will come later after completion and testing. First we will solder the LED wiring (ie, the 4-wire rainbow cable) to the board in the positions shown. NOTE: a 100kΩ ½W resistor should be connected across the Varistor as shown in Figs.2 & 3, to safely discharge the X2 capacitors when power is switched off. Computer cable Now it’s time for the computer cable. In all probability, you’ll be using a “ratted” Centronics printer cable but if you have to make up a new one, that’s not too difficult using a standard D-25 male plug and backshell assembly and some 2-core shielded cable. See Fig.4 for the plug detail. This cable must be passed through the box in similar manner to the mains cable but to hold things together, a short length of heatshrink is first heated onto it. The essential thing about this cable is that none of the wires is long enough to reach the power outlet should one come adrift later. The distance from the side wall of the box to the closest point on the power outlet was 50mm so we cut our cable to 45mm. That makes it a tight job to solder to the PC board, but it can be done. Testing Front and rear close-up views of case. You will note that for safety there are no metal screws used – the warning on the back panel means what it says! You should not build this project if you are not experienced in mains wiring construction. 42  Silicon Chip As we said before, for safety’s sake you really should check the operation with a 12V battery. The easiest way to do this is with a pair of wires temporarily soldered to the back of the PC board across where the Zener would normally go – just watch the polarity. Apply 12V power and ensure that the red LED lights. The green LED should not light nor should you hear the relay click in. If OK, plug the D-25 connector into your computer’s parallel port and run the pcms.exe software (in DOS mode). Remember to set the port to ECP mode at boot-up. Following the processes outlined above, ensure that the software does indeed control the board as intended. You can check the relay operation with a multimeter. If all is OK, turn off power, disconnect from the computer and remove www.siliconchip.com.au Same-size PC board pattern and labels for the back and front of the case. The labels should be glued on before final assembly. On the front panel, the largest hole is 40mm diameter, the LED holes are 5mm and the other two are 4mm. Use a copy of the label as a template for drilling the case. The PC board pattern and labels can be downloaded from www.siliconchip.com.au 44  Silicon Chip SILICON CHIP www.siliconchip.com.au OUTPUT ON POWER APPLIED PC CONTROLLED MAINS SWITCH All parts of this circuit have 240VAC applied even when the output is switched off. Contact with this voltage could be lethal: use extreme caution when servicing or testing this apparatus. WARNING Almost ready to close – these two photos more clearly show the wiring between the PC board and the power outlet on the front panel, and also the wiring to the LEDs and to the computer parallel port plug. At left is the sheet of insulation material, a piece of elephantide or similar, or it can be cut from a plastic sheet such as an ice-cream container. which is inserted between the PC board (component side) and the wiring to the power outlet. It’s just another bit of insurance should the “impossible to happen” happen – a wire works its way loose which could jeopardise the inherent safety built into the switch. www.siliconchip.com.au Another view of the almost-completed project, this time from above and with the insulation in place. Once again, note the use of nylon nuts and bolts – for safety reasons. the two wires you temporarily soldered to the back of the board and solder in the Zener diode (the right way around). Make sure you don’t leave any solder bridges or splashes. Mains wiring Follow the wiring diagram exactly. The brown wire from the power outlet solders to the centre of the PC board, the blue wire from the power outlet solders to the edge of the board and the brown wire from the mains lead also solders to the edge of the PC board. To complete, fit some form of insulating cover over the fuse. Final assembly It is important to fit cable ties to hold the various lengths of wiring together – this should ensure that wiring cannot move around in the event of something coming adrift. Cable ties must also be fitted to the mains cable and the parallel cable on the inside of the grommets to prevent the cables from being either pulled out or flexed unduly. Now the PC board must be secured to the case “lid” with nylon nuts and bolts. This again is not real easy given the fact that the wiring lengths have been kept short. But it can be done! First drill the case lid in the positions shown and fit a nylon bolt and nut to each of the holes. Tighten completely, then slide the PC board down onto the nuts and fit another nut to the top side. Ensure these are also tightened. Before screwing this assembly into the box, cut a piece of insulation material the size of the box with corners trimmed for the mounting pillars. This goes between the mains outlet and the PC board components. Elephantide has been traditionally used for this role; a piece of thin plastic (eg, cut from an ice-cream container) would serve as well. Slide this insulation into the box, push the PC board and lid assembly down on top of it and fit the four case screws. Your PC controlled switch is now finished and should work exactly the same way as when you tested it. NOTE: updated software for this project is available from: http://members.optushome.com.au/video1/macksprograms SC www.siliconchip.com.au September 2001  45