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A LAP COUN for Swimming Pools By RICK WALTERS Do you swim laps of the pool to keep in shape? It is a great form of exercise but you’ll know how easy it is to lose count of the number of laps you have done. This PICAXEpowered counter will keep track of the number of laps completed, leaving you to get on with the swimming. 38  Silicon Chip siliconchip.com.au NTER T HOSE FORTUNATE ENOUGH to swim in a 50-metre pool don’t have to count very many laps in order to cover a reasonable distance. For example, just 20 laps means that you have swum a kilometre. But even then, as you plough up and down the pool, it is pretty easy to get distracted and lose count. Some people cope with the problem by swimming five laps freestyle, five breast-stroke, five back-stroke and so on. The problem is worse if you’re swimming in a 25-metre pool (as many top-level swimmers regularly train in) and much worse if you’re swimming in your home pool, which may be only 10 or 15 metres long. For a 10-metre pool, you need to do 100 laps to cover a kilometre. Believe us, trying to keep track of that many laps in a home pool while you swim back and forth is practically impossible. This is where our Pool Lap Counter comes to the rescue. It will display the number of laps you have completed on a 2-digit or 3-digit readout, so you can let your mind wander, do mental arithmetic or compose your new symphony while you swim up and down. The Pool Lap Counter consists of two small plastic boxes. One, the “main” box, contains the Picaxe counter circuit and 2-digit readout, while siliconchip.com.au the other contains a large air-switch pushbutton which connects to the main box via a thin air hose and actuates a microswitch when pressed. This is to avoid an electrical connection (even in a battery-powered, low voltage device) around the very damp(!) chemical-laden pool environment. If you swim more than 99 laps, you will have to add 100 to the count or add the third 7-segment LED display. Two ways of counting The way it works is as follows. You place the air-switch at the far end of the pool (from where you normally start). You then dive in (or gingerly wade in), swim to the other end and push the button, whereupon the display indicates “01”. Congratulations, you have completed one lap. When you swim up and back and press the button again, the display will indicate “03”. In other words, the display increments by two each time the button is pressed. As an alternative, because this Pool Lap Counter uses the intelligence of a Picaxe, you can start and finish your laps at the same end of the pool. In this case, you push the button to start and it displays “00”. You then swim up and back, press the button and it displays “02” and so on, until you are exhausted! Eight AA cells (12V) power the counter. To obtain a reasonable battery life, the 7-segment displays are lit for just five seconds each time the button is pressed. Of course, the counter ICs are powered while ever the unit is switched on but this amounts to only a couple of milliamps. How the circuit works Looking at the circuit of Fig.1, IC2 is a 4553 3-digit counter (normally, we only utilise two digits) with a multiplexed output. IC2 internally selects digit one, two or three and places the BCD data for this digit on outputs Q0Q3. These feed IC3, a 4511 7-segment decoder, which energises the segments of the two digits, corresponding to the BCD code. At the same time, output DS1 or DS2 (pin 2 or pin 1) turns on transistor Q4 or Q5 to power the corresponding LED display. The 10mF capacitor and the 100kW resistor on pin 13 of IC2 reset the count to zero when power is applied. The 1nF capacitor between pins 3 & 4 sets the display multiplexing frequency. All this is fairly straightforward. The tricky bits are carried out by IC1, a Picaxe-08 microcontroller. Among other things, the Picaxe needs to cater for people who place the Lap Counter at their start end or at the far end. As noted above, if you place it at the far March 2005  39 Here’s what it looks like close up. The box at left is merely the lap sensor – hit the switch and it sends a burst of air via the clear hose to the main box, right. This actuates a microswitch which in turn increments the count by two. You can set the count for odds or evens, depending on which end of the pool you mount the unit. The air hose can be quite long. end, the Lap Counter should count to one the first time you touch the button and then increment by two for each subsequent touch. We cover both contingencies by fitting jumper J2 for odd increments and omitting it for even. SK1 is arranged to allow programming of the chip “in circuit”. Jumper J1 has to be removed to do this although with the 47kW base resistor for Q1, it is probably unnecessary. This method means you must remove jumper J1 (thus removing any load from pin 7) before you can reprogram the chip. We also use IC1 to debounce the pushbutton microswitch S1. This achieves two things. First, it stops multiple counts from being recorded because of contact bounce within the microswitch itself. Second, it prevents a miscount if you accidentally push the button twice within five seconds. You could easily do this if you come to the end of a lap, touch the button (or plate or whatever) and then press it again as you push off for another lap. Each time the Picaxe registers the closing of the microswitch, it gener- ates two clock pulses to increment counter IC2. If you look at the Picaxe listing (LAPCOUNT.BAS), you will probably be able to glean what it does but let’s just briefly outline the procedure. Each time you push the button, several things happen. First, IC2 is incremented by two counts (or one count if it is the first time) and then it is disabled, preventing it from registering multiple counts. At the same time, the display is unblanked for five seconds so that you can see the count. Three outputs from IC1 are used to achieve this procedure. Pin 6 disables the counter by going high (for five seconds) to turn on transistor Q2 which then pulls pin 11 (DIS) of IC2 low. Pin 5 of IC1 provides the clock pulses which are inverted by transistor Q3 before being fed to pin 12 (CLK) of IC2. Finally, pin 7 of IC1 unblanks the display by turning on transistor Q1 to pull pin 4 (BL-bar) of IC3 low for five seconds. The three transistors (Q1-Q3) also provide level translation between the 5V signals from IC1 and IC2 & IC3 which run from the full 12V provided by the eight AA cells. Regulator REG1 is fitted to provide the 5V rail for the Picaxe. As noted in previous issues, there is a great deal of confusion over the way the Picaxe ports are numbered, for what they call pin 3 is actually pin 4 on the IC and so on. We have taken the liberty of renaming them in the more conventional manner as P0, P1, P2, etc.We have used the decimal point (pin 8) of the units display as a power indicator to remind you to turn the Lap Counter off. This stays illuminated even when the lap count is blanked. Air-switch S1 is an all-plastic “air-switch” which is normally used in spas and other areas where water and power don’t mix. We got it from our local pool shop, along with a matching microswitch and a metre of 5mm clear plastic connecting tube. The length of tube can be much longer – depending on your requirements, it could be as much as several metres. We use it here mainly because any electrical switch put near a pool with (Left) the air-powered switch we used to actuate the counter. It’s normally used in spas and should be available from most pool shops. (Right): the switch fitted in an open UB3 case. The switch just fits in this case but you might need to perform minor surgery on the ridge inside the lid to make sure it doesn’t foul the switch nut. The length of 5mm plastic air hose can be as long as required. 40  Silicon Chip siliconchip.com.au salt and chlorine would not last very long. When the air-switch button is press­ ed it compresses small bellows which transmit the pressure along the plastic tube to the microswitch mounted in the Lap Counter case. If you don’t wish to go to the added expense of the air-switch, you could use a standard pushbutton in the actuator box and run a piece of light duty figure-8 flex to the Lap Counter case. Construction All the circuitry for the Pool Lap Counter is mounted on a PC board measuring 141 x 83mm and coded 08103051. It has a notch at one end to accommodate the microswitch and chamfers on the four corners. Even though most people will only use two 7-segment displays, we have made provision for a third display (DS3), together with its driving transistor (Q6). If you fit the third display, you will have to install another 10 machined pins for DS3 as well as fitting Q6. We have shown the jumper, which connects IC2 to the base of Q6 Fig.1: the circuit consists of two basic parts – the Picaxe-08 which senses the input from S1 and a display circuit, consisting of IC2, IC3 and giant LED displays. Display DS3 is optional and is only required if you want to count more than 99 laps. Who do you think you are, Grant Hackett? The main box end-on, showing the connection for the air hose to the pushbutton lap counter switch. Here are the giant LED displays we used – they’ve visible for miles kilometres a long way! We’ve turned one upside down so you can see the pin arrangement. Take care: you can get them upside down. siliconchip.com.au March 2005  41 DS2 DS1 CON2 220Ω 220Ω 220Ω 220Ω IC3 4511B 100k Q2 BC549 220Ω 47k 1n 47k 220Ω J2 ODD 100 µF 47k 10k 10 µF 220Ω TO S1 1 1 1 IC2 4553B CON1 + 47k 10k IC1 PIC-08 PROG E ROF TUOTUC 22k POWER CON3 HCTIWSORCIM 10k Q4 Q6 BC327 BC327 DS3 Q3 BC549 47k 100nF REG1 78L05 47k Q1 BC549 1.5k Q5 BC327 Fig.2: the component overlay shows the position of all components. Note that the sockets for the LED displays are mounted on the track side of the PC board. 5002 C 15030180 RETNUOC PAL This is the completed “main box” immediately before the PC board is folded over and mounted upside down on the four tapped pillars. The battery holders are held in place with our highly technical (and patented) battery holder holder. on the overlay so this link will already be in place. The board assembly is reasonably straightforward but as usual, first 42  Silicon Chip check the board for open circuit tracks and etching faults, particularly where the tracks go between IC socket pins. You will most likely have to make the cutout for the air-switch yourself. Use a small hacksaw to make the cuts parallel to the longer board edges then use a large pair of bullnose pliers to break the fibreglass away in small pieces. If you scribe a deep line, you will get a clean break but if it’s a bit ragged, a quick rub with a file will give you a neat edge. The first components to mount are the LED display sockets which mount on the copper (ie, solder) side of the PC board. To get the spacing exact, we use the displays themselves to hold the pins while we “tack” the pins in. Cut the pin strip into four pieces of five pins and carefully align the LED pins with the strips and push them on. Now place the LED sockets on the track side of the PC board – not the component side – in the DS1 and DS2 (units & tens) positions. That done, place the PC board on a flat surface and solder the outside pins on each pin strip on both the top and bottom of the display. There is no need to worry about the display orientation at this stage. Now carefully remove the displays and solder the remaining pins. A pointed tip on your soldering iron will make the job easier but we managed with the usual spade tip and a lot of care. Cut about 2mm off each pin on each display so that it fits flush against the pin strip. Now turn the board over to the component side and fit the seven siliconchip.com.au Fig.3: there’s not much wiring required – most is on the PC board and what’s left uses plugs and sockets for convenience. Power is switched between the batteries simply to make the wiring simpler – this way there are only two wires to go to the PC board. CON2 1 2 3 4 CON3 JUMPER SHUNT S1 PRESSURE SWITCH 4 x AA CELL HOLDER 4 x AA CELL HOLDER S2 POWER links, then the resistors, followed by the IC sockets, jumper, transistors, electrolytics and the three polarised connectors. Make sure you insert the electrolytics with the correct polarity – and note that the 10mF electrolytic must lie flat on the PC board to prevent it fouling the batteries. The 3-pin header must also lie flat on the PC board. As right-angle connectors are rare, put a dob of glue on the flange and use cut-off resistor leads to connect it to the board. Only the outside pins need to be connected. The mating header has pin 1 marked on it when you come to connect wires. Next, fit the mini-shunts to J2 and, if you are using a pre-programmed PIC, to pins 3 & 4 of SK1. Power switch S2 is wired between the two AA battery holders to simplify the wiring. Solder one lead from each battery holder to the switch (one red, one black) and then the other battery wires got to connector PL3: black to pin 3 and red to pin 1. Plug PL3 in. Resistor Colour Codes o o o o o o o siliconchip.com.au No. 1 6 1 3 1 7 Value 100kW 47kW 22kW 10kW 1.5kW 220W 4-Band Code (1%) brown black yellow brown yellow violet orange brown red red orange brown brown black orange brown brown green red brown red red brown brown 5-Band Code (1%) brown black black orange brown yellow violet black red brown red red black red brown brown black black red brown brown green black brown brown red red black black brown March 2005  43 Parts List – Swimming Pool Lap Counter 1 PC board, code 08103051, 141 x 83mm 1 plastic case, 158 x 95 x 53mm; Jaycar UB1 or equivalent 1 plastic case, 130 x 67 x 43mm; Jaycar UB3 or equivalent 2 16-pin IC sockets 1 8-pin IC socket 1 air switch (S1) – see text 1 SPST miniature toggle switch (S2) 2 flat battery holders to suit 4 AA cells; Jaycar PH-9204 or equivalent 8 AA cells 20/32 of IC socket strip; Jaycar PI-6470 or equivalent 1 2-pin strip 0.1-inch spacing (J2) 2 mini-shunts 1 2-pin polarised male connector 1 2-pin header (with pins) 1 3-pin polarised male connector 1 3-pin header (with pins) 1 4-pin polarised male connector (for PIC programmer cable) 4 25mm threaded hex spacers 1 10mm threaded hex spacer 2 3mm x 20mm countersunk head bolts (air switch) 5 3 x 6mm countersunk head bolts 1 3 x 10mm countersunk head bolt 4 3 x 6 mm cheese head bolts 7 3mm nuts 6 3mm star washers 1 65 x 20mm aluminium or fibreglass (battery clamp) Suitable length hookup wire for air switch Semiconductors 1 Picaxe PIC-08 programmed with LAPCOUNT.BAS (IC1) 1 4553 3-digit counter (IC2) 1 4511 BCD to 7-segment decoder (IC3) 3 BC549 NPN transistors (Q1-Q3) 2 BC327 PNP transistors (Q4-Q5) 1 78L05 5V regulator (REG1) 2 70mm 7-segment displays (DS1-2; Jaycar ZD1850 or equivalent) 1 70mm 7-segment display (optional) Capacitors 1 100mF 16V PC-mount electrolytic 1 10mF 50V RB low leakage electrolytic 1 100nF (0.1mF) 50V monolithic ceramic (code 104 or 100n) 1 1nF (.001mF) MKT polyester (code 102 or 1n0) Resistors (0.25W, 1%) 1 100kW 3 10kW 6 47kW 1 1.5kW 1 22kW 7 220W Now fit the batteries, turn the switch on and measure the voltage between pins 16 & 8 on both IC2 & IC3 (the meter’s red test lead goes to pin 16 in each case). It should be slightly more than +12V. Similarly the voltage between 44  Silicon Chip ; PICAXE-08 CODE for LAP COUNTER ; using 4553 and 4511 to drive 2 ZD1850 displays ; ;Define inputs and outputs ; symbol msin = pin4 symbol evenodd = pin3 symbol blankdisp = 0 symbol addcount = 2 symbol odd = 1 ; ;Set output states ; high blankdisp high odd low addcount ; ; wait 3 ;allow IC2 to reset ; init: if evenodd > 0 then initeven ;if jumper missing start at 0 & inc by 2 if msin = 0 then initodd goto init ; ; initodd:low odd ;else jumper fitted, IC2 pin 11 high pause 10 ;hold high for 10 mS high odd ;then take low, 1 clocked into counter goto unblank ;(Q2 inverts logic) ; initeven:if msin = 0 then inccount ;wait for microswitch to close goto initeven ; ; inccount:high addcount ;2 counts must be added to the display pause 10 ;take IC2 pin 12 low for 10mS (Q3 inverts) low addcount ;then high for 2 mS pause 2 ; high addcount ;then low for another 10 mS pause 10 ; low addcount ;then high again goto unblank ;now show the new count ; unblank:low blankdisp ;take IC3 pin 4 high for 5 seconds wait 5 ;(Q1 inverts logic) high blankdisp ;turn display off goto initeven ;wait for next closure of microswitch pins 1 & 8 of IC1 should be within 10% of 5V. Once these voltages are correct, turn off the power, insert the three ICs and if you intend to program your own PIC, do it now. Then fit J1 between pins 3 & 4 of SK1. Turn the power on and after a second, the decimal point on the righthand display should light. So far so good. Run two twisted wires from the microswitch NO and C(ommon) contacts to the 2-pin header (PL2). The polarity is immaterial. Plug it in and after connecting the tubing from the airswitch pushbutton to the microswitch connector, each push of the button should advance the counter by two counts. After five seconds, the count should blank. Note: the count will only advance after the 5-second delay when the display is blank. If everything is operating correctly, you can drill the siliconchip.com.au Left: this view shows the PC board mounted inside the case before the 7-segment LED displays are fitted. Note that the display sockets are fitted to the track side of the PC board. At right is the same shot but with the displays inserted. The decimal point goes to the bottom, as shown here 08103051 holes in the plastic case and fit the four 25mm spacers, first fitting a 3mm nut on each of the countersunk screws. The nut brings the front of the displays flush with the rear of the perspex, thus holding them firmly in place. Mount the air-switch and power switch, fit the batteries into the battery holders and drop them into the case, then sit the PC board on the spacers. Adjust the spacers until the four of them align with the board holes. A Spintite and a little gentle leverage will do the trick. Place the clamp strip on top of the batteries to prevent them moving, then secure the PC board using four cheese-head machine screws and star washers. The front panel cutout may prove a challenge. We obtained a small piece of 3mm neutral tint perspex from a plastics supplier and took it to an engraver who cut it to size with a chamfer on all four sides. We carefully cut the hole in the case lid with the reverse chamfer, thus allowing the perspex to almost sit flush with the lid. A few drops of superglue held it firmly in place. C 2005 LAP COUNTER + CUTOUT FOR siliconchip.com.au MICROSWITCH The pushbutton switch we used is great for keeping water and chemicals away from the “works” but is not particularly convenient as far as the swimmer is concerned. Our swimmer found it a real drag (no pun intended) to have to stop at the end of each lap and press the button. With a little thought, we’re sure you can come up with a much better arrangement. One possibility is to use a reasonably-sized hinged flap which the swimmer merely has to make slight contact with at the end of each lap. Given the mechanical advantage such an arrangement could produce, a small movement of the flap could translate into a very positive movement against the air-switch via a suitable actuator. Such an arrangement could also be used for swimmers making tumble-turns. As long as the flap was anchored securely at the end of the pool, the swimmer’s feet could do all the switching as he/she pushed off at the end of each second lap. Whatever you do, just make sure that it is suitably anchored so that there is no danger of injury to the swimmer. We also mentioned before that you could run a much longer air hose than the length our photos show (merely for a convenient photo!). The pressure system is quite E The lap “sensor” Fig.4: full-size PC board artwork. sensitive, so we assume several metres would not be a problem. That’s it: a lap counter that will keep track for you whether you are swimming for fitness. . . or in training for the Beijing Olympics. SC March 2005  45