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By NICHOLAS VINEN Remote-Controlled Digital Up/Down Timer This remote-controlled digital timer has a bright 20mm-high 7-segment red LED display & can count up or down from one second to 100 hours in 1-second steps. Its timing period can either be set and controlled using the remote control or it can be automatically controlled via external trigger/reset inputs. An internal relay and buzzer activate when the unit times out. T HIS NEW DIGITAL TIMER is a very flexible project. We can think of many uses for it but we are sure there are a lot more that we haven’t even considered. We’ve done lots of timers before but this one has the convenience of remote control. Its timing period can be programmed using the numerical keypad button on the remote, while the remote’s Power/Standby button provides a Reset function. 34  Silicon Chip The simplest way to use it is like a kitchen timer. In this mode, it can count up or down for the timing period, as entered via the keypad on the remote. Pressing the remote’s Channel Up button make the unit count up to the programmed time, while pressing the Channel Down button makes it count down. When the time runs out, the LED display flashes and a buzzer sounds for a preset period (the default is one minute) or until the reset button is pressed. You can either use the Power/ Standby button on the remote to reset the unit or an external reset button. The internal relay also switches at the end of the timing interval. This relay can directly control a DC device (30V DC or 24V AC max.) or it can indirectly control a mains-powered device via a separate external mainsrated relay (see panel). Note, however, that this unit is definitely NOT RATED siliconchip.com.au OUT A 100nF 470Ω 10k E B f PD2 IC1 ATTINY 2313 K D3 2 10k A 8 K 100nF 3 TRIG IN 1 PD4 D4 PA2/RST A PD5 2 +5V CON3 PD1 10k XTAL2 A 7 K PD3 D6 100nF XTAL1 GND 10 A D3–D6: 1N4148 A 2010 b c f e g d dp a K 9–12V DC IN b f g e c dp d g f e d c b a dp DISP3 NFD-5621BS a b f e c a b g d dp f e c g d a b f g e c d dp dp c dp e d g g f e d c b a dp b c dp f b a 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 15 14 13 12 11 16 17 18 19 2 1 +5V RLY1 K D2 9 CON1 A 3 COM NC NO K D5 SC  d + – 47 µF DISP2 NFD-8021BS a 1 2 3 4 5 6 7 8 9 10 PB3 PB2 PB1 PB0 PD6 PB4 PB5 PB6 PB7 PD0 +5V 3 g e 6 RESET IN a C 2 1 DISP1 NFD-8021BS 20 Vdd Q1 BC556 D1 D2 λ 1 A CON4 D1 D2 3 IN GND 100 µF +5V K K D2 D1 λ LED1 100nF IRD1 IR RECEIVER D1 REG1 7805T +5V 4 5 + COM NC NO PIEZO BUZZER X1 8MHz – 33pF 10k C B 33pF CON2 Q2 BC546 E D1, D2: 1N4004 A REMOTE-CONTROLLED DIGITAL TIMER LED K B K A 7805 BC546, BC556 E GND IN C GND OUT Fig.1: the circuit is based on an Atmel ATTiny2313 microcontroller (IC1), three dual 7-segment LED readouts and an infrared receiver (IRD1). The micro drives the LEDs, controls the timing and drives a DPDT relay via transistor Q2. to directly switch mains devices. By default, the relay is energised while the timer is running. As such, the timer could be used to run an oven for the programmed timing period, expose a PC board to UV light, or run a fan or light for a fixed period, etc. The trigger and reset inputs can be used to automatically start and stop the timer when certain events occur, eg, when a door opens, an external button is pressed or a PIR (passive infrared) sensor is triggered by motion, etc. This means that you could set it up to turn on a light or fan when a door is opened and then subsequently switch the device off when the door is shut or after the programmed period expires. It could even be used as the basis of a very simple alarm system. All you siliconchip.com.au have to do is connect a PIR sensor to the trigger input, a key-switch to the reset input and a siren to the relay. You then set the timer to a short period (say 30 seconds) and the alarm period to a value that’s longer than the default (say three minutes) and voila! . . . you have a basic motion-triggered alarm with key deactivation. By the way, the unit will work with virtually any universal remote control that’s capable of transmitting Philips RC5 codes (nearly all do). So if you have a spare universal remote control, it will do the job quite nicely. Circuit description Take a look now at Fig.1 for the full circuit details. It’s based on microcontroller IC1 plus three dual 7-segment LED readouts. However, instead of using a PIC micro as in most other projects, this time we’ve opted for an Atmel ATTiny2313 with 2048 bytes of flash memory. The micro normally runs at 8MHz, as set by an internal 8MHz oscillator and crystal X1. This clock frequency is reduced to 1MHz (via a clock divider) when the micro is in standby mode. Note that although the micro actually has an internal 8MHz oscillator, the crystal is necessary for accurate timekeeping. Typical crystal error is less than 100ppm or 0.01%, giving a maximum timing error is one second per three hours although it will normally be well under half that. The unusual part of this circuit is the way in which the six 7-segment August 2010  35 Parts List 1 PC board, code 19108101, 89 x 80mm 1 sealed polycarbonate enclosure, 115 x 90 x 55mm with clear lid (Jaycar HB-6246) 1 universal remote control with numeric keypad (eg, Jaycar AR-1726, Altronics A-1012) 1 9-12V DC 300mA plugpack (Jaycar MP-3147, Altronics M-8928 or similar) 1 6-way chassis-mount terminal barrier (Jaycar HM-3168, Altronics P-2076A) 1 5V DPDT DIL relay (Futurlec HFD2-05, Altronics S-4147 or equivalent) (RLY1) 1 PC-mount 5V mini piezoelectric buzzer (Jaycar AB-3459, Altronics S-6105) 1 8MHz HC-49 crystal resonator (X1) 1 20-pin DIL IC socket 3 mini 3-way terminal blocks (5.08mm pitch) (CON1-CON3 1 2-way polarised header (2.54mm pitch) (CON4) 1 2-way polarised header connector (2.54mm pitch) 1 2.1mm ID panel-mount DC socket (Jaycar PS-0522, Altronics P-0622) 4 M3 x 15mm tapped Nylon spacers 6 M3 x 20mm pan head machine screws 2 M3 nuts 2 M3 flat washers 2 M3 spring washers Medium-duty hook-up wire: 50mm lengths of black and red, 130mm lengths of brown, orange, yellow, green, blue and white LED digits (DISP1-3) are driven. Just 10 of IC1’s 20 pins are used to drive the 48 segments (seven per digit plus the six decimal points). What’s more, we have not used any discrete transistors or current limiting resistors in the LED drive circuit. This makes the project smaller, cheaper and easier to build but how do we get away with it? First, we are using a “charlieplexing” system (popularised by Charlie Allen at Maxim) which cuts down on the number of pins required to drive the LEDs. This is a special form of multiplexing and to understand how it works, first consider display DISP1. This contains two of the digits and has 10 pins – two common anodes and eight shared cathodes. If we wire up just this display, then turning on any single segment is easy. We start by pulling one of the common anodes pins high – pin 1 for the first digit or pin 2 for the second digit. We then drive one of the cathode pins low, so that one of the 16 LEDs in the display has a complete circuit, ie, is driven at both ends. This ensures that only that segment lights up. The other eight lines remain high impedance (“Tri-stated”) in order to avoid turning on any of the other segments. To drive the second display, we reuse the same set of pins on the micro but we use two different ones for driving the anodes. For example, here we are using pins 15 & 14 of the micro to drive the anodes in DISP1, while pins 11 & 12 drive the anodes in DISP2. 36  Silicon Chip Semiconductors 1 ATTiny2313 microcontroller (IC1) programmed with 1910810B.hex 1 7805T 5V regulator (REG1) 1 infrared receiver (IRD1) 1 BC556 PNP transistor (Q1) 1 BC546 NPN transistor (Q2) 2 7DR/NFD-8021BS 20mm dual high-brightness common anode 7-segment LED displays (DISP1-2) (available from Futurlec) 1 7DR/NFD-5621BS 14mm dual high-brightness common anode 7-segment LED display (DISP3) (available from Futurlec) 1 green 5mm LED (LED1) 2 1N4004 diodes (D1-D2) 4 1N4148 diodes (D3-D6) Capacitors 1 100µF 16V electrolytic 1 47µF 25V electrolytic 4 100nF MKT 2 33pF ceramic Resistors 4 10kΩ 1 470Ω With this arrangement, when any segment in display DISP1 is illuminated, there is also a voltage present across one of the segments within DISP2. However, because DISP2’s anode pins are connected only to DISP1’s cathodes, that LED is reverse biased and so it does not light. The same is true in reverse, ie, driving a segment in DISP2 will reverse bias a segment in DISP1. The same applies for DISP3, which has its anodes driven from pins 18 & 19 of the micro. As a result, no two common anodes are joined to the same microcontroller output. Thus, by being clever as to which lines are driven high and low at any one time (as set by the micro’s internal firmware) and leaving the rest at high impedance, we can light any one of the 48 segments. Multiplexing While this scheme theoretically allows us to light more than one segment at once (in fact we could light all the segments in a single digit quite easily), in practice we would need external anode driver transistors to do this. The microcontroller outputs simply can’t provide enough current to light multiple segments simultaneously, at least not without affecting their brightness. So each segment in the display is lit individually in sequence. Because this happens so rapidly, the persistence of vision effect in our eyes makes it appear as if all the segments are lit simultaneously. This is much the same technique that’s generally used to multiplex a multi-digit 7-segment LED display, except that normally all the segments of each digit are lit simultaneously. In this case, we have taken the multiplexing to its extreme and as a result, the individual segment duty cycle is less than 2%. In other words, each segment is lit for less than 1/50th of the total time. We can get away with this for two reasons. First, the LED displays are very bright, so despite each segment being lit for such a short period, they are still quite visible. Second, we are driving them above their rated DC current (but below their rated pulse current), thereby increasing their instantaneous (and thus average) brightness. This scheme has yet another advantage. Because the number of segments being lit at any one time never varies siliconchip.com.au (it’s always one), the displays do not vary their brightness according to the value. Look carefully at a commercial device with a 7-segment LED display (eg, a microwave or clock/radio) and you will find that in many cases, the brightness varies quite dramatically between a digit reading “1” and one reading “8”. Current limiting The microcontroller runs off a +5V rail (more on this later) and the LED segments have a typical forward voltage of around 2V. So how does the microcontroller drive the LEDs, or for that matter its internal output transistors, without burning them out? The answer is that these output transistors, for both the anode and cathode drive, have a fairly significant internal resistance. This limits the current to a safe level but only if the segment duty cycle is kept low. As mentioned earlier, the duty cycle has to be less than 2% due to the number of segments and calculations show that this is safe for both the micro and the displays. Let’s take a closer look at these calculations. The ATTiny2313 datasheet does not specify any dissipation limits but we can estimate them from its current limits. In this case, the maximum current per I/O pin is given as 40mA, while the maximum current for the entire micro is 200mA. By referring to the “I/O Pin Source Current vs. Output Voltage (VCC = 5V)” and “I/O Pin Sink Current vs. Output Voltage (VCC = 5V)” graphs, we can calculate the maximum average dissipation for the output transistors in the worst case temperature. This is 48mW for the pull-up transistors and 42mW for the pull-down transistors. Since it is permissible to have up to five I/O pins sourcing 40mA and five I/O pins sinking 40mA simultaneously (40mA x 5 = 200mA) then we can calculate that the maximum package dissipation must be at least (48mW + 42mW) x 5 = 450mW. Average dissipation We can now calculate the actual dissipation in the output transistors to check that it is safe. First, we assume that the voltage drop across each LED segment is around 2V. In reality, it will be higher than this due to the higher than normal current but using a 2V figure is the conservative approach. This means siliconchip.com.au Specifications Timing range: 1 second to 100 hours (360,000 seconds) in 1-second steps. Timing direction: unit can count up or down. Remote control: can be set and controlled using a universal remote control. External inputs: can be triggered and reset using external inputs; timer counts up or down from a preset value when externally triggered. Outputs: DPDT (double-pole double-throw) relay outputs – relay can be on or off while counting and then changes state for the duration of the alarm period. Relay contact rating: 30V DC or 24V AC (must NOT be used to switch mains appliances). Power supply: 9-12V DC 300mA plugpack or a battery. the current through the LED will be such that the sum of the voltage drops across the output transistors is 3V (ie, 5V - 2V). By referring to the sink and source graphs previously mentioned, we can calculate that the worst case current flow is 65mA at -40°C. The instantaneous dissipation will thus be 118mW in the source transistor, 130mW in the LED and 76mW in the sink transistor. Since the current source transistors have a duty cycle of no more than 1:6 (there are six digits) and the sink transistors have a duty cycle of no more than 1:8 (eight segments), we can calculate the maximum average dissipation figures. These turn out to be 19.7mW for the source transistors, 2.7mW for the LEDs and 9.5mW for the sink transistors. The total average dissipation in the microcontroller is just 194mW. These figures are all well below the maximum continuous ratings. So as long as we are careful to turn on each segment for just a short period (to prevent heat build up), then no damage should occur. In fact, in this design, each segment is lit for 10-20µs at a time and thus the refresh rate is around 1kHz. Measurements on the prototype confirm these calculations. With the microcontroller running at 8MHz and no segments lit, the current drain is around 12mA. Conversely, with all the segments lit, it is around 50mA. This suggests that the instantaneous current through each LED is in the range of 40-50mA, which is slightly less than we have calculated. Infrared remote control Control signals from the remote are picked up by infrared receiver IRD1 and fed to the PD2/INT0 input (pin 6) of IC1. IRD1 also drives LED1 (a green 5mm type) via PNP transistor Q1 and this LED flashes when ever an infrared transmission is received. However, it does not guarantee that there were no errors in the reception – if there are then IC1 will ignore the signal. LED1 simply flashes brightly when infrared (IR) data is received. A typical infrared remote control produces a modulated signal at around 36-38kHz. The IR receiver (IRD1) includes an internal 30-40kHz bandpass filter in order to remove any signals that may be present from flickering lights or other infrared sources. Unfortunately, while this filter does a good job of preventing unintentional signals from triggering its output, it is not perfect. As a result, some red light reflected back to the receiver from the LED displays can cause occasional false triggering and this can be made worse if there are lights shining directly on the unit, as their flickering can interact and produce beat frequencies. Ultimately, this isn’t a problem because the microcontroller recognises only legitimate 889µs-long control pulses and ignores the shorter pulses caused by interference. As a result, false triggering at the IR receiver’s output is rejected by the micro’s firmware and has no effect on the timer’s operation. Minor effects The false triggering does have two minor effects, though. One is that the onboard green LED can briefly flicker under some situations, as it directly monitors IRD1’s output. However, the LED lights much more brightly when August 2010  37 r emiT latigiD pih C no ciliS 8888 BUZZER 100nF 4148 4148 33pF x2 girT TRIG GND RESET t es eR D N GCON3 CON1 COM 5V DPDT RELAY LED1 RLY1 0102 © © 2010 DISP3 CON2 COM NC NC NO 88 NFD-5621BS 100nF 100nF 10k 10k 470Ω D4, D6 10k BC556 Q1 D2 BC546 4004 Q2 8MHz IRD1 19108101 10180140 + D3, D5 10k CON4 100nF IC1 ATTINY2313 4148 4148 47 µF 25V 7805T D1 4004 + POWER + – DISP2 NFD-8021BS 100 µF Silicon Chip Digital Timer NFD-8021BS DISP1 NO Fig.2: follow this parts layout diagram to build the PC board. Be careful not to get transistors Q1 & Q2 mixed up and note that the displays must be mounted with their decimal points towards the bottom. It is also switched alternately on and off at 1Hz to save power and make its sound more obvious. Note that its 1-minute period is the default value and this can be altered if necessary. Relay RLY1 (a standard 5V micro DPDT type) is driven from output PD5 (pin 9) of IC1, in this case via NPN transistor Q2. Diode D2 protects the transistor by quenching the back-EMF voltage spikes that are produced when the relay is switched off. All six relay contacts are connected to terminal blocks CON1 & CON2 so they can be connected to the output terminals on the outside of the case as you see fit. The trigger and reset inputs are provided via 3-way terminal block CON3 and a pair of RC filters (10kΩ and 100nF). These serve two purposes: (1) they filter out any noise or transients from the signals; and (2) in combination with diodes D3-D6, they protect IC1 from excessive voltage in either direction. As a result, it is safe to apply at least ±36V to either input. These inputs are connected to ports PD3 and PD4 (pins 7 & 8) of IC1. Voltages below 1.5V are considered “low” while voltages above 3V are considered “high”. The micro can be configured as to whether a low or high state activates the appropriate function (trigger or reset). PD3 and PD4 also have a weak pull-up resistor enabled within the microcontroller. This allows you to attach a switch, pushbutton or relay between the inputs and ground for passive triggering. In this case, you would configure the input as active-low for use with a normally open switch or active-high for use with a normally closed switch. Power supply This photo shows the fully-assembled prototype board. Note that there are a few minor differences between this board and the final version shown in the wiring diagram of Fig.2 the device is receiving genuine signals from the remote, so it’s easy to distinguish between the two situations. The second problem is that if there is a lot of light shining directly into the device, it can cause occasional reception errors when using the remote. Our tests have shown that the device can be reliably controlled from at least 5m away in most situations. It still works under adverse conditions but 38  Silicon Chip you may occasionally have to press a remote button more than once or correct a misinterpreted command when programming the unit. Support circuitry Pin 3 of IC1 drives the piezoelectric buzzer and this is activated for one minute at the end of the timing period. It is driven directly from output PD1 as it only consumes a few milliamps. Power for the unit can either be derived from a 9-12V DC 300mA plugpack or from a suitable 9-12V battery. The positive rail is fed in via diode DI, which provides reverse polarity protection, and applied to 3-terminal regulator REG1 (7805). REG1 then provides a regulated +5V rail to power the circuit (including the relays), while the 47µF and 100µF capacitors on either side of REG provide the necessary supply line filtering. The idle current is around 8.6mA and the maximum current drain is about 100mA with all LEDs lit, the relay on and the buzzer sounding. siliconchip.com.au Most of the idle current is consumed by the 7805 regulator (up to 6mA) and the infrared receiver (up to 4mA). If you want to power it from a battery, especially one comprising alkaline cells, it would be a good idea to replace D1 with a 1N5819 Schottky diode and REG1 with an LM2940IT-5 low drop-out regulator. The LM2940 has a slightly higher quiescent current but will allow the timer to run down to a much lower battery voltage. Board assembly Most the parts are installed on a PC board coded 19108101 and measuring 89 x 80mm. Begin by carefully checking the copper side for defects (breaks or short circuits), then check that all the holes have been drilled to the correct size. You may have to test fit some of the parts (eg, the terminal blocks and displays) to confirm this. Check also that the four corner mounting holes have been drilled to 3mm and that the board fits inside the plastic case. If it won’t go in, you may need to file the corners slightly. Fig.2 shows the parts layout on the PC board. Install the resistors first, followed by the four 1N4148 small signal diodes (D3-D6) which go in the middle of the board. The two larger 1N4004 diodes (D1 & D2) can then be installed. Make sure that all diodes are correctly orientated. Next, install the IC socket with its notch closest to D1 – see Fig.2. Solder its two diagonally opposite pins first, then make sure it’s sitting flat on the board before soldering the rest. The two ceramic and four MKT capacitors can then be installed. Follow these with the two transistors (Q1 & Q2). Note that Q1 is a PNP BC556 type while Q2 is an NPN BC546, so be careful not to get them mixed up. If their leads are too close together to fit through the holes on the board, crank them out with small pliers, then back down again so that they slide easily into place. Mounting the displays It’s now time to install the three dual The PC board is installed by fitting M3 x 15mm tapped Nylon spacers at each corner and then fastening it to the integral pillars in the case. Note that you will have to run the wiring to the DC socket and the barrier terminal strip before this is done. LED displays (leave the protective plastic on while you do this). For best appearance, they must sit perfectly flat against the PC board and should be parallel with the board edges. They also fit the board if installed upsidedown, so be careful with their orientation – the decimal points must be towards the bottom. Before mounting the displays, check that their pins haven’t been bent during transport. If so, they can be carefully straightened with pliers. Be sure to push each display all the way down so that it sits flush against the board. It’s best to solder two diagonally opposite pins first. That way, you can check that the display is correctly orientated and is flush with the board before soldering its remaining pins. The two electrolytic capacitors are next on the list. Check their polarity carefully when installing them and be careful not to get them mixed up. They should both be mounted about 3mm proud of the board so that they can later be bent over at about a 45° angle – see photos. That way, they won’t intrude on the display. Once these parts are in, install the green LED (LED1). This goes in with its flat (cathode) side towards 7-segment LED display DISP3. Push it all the way down onto the board and check its orientation before soldering its leads. Now for the infrared receiver (IRD1). Table 2: Capacitor Codes Value µF Value IEC Code EIA Code 100nF 0.1µF 100n 104 33pF   NA   33p   33 Table 1: Resistor Colour Codes o o o siliconchip.com.au No.   4   1 Value 10kΩ 470Ω 4-Band Code (1%) brown black orange brown yellow violet brown brown 5-Band Code (1%) brown black black red brown yellow violet black black brown August 2010  39 the programming pins are connected across LEDs. Install the hex file (available from the SILICON CHIP website) into its flash memory and don’t forget to set the fuse bits, which are documented in the accompanying text file, otherwise it may not work correctly. 6-WAY BARRIER TERMINAL STRIP Final assembly – 4148 + 4004 4148 88 COM girT TRIG RESET t es eR GND DNG NC NO COM NC 10180140 + 0102 © NFD-8021BS 8888 4148 4148 + 4004 DC INPUT SOCKET (REAR) NFD-8021BS r emiT latigiD pih C no ciliS NO Fig.3: here’s how to wire the DC input socket and connect the external Trigger & Reset inputs plus one pole of the relay to the 6-way barrier terminal strip. Alternatively, if you don’t need the Trigger & Reset inputs, you can connect both relay poles or you can use a second terminal strip. As shown in Fig.2, this is installed with its body flat against the PC board (domed lens facing upwards). This simply involves bending its leads down by 90° about 3mm away from its body before soldering it in position. The three screw terminal blocks (CON1-CON3) can now be soldered in. Note that CON1 & CON2 must be orientated so that their entry holes face away from the relay. Similarly, CON3 should be installed with its entry holes towards the adjacent edge of the board. Check that they sit flush against the board before soldering their pins. Follow these with the relay, which again should sit flat against the board. After that, fit the buzzer, which must be installed with its positive pin (indicated on the body) towards CON4. The 2-pin polarised header (CON4) can then go in – install it with its 40  Silicon Chip locking tab towards the adjacent edge of the board. The 8MHz crystal and the 7805T regulator are next. The crystal can go in either way around while the 7805T must go in with its metal tab towards the adjacent edge of the board. Solder the regulator’s leads, then bend it away from the displays at a 45° angle so that it doesn’t later impinge on display visibility. Microcontroller You can now complete the board assembly by installing the microcontroller. If it came pre-programmed (as in a kit), all you need to do is make sure its pins are straight and then push it down into the socket with the correct orientation. If you need to program it first, you must do it out-of-circuit as some of The PC board is designed to fit in a Jaycar HB-6246 polycarbonate case with clear lid. We have also produced a slightly modified board to suit the similar Altronics H-0324 box (both board patterns can be download from the SILICON CHIP website). Basically, you can customise the connections on the box to suit your needs. For example, if you want to power the unit from a battery you may decide to install an on/off switch to avoid draining the battery when you are not using it. And if you don’t need the trigger and reset connections (ie, you will be using the remote control only), then you won’t need to run leads from CON3 to an external connector. As shown in Fig.3, we used a 6-way chassis-mount terminal barrier to terminate the trigger/reset inputs and one relay pole. A 2.1mm chassis-mount DC socket mounted on one side of the case is used for the power input. This is connected to a polarised header plug via two short leads (red for positive, black for negative) which is then plugged into CON4. The second relay pole was not connected in our prototype. If you do want to connect it, there is room on the other (bottom) side of the case for a second terminal barrier. We left the bottom clear so that the completed unit can rest on a flat surface but if we were mounting it on a wall, the bottom would be the logical location for the connections to be made. Assuming you want to assemble your timer as shown in Fig.3, you will need to drill eight holes along the top edge of the box and one hole in the lefthand side for the DC connector. Fig.4 shows the drilling details. This can either be photocopied and the sections used as drilling templates or you can download the diagram from the SILICON CHIP website and print it out. You can attach the templates using adhesive tape. Make sure they are correctly positioned before drilling the holes (the terminal barrier and DC socket must both sit low enough to clear the PC board when it is installed siliconchip.com.au in the case). Drill small pilot holes at each location first, then enlarge them by stepping up to the correct drill size. Finally, deburr each hole using an oversize drill. The terminal barrier can now be pushed through and secured using two M3 x 20mm machine screws (one at either end). Use a flat washer under the head of each screw and a spring washer and nut inside the case. The DC socket can then be installed but you will have to discard its washer as the box is too thick for it. Do the nut up firmly so it can’t rotate. 4.75 9.5 A 9.5 B 4.75 9.5 B 9.5 B B 9.5 B 9.5 A B 13 BASE OF JAYCAR HB-6246 ENCLOSURE – LONG SIDE CL FULL ENCLOSURE MEASURES 115 x 90 x 55 HOLES A = 3.0mm DIA, HOLES B = 3.5mm DIA. CL Wiring It’s now just a matter of completing the wiring as shown in Fig.3, using medium-duty hook-up wire. Cut the wires to the lengths specified in the parts list, then strip and tin the ends before making the connections. The leads to the 6-way terminal barrier are soldered to the various tags, while the supply leads are crimped and soldered to the polarised header pins. These pins are then inserted into the plastic header shell (watch the polarity). Before soldering the supply lead to the DC socket, it’s a good idea to test the current drain. To do this, you will need a 9-15V DC supply, a multimeter and some alligator clip test leads. It’s then simply a matter of applying power with your multimeter (set to mA) connected in series with one of the supply rails. The current drain should be in the region of 10mA. If it’s significantly more, disconnect the supply and check for faults. If it is close to (or exactly), zero then you may have the supply leads transposed. Once the wiring to the terminal barrier and the DC socket is completed, the board can be installed in the case. To do this, first attach an M3 x 15mm tapped Nylon spacer to each corner of the board using M3 x 20mm machine screws. Wind the spacers all the way onto the screws but don’t tighten them – you must still be able to easily rotate the screw head. Next, attach the three leads to screw terminal block CON3 (it’s much more difficult to attach them once the board is in place). Having done that, route the soldered leads from the barrier terminal strip and the DC socket to either side of the case (see Fig.3), then lower the board into place until its mounting screws meet the integral pillars. siliconchip.com.au ALL DIMENSIONS IN MILLIMETRES C 11 BASE OF JAYCAR HB-6246 ENCLOSURE – SHORT SIDE HOLE C = 8mm DIA. Fig.4: these diagrams can be copied and used directly as drilling templates for the plastic case. Note that hole “C” is best made using a pilot drill and then enlarging it to size using a tapered reamer. The assembly can now be completed by tightening the four screws to hold the board in place, connecting the appropriate wires to the relay terminals (either CON1 or CON2, or both) and plugging the power connector into CON4. Check that the positive supply lead is closest to IC1 (this lead should also go back to the centre terminal of the DC socket). Finally, push any excess wire down under the board through the gaps on either side and install the lid (with the neoprene seal pressed into its channel). Waterproofing Since the box is IP65 rated (ie, water and dust proof), it’s possible to waterproof the timer if you wish to use it outdoors. However, because of the holes drilled for the barrier terminal strip and the DC socket, our prototype is more splash-proof than waterproof. If you like, you can apply silicone sealant to the inside of both connectors to improve this. The difficulty of properly waterproofing the timer is that all connections must be made via IP65-rated connectors or cable glands. Perhaps the easiest method is to install a small cable gland on one side of the box and pass a multi-core cable through it, carrying power and all the signal lines. With an 8-way cable, it’s possible to run the power, the two trigger wires (ground can be shared) and up to four relay connections. Getting the remote working To use the Digital Timer you will need a universal infrared remote control which is set to a standard Philips RC5 remote control code (this is the default in many cases). The green LED in the timer will flash whenever an IR signal from the remote control is detected. To test whether you are using the right code, simply point the remote at the timer (make sure it is switched on) and press some of the numeric buttons. The corresponding numbers should appear on the timer’s 7-segment displays. If they don’t, either the timer has a fault or the remote control is set to the wrong code. Try setting the remote to other Philips codes until you find the correct one. For example, the Digitech remote control pictured in this article August 2010  41 A barrier terminal strip on one end of the case can be used to terminate the external trigger & reset inputs plus one set of relay contacts, or you can use it to terminate both sets of relay contacts. Don’t forget the ratings sticker. (Jaycar Cat. AR-1726) should be set to TV code 103. Once it’s working and the correct numbers appear, press the Power/ Standby button on the remote to clear the display. Adjusting the settings Before putting the timer to work, you need to configure it for your application (unless you just want to use the default settings). The procedure is as follows: (1) Default settings: for the first set of options, refer to Table 3. Decide on the default settings you want, then enter the corresponding digits in turn, from the first digit through to the sixth. When you have entered all six digits, press the mute button on the remote. The display will now blank and your settings are saved. They can be updated at any time by repeating the above procedure. An example will make this clearer. Let’s say that you: (1) want the buzzer to sound at the end of the timing period, (2) want the relay to turn on at the end of the timing period (ie, for the duration of the alarm period), (3) want the trigger input active high, (4) the reset input active high, (5) the unit to count up when externally triggered and (6) the alarm period set to four minutes. In that case, it’s just a matter of pressing 1, 2, 2, 2, 0, 4 on Fig.5: these labels should be attached inside the lid and to the panel above the barrier terminal strip using silicone sealant. the remote in sequence, followed by the Mute button. (2) Adjusting the brightness: the next step is to set the display brightness. This is done using the Volume Up (increase brightness) and Volume Down (decrease brightness) buttons. There are 32 possible levels and the brightness can be changed either when the timer is running or while setting the timing period. Initially, you can just press some random number buttons to get digits on the display and adjust the brightness from there. That done, clear the display by pressing the Power/ Standby button then press the Mute button. Each time the device is powered up after this, it will automatically load the set brightness level. You can use the same procedure to change it again later, if necessary. (3) Automatic timing: the final setting is the timing period you want programmed in for automatic triggering. Enter the time using the keypad, keeping in mind that the first two large Table 3: Setting Up The Presets Digit Setting 0 means 1 Means (Default) 2 Means First Buzzer Always off On during alarm period N/A Second Relay Always off On while counting On during alarm period Third Trigger input Disabled Active low Active high Fourth Reset input Disabled Active low Active high Fifth When triggered Count up Count down N/A Sixth Alarm period Enter number of minutes (0-9) 42  Silicon Chip siliconchip.com.au Controlling Mains Or High-Current DC The relay used in this project is rated at 30VDC/2A and 125VAC/1A. However, as used here, it should not be used to switch any AC voltage higher than 24V. DO NOT under any circumstances use the on-board relay to switch 230V AC mains appliances – that would be quite dangerous. To switch a mains load, you will need to use the on-board relay to trigger an external mains-rated relay (mechanical or solid state). This must be mounted and wired in a safe manner. Don’t attempt to do this unless you know exactly what you are doing and are experienced with 230VAC wiring! You can also use an external relay if you need to switch high-current DC. If you plan on adding an external relay, it’s best to use one with a 12V DC coil and run the Digital Timer from a 12V DC supply. It is then simply a matter of connecting the timer’s 12V rail to one of its internal relay’s COM contacts (either on CON1 or CON2). The positive side of the external relay’s coil is then connected to the corresponding NO contact, while the negative side goes directly to the negative output of the 12V DC supply. A reverse-biased diode should be connected across the external relay’s coil to quench switching spikes. Now when the internal relay switches on, it supplies power to the external relay’s coil and it too switches on. The contacts of the external relay can then be used to switch on a mains device or supply power to a high-current DC load (provided these contacts are adequately rated). Keep in mind that your 12V DC supply must be able to provide at least 100mA for the Digital Timer itself plus the rated coil current of your external relay. A 300mA plugpack supply should do the job quite nicely. digits represent the number of hours, the next two the number of minutes and the two smaller digits the number of seconds. Then press the “1-” key on the remote (the one normally used to enter 2-digit TV station numbers). This programmed time will now be placed in memory and recalled whenever the timer is started via its trigger input. Using the timer manually To use the timer manually, simply enter the timing period you want using the keypad, then press either the “Channel Up” or “Channel Down” button. If you press “Channel Up”, the display will start at 00:00:00 and count up to the timing value you have entered. Alternatively, if “Channel Down” is pressed, the display will start at the timing value you have specified and count down to 00:00:00. When the timing period ends, the alarm period will begin (unless it has been set to 0 minutes in which case the timer will immediately reset). When the alarm period expires, the unit resets automatically or you can press the Power/Standby button to reset it before it expires. If you want to stop counting simply press the remote’s Power/Standby button and the device will reset and go to siliconchip.com.au Charlieplexing Earlier in the article, we referred to the method used to drive the LED displays as “charlieplexing”, which is really just a special form of multiplexing. If you want to know more about charlieplexing, refer to our feature in the forthcoming September 2010 issue of SILICON CHIP. standby mode. You can also pause the timer by pressing the pause button (assuming your remote control has it – it is actually a VCR function). To resume, press play (another VCR function). Note that the buzzer is quite audible but not particularly loud once it is sealed inside the box. If you want to make it louder, drill some small holes in the lid immediately above the buzzer’s location. Finally, Fig.5 shows some labels which should be affixed to the inside lid of the case and to the panel immediately above the barrier strip terminal. These indicate the power supply requirements (and polarity) and also indicate the maximum voltage ratings for the relay contacts. That’s it! We are sure you can think SC of many uses for this project. Helping to put you in Control Control Equipment Relayduino The KTA-225 is a new version of our popular Arduino compatible USB controller featured in SC April 2010. Features ASCII Commands, 8 Relays, 8 Flexible I/O (Digital Input or Analog Input (05V/4-20mA). Windows/Mac/Linux compatible . $135+GST Rolls Of Heatshrink We now have rolls of heatshrink available. Colours of red, black, blue, yellow, green, white and clear available Diameters from 1.5/0.75 to 50/25mm From $75.00 +GST Industrial Grade Switches and Indicators We now have a selection of 22 mm diameter industrial switches. Fitted with NO+NC contacts. Screw Connections. Color Black, Red, Green, Yellow and Blue From $9.95 +GST DIN Rail Enclosure An ABS plastic enclosure that can be bolted to a panel or mounted on DIN rail Size: 145x90x40mm From $12.95 +GST 70W Brushed DC Servo Motor CNC Kit This 3-axis CNC kit contains all the drives, motors power supplies to build or retrofit a mill or lathe for CNC work. $929+GST Isolated RS232 to RS422/485 Converter A high performance RS-232 to RS485/422 converter. Features both 2.5KV opto-electrical isolation and internal power isolation $75+GST Ph: 03 9782 5882 New, Easier to Use Website www.oceancontrols.com.au August 2010  43