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Ever missed an important call because you and your mobile were separated? Here’s the SILICON CHIP solution! Mobile Phone LOUD RINGER! by John Clarke You know the scene: you’re working outside and the mobile is inside. Or maybe you’ve left it in the work ute while you’re at a job. Either way, you pick up the phone and all you see is “missed calls”. Rats! S ure, they could have left a message (but many people don't like doing that). Either way, you now have to return the call (at your cost!) and the odds are it's someone trying to flog you something you don’t want, someone who wanted you to do a job but has gone elsewhere in the meantime, someone seeking a donation to a worthy cause, or even a wrong number. Whatever it is, it’s an inconvenience. And an expense. Wouldn’t it be nice if you could hear the phone ring ’cos it's now REALLY LOUD? Yes it would be! We can’t change the ring volume on your phone itself but we can help you out by adding a mobile phone ring “extender”. This simple device picks up the vibration of the mobile phone ringing (and pretty well all mobile phones have this feature so you can “feel” the phone ringing in a noisy environment) and uses that vibration to trigger a loud piezo siren that you can position wherever you like. The vibrating alert on a mobile phone typically produces a 150-180Hz “buzz”. It’s produced by a small electric motor 38  Silicon Chip running at around 10,000rpm that rotates an eccentric (or off balance) mass on its shaft. The Mobile Phone Ring Extender (let's call it the MPRE for short) is housed in a small case. The idea is that when you don’t want the phone in your pocket or even close by, you place it on top of the MPRE case. The MPRE then provides a (very!) loud phone ring alert that allows you to get to the phone and hopefully answer it before it stops ringing. How it works Fig.1 shows the general arrangement. A piezo transducer is the sensor that detects the vibration from the phone. The vibration from the phone is transferred to the case lid and that movement is further transferred to the piezo element via an actuator made from a short length of Nylon or polycarbonate M4 thread, cut from a screw. Signal from the piezo transducer is amplified and converted to a DC voltage. This DC voltage is monitored using a comparator that compares the voltage against a reference siliconchip.com.au AMPLIFIER COMPARATOR AC TO DC CONVERTER ACTUATOR (IC1a) INTEGRATOR (D5,VR2) (D3, D4) (IC2, VR3) (IC1b, VR1) PIEZO TRANSDUCER REFERENCE VOLTAGE  CASE LID Fig.1: the basic arrangement of our Mobile Phone Ring Extender. A piezo transducer is mechanically connected to the case lid which vibrates when the phone vibrates. This signal is rectified and if high enough, causes two oscillators to function – the output of these is fed via a small driver into a piezo siren. voltage. With no signal, the DC voltage is below the reference and the comparator output is low (near to the ground supply). With vibration detected, the DC voltage rises above the reference voltage and the comparator output goes high (towards the positive supply). The following circuitry forms a delay circuit whereby the high level is integrated over time. This integrator is included so that brief vibrations – such as the phone bouncing to footsteps – are not sufficiently long enough to be detected by the following Schmitt trigger (IC2c). Only longer periods of vibration that really do mean there’s an incoming call are detected. The integrator delay is adjustable with VR2 so that the time period can be set correctly; that is, not too short to detect the placing of the phone onto the MPRE case but not too long so as to signifi- SCHMITT TRIGGER & MODULATION OSCILLATOR VOLUME VR4 DETECT LED (LED2) DRIVER (Q1) PIEZO SIREN cantly delay the detection to an incoming call. The Schmitt trigger is a part of the modulation oscillator and starts oscillation with sufficient signal from the integrator. The detect LED driven from IC2b visually indicates the detection of an incoming call. IC2b in turn drives IC2d and IC2a respectively and allows the modulation oscillator to switch the tone on and off. Modulation rate is adjustable using VR3. Output drive from IC2a is adjustable with VR4 and the wiper voltage is buffered with voltage follower Q1 to drive the external piezo siren. Circuit Circuitry for the MPRE is mainly based on just two ICs, a dual op amp (IC1) and a quad Schmitt trigger NAND gate Here’s how it works: simply place your mobile phone on top of the Mobile Phone Ring Extender (with vibrate turned on). The unit detects the vibration from incoming calls and sounds the piezo siren at right. The siren shown is one of several options; more information is in the text. siliconchip.com.au February 2013  39 +8.8V IC1: LM358 PIEZO TRANSDUCER 5 SIG 7 IC1b 6 A VR1 500k 2 100nF D3 47k 8 3 K K GND 1M D4 100nF IC1a VR2 100k D5 1 A K 4 1M 10F 1M A 100nF AC TO DC CONVERTER AMPLIFIER 22k 36k +4.4V COMPARATOR INTEGRATOR +950mV 10k 10F +8.8V 8 IC2c 5 10 9 13 4 6 3.3k VR3 500k 1F A 10F IC2a IC2d IC2b MODULATION 11 2 12 DETECT  LED1 1 14 3 7 VOLUME 1k VR4 10k Q1 BC337 100nF C B 47 E IC2: 4093B – 330 K CON1 9V DC PLUGPACK INPUT + OUTPUT TO PIEZO CON2 BUZZER S1 A K D1 1N4004 +8.8V K A POWER D2 1N5819 CON1: 2.1mm DC POWER SOCKET CON2: 3.5mm PHONO SOCKET 9V BATTERY D3–D5: 1N4148 A SC 2013 MOBILE PHONE RING EXTENDER B 1N4004, 1N5819 A LED BC337 K K E C K A Fig.2: the circuit is based on two low-cost ICs, a dual op amp (IC1) and a quad Schmitt trigger NAND (IC2). It can be operated from either a 9V battery or, for longer term operation, a 9V DC plugpack. (IC2). Fig.2 shows the full circuit. IC1b is the piezo transducer amplifier. This is biased at 4.4V using a voltage divider comprising a 47kΩ, 36kΩ and 10kΩ resistor string connected across the 8.8V supply. Pin 5 is held at this 4.4V via the 1MΩ resistor that provides a high impedance loading for the piezo transducer. Amplifier gain is set by the 22kΩ resistor connecting to the 4.4V reference and VR1’s setting. Low frequency roll off is at 72Hz, due to the 100nF capacitor in series with the 22kΩ resistor. The amplifier mainly amplifies signal above 72Hz and does not amplify a DC signal. Gain is variable from 1-23.7, with VR1 set between zero ohms to 500kΩ respectively. Output from IC1b is rectified using diodes D3 and D4. The 100nF coupling capacitor at IC1b’s output only allows AC signal to pass and the signal is clamped at about 0.7V below 0V by diode D3. Positive signal passes through diode D4 and is filtered with a 100nF capacitor. The 1MΩ resistor discharges the capacitor over a 100ms period. IC1a is the comparator that monitors the filtered DC 40  Silicon Chip voltage at the non-inverting input (pin 3) and compares this against the 950mV reference voltage at the inverting input (pin 2). The 950mV is derived from the same voltage divider that produced the 4.4V, only from the lower tapping across the 10kΩ resistor. With the pin 3 input lower than 950mV, IC1a’s output is low, at near to 0V. When pin 3 voltage rises above 950mV, then IC1a’s output goes high, at close to the 8.8V supply. This high output from IC1a charges the 10µF capacitor via diode D5 and the resistance set by VR2. When IC1a’s output is low, the 10µF capacitor discharges via the 1MΩ resistor. When the 10μF capacitor is discharged, the pin 8 input to IC2c is low and the output at pin 10 remains high, because the NAND gate output will only go low when both the pin 8 and pin 9 inputs are high. The 1μF capacitor at the second input at pin 9 is charged to a high level via VR3. IC2b inverts this high to a low output at pin 4 and so IC2d’s output also remains with its output (pin 11) high. IC2a inverts this high so that its pin 3 output sits low and there is no drive to the piezo siren. siliconchip.com.au Here’s what it looks like fully assembled, with the end-on view above showing the minimal controls. We used a “remote control” case because it already has provision for an internal 9V battery (battery and output sockets are on the side of the case in purpose-cut holes). Upon detection of a vibration signal (and the IC1a output going high), the resulting high at pin 8 of IC2c’s input allows the modulation oscillator to run. IC2c’s output goes low and discharges the 1µF capacitor via VR3 whereupon IC2c’s output goes high again to recharge the 1µF capacitor via VR3. This cycle repeats. The input threshold for the NAND gate includes hyster- esis that is internally provided within IC2. Each time IC2c’s output is low, IC2b’s output is high and this also drives the detect LED via a 3.3kΩ resistor. The LED switches on and off at the modulation rate. IC2d buffers the modulation signal from IC2b while IC2a inverts the logic level again and applies the signal across the volume potentiometer (VR4). The output at the wiper drives the base of the emitter follower Q1. When the base voltage goes high, the emitter of Q1 supplies power to the piezo siren via CON2. A 330Ω resistor is included in series with the volume control (VR4) to reduce the “dead area” at the full anticlockwise pot travel where there is no volume. The wiper voltage for VR4 needs to go above about 0.6V for Q1 to switch on. The 330Ω resistor sets the wiper voltage at 268mV when IC2d’s output is high and the wiper is set fully anticlockwise. Without this resistor, the wiper voltage would be 0V and would require more clockwise travel before sound is heard from the siren. Power for the MPRE can be either from a 9V battery or a DC supply such as from a 9V plugpack. The 9V battery supply is via Schottky diode D2 providing reverse polarity connection protection for the circuitry with minimal voltage drop. Whenever power is connected via the DC socket, the battery is automatically disconnected. Both supplies are isolated from each other by the diodes. With the 0.2V drop across diode D2, the rail voltage with a fresh battery is very close to 8.8V, as shown on the circuit diagram. It is usually a little higher from a plugpack because even though branded “9V”, the output from these can be (and usually is) anywhere up to about 12V at low currents. Why detect the vibration ? Why have we gone to the trouble of detecting the vibration of the mobile phone? Why not simply detect the ring of the phone, say via a microphone, and use that to trigger the siren? The reason is pretty simple: there are so many ring tones, so many tunes and so many variations on a theme in mobile phones that it was difficult to create a “one size fits all” detector; one that would work with everything. And there was a second problem: how sensitive do you make it, so that it reliably triggers with a ring but doesn’t false trigger when the dog barks? Just about everyone has their vibration alert turned on all the time – even if the ringer itself is turned off (and that siliconchip.com.au was another problem!). So the vibration detector was the way to go – reliable, worked with all phones, etc. Believe it or not, we tried yet another method of detection based on RF. You know how the phone’s handshaking (beep beep, beepity beep beep) gets into everything? We thought this would be a great way to detect an incoming call even though mobile phone transmitter power varies significantly with distance to the cell tower. But again, we couldn’t make it reliable with all brands of phone – and it even had more problems detecting 3G calls than it did 2G. 4G? Don’t know – none of us has a 4G phone! So we figured detecting the vibration was the best option! February 2013  41 DETECT LED 330 A 100nF Mobile Phone Ring Extender 1k S1 K 3.3k VR4 10k 100nF PIEZO SIREN D3 D2 1N5819 D1 1N4004 4004 22k IC1 LM358 10k 4148 CON2 100nF 1M D3-D5: 1N4148 10F + – 100nF 36k D4 47 500k 1M 47k 100k B Q1 10F VR1 4148 C 2013 D5 4148 E 1F VR3 500k 10F VR2 IC2 4093 C BC337 1M GND SIG TO 9V BATTERY CLIP + – CON1 THREAD THROUGH HOLES FOR STRAIN RELIEF PIEZO TRANSDUCER MOUNTS ABOVE OTHER COMPONENTS ON PCB 9V DC PLUGPACK SUPPLY + – Fig.3 (above): the same-size PCB component overlay, with an early prototype photo alongside (some components have been changed since the photo was taken). While the electrolytic capacitors are shown above in traditional position, the photo at right shows that these are all “laid over” to give room for the case lid to fit. Also, the two links shown above will only be required if the PCB is single-sided. Inset at right is a close-up of the piezo transducer with a short length of 4mm nylon screw thread, used to provide a mechanical connection between the transducer and case lid. It simply relies on touching the lid; it is not glued in. “At rest” current consumption is about 6mA. Construction All components for the MPRE are mounted on a PCB coded 12110121 and measuring 63.5 x 86mm. The PCB and components are housed in a “remote control” case measuring 135 x 70 x 24mm. This case is used because it also houses the 9V battery. A panel label attaches to the front face of the case (or, depending on the kit source, may be supplied already printed). The PCB is designed to mount onto the integral mounting bushes within the box. Make sure the corner edges of the PCB are shaped to the correct outline so they fit into the box. They can be filed to shape if necessary using the PCB outline shape as a guide. It is rare to find faults with modern PCBs, but it’s worth checking the PCB 42  Silicon Chip for breaks or shorts between tracks or pads. Repair if necessary. Check the hole sizes for the PCB mounting holes – they should be 3mm in diameter. Assembly can now begin. Start by the inserting the resistors and use the resistor colour code table to help in reading the resistor values. A digital multimeter can also be used to measure each value – in fact, it’s a good idea because many colour bands on resistors look very similar. If you use a PCB purchased from the SILICON CHIP Partshop, it will be double-sided but other PCBs may be single sided and require two wire links (above and below IC2) to be soldered in. The diodes can now be installed and being polarised, must be mounted with the orientation as shown. IC1 should be mounted directly on the PCB since there is insufficient room (height wise) for a socket once the piezo transducer is installed. IC2 can be mounted on a socket if desired. When installing the ICs, take care to orient them correctly with the notch (or circle marking pin 1) as shown on the overlay. Capacitors can be mounted next. The electrolytic types must be oriented with the shown polarity and far enough above the board (~6mm or so) so that they can be bent over to lie parallel, or near-parallel, to the surface. Otherwise you will not be able to put the lid on. This simply means you need to have sufficient capacitor lead length to allow each part to bend over. Trimpots VR1-VR3 can be mounted next. They’re not all the same – VR2 is 100kΩ (code 104) while the others are 500kΩ (code 504). Transistor Q1 is next to install. siliconchip.com.au CON1 (DC input socket) and CON2 (3.5mm output to siren) should be mounted right down on the PCB surface. Potentiometer (VR4) and the PCB mounted switch (S1) can also be fitted. LED1 and its series 3.3kΩ resistor can be regarded as optional if you don’t require a visual indication of detected ring (leaving them out will also save a little bit of power if running from a battery). If you do fit them, mount LED1 horizontally but at a height of 6mm above the PCB. Bend its leads at 90°, 7mm back from the LED body making sure the anode lead is to the left. Panel holes The side of the base of the case needs to be filed using a rat tailed file to allow connections to both CON 1 and CON2 through the side the case. Position the PCB in the base of the case with the PCB mounting holes aligned with the mounting pillars. Mark out the socket positions and file to shape. A similar shape is required on the lid and its position is found by placing the lid onto the base of the case (with the PCB removed) and filing out the lid half for a circular hole. Before securing the PCB in place, drill out the small front edge panel for the potentiometer, switch and LED (if used). A drill guide is available and is provided with the front panel label. This can be used as a guide as to the drill hole positions. Nuts for the potentiometer and 3.5mm socket are not required. The potentiometer shaft is fitted with a knob after the front edge panel is placed over the shaft, switch S1 and the LED. Wiring Follow the wiring diagram to make the connections from the piezo transducer to the PCB. The battery clip lead is inserted first from within the the battery compartment before being looped through the strain relief holes and attaching to the PCB. Make sure the polarity is correct with the red battery clip lead as the plus lead. Piezo transducer The piezo transducer is raised above the PCB using two 6.3mm tapped standoffs. M3 screws secure the standoffs from the bottom and the piezo is secured with two more M3 screws into the standoffs. Note that the mounting holes in the piezo transducer mounting lugs will need to be carefully enlarged with a 3mm (or 1/8”) drill bit. The wires are attached to the ‘Sig’ and ‘GND’ inputs on the PCB. An M4 Nylon screw, which provides the mechanical connection between the vibrating case lid and the piezo transducer, is cut so that you have a 4mm long length of thread. The head of the screw is not used. This length is inserted into the centre hole of the piezo transducer. The length of this screw thread is important. Too short and it will not make contact with the lid. Too long and the lid will not fit onto the case without excessive bowing. The PCB is secured to the base of the case using four M3 x 6mm screws that screw into the integral mounting bushes in the box. Label As mentioned earlier, some kitset suppliers are now pre-printing labels onto their cases, so you won’t have to do anything. But if yours is blank, or you’ve assembled your own bits, the panel label for this project can be downloaded from the SILICON CHIP website (www. siliconchip.com.au). When downloaded, you can print onto paper, Resistor Colour Codes No. o 3 o 1 o 1 o 1 o 1 o 1 o 1 o 1 o 1 Value 1MΩ 47kΩ 36kΩ 22kΩ 10kΩ 3.3kΩ 1kΩ 330Ω 47Ω siliconchip.com.au 4-Band Code (5%) brown black green gold yellow violet orange gold orange blue orange gold red red orange gold brown black orange gold orange orange red gold brown black red gold orange orange brown gold yellow violet black gold 5-Band Code (1%) brown black black yellow brown yellow violet black red brown orange blue black red brown red red black red brown brown black black red brown orange orange black brown brown brown black black brown brown orange orange black black brown yellow violet black gold brown Parts List – Mobile Phone Ring Extender 1 PCB coded 12110121, 63.5 x 86mm 1 panel label 113 x 50mm 1 remote control case 135 x 70 x 24mm (Jaycar HB5610) 1 piezo siren (Jaycar AB-3456, Altronics S-6127) 1 piezo transducer (Jaycar AB3440, Altronics S6140) 1 PCB mount SPDT switch (Altronics S1421 or equivalent) (S1) 1 PCB mount DC socket (Jaycar PS-0520, Altronics P0621A) (CON1) 1 3.5mm stereo PCB mount socket (Jaycar PS-0133, Altronics P0092) (CON2) 1 3.5mm mono plug [to connect siren] (Jaycar PP-0144, Altronics P-0028) 1 knob to suit VR4 1 9V battery, with clip 8 M3 x 5mm screws 2 6.3mm long M3 tapped nylon spacers 1 M4 polycarbonate or Nylon screw (cut for a 4mm thread section without the head) 4 PC stakes (optional at wiring points) Suitable length polarised figure-8 cable if siren is to be remotely mounted Semiconductors 1 LM358 dual op amp (IC1) 1 4093 CMOS quad Schmitt NAND gate (IC2) 1 1N4004 1A diode (D1) 1 1N5819 Schottky diode (D2) 3 1N4148 switching diodes (D3-D5) 1 BC337 NPN transistor (Q1) 1 3mm high intensity LED (LED1)* Capacitors 3 10µF 16V PC electrolytic 1 1µF 16V PC electrolytic 4 100nF MKT polyester (code: 104) Resistors (0.25W, 1%) 3 1MΩ 1 47kΩ 1 36kΩ 1 22kΩ 1 10kΩ 1 3.3kΩ* 1 1kΩ 1 330Ω 1 47Ω 1 100kΩ horizontal mount trimpot (code 104) (VR2) 2 500kΩ horizontal mount trimpots (code 504) (VR1,VR3) 1 10k log 9mm potentiometer (Jaycar RP-8610 or equivalent) (VR5) * optional (see text) February 2013  43 Volume Detect Power SILICON CHIP Output to Piezo Siren Figs. 4 & 5: front panel artwork for the Mobile Phone Ring Extender, and below right the template for drilling the end (top) panel holes. These images can also be downloaded from www.siliconchip.com. au it can be more easily heard – outside, for example. In this case, you’ll need to connect a suitable length of figure-8 polarised cable to the siren and in either case, you’ll need to solder on a 3.5mm mono plug so that it can plug into the MPRE. The siren is polarised – the red (+) wire goes to the centre pin on the 3.5mm plug. If you do decide to mount the siren outside, you will need to fit it so it’s protected from the elements – under an eave, for example. Within reason, there is no limit (say to a standard suburban house boundary) to the length of wire between the piezo siren and MPRE. - Mobile Phone Ring Extender Place phone on this top panel with “vibrate” turned on Pot 7mm . LED 3mm + Switch 5mm 9VDC Input End Panel Drill Guide Testing sticky-backed photo paper or onto plastic film. When using clear plastic film (overhead projector film) you can print the label as a mirror image so that the ink is behind the film when placed onto the panel. Once the ink is dry, cut the label to size. Glue the panel to the lid of the case with silicone sealant, contact adhesive or similar glue. Where you use the clear film, a contrasting silicone colour can be used such as white or grey to show up the printing on a black panel. Clear silicone can be used for non-white panels since the panel itself will provide the contrast against the printed label. Piezo siren The piezo siren is pretty loud – you might find it loud enough to mount close to the MPRE via the short length of cable it comes with. Or you might prefer to mount the siren elsewhere, where Another “siren”? 44  Silicon Chip Initially, don’t connect the siren – it will deafen you at close range! When you switch on, using a 9V battery, there should be around 8.8V between pins 4 & 8 of IC1 and between pins 7 and 14 of IC2. Pin 2 of IC1 should be about 950mV above 0V (the GND terminal). Pin 5 of IC1 should be about 4.4V above 0V. Note that these voltages might differ a little from these values depending on the supply voltage. With a plugpack supply they will almost certainly be higher but still should be in much the same ratio. Now set VR1, VR2 and VR3 to mid position and attach the piezo siren. You should be able to trigger the MPRE into operation by repetitively tapping the case. That should introduce sufficient vibration to be detected by the piezo transducer and you should hear the alert sound and see the detect LED flash. You can adjust VR3 and VR4 for the desired sound, with VR3 adjusting the rate of switching the tone on and off. Clockwise will increase the frequency. Final testing is done with a mobile telephone (set to vibrate). Place the phone on top of the MPRE and make a call to the phone using another phone. Again, the MPRE should begin flashing the detect LED and the siren should sound. If neither happens, adjust VR1 further clockwise for more sensitivity. VR2 should be adjusted so that the MPRE does not sound unless there is an incoming call. It should not detect a single tapping on the case with your finger nail. VR2’s adjustment is usually at mid-setting but may need to be set more anticlockwise to ensure that an incoming call is detected without too much delay or more clockwise to prevent detection of single tapping on SC the case. Two piezo sirens have been specified for this project but since building the prototype, we’ve come across a possible alternative – albeit not made for the purpose but nevertheless we believe would be quite suitable. By coincidence, Jaycar Electronics advertised a “Water Leakage Alarm” (Cat LA-5163) in the January issue of SILICON CHIP for just $9.95 – cheaper than either of the piezo sirens. We weren’t particu- larly interested in detecting water but we were interested in the alarm side. On opening the case, we found it very easy to connect to the two solder pads which trigger the alarm. The photo above shows the two pads to connect to (clip off or unsolder the existing water sensor wires). TRIGGER CONNECTIONS siliconchip.com.au