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Songbird By Andrew Woodfield Here’s a decades-old design brought up to date in a new package and made to appeal to beginners as well as experienced builders. It’s quick and easy to build and a great project if you’re new to electronics. W hen the festive season or birthdays approach, those interested in electronics often look for a small, easy-to-build project to give as a gift. Something with flashing lights or a variety of sounds has universal appeal, especially for our (grand)children. Helping a beginner to build one of these is the perfect way to spark an interest in the hobby. The problem is identifying a suitable design. During a recent search, I came across an ‘electronic canary’ designed by Ron de Jong, published in Electronics Australia way back in May 1981. Unfortunately, the 74C-series CMOS chip used in the original design is not as widely available as 74HC-series devices. Also, the original design used a large square PCB mounted in a very large plain rectangular plastic box with a mostly bare aluminium front panel. I felt it lacked the visual appeal to capture the imagination of today’s younger audience. This revision was my solution. Along with migrating the circuit to the 74HC-series CMOS logic family, I also redesigned the printed circuit board (PCB) into a more compact and attractive bird shape – something between an overfed festive budgie and a kookaburra! Modern PCB manufacturing provides a choice of PCB solder mask colours. I chose purple, but you could also go with something like green, yellow or red (after all, it was initially a ‘canary’). Contrasting with the colourcoded bands of the resistors on the PCB, the overall effect is bright and cheerful. The double-sided PCB design The ‘inspiration’ for the Songbird project came from the May 1981 edition of Electronics Australia. The image shown is the lead photo used for that article. Practical Electronics | May | 2024 also makes it much easier to build than the original design. I removed the original large and costly 8W speaker and its driver transistor in favour of a modern, inexpensive piezo speaker. Mounted on the rear of the PCB, it produces a bright sound without driving parents to utter despair. The original used a somewhat expensive 9V battery, while a pair of inexpensive AAA cells power my new version. The new 3V supply also significantly reduces the current draw to under 2mA. What makes it sing? The Songbird consists of two almost identical sets of three coupled oscillators, ie, circuits that produce a continually changing voltage level. Each oscillator uses one of the six CMOS schmitt-trigger inverters inside the 74HC14 integrated circuit (IC). Fig.1 shows the basic oscillator circuit used in each case. The inverter (triangle) produces a low output voltage when its input voltage is high and vice versa. Connected to it are a resistor, ‘R’, and a capacitor, ‘C’. The values of C and R vary in each oscillator. When power is switched on, capacitor C is discharged, and the inverter input is at ‘ground’ potential (0V, or logic ‘low’ level). As a result, the 33 Fig.1 (above): the Songbird circuit uses six oscillators, all based on this simple RC (resistor-capacitor) oscillator configuration. Fig.2 (right): these three waveforms are created by each set of three schmitt-trigger inverter-based oscillators. output of the inverter is near +3V (a logic ‘high’ level). The voltage across capacitor C begins to rise as current from the high level at the inverter output flows via resistor R. When the voltage across C rises above the schmitt-trigger low-to-high transition voltage (about 1.5V in this case), the inverter input recognises that the input has gone from a logic ‘low’ to a logic ‘high’. It immediately changes the inverter’s output to a logic ‘low’ voltage, almost at ‘ground’ potential or 0V. The voltage across capacitor C starts to fall as current flows from the capacitor back to the low-level output via resistor R. When the input voltage falls below the schmitt-trigger high-to-low transition voltage (about 0.7V), the inverter input voltage is detected as a low, and output suddenly switches to high. The whole cycle then repeats. Over many such cycles, the result is a sawtooth voltage at the input pin varying from 0.7 to 1.5V, and a square wave at the output ranging from almost 0 to 3V. The frequencies of these waveforms are identical and proportional to the product of the values of resistor R and capacitor C (the ‘time constant’). The basic bird sound is made from two pairs of three of these oscillators coupled together. In each tri-­oscillator group, one sets the basic timing, the second creates the chirp, while the third makes the tone of the bird sound. Other components around each oscillator modify and combine these three to produce the final sound. The resulting waveforms are shown in Fig.2. At the top of Fig.2 is shown the timing oscillator, in the middle is the chirp oscillator and at the bottom is the note oscillator. 34 The full Songbird circuit is shown in Fig.3. In each oscillator, a series diode/ resistor combination placed in parallel with resistor R results in an asymmetric square-wave shape by changing the resistance depending on whether the capacitor is being charged or discharged. Different capacitor and resistor values in each set of three timing-­ chirp-note oscillators produce two slightly different bird sounds. These signals are combined by using each output to drive one side of the relatively high-impedance piezo speaker, which produces the final desired bird sounds. The circuit is powered by a battery, shown at upper-right in Fig.3, comprising two 1.5V cells in series to produce 3V. It is connected to the circuit via switch S1, which acts as a power on/ off switch. A 100μF capacitor stabilises the battery voltage so that it does not vary in the short term as the oscillators draw varying currents. Building the Songbird Remember that this is designed to be an ideal beginners’ project, so the following description is primarily written for those with limited experience. Children from around nine or ten years of age can build it (with help). However, it’s equally suitable for those interested in building a little project that is just a bit different. Simply put, you can never be too old to build the Songbird! The basic version of the Songbird uses a simple unetched PCB as the base. If using the battery box with an integral switch, the base will need to be slightly wider (63mm) as the box is longer than the holder shown here. Still, it does save you from having to mount and wire up the switch. Practical Electronics | May | 2024 Silicon Songbird Fig.3: the full circuit of the Songbird replicates the oscillator configuration shown in Fig.1 six times. This is convenient as IC1 contains six inverters, so only one chip is needed. Each triplet of oscillators uses a different set of feedback components to produce different frequencies. They are ganged up via resistors and capacitors, ultimately feeding the piezo speaker together via connector CON2. Children and beginners will need help from a more experienced builder, given the inherent risks of a hot soldering iron and other possibly dangerous tools like side-­cutters. The instructions assume it will be built in four stages, each taking between 20 and 45 minutes. You might prefer to make it in several shorter 10-to-15-minute bursts to better match a younger child’s concentration. For the more experienced, you can probably build the whole thing in about 1½ to 2 hours. Still, there’s no rush. The Songbird will happily wait to burst into song until you’re finished. You will likely make fewer mistakes if you take your time. Check each part before soldering and enjoy the relaxed pace of the construction process. 5 A soldering iron holder – it helps you to avoid accidental contact with the iron’s hot tip! A good soldering station will come with one. 6 A ‘solder sucker’ desoldering tool and/or solder wicking braid – these help you to remove solder if you get it in the wrong place or incorrectly place a part and need to remove it (that can happen to anyone). 7 A multimeter – you might find this helpful for checking resistor values, checking battery voltages and testing for shorts and open circuits. They start under £5 (eg, Jaycar Cat QM1500, Altronics Cat Q1053B)! Some tools you’ll need include: 1 A 15-25W soldering iron with a fine to medium tip. Keep this clean by carefully wiping the tip periodically on a damp rag or sponge. 2 0.5-1.0mm fine rosin-cored solder. If this is your only project, a 15g ‘hobby tube’ will be enough 3 Sharp pair of small side cutters. Find a clear space to build the Songbird, such as a kitchen table, with plenty of light. Also, ensure you have good ventilation because soldering will create some fumes. Place a cloth or a layer of newspaper (or similar flat disposable material) over your working area to avoid marking the tabletop with your tools, the PCB or molten solder during assembly. A helpful way to handle the parts during construction is to place them in a small plastic tray, say 300mm × 200mm, on one side of your workspace. Other useful tools include: 4 Fine needle-nosed pliers or a component bending jig (Jaycar Cat TH1810 or Altronics Cat T1495); these bend the component leads. Construction step #1 (resistors) The location for each resistor is shown in Fig.4. It’s usually easiest to install the resistors in groups. Double-­ c heck the value of each Practical Electronics | May | 2024 resistor using its coloured bands before fitting (or even better, verify the value with a DMM set to measure ohms) because different resistors have very similar bands (eg, 1kW, 10kW and 100kW). Your parts supplier may only have (smaller) 1/8W resistors or (more precise) 1% tolerance resistors, which will work just as well. 1% resistors have five bands rather than four. See the table in the parts list, which shows how they vary. You will need to bend the leads of the resistors into a U-shape so you can insert them into the pads on the PCB, as shown in Fig.5(a). You can do this with your fingers or pliers, but it’s more precise to use a lead-bending jig (available at low cost from stores like Jaycar and Altronics), as it will form the bends precisely the right distance apart. Then, insert the resistor as shown in Fig.5(b). Solder the leads, making sure to form a shiny fillet like in Fig.5(c), then trim the excess leads using side-cutters at the height indicated by the dashed line. Protect your eyes when doing this, as the cut leads can be sharp and will fly off if you don’t hold them while cutting. Note that there are two ways to insert each resistor but the circuit will work either way. Still, it’s neater to place them all in the same orientations, as in Fig.4. 35 Fig.4: this shows the shape of the Songbird PCB and where each resistor is soldered. The colour bands are shown for four-band (5%) resistors; see the parts list for the equivalent five-band codes. It’s still a good idea to check them all using a DMM set to measure ohms, as some colours can be easily confused (eg, red and orange). Construction step #2 (diodes and capacitors) Next, fit the six diodes as shown in Fig.6. These are all the same type, but your diodes may have a slightly different body colour to those shown here. Their size is exaggerated for clarity in Fig.6; the important thing is that, in each case, the black stripe on the end of the glass body must face down or to the right as shown. Bend each diode’s leads as you did for the resistor. When you insert it, make sure to align the diode’s black band with the band printed on the PCB overlay. Solder and trim the leads in the same way as for the resistors. Next, fit the four ceramic capacitors, shown in yellow in Fig.6. Two have the same value. Take care to place the correct part in the right location, although they are non-polarised, so it doesn’t matter in which of the two possible orientations you fit them. The PCB silkscreen overlay shows the value of each capacitor to help you. Ceramic disc capacitors may be marked in various ways. The most common markings are shown in Fig.6. After fitting each component, solder and trim the leads similarly to before. Next, fit the three smaller axial electrolytic capacitors, which are mounted on the top side of the PCB. They come in metal cans with a plastic covering except at the top. Electrolytic Fig.5: each resistor should be (a) bent to shape, (b) placed down on the PCB, soldered, and then trimmed with side cutters (dotted line height) to produce the result at (c). 36 capacitors are polarised, meaning you must orient them correctly. The negative lead is marked by a stripe on the capacitor body, while the overlay diagram indicates where the longer positive lead is inserted. Once they are in the right places and have the correct orientations, solder each capacitor and trim the leads. The two larger electrolytic capacitors go on the rear side, allowing the Songbird’s eye to be more clearly seen. Mount them last. Construction step #3 (the integrated circuit) You must fit the 74HC14 CMOS IC to match the pattern shown on the white PCB overlay. One end of the IC is marked by a notch in its body (some ICs have a divot or dot in the nearby corner instead). This end goes closest to the Songbird’s eye, as shown in Fig.8. Before trying to fit the IC, it’s helpful to slightly bend each row of IC pins until they are close to parallel. Gently roll each side of the IC towards the ends of the pins on a hard flat surface, as shown in Fig.7, so that the IC pins lie parallel (or close to it). You can also buy a tool to do this (again, check Jaycar and Altronics), which is easier to use, but the flat surface method does work well provided you are careful. Fig.6: this diagram will help you to fit the diodes and the capacitors on the Songbird’s PCB. The ceramic capacitors are not polarised and can go in either way around. However, the electrolytic capacitors must have their longer leads inserted in the pads marked with a + (the stripe on the can indicates the opposite, negative lead). Similarly, the diodes must be fitted with the cathode stripes facing as shown. Practical Electronics | May | 2024 Parts List – Songbird The ‘basic’ version of the Songbird. The main PCB is soldered along its base to a single-sided unetched PCB. The battery holder and slide switch are also mounted to the unetched PCB. Now fit the IC into the PCB as illustrated in Fig.8 and solder all the pins. You don’t need to trim the pins after soldering, as they should only just project through the other side of the PCB. Construction step #4 (speaker and battery) There are two ways to complete the Songbird. You can use a simple square PCB for the base. This version is quick and easy to build. Alternatively, you can create a more elaborate birdcage and base. That will take more time, but it gives a more attractive finish to the project. Option 1 – simple PCB base The photo at upper left shows the basic version with the PCB mounted to a single-­sided, unetched 52 × 45mm PCB base by soldering a few spots Fig.7 (above): bend the IC pins carefully to be approximately parallel before inserting them into the PCB. It’s better to use a lead straightening tool, but easy enough to do it with a flat surface as long as you don’t apply more force than needed. Fig.8 (right): the 74HC14 hex inverter IC must be fitted with its notch (pin 1 marking) matching the pattern printed on the PCB, as shown here. Practical Electronics | May | 2024 1 double-sided purple, green, yellow or red PCB coded 08103231, 61 × 75mm 1 2×AAA switched battery box with flying leads (BAT1+S1) OR 1 2×AAA battery holder and toggle or slide switch (BAT1/S1) 1 27mm diameter piezo loudspeaker (SPK1) 1 52 × 45mm (63 × 45mm if using battery box) unetched copper-clad PCB (optional; stand for basic version) Resistor Colour Codes Semiconductors 1 74HC14 hex schmitt-trigger inverter, DIP-14 (IC1) 6 1N4148 75V 200mA diodes, DO-35 (D1-D6) Capacitors 1 220μF 16V radial electrolytic 2 100μF 16V radial electrolytic 2 10μF 16V radial electrolytic 2 1nF 50V ceramic 1 680pF 50V ceramic 1 470pF 50V ceramic Resistors (all 1/4W axial, 5% or better) 2 1MW 2 680kW 1 470kW 3 330kW 2 100kW 2 68kW 2 47kW 2 39kW 2 10kW 2 1kW along the lower edge of the Songbird PCB. The result is surprisingly robust. The double AAA-cell battery holder and slide switch are then mounted directly to this blank PCB, the former with a couple of drops of epoxy glue and the latter by soldering three of the unused lower tags of the slide switch to the blank PCB base. Note that kits will include a battery box with an integral switch, simplifying construction somewhat. The kit will also have a double-sided tape pad that you can use to stick that box to the base very easily and quickly. Since the battery box is a bit longer than a simple battery holder, it would be best to use a 63 × 45mm unetched PCB for the stand in this case (not included in the kit). Alternatively, you could use hot melt glue or silicone sealant to attach the Songbird PCB to the side of the battery box. Just make sure you can still open it to replace the cells! The piezo speaker can be mounted on the rear of the main PCB using a 3D-printed speaker mount (see Fig.9) and a couple of dabs of hot glue. You could print this yourself if you have a 3D printer – STL files for all the 3D-printed items used in this project are available from the May 2024 page of the PE website: https://bit.ly/pe-downloads The two piezo speaker wires may be connected either way around to the PCB at the two points marked ‘Piezo’ on the overlay, as shown in Fig.10. You can trim the wires slightly if they are too long before soldering them in place. These wires may be almost any colour, and some can be pretty delicate, so a little care is required. Finally, add the battery and switch wiring; the switch is not required for the battery box included in the kit, as it is already integrated into the box. In that case, you just need to connect the two wires from the box to the PCB but watch the polarity; the red wire must go to the terminal marked + on the PCB. Option 2 – bird cage I designed a 3D-printed base for the prototype. Those with a lathe may prefer to create a more elegant base from suitable timber. Alternately, a careful hunt around the supermarket shelves may locate a suitable 15mm-tall, 70mm diameter screw-on plastic jar lid. The battery holder and switch can then be mounted in this base. I used a toggle switch for this, rather than a slide switch, because it’s easier 37 The 3D-printed piezo speaker mount The piezo speaker recommended is a low-cost 27mm diameter part commonly used in greeting cards and small toys. They are readily available from a variety of suppliers. Slightly more expensive piezo speakers are made complete with a thin pressed metal enclosure to form a resonating chamber, but they are harder to mount to the Songbird. The 3D-printed holder used here has three benefits. It simplifies mounting (just use glue!), the sound is significantly improved, and it’s all quite cheap and easy to do. It’s surprising the difference this simple piezo mount makes to the overall sound volume. The piezo sits on the circular lip of the mount facing outwards. A tiny drop of super glue holds the piezo to the mount. It’s also possible to make a 5-10mm-high 27mm -diameter tube speaker mount using rolled-up paper. Produce a wall thickness of about 1mm, gluing the paper with PVA or similar glue to give it a little rigidity. Glue the circumference of the piezo speaker to the top surface of this tube with a drop of super glue, then hot glue the assembly into place on the rear of the PCB. Fig.9: this simple 3D-printed speaker mount improves the sound quality and simplifies construction. to mount on a curved surface. The Songbird is then mounted on the base using two small PCB off-cuts measuring about 3 × 6mm. These are soldered on the lower edge on the rear of the main PCB, separated by a gap of about 10mm. This method allows the Songbird to be mounted into the slot in the base and then adjusted from side-to-side in the slot to centre the Songbird in its cage. The gap in the slot is used for the wiring to the switch and battery. The wiring details inside the base are shown in Fig.11. The piezo speaker is mounted in the same way as the basic version (Option 1). The battery and speaker wiring to the PCB is the same as shown in Fig.10. If you prefer that the speaker is out of sight, there is enough space in the base for it to be glued there using the 3D-printed speaker holder. However, the bird sounds will be less audible. The birdcage is made from 18-gauge (1.2mm diameter) galvanised wire and a 20mm diameter piece of tinplate. You can obtain the galvanised wire from most garden centres or hardware stores. I cut the circular piece of tinplate from a discarded tin can. It’s easiest to begin by unrolling about a metre of wire from the wire roll. Get this as straight as possible by holding one end of the wire in a vise and pulling on the other end with a pair of heavy-duty pliers. Modest force is sufficient. Then cut eight 105mm lengths from this straight piece. Fig.11: if building the birdcage version, glue the battery holder into the base before installing the switch and completing the wiring. 38 The ‘bird cage’ version of the Songbird uses a 3D-printed base and some wires to act as a ‘cage’. The speaker is attached to the rear of the PCB using the mount from Fig.9. Fig.10: the battery and piezo speaker wiring are shown here. This diagram also shows the overlay markings for these connections to help you identify them. If your battery holder has an integral switch, you don’t need the external switch; just run the red wire from the battery holder straight to the pad marked + on the PCB, parallel to the negative (black) wire. Practical Electronics | May | 2024 Adding signs You can add the optional ‘Please Do Not Feed The Bird’ sign. This, and the equally optional extra sign for the other side, can be glued to the front and back of a piece of card or onto a 3D-printed frame (the latter is also available as a download). This can be glued to a suitable location on the Songbird’s cage. Operation Turn on the Songbird’s switch and the Songbird will burst into song almost instantly. The prototypes I made were joined by several additional copies as budding builders added their own efforts. The chorus of the Songbird birds produced a fantastic sound. Parents will be ‘delighted’ to learn that battery life is at least six months of regular use! If you want to adjust the Songbird’s sound, changing the value of the 330kW and 470kW resistors in series with the 1nF capacitors will have the most significant impact. Fig.12: the optional signs for the birdcage version of the Songbird. You can download the sign artwork and 3D printer (STL) files from the PE website. Reproduced by arrangement with SILICON CHIP magazine 2024. www.siliconchip.com.au BACK ISSUES Practical Electronics All of our stock is RoHS compliant and CE approved. Visit our well stocked shop for all of your requirements or order on-line. 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ESR Electronic Components Ltd Fig.13: The 3D-printed sign frame (28 × 18mm) for holding the Fig.12 signs. – N NEW E EW PE D NA – ES M IG E N ! Using a piece of waste timber or plywood, place these wires radially around the circular tinplate as evenly as possible. Tape them in place temporarily using short pieces of painter’s masking tape. Once everything is nicely aligned – the tape really helps with this – solder the wires to the circular tinplate. The timber insulates the soldered wire and plate and protects your work surface. Bend each wire into the final birdcage shape by hand. The wire is very easy to bend yet holds its shape well. You can then ease the ends into the eight holes in the base of the 3D-printed base or your timber base. To ensure a good fit, you may need to drill out each of the eight holes in the 3D-printed base. This depends on the accuracy of the 3D printer. These 1.2mm diameter holes are evenly spaced on a 65mm diameter circle centred on the 70mm diameter base for those making up their own base from other materials. Add a small drop of epoxy or hot glue inside the base to hold each of the wires in place. It all sounds complicated, but in practice, it takes surprisingly little time and effort and gives a pleasing visual finish to the project. <at>practicalelec Superb PE PIC Development Board Transformers and LTspice Audio Out Make it with Micromite Accessing Internet data with your MKC Superb microphone preamplifier Touchscreen Wide-range RCL Box WIN! Microchip PIC24F LCD and USB Curiosity Development Board Programmable Thermal Regulator WIN! Microchip MCP19114 Flyback Standalone Evaluation Board Apr 2021 £4.99 04 9 772632 573016 practicalelectronics PLUS! Techno Talk – No blame, no shame? 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We stock magazines back to 2006, except for the following: 2006 Jan, Feb, Mar, Apr, May, Jul 2007 Jun, Jul, Aug 2008 Aug, Nov, Dec 2009 Jan, Mar, Apr 2010 May, Jun, Jul, Aug, Oct, Nov 2011 Jan 2014 Jan 2018 Jan, Nov, Dec 2019 Jan, Feb, Apr, May, Jun Issues from Jan 1999 are available on CD-ROM / DVD-ROM If we do not have a a paper version of a particular issue, then a PDF can be supplied – your email address must be included on your order. Please make sure all components are still available before commencing any project from a back-dated issue. 39