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Keep your phone bills low with the TELEPHONE CALL This project helps you keep track of the time while you make those expensive overseas phone calls. It times for up to 19 minutes and provides four warning beeps during the last 12 seconds of each minute. By DARREN YATES How often have you lost track of the time while making an overseas phone call? No doubt , you haven't worried about it at the time - until the next phone bill came in, that is! For example, making overseas (IDD) calls can get quite expensive if you lose track of the time. Not only that, but you also'get charged a full minute's worth for every part minute that you use. 62 SILICON CHIP Thus, if you make an IDD call that lasts for three minutes and five seconds, you get charged for four minutes. That's because IDD calls are always rounded up to the next minute for billing, which means that you can wind u p paying an extra cou ple of dollars for just a few seconds. Our Telephone Call Timer can save you or your business big m oney. It keeps track of the time for you - for up to 19 minutes - and it gives four warning beeps 12 seconds before the end of every minute. It then lights one or more LEDs to indicate the elapsed time since the start of the phone call. That way you don 't end up paying for the minute you don't use. Alternatively, by using the timer, you can keep talking until the next minute is almost up to make sure you get your money's worth. The timer uses only common components, many of which you'll probably already have lying around in your junkbox. To keep the cost down, it uses a series of LEDs to indicate the elapsed time instead of the normal?segment LED displays. There are 10 LEDs in all, with each unit LED lighting in turn to indicate the elapsed time during the first nine minutes of the call. RING OF TEN COUNTER IC3 ALARM TONE IC5 Fig.1: block diagram of the Telephone Call Timer. Clock signals from 3-second timer ICl are first divided by two & then fed to decade counters IC3 & IC4 wired in cascade. IC3 activates the alarm tone circuitry, while IC4 & IC2b drive the LEDs to indicate elapsed time. a: w :E j:: ..I ..I <( u After that, the 10-minute LED lights and remains lit for the next nine minutes as the other LEDs again light in turn. An advantage of this unit is that it doesn't require any connection to the telephone line. That does away with the need for isolation transformers, interfacing circuitry and connecting sockets. All you have to do is switch the unit on the moment the called party answers the phone. w z 0 ::c c. w w ..I I- Block diagram Refer now to Fig.1 which is a block diagram of the Telephone Call Timer. Clock signals for the circuit are provided by timer stage . . .YN,.......1-----''f\-.......~u....l1, TIMER 0 ci '-' ,. ..J '-' ICl. This provides a square wave output with a period of three seconds. This output is then fed to a divide-by-2 circuit (IC2a) which increases the period to six seconds. The output from IC2a is fed to a decade counter with decoded outputs (IC3). This stage is used to activate the warning tone alarm (IC5), while its divide-by-10 output gives us a square wave with a period of one minute. This square wave output is then fed into another decade counter (IC4) whose outputs go high in turn after every minute. We use these outputs to drive the LED display. The divide-by-10 output from IC4 is another square wave with a period this time of 10 minutes. It is fed into :;; a: ci '-' ;::: 0 ., Fig.2 (right): the circuit uses 7555 timer IC1 to generate the clock signal. NANO gates IC5a & IC5b make up the tone oscillator. This oscillator is activated for four 3second periods during the last 12 seconds of each minute & drives complementary transistor pair Ql & Q2 via a 33kQ resistor. MARCH 1992 63 ®~~u , - - - - - - - - - - - - - - - - - - -- ·02- ~~ 0} ®fLPD [~~~ 2"'" ·, " ® ""si: ,®~®~®~ """" LED1·9 LE010(!) (!) WG) G) G) G) G) G) CD Fig.3: the parts can be installed on the PC board in virtually any order but make sure that the link wires are straight to avoid short circuits. Install the two electrolytic capacitors so that they can be bent over to lie flat against the board. IC2b , which is another divide-by-2 circuit, and this in turn drives the 10minute display LED. As you can see, the accuracy of the circuit relies on the 3-second timer, so you must get that as close to correct as possible. Circuit diagram Fig.2 shows the complete circuit details . IC1 (7555) is a CMOS version of the popular 555 timer and is wired here in the astable configuration. The 4.7MQ and 3.3MQ resistors, the 2MQ trimpot (VR1) and the 0.33µF capacitor set the timing period When the trimpot is adjusted correctly, the output at pin 3 of IC1 is a square wave with a 3-second period as described previously. The advantage of using the CMOS version of the 555 is that it allows us to use much higher resistor values in the timing circuit and h ence a low value capacitor to get the required time delay. The output at pin 3 is fed into pin 11 of IC2a, which is one half of a CMOS 4013 dual-D flipflop. Because the Q-bar output is connected back into the D input, it forms a toggle flipflop which simply divides the clock frequency by two. The output is taken from the Q output (pin 13) and is a square wave with a period of six seconds. This output is now fed into the clock input (pin 14) of IC3 which is the first of the two 4017 decade 64 SILICON CHIP counters . Among other things, this IC provides the required outputs to activate the 12-second warning circuit. Here's how it's done: outputs 8 and 9, which correspond to the 48-second and 54-second marks of each minute , are used to drive diodes D3 & D4. These diodes, together with the associated lOkQ pull-down resistor, form an OR gate. The output from this OR gate is then fed into the cathode of diode D2. D1, D2 and the associated lO0kQ pull-up resistor form a simple AND gate. D3 & D4 drive one input of this AND gate, while pin 3 of IC1 drives the other. The output of the AND gate (ie, the anodes of D1 & D2) is high only when both inputs are high. This only occurs each time pin 3 of IC1 goes high during the last 12 seconds of each minute (ie, from the 48-second mark onwards). Because IC1 has a 3-second period, it follows that the output of the AND gate (and thus pin 13 of IC5a) goes high and low four times during the last 12 seconds of each minute. This signal is used to gate the alarm oscillator on and off to provide the four warning tones. The alarm oscillator is made up using NAND gates IC5a & IC5b, which are wired together in a conventional manner. The associated 4 7kQ resistor and .015µF capacitor set the oscillator frequency. The resulting square wave output appears at pin 10 and drives complementary transistor pair Q1 & Q2 via a 33kQ resistor. Q1 & Q2 in turn drive a miniature 8-ohm loudspeaker via a lOµF capacitor. Note that no quiescent bas e biasing has been provided for the transistors; nor is it necessary, since they are only being fed with a square wave signal. So much for the alarm tones. We'll now return to the main timing part of the circuit and find out how the LED indicators work. The divide-by-10 output (CO) from IC3 (pin 12) is fed to the clock input of the second decade counter, IC4 . Because IC3 's output has a period of 60 seconds, IC4 's 1-9 decoded outputs go high in turn at the end of each successive minute to light the relevant LED indicator. When a count of 10 is reached, the divide-by-10 output (pin 12) goes high and clocks divide-by-2 stage IC2b. IC2b 's Q-bar output thus switches high and drives LED 10 (the 10-minute indicator) via a 3.3kQ current limiting resistor. Because it is now latched by IC2b, LED 10 now remains on while IC4 cycles through the next nine counts, with LEDs 1-9 again switching on in turn at the end of each minute. After 19 minutes, both LED 9 & LED 10 will be on and this is the longest practical time for the Telephone Call Timer. After 20 minutes, IC2b is clocked again and LED 10 turns off. To ensure that the circuit is correctly reset at switch-on, IC2b 's Set input is momentarily pulled high by an RC timing network. This initially sets IC2b's Q-bar output low and thus ensures that LED 10 is off. Counters IC3 & IC4 are reset at switch-on by similar RC timing networks connected to their Reset inputs (pin 15). Power for the circuit is derived from a 9V battery via on/off switch S1 and is decoupled using a lO0µF capacitor. Alternatively, you can delete the battery and use a DC plugpack supply. Construction All of the parts , including the miniature foudspeaker, are mounted on a small PC board, codeSC12104921 (110 x82mm). Before starting construction, check the PC board carefully for any shorts or breaks in the copper tracks. If you find any, use an artwork knife or a dash of solder as appropriate to repair the problem. PARTS LIST 1 PC board, code SC12104921, 110 x 82mm 1 plastic utility case, 150 x 90 x 50mm 1 adhesive front-panel label 1 miniature toggle switch (S1 ) 1 battery clip 1 9V battery 4 10mm-long plastic standoffs 1 25mm-dia. miniature 8-ohm loudspeaker 1 2MQ horizontal-mount trimpot (VR1) The miniature loudspeaker is mounted directly on the PC board using short lengths of tinned copper wire. Power comes from a 9V battery but there's no reason why you couldn't use a DC plugpack supply instead. When you sure that the board is OK, check that the horizontal trimpot (VRl) fits snugly into its mounting holes. If the holes are too small, enlarge them slightly so that the trimpot does fit. Fig.3 shows how the parts are mounted on the PC board. You can begin construction by installing the wire links. Make sure that they are all nice and straight so they don't end up shorting each other out. You can CAPACITOR CODES Value IEC Code EIA Code 0.33µF 0.1µF 0.015µF 330n 100n 15n 334 104 153 straighten the link wire if necessary by first clamping one end in a vyce and then pulling on the other end with a pair of pliers. Once all the links are in, you can install the resistors and trimpot VRl. Table 1 shows the resistor colour codes. It's also a good idea to check each value with your multimeter as it is installed, just to make sure. The polyester capacitors can be installed next, followed by the two electrolytics. Bend the leads of the electrolytics at right angles to their bodies so that they lie flat against the board and check their polarity carefully before soldering them into position. The diodes, transistors and ICs can now all be installed. Make sure that you don't mix up the two transistors since one is an NPN device and the · other is a PNP (see Fig.2 for pinouts). Semiconductors 1 7555 CMOS timer (IC1) 1 4013 dual-D flipflop (IC2) 2 4017 decade counters (IC3,IC4) 1 4011 quad NANO gate (IC5) 1 BC337 NPN transistor (01) 1 BC327 PNP transistor 4 1N914 diodes (D1-D4) 10 red LEDs (LED 1-10) Capacitors 1 100µF 16VW PC electrolytic 1 10µF 16VW PC electrolytic 1 0.33µF MKT polyester 4 0.1 µF MKT polyester 1 .015µF MKT polyester Resistors (0.25W 1 4.7MQ (5%) 1 3.3MQ (5%) 4 100kQ 1 47kQ or 0.5W, 1%) 1 33kQ 4 10kQ 10 3.3kQ Miscellaneous Hook-up wire, foam rubber to secure battery, machine screws and nuts, tinned copper wire (for links). Note: 0.25W 5% resistors can be used in this project. TABLE 1: RESISTOR COLOUR CODES 0 0 0 0 0 0 0 0 No. 4 1 4 10 Value 4-Band Code (1%) 5-Band Code (1%) 4.7MQ 5% 3.3MQ 5% 100kQ 47kQ 33kQ 10kQ 3.3kQ yellow violet green gold orange orange green gold brown black yellow brown yellow violet orange brown orange orange orange brown brown black orange brown orange orange red brown yellow violet black yellow brown orange orange black yellow brown brown black black orange brown yellow violet black red brown orange orange black red brown brown black black red brown orange orange black brown brown MABCH 1992 65 the sound escape from the loudspeaker. Begin by attaching the adhesive label to the front panel (ie, to the case lid), then (working from the front) drill 3mm holes for the loudspeaker and at the P.C-board mounting points. The holes for the LEDs are best made by first drilling small pilot holes and then slowly reaming them out until the LEDs are a snug fit. This done, mount the LEDs with their cathode leads adjacent to the edge of the PC board, then secure the board to the front panel using screws, nuts and spacers. Fig.2 shows how to identify the LED leads. The cathode lead is the shorter of the two . The LEDs can now be gently pushed through the front panel holes and checked for correct orientation before finally being soldered. Don't worry if the LEDs don't perfectly line up with the hole positions. Just bend their leads slightly so that they go in. The PC board can now be removed from the front panel so that the supply wiring can be installed. The battery clip negative lead goes directly to the PC board, while the positive lead goes to one of the outer switch terminals. A short length of hook-up wire is then used to connect the switch centre terminal (wiper) to the positive supply terminal on the board. ..-< (\J °' 'Sj- C) ..-< (\J ..-< 0 ~_! _Qj ...._l_~_~_?_!_).~_ Fig.4: this is the full-size etching pattern for the PC board. Check your board against this pattern for defects before mounting any of the parts. Pin 1 of each IC is identified by the adjacent notch at one end of the plastic body. The loudspeaker used in the prototype is a miniature 25mm type (available from Jaycar Electronics), although other speakers could also no doubt be used. The best way to install it is to first solder a couple of link wires to its terminals and then solder the other ends of these links directly to the board (see photos). Installing the LEDs Before you install the LEDs, you need to drill all the necessary holes in the front panel. In addition to the mounting holes for the 10 LEDs, there are four mounting holes for the PC board plus a number of holes to let TELEPHONE CALL TIMER + 4 warning tones will sound 10 seconds before end of each minute + + + MINUTES 12 3 4 5 + + + + .10 + 67 8 9 • ••••••• •• Fig.5: this full-size artwork can be used as a drilling template for the front panel. The holes for the 10 LEDs are best made by first drilling small pilot holes and then slowly reaming them out until the LEDs are a snug fit. 66 SILICON C HIP You can now afford a satellite TV system For many years you have probably looked at satellite TV systems and thought "one day". You can now purchase the following K-band system for on ly: $995.00 Here's what you get: * A 1.8-metre prime focus dish antenna,. complete with al l the mounting hardware. * One super low-noise LNB (1.4d8 or better) . *magnetic One Ku -band feedhorn and a signal polariser. * metres of low-loss coaxial cable with a single pair control line. *receiver lnfrared remote control satellite with selectable IF audio 30 & bandwidth, polarity & digital readout. The PC board is mounted on the lid of the case & secured on 10mm spacers using screws, nuts & lockwashers. Note the circular pattern of holes drilled in the lid to allow the sound from the loudspeaker to escape. The on/off switch can be mounted on the front panel or on the side of the case, depending on your personal preference. Testing To test the unit, connect the 9V battery and wire your multimeter in series with the positive supply lead (you can do this simply by connecting the multimeter across the open switch terminals). Check that the current consumption is about 2-3mA when no LEDs are lit. If it is much more than this, switch off immediately and check for incorrect parts placement and orientation. If the current consumption is in the ballpark, switch the project off by disconnecting the multimeter. You should hear a low level squeak from the speaker about two seconds later. At this stage, you're ready to adjust the timing oscillator. To do this, start the timer and check the time taken for LED 1 to come on. Adjust VRl as necessary so that LED 1 comes on after exactly one minute, then remount the PC board and secure the lid to the case. Your receiver is pre-programmed to the popular AUSSAT transponders via the interna l EEPROM memory. This unit is also suitable for C-band applications. You're now ready to start timing those long-distance phone calls. Troubleshooting Call, fax or write to: If it doesn't work, you can quickly track down the faulty stage using your multimeter. The first step is to check that the +9V rail is present on the supply pins of the five !Cs. If this is OK, use your multimeter to check that pin 3 of !Cl successively switches high at 3-second intervals. Similarly, pin 13 ofIC2a should switch high at 6-second intervals, pin 12 of IC3 at 60-second intervals, and pin 12 of IC4 at 600-second intervals. If any of the LEDs fails to light while the others work OK, it is probably connected the wrong way around. Finally, if the LEDs all work OK but you don't get any sound from the loudspeaker, check diodes Dl-D4, IC5 and Ql & Q2. The cathodes of D3 & D4 should go high for the last 12 seconds of each minute, during which the anodes of Dl & D2 should switch high and low four times. If you strike problems here, the most likely cause is an incorrectly oriented ilia&. ~ AV-COMM PTY LTD PO BOX 386, NORTHBRIDGE NSW 2063. Phone (02) 949 7417 Fax (02) 949 7095 All items are available separately. Ask about our C-band LNBs, NTSCto-PAL converters, video time date generators, FM 2 & EPAL & Pay TV hardware. I I II ----------Name .. .. .......................................... I I II I Address ....................... ................... I I ........................... P/code ................ II Phone..................... ....................... . I I I II I I ., YES GARRY, please send me more information on K-band satellite systems. ___________ ,. ACN 002 174 478 01/92 MARCH 1992 67