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Stop those intrusive meal-time phone calls! By JOHN CLARKE "DO NOT DISTURB!” Phone Timer Do marketing companies conspire to call you right on dinner time? It certainly seems so! Or perhaps you want the phone to be out of action for an hour or so, while you take an afternoon nap? This little timer will solve both those problems and it will “remember” to put the phone back in action because we know how easy it is to forget! Y ou know how it goes – you sit down to dinner and you are savouring your first mouthful... and then the &(*%$ ^ phone rings. It might be some nincompoop from a marketing company selling you something that you cannot possibly 64  Silicon Chip do without, or a call centre in India or the Philippines. Or it could even be one of your closest friends or relatives. Whoever. It doesn’t matter – you don’t want to talk – you just want to enjoy your meal. Of course, you could simply take the phone handset out of the cradle (“off-hook” in 1950s telephone speak) and that effectively silences it . . . but then you realise a few days later that the phone has been awfully quiet. Doh! And yes, many cordless phones have a “do not disturb” button but siliconchip.com.au the same problem handset off the craapplies; you forget dle while the unit to switch it back to is timing? That’s a • Five convenient time settings from 15 to 120 minutes normal operation. bit uncertain - it de• Time set indication Worse still, if you pends on your par• Time remaining indication do want to have a ticular phone and nap, pushing the “do how it reduces the • Automatically returns phone to “ready” (on hook) after time-out not disturb” button DC voltage across • Easy push-button timer setting does not usually the phone lines • End button silence the phone from a nominal completely; it will 50V DC to around ring several times 6V or thereabouts. before it goes to message mode – which says they’re expecting an absolutely Either way, neither the phone nor the can be pretty frustrating if you are just vital call!) just press the End button timer can be damaged. drifting off to the land of Nod. to restore phone operation. Simple. The DO NOT DISTURB! Phone That’s where our new “DO NOT Timer is housed in a small plastic box DISTURB!” Phone Timer is such a LEDs show the time with the telephone line plugged into good solution. Three LEDs display the set time. one RJ12 socket and the telephone into It connects in parallel with your With one LED on, they indicate 15, 60 the second RJ12 socket, so you’ll need phone, or one of your phone exten- or 120 minutes. Intermediate set times a short phone “extension” cable . sions if you have more than one (or are indicated with two LEDs on, ie, 30 Both the RJ12 sockets are located with your cordless phone base sta- or 90 minutes. at one end of the box. On the top of tion, if you don’t have conventional When you push the Set/Start button the box are the two pushbuttons (Set/ phones). the LEDs will show the previous set Start and End) and the timer indicaThen, if you want to disable the timer period. Further button pushes tion LEDs. No batteries are required phone you just press the Set/Start but- will cycle though the available times: since the circuit is powered from the ton a few times to set the time period 90, 120, 15, 30 and so on. Just pick the phone line. you want and the phone will be muted. one you want. Callers will get the engaged signal – so Timer operation starts as soon as the Is it legal? they won’t have to pay for a call. period is selected. After five seconds, Strictly speaking, you aren’t allowed You get peace and quiet for a preset the LED (or LEDs) will flash at a one- to connect any non-approved device 15, 30, 60, 90 or 120 minutes. second rate and they also indicate the to the phone line, in case it causes After the preset time has passed, the next highest time-out period remain- damage to the line/exchange and/or Timer will reconnect the phone. ing. All LEDs extinguish at the end of endangers those working on the telIf you finish your meal or nap or the time-out period as normal phone ephone system. whatever earlier than you anticipated, operation is restored. However, this device is powered by (or maybe son/daughter/spouse/etc What happens if you lift a phone the phone line itself, so no dangerous Features TO TELEPHONE 10k D1 K A K K A A K D3 GP1 4 D1–D4: 1N4004 MCLR END (RESET) CON2 (RJ12) 100F 16V ZD1 5.6V A 2013 SET/ START 7 GP2 GP0 S1 NOT DISTURB” PHONE TIMER Fig.1: the circuit is simply connected in parallel with two phone sockets, one of which goes to the phone line and the other to the phone. When activated, it fools the system into believing that the line is engaged – hence the phone won’t ring. siliconchip.com.au 180 (MJE340) 1.5k 2 Q1 BF469 E 180 1.5k 1.5k 5 (MINUTES) A A Vss 8   K SC “DO  C B GP4 S2 K 33k 6 IC1 GP5 PIC12F675 -I/P 3 (MJE350) 10 A 1 Vdd 10k Q2 BF470 C 3.3k D5 1N4004 100nF TO TELEPHONE LINE E B 100k D2 A D4 CON1 (RJ12) K LED3 K LED2 A K 90  15 K 60 (MINUTES) 120 LED1 LEDS K ZD1 A BF469, BF470 1N4004 A 30 K A B C E May 2013  65 The completed project immediately before mounting it in its case. The cable to the phone line and the cable to the phone can plug into either of the RJ12 sockets – it doesn’t matter which way around. ensures correct polarity. The microcontroller, IC1, is powered from 5.6V DC, derived via a 100kΩ resistor, zener diode ZD1 and 100µF capacitor. Thus the 50V from the telephone line provides about 400µA to ZD1 while IC1 draws about 100µA. This current is low because IC1 is initially set in sleep mode where it is stopped from running, with its internal oscillator off. IC1 also has a brownout detector incorporated so that the slow start up voltage applied through the 100kΩ resistor and 100µF supply capacitor allows the IC to reset correctly. Current draw is higher when the timer function is started with Set/ Start switch S1. This current can be up to 10mA and the 100kΩ resistor across the telephone supply will not provide this. We derive the extra supply current 100F 66  Silicon Chip 10k 10 100nF 33k IC1 ZD1 5.6V 13140121 4004 4004 CON2 LED3 S2 RESET The DND Timer is constructed using a PCB coded 12104131 and measuring 79 x 46mm. It is housed in a small plas- Q2 METAL SIDE 180 1.5k A PIC12F675 LED2 10k 1.5k A 180 D1 D2 D3 D4 S1 SET LED1 A 100k D5 4004 1.5k 4004 4004 C 2013 CON1 Construction BF470 Fig.1 shows the circuit which comprises an 8-pin microcontroller, a couple of high voltage transistors, three LEDs, some diodes and capacitors. The microcontroller provides the timing, switches the high voltage transistors and drives the LEDs. There are two RJ12 connectors, CON1 & CON2 which provide connection to the incoming phone line and to one of the phones in the dwelling. These connectors are wired in parallel, so there is no break in the telephone line connection. When the phone is not in use, (ie, “on-hook”) there is about 50V DC present across the line. The bridge rectifier consisting of diodes D1-D4 feeds that 50V DC to the rest of the circuit and 3.3k Circuit details BF469 voltages can possibly get back into the system. in another way. When the set switch is pressed, the GP1 output of IC1 goes high (to 5.6V) and this switches on transistor Q1 via its 33kΩ base resistor. Q1 in turn switches on transistor Q2 and this connects two series connected 180Ω resistors across the telephone supply. The load drops the telephone line to around 6V and it becomes “off-hook”. With transistor Q2 on, supply for IC1 is fed from the 6V telephone supply via a 10Ω resistor and diode D5. This provides the required extra current. Q1 and Q2 are high voltage transistors, specified to cope with the high AC of around 140V peak-to-peak when the telephone rings. Note if the handset (receiver) is lifted off the telephone, the DND Timer might reset. That’s because of the extra load on the telephone line. If you still want to the DND Timer to work, you should hang up the phone and push the Set/Start button which will restart the timing cycle. LED1 to LED3 are driven by their respective micro outputs at GP5, GP4 and GP2, each via 1.5kΩ resistors. Normally, the GP0 input is pulled to the 5.6V supply via an internal pull-up resistor. This input drops to 0V when the set switch is pressed, waking up IC1 and starting the internal program running. IC1 goes back to sleep at the end of the time-out period. Both Q1 and Q2 are then switched off and normal phone operation is resumed. IC1 can also be reset by pressing switch S2. This pulls the MCLR (Master Clear) low to reset the IC. Once released, the 10kΩ resistor to VDD pulls the MCLR high and IC goes back to sleep with the internal oscillator stopped. Q1 Fig.2 (left): component overlay with matching same-size photo at right. siliconchip.com.au tic box 83 x 54 x 31mm, used “upside down” – ie, the normal lid becomes the base and the four rubber “pips” which hide the case screws act as feet. We used a translucent blue box (because it looks schmick!) but black or grey boxes of the same size are also suitable. A label measuring 48 x 78mm affixes to the lid of the box. If you use the blue box this label can go inside the lid and is thus protected against damage. At one end of the box are located the two RJ12 PCB mount sockets. Fig.3 shows the details. Before installing the parts, check the PCB for any faults. If you are using a board supplied from the SILICON CHIP Partshop or building from a kit, you will find that these PCBs are of excellent quality and rarely have any faults. If you do happen to find a fault (open track, hole not drilled etc) repair it before assembly. Follow Fig.2 when installing the components. Install the resistors, diodes and the zener diode first. The resistors are colour coded and the table shows the colour bands for each resistor used. A digital multimeter should also be used to check the values of resistance because it’s easy to mistake red for orange or brown, especially on tiny resistors. Make sure the diodes and zener diode are installed with the correct polarity – the striped end must be oriented as shown in the overlay diagram. We use two types of IC sockets. One is the DIP8 socket for IC1, which must be oriented with the notched end as shown on the overlay diagram. Do not insert the IC into the socket yet. The other sockets are DIP6 types used to raise switches S1 and S2 sufficiently above the PCB to protrude through the box lid. These sockets will need to be cut (using wire cutters) into two separate 3-way single in-line sockets and with the centre two socket pins removed before installing on the PCB. The switches must be inserted into these sockets positioned with the “flat” on the switch oriented as shown on the overlay diagram. Capacitors can be installed next. The electrolytics are polarised – install them with the polarity shown. Likewise, transistors Q1 and Q2 must be mounted in the right positions and they must be oriented correctly – their metal sides face away from the PCB edge. Solder these in so that the top of the transistor body is 15mm above the top of the PCB. LEDs need to poke through the top panel so are mounted with the top of each lens 17mm above the PCB surface. Make sure the LEDs are oriented correctly with the anode (longer lead) positioned in the pad marked ‘A’. We used blue LEDs, but you can use aqua, red, green, yellow, orange or white; whatever is your favourite. (You don’t even need to use the same colours but you might end up with different brightness LEDs). Parts List – DO NOT DISTURB! Timer 1 PCB coded 12104131, 79 x 46mm 1 panel label 48 x 78mm 2 UB5 plastic box, 83 x 54 x 31mm 2 RJ12 PCB mount sockets (Jaycar PS-1474, Altronics P1425) (CON1,CON2) 2 SPST PCB mount snap action round white switches (Jaycar SP-0723, Altronics S1099) (S1,S2) 1 DIL8 IC socket 2 DIL6 standard wiper contact IC sockets 2 10mm M3 tapped spacers (or use 9mm spacers with washers to make up the extra 1mm) 2 M3 x 6mm screws 1 300mm RJ12 6P/4C extension cable Semiconductors 1 PIC12F675-I/P microcontroller programmed with 1210413A (IC1) 1 BF469/MJE340 NPN transistor (Q1) 1 BF470/MJE350 PNP transistor (Q2) 3 3mm high brightness LEDs (LED1-LED3) 5 1N4004 400V diodes (D1-D5) 1 5.6V 1W zener (1N4734) (ZD1) Testing To test the DO NOT DISTURB! Phone Timer, firstly make sure that IC1 is still out of its socket and then plug the telephone line into one of the RJ12 sockets (you don’t need the phone itself plugged in yet). Measure the voltage across zener diode ZD1. This should be around 5 to 5.6V. Now unplug the telephone line and insert IC1 making sure the orientation is correct. Reattach the telephone line and the DO NOT DISTURB Timer should operate when pressing the Set/ Start button by showing the timer LED or LEDs. You should be able to select the Capacitors 1 100µF 16V PC electrolytic 1 100nF MKT polyester Resistors (0.25W 1%) 1 100kΩ 1 33kΩ 2 10kΩ 1 3.3kΩ 3 1.5kΩ 2 180Ω 1 10Ω required time-out period by pressing the switch until the required setting is displayed. Then the time-out LED or LEDs should flash after about five seconds from when S1 is released. If the LEDs do not light, check the orientation of IC1. Also check that Q1 and Q2 have been inserted in the right LED RJ12 SOCKET SWITCH M3 SCREW PCB TRANSISTOR UPSIDE-DOWN UB-5 PLASTIC JIFFY BOX 3-PIN SECTIONS OF SIL SOCKET STRIP (SEE TEXT) 10mm LONG M3 TAPPED SPACER CASE LID RUBBER SCREW COVERS (ACT AS FEET) The case is used “upside down) with the lid as the base. Here the PCB is shown fitted into the case. siliconchip.com.au Fig.3: this diagram shows how it all goes together. The two switches are not soldered to the board but mounted instead inside some cut-down DIL sockets. This gives them some “play”, making the board easier to fit in the case. May 2013  67 Where did these expressions come from? We’ve talked about things like “off hook” and “on hook” in this article. You may also have heard expressions such as “transmitter” and “receiver” when phones are being described. But where did these expressions come from? We thought we’d digress from our story with a little bit of telephone nostalgia! Too long ago for most of us – but well within living memory for many – phones were rather different from what we have today. At right is a photo of an early wall phone, used on a manual telephone exchange (probably in the country) and this gives a good idea of where many of the terms came from. There is a “receiver” (or earpiece) hanging on a spring-loaded hook on the left side. It’s “on hook”, it’s ready to receive a call. Take the receiver off the hook to answer a call and, surprise surprise, it’s “off hook”. When the receiver is removed, the hook moves up and closes contacts inside the phone. In the middle of the phone is the “transmitter” (you may think of it as the mouthpiece) while just visible on right side is a handle which you turned vigorously to attact the attention of the telephonist, or switchboard operator. This handle was attached to a generator inside the phone which produced the voltage necessary to ring a bell at the exchange. Such generators were in big demand by schoolboys of the day because you could generate enough voltage to give your mates a decent (though harmless) “belt!” In fact it was fun to arrange a ring of kids, all holding hands, with the generator connected to the last two in the ring so that all got the “experience!” Low voltage DC was provided by a couple of quite large 1.5V batteries (hence the size of the box in the pic above) – also prized by kids of the day and the cause of more than one public phone being out of action until they were replaced. One final bit of trivia: city visitors (used to automatic exchanges) to homes in country towns with manual exchanges almost invariably picked up the handset, or receiver, before turning the generator handle. Of course, the phone recognised this as being “off hook” and effectively shorted out the generator – so the exchange never answered. They couldn’t understand why their country cousins always managed to make a call while they couldn’t! places (Q1 is the BF469 or MJE340 and Q2 is the BF470 or MJE350) with the correct orientation. As mentioned earlier, we use the plastic box upside down, with the switches and LEDs protruding through the base of the box instead of the lid. We have provided a panel label for you to print out (available on our website www.siliconchip.com.au). The RJ12 sockets protrude through a 27 x 15mm cutout in one end. The RJ12 sockets support the PCB in place at this end. At the other end of the PCB, it is supported using two M3 tapped spacers. These spacers can be 10mm long or 9mm long with washers between the PCB and spacer to make up the extra 1mm length required. The spacers are secured to the PCB with M3 x 6mm screws. We did not secure the other end of the spacers to the box since the PCB is held in position with the transistors preventing upward movement. Fig.3 shows the arrangement. A diagram (Fig.4) is included which shows the positioning of the rectangular cut-out in the end of the box for the RJ12 sockets. The front panel label can be also be used as the template for the hole positions for the LEDs and switches. Once drilled out, the front panel can be glued in with an adhesive such as contact adhesive or silicon sealant. Once the adhesive has cured, the holes are cut out with a sharp hobby knife and filed with a rat tailed needle file to clean up the panel edges. The white edges of the photo paper inside the hole can be made less obvious by running a permanent black marker pen around the inside of the holes. Shoe-horning in the PCB: first slide the board in at an angle so the two RJ12 sockets fit in their cutout. Next, jiggle the switch buttons a bit so that they emerge through the front panel (ie, case bottom!) holes. And finally, push the PCB up from underneath so the pushbuttons and LEDs poke through the panel. Enclosure 68  Silicon Chip Here’s a close-up of the way we mounted S1 and S2 in cut-down DIL sockets to allow easier assembly siliconchip.com.au C L 10 mm 10 C Lmm 28 mm 28 mm +  + 15 END + + 60 SET/START 120 TIMER SET/START + DO NOT DISTURB DO NOT Phone timer DISTURB + TIMER + 15 15 Phone timer mm mm 15 mm 15 mm 15 mm ONLINESHOP . . . it’s the shop that never closes! 24 hours a day, 7 days a week Minutes + + 30 90 60 120 END 15 27 mm 10 mm Minutes 30 90 + 27 mm SILICON CHIP SILICON CSHIP ILICON CHIP 10 mm 15 mm RJ12 Cut-out RJ12 28mm Cut-out . . . it’s the shop that has all recent SILICON CHIP PCBs – in stock* . . . it’s the shop that has those hardto-get bits for SILICON CHIP projects . . . it’s the shop that has all titles in the SILICON CHIP library available! . . . it’s the shop where you can place an order for a subscription (printed or on-line) from anywhere in the world! . . . it’s the shop where you can pay on line, by email, by fax, by mail or by phone 28mm Fig.4: the front panel artwork and end-panel cutout diagram, which can be copied and used as a template. Both of these can be downloaed from www.siliconchip.com.au Inserting the PCB So how do you insert the PCB into the box when it is used with the base of the box as the top panel? There’s an art to it but once you’ve done it, you’ll find it easy. Simply angle the two switches slightly forward (toward the RJ12 sockets). The * Every effort is made to keep all boards in stock. In the event that stocks run out, there is normally only a two week delay in restocking. Applies to all boards since 2010, excepting those where copyright has been retained by the author. Order online now at www.siliconchip.com.au/shop switches can be angled because they are inserted into sockets and so can be easily moved. Tilt the RJ12 connector end of the PCB at an angle to first insert these connectors into the cut-out in the end of the box and then rotate the PCB to lie horizontal to the box base. The switches will then enter the holes in the box top. These switches can be seated correctly into their sockets by pressing them once the PCB is in place. The 10mm spacer prevents the PCB from dropping inside the box. To connect up to the telephone, connect the telephone line plug into one RJ12 socket of the DO NOT DISTURB! Timer and use the extension RJ12 lead to connect between the other RJ12 socket on the DO NOT DISTURB! Timer and the telephone. SC Resistor Colour Codes o o o o o o o siliconchip.com.au No. 1 1 2 1 3 2 1 Value 100kΩ 33kΩ 10kΩ 3.3kΩ 1.5kΩ 180Ω 10Ω 4-Band Code (1%) brown black yellow brown orange orange orange brown brown black orange brown orange orange red brown brown green red brown brown grey brown brown brown black black brown 5-Band Code (1%) brown black black orange brown orange orange black red brown brown black black red brown orange orange black brown brown brown green black brown brown brown grey black black brown brown black black gold brown May 2013  69