Fullscreen HTML5Med Res (??MB)HTML4

Flexitimer An Easy-To-Program Digital Timer This new multi-purpose timer is much more flexible than previous designs. You can program it for a single time period ranging from one second to 99 minutes and 59 seconds, or a sequence of two such (independently programmed) time periods, or up to 99 cycles of one or two time periods. It’s also easy to program – just like a microwave oven. By JIM ROWE E LECTRONIC TIMERS have always been popular. In fact, there are so many applications for this kind of project that it’s only scratching the surface to mention the following: parking meter reminders, EPROM erasure timing, darkroom printer/ enlarger timing, PC board etch timing, battery charge timing, industrial process timing, chess and other board game timing, debate timing and even kitchen timing. 38  Silicon Chip If you want to make a timer with the widest range of applications, it needs to have at least two independently adjustable or “programmable” timing periods. Ideally, it also needs to be flexible in terms of the number of time periods and/or time period sequences (or cycles) that can be programmed. Some applications need just a single time period, timed in “single shot” fashion, while others need a single sequence of one time period followed by a second (and probably different) time period. Still other applications may need a sequence of two time periods repeated many times, say for a total of 20 cycles. Previous timer designs published in SILICON CHIP and other magazines have provided most of these features but at the cost of operating and programming complexity. This made them a bit daunting to use and limited their popularity as a result. By contrast, this new timer is programmed in exactly the same intuitive fashion as a microwave oven. First, it has tens and units buttons to allow you to key in the exact number of minutes and seconds for the time period(s) you want and also the number of timing cycles you want. There are also buttons to start and stop the timer manually and to save its settings for the next time it’s used and so on. We’ve dubbed this new unit the “Programmable Flexitimer”, because it’s designed to provide the same order of flexibility as the Flexitimer siliconchip.com.au siliconchip.com.au August 2005  39 Fig.1: the circuit is based on a programmed PIC16F84A-04 microcontroller and this drives an LCD module, two relay driver circuits (one for Time A and one for Time B) and a piezo buzzer circuit. It’s programmed using 10 pushbutton switches. Resistor RBL sets the current through the backlighting LEDs on the Altronics and DSE modules (see text). Par t s Lis t 1 Jiffy box, 158 x 95 x 58mm 4 6mm-long untapped spacers 5 12mm-long untapped spacers 1 M3 x 6mm machine screw 4 M3 x 12mm machine screws, csk head 5 M3 x 20mm machine screws, csk head 11 M3 nuts and star lockwashers 1 75mm length of 16-way IDC ribbon cable 2 16-way IDC ribbon connectors Main Board 1 PC board, code 04108051, 141 x 83mm 1 12V piezo buzzer (PB1) 1 4MHz quartz crystal (X1) 2 12V SPDT relays to suit 1 PC-mount 2.5mm DC input connector (CON1) 2 PC-mount 3-way terminal blocks (CON2, CON3) 1 PC-mount 16-way DIL pin header (CON4) 1 18-pin DIL IC socket 1 TO-220 heatsink, 6021 type, 30 x 25 x 13mm Semiconductors 1 PIC16F84A (IC1) programmed with PICTIME2.HEX firmware 1 7805 5V regulator (REG1) 2 2N7000 MOSFETs (Q1,Q2) 1 PN100 NPN transistor (Q3) 3 1N4004 1A diode (D1,D2,D3) Capacitors 1 2200mF 25V RB electrolytic projects described by Rob Evans in “Electronics Australia” back in the early 1990s. However, this new design is based around a programmed PIC microcontroller chip and, as a result, is much easier to “drive” than those earlier timers. Main features Here’s a quick summary of its capabilities. First, it provides either one or two programmable time periods (Time A and Time B), each of which can be set independently to any time between one second and 99 minutes 59 seconds – with a resolution of one second. Second, you can set it for just a single Time A period, or a single 40  Silicon Chip 1 100mF 16V RB electrolytic 3 100nF multilayer monolithic 2 33pF disc ceramic Resistors (0.25W 1%) 1 100kW 1 4.7kW 4 22kW 2 10W 2 10kW Display Board 1 PC board, code 04108052/3/4 to suit DSE, Jaycar or Altronics LCD, 132 x 84mm – see text 1 LCD module, 2 lines x 16 chars (see text) 1 14-way or 16-way length of SIL or DIL pin header strip, to suit LCD module used 10 PC-mount SPST pushbutton switches (S1-S10) 1 90° PC-mount 16-way DIL header (CON5) 4 M2.5 x 10mm machine screws, round head 4 M2.5 hex nuts and lockwashers 8 M2.5 flat washers 4 M3 hex nuts (used as spacers) Capacitors 1 10mF 16V RB electrolytic Resistors (0.25W, 1%) 1 68kW 1 12W to suit DSE Z-4172 LCD module (RBL) – see text 1 18W to suit Altronics Z-7011 LCD module (RBL) – see text 1 10kW mini horizontal trimpot (VR1) (Time A + Time B) sequence, or for multiple Time A or (Time A + Time B) cycles. In fact, there can be anything from 2-99 such cycles. Third, the timer has two internal relays, one of which is activated during the Time A period and the other during Time B. Both relays have a set of mains-rated single pole, double throw (SPDT) contacts, so they can be used either separately or together to switch a wide variety of loads. Finally, the unit operates from 12V DC, which can come from either a battery or a plugpack power supply. Programming As mentioned earlier, the time periods and cycles are programmed very easily using four pushbuttons: one each for tens of minutes, units of minutes, tens of seconds and units of seconds. The “10-minute” and “1-minute” buttons are also used to program the desired number of cycles, when you want more than a single cycle (the default). Three further buttons allow you to set the current input as either Time A or Time B, or to set the number of cycles. Another button (Enter) is then used to save all of the current time and cycle settings in the PIC’s non-volatile memory, so that it “remembers” them when it’s powered up next time. Finally, the Start and Stop buttons do exactly as their names suggest – ie, either start the timer operating or manually stop it if the need arises. All of the timer settings and operations are displayed on a small 2-line x 16-character LCD module. This makes it really easy to operate. How it works Fig.1 shows the circuit details of the Programmable Flexitimer. All of the real work is done by microcontroller IC1, a PIC16F84A which is programmed with a dedicated firmware program called PICTIMER.HEX. In operation, the microcontroller runs from a 4MHz crystal clock and does all of the timing by counting clock cycles – using a combination of both hardware and software counting. This gives a timing accuracy of better than ±0.02%. The 10 buttons used to program the various settings and commands into the PIC microcontroller are connected in a 3 x 4 matrix configuration. As shown, the three rows are connected to the three most significant bits of IC1’s Port B (RB7, RB6 & RB5), while the four columns go to the four least significant bits of this port (RB3, RB2, RB1 & RB0). This allows the microcontroller to scan all the keys very efficiently and respond quickly when they are pressed. The LCD module is directly driven by the microcontroller. It’s connected to the four most significant bit Port B lines (RB7-RB4) and to the two most significant bit Port A lines (RA4 and RA3). The two Port A lines are used to enable the LCD controller input for writing (EN) and to select either its siliconchip.com.au Fig.2: install the parts on the main PC board as shown here. Take care to ensure all polarised parts are correctly orientated and note that connector CON4 goes in with its keyway slot to the left. A small heatsink is fitted to REG1, so that it can handle the current requirements of backlit LCDs. data or address/instruction registers (RS). By contrast, the four Port B lines are used as a data bus to feed display character codes and position addresses to the LCD controller, along with various other function commands. Trimpot VR1 is used to adjust the display contrast. It does this by varying the DC voltage applied to pin 3 of the LCD module. The two least significant bit Port siliconchip.com.au A lines (RA0 & RA1) function as outputs and are used to drive Mosfets Q1 & Q2, which then control the two relays. When the unit is running, the microcontroller turns on Relay 1 (via Q1) during Time A and Relay 2 (via Q2) during Time B. The remaining Port A output line (RA2) is used to control Q3, which in turn controls piezo buzzer PB1. In operation, output RA2 briefly goes high and turns on Q3 to produce a short “beep” at the end of the programmed time period(s) or cycles. Power supply Power for the unit comes from a 12V DC plugpack (or battery), with diode D1 providing reverse polarity protection. This then feeds regulator REG1 which provides a +5V rail to power IC1 and the LCD module. The relays and August 2005  41 Fig.3: the display board layout for the Altronics LCD modules. Install resistor RBL (18W) only if you are using a backlit display (Cat. Z-7001) & don’t forget the backlight connections. Fig.4: follow this display board layout if you are using a DSE LCD module. Again, resistor RBL (12W) is installed only for the backlit display (Cat. Z-4172). the buzzer (PB1) are powered directly from the +12V rail after D1. Construction Construction of the Programmable Flexitimer is easy, with all parts mounted on two PC boards – a main board coded 04108051 (141 x 83mm) and a separate display board (132 x 84mm). The latter carries the LCD and the pushbutton switches, plus a few 42  Silicon Chip other minor parts. These boards fit inside a standard UB1 Jiffy box (158 x 95 x 58mm) and are interconnected by a short 16-way ribbon cable fitted with 16-way IDC connectors at each end. The connections to the timer relay contacts are made via screw terminal blocks located at one end of the main board. Note that there are actually three different versions of the display board, to suit the three different LCD modules currently available on the Australian market. One version (code 04108052) suits the Z-4170/2 module from Dick Smith Electronics; a second version (code 04108053) suits the QP-5515/6 module from Jaycar Electronics; and the third version (code 04108054) suits the Z-7000A/Z-7011 module available from Altronics Distributors. Fig.2 shows the assembly details for siliconchip.com.au Fig.5: the Jaycar LCD modules have only 14 pins and don’t require an external resistor to set the current through the backlight LEDs. This completed display board uses the DSE Z-4170 LCD module – ie, no backlighting, so RBL is left out. Take care to ensure that the flat side of each switch goes to the left. the main board. Start by fitting the DC input connector CON1 (may need to elongate the PC board holes slightly with a needle file before the connector lugs will pass through), then fit the two screw terminal blocks (CON2 & CON3). Note that the latter must be fitted with their wire entry sides facing the edge of the board. Next, fit the 16-way DIL pin header CON4, making sure its locating spigot siliconchip.com.au slot goes towards the lefthand end of the board. That done, fit the two wire links, followed by the resistors and the three diodes (D1-D3). Make sure that the diodes are correctly oriented. The 4MHz crystal (X1), regulator REG1 and transistors Q1, Q2 & Q3 are next in line. Take care with the orientation of REG1 and the transistors and be sure to use the correct transistor type at each location. Regulator REG1 is installed by first bending its pins downwards through 90° about 6mm from its body. It’s then fitted to the PC board along with its heatsink and secured using an M3 x 6mm machine screw and nut, before soldering its leads. Smear its metal tab with heatsink compound before mounting it, to ensure good heat transfer. The next step is to fit an 18-pin sockAugust 2005  43 Fig.6: here are the drilling an cutting details for the base of the case and for the lid. They are reproduced actual size, so that you can use photocopies as drilling templates. 44  Silicon Chip siliconchip.com.au et for IC1 – it goes in with the “notch” end facing the adjacent edge of the board (see Fig.2). Follow this with the two relays and the piezo buzzer (PB1). There are two buzzer types commonly available and the PC board caters for both. It’s just a matter of fastening the supplied unit in position using two M3 x 12mm machine screws and nuts and soldering its leads to the board (red to “+”, black to “-”). In either case, the buzzer’s connection wires can be cut fairly short before soldering, to keep the assembly neat and tidy. The small non-polarised capacitors can now be fitted, followed by the two larger polarised electrolytics. Be sure to install the electrolytics with the positive leads oriented as shown. The main board assembly can now be completed by plugging the programmed PIC16F84A chip into its socket. It must be installed with its notched end towards the bottom edge of the board, as shown in Fig.2 By the way, if you’re building the timer from a kit, the PIC will be supplied pre-programmed. However if you’re building the timer from scratch, you’ll need to program the chip yourself (or have someone do it for you) before it’s plugged into the socket. The PICTIMER.HEX program file will be available as a free download from the SILICON CHIP website at www.siliconchip.com.au Display board assembly Before installing any parts on this board, make sure it suits the particular LCD module you’re using. Of course, if you’ve bought a kit, then you won’t have any worries on this score. Figs.3, 4 & 5 shows the parts layouts for the Altronics, Dick Smith Electronics and Jaycar versions respectively. Begin by installing the wire links and the 68kW resistor, then fit the 16- Fig.7: here are the drilling details for the end of the case, again reproduced actual size. way 90° DIL pin header. Follow these with trimpot VR1 and the 10 pushbutton switches. Note that the latter are all mounted with their “flat” side facing towards the left. The 10mF electrolytic capacitor is next on the list. As shown in one of the photos, it should be mounted “leaning over” to the left by a small amount, to reduce its effective height to below 10mm (to ensure it later clears the back of front panel). Take care with its orientation. The next step is to fit the header strip for the LCD module. This is a 16-way SIL strip for the DSE module, a 7 x 2-way DIL strip for the Jaycar module or a 14-way SIL strip for the Altronics module. In each case, push the shorter ends of the pins through the board from above and solder them carefully to the pads underneath. Basically, there are six different LCD modules that can be used with this unit – three with backlighting and three without. The three modules with backlighting are the Altronics Z-7011, DSE Z-4172 and the Jaycar QP-5516. The corresponding versions without backlighting are Altronics Z-7000A, the DSE Z-4170 and the Jaycar QP5515. Note that the Jaycar modules have 14 pins, while both the Altronics and DSE modules have 16 pins. Installing the LCD module is easy – it slips down over the header pins and is secured using four M2.5 x 10mm screws, lockwashers and nuts. In addition, an M3 nut and two M2.5 flat washers are used to form a 3mm3.5mm spacer between the module and the board at each mounting screw point. Alternatively, you can use two M3 “half nuts” to make the spacer at each point. Once the module is in position, it’s simply a matter of soldering its connection pads to the header pins. The display board will now be complete, except for resistor RBL which sets the current for the backlighting LEDs. This is fitted only if you’re using an LCD module with backlighting but is not required for the Jaycar LCD, since the resistor is part of the module. Table 1: Resistor Colour Codes o o o o o o o o o siliconchip.com.au No.   1   1   4   2   1   1   1   2 Value 100kW 68kW 22kW 10kW 4.7kW 18W 12W 10W 4-Band Code (1%) brown black yellow brown blue grey orange brown red red orange brown brown black orange brown yellow violet red brown brown grey black brown brown red black brown brown black black brown 5-Band Code (1%) brown black black orange brown blue grey black red brown red red black red brown brown black black red brown yellow violet black brown brown brown grey black gold brown brown red black gold brown brown black black gold brown August 2005  45 The main board in this prototype unit used a 78L05 regulator. It was later modified to accept a 7805 regulator (with heatsink), so that backlit LCDs could be used. Note that for the Altronics module, you’ll also need to make the “A” and “K” connections for the backlighting power (at right). Once the assembly is completed, adjust contrast trimpot VR1 with a small screwdriver to about 10° back from fully clockwise. This will ensure you get some kind of display when the timer and module are first powered up. The control can be “fine tuned” for best contrast later, via the small hole in the front panel. The next step is to make the short ribbon cable that’s used to link the two boards. This is formed from a 75mm-length of 16-way IDC ribbon, with a matching IDC connector at each end – see Fig.8. The connectors fit the opposite way around at each end, so that the cable can link the two boards without having to be twisted. Preparing the box If you’re building the timer from a kit, the box will probably be supplied with a silk screened front panel and with all holes pre-drilled and cut. However if you’re building from scratch, you’ll need to drill the box yourself. Figs.6 & 7 show the drilling and cut- ting diagrams for both the box and its lid. These are reproduced actual size, so you can directly use photocopies as drilling templates. Make sure you countersink the 3.5mm holes in the bottom of the box and also those in the lid. This can be done with a 7mm or larger twist drill if you don’t have a countersink bit. Also, make sure that you cut the access holes for the timer’s DC input connector and terminal blocks at the right-hand end of the box – see Fig.7. Next, the front panel artwork can be attached to the lid. That done, you can cut the various holes in the label using a sharp hobby knife. Final assembly The main board mounts on the bottom of the box on four 6mm-long untapped spacers and is secured using four M3 x 12mm countersink-head screws and nuts (it only fits one way, due to the asymmetrical mounting screw positions). By contrast, the display board is mounted on the box lid and is secured on 12mm-long untapped spacers using five M3 x 20mm countersink-head machine screws, star lockwashers and nuts. With some LCD modules, Fig.8: follow this diagram to fit the headers to the short ribbon cable that links the two PC boards together. 46  Silicon Chip you may also need M3 flat washers to augment each of the spacers, to make sure there is enough clearance. Your timer can now be completed by fitting the ribbon cable between the two boards and securing the case lid. Using the timer When you first connect the timer to 12V DC power, it initially displays “Silicon Chip FlexiTimer3” on the LCD panel. This message then disappears after a few seconds and is replaced with a “screen” giving you the timer’s current settings – plus “Stop” at lower right to show that it’s not running. When the timer is powered up for the very first time, its initial settings are these defaults: Time A programmed to 10 seconds, Time B not programmed at all (and not even displayed), and the Cycles set to 1 (for a single timing sequence). But if you program it with other settings and save them, these settings will appear when the timer is next powered up. Changing the settings for Time A or Time B is done using the four uppermost buttons on the left – marked “10 MIN”, “1 MIN”, “10 SEC” and “1 SEC”. Pressing any of these buttons causes the timer to change into “Input” mode, to allow you to key in any desired time setting from 00 minutes and 1 second up to 99 minutes and 59 seconds. If you press any button too many times, just keep pressing it until the digit concerned reaches the maximum and then returns to 0, after which you can program the value you wanted. When you have entered the time value you want, the timer can be siliconchip.com.au Fig.9: this artwork can be photocopied onto an A4 label sheet, which can then be affixed to the lid after peeling off its backing. Clear “Contact” adhesive film can then be fitted over the top, to protect it from dirt and damage. directed to make this the setting for either Time A or Time B, simply by pressing either the “Time A” or “Time B” button. It’s as easy as that. Changing the Cycles setting is just as easy. In this case, you use only the “10 MIN” and “1 MIN” buttons to enter the number of cycles (from 1-99), and then press the “SET CYCLES” button. Once the settings for Time A, Time B (optionally) and Cycles have been entered, the timer can be started simply by pressing (you guessed it) the “START” button. You’ll then see it counting down on the LCD panel, where its status is also shown continuously – ie, whether it’s in Time A or Time B and the current cycle. When it reaches the end, it will give a short beep from the piezo buzzer and display “Stop” again on the LCD panel (at lower right). This will also happen if you press the “STOP” button, to stop the unit before the end of the programmed time settings. To save the current settings in memory for use next time it’s powered up, just press the “ENTER (SAVE)” button when the timer is stopped. As soon as the settings have been saved, the message “Settings Saved” will be displayed for a few seconds, to confirm that it has been done. To program Time B as well as Time siliconchip.com.au A, all you need do is enter its time setting and then press the “TIME B” button. Time B will then be enabled and its setting displayed after Time A. On the other hand, if you have Time B already programmed and you want to disable it again, simply enter a zero time value (ie, 00:00) and again press the “TIME B” button. The timer will recognise the zero time setting and Time B will be disabled and disappear from the display. You can use the timer’s relay contact terminals to allow it to control all manner of things. All you need to know is that when the timer is running the contacts of Relay 1 are activated during Time A, while those of Relay 2 are activated during Time B. So by connecting to these terminals, you can arrange for the timer to turn things on or off during Time A and/or Time B. Finally, note that this project should be used to control low voltage equipment only (up to about 50V). Do not use it to directly switch mains voltages. If you do want to switch mains voltages, we suggest that you use this unit to trigger an external relay which then does the switching. Make sure that this external relay and any mains wiring that’s run to it is properly anchored and isolated. However, don’t attempt this unless Specifications • • • • Two independent timing periods: Time A and Time B Time A and Time B periods can be set from 00min-01sec to 99min-59sec 1-99 timing cycles or continuous cycling – see below Relay outputs for switching external devices Continuous Cycling A late software modification to this unit involved adding a continuous cycling mode. This mode is set simply by entering zero (00) as the setting for “Cycles”. The second line of the display shows “Cont” when the timer is in this mode. It can be returned to finite multiple cycle mode simply by setting the number of “Cycles” to any allowed non-zero value – ie, 1-99. you know what you are doing and are completely familiar with mains wiring SC practices and techniques. August 2005  47