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damaged, or the roll button needs to be held for longer. Taking Projects Further Fig. 23. The completed projects – all three can form the basis of more advanced projects. be handy in checking the 555 capacitor voltages as well as the output of the 555 timer ICs, as shown in Fig.23. However, if you are nervous about damaging your kit and have access to a PSU, then you can use the current limiter to prevent the kit from damaging itself. Start by setting the current limiter to its lowest setting, connect the kit, and slowly increase the current level. If the PSU shows current consumption beyond 20mA, then it is possible that something may be wrong (MitchElectronics kits rarely consume more than 50mA). Troubleshooting These kits are deliberately simple, so there isn’t a lot that can go wrong with them. However, it is more than possible for something to break, whether it is due to incorrectly inserted parts, components being soldered for too long and being damaged by heat, or through static shock that can fry the sensitive electronics inside ICs. If the kits don’t show blinking LEDs when powered, then the first step to do is to check that the LEDs are inserted in the correct orientation, and that they are not damaged. Using the continuity setting on a multimeter, it is possible to probe an LED and power it up slightly to confirm that it is working. If the LEDs are correctly inserted and working, then it is likely that the ICs are damaged and/or not inserted correctly. Thus, the first step here is to check that the ICs are inserted correctly, taking extra care to see where pin 1 of the IC is (top left pin with the notch facing upwards). If the ICs are inserted correctly, then check the temperature of the IC when it’s in operation – an IC that feels very warm or even hot is likely damaged. Replacing the ICs in this case will resolve 99% of the problems, as the remainder of the components in these kits are passive (except for the transistors in the Electronic Dice kit). In the Traffic Light kit, the orientation of the external traffic light also matters, so make sure they are have been soldered with the correct orientation. If the Electronic Dice repeatedly falls on the same number, then either the 555 monostable is Besides the obvious uses for the kits mentioned in this article, there are a number of potential project ideas that you can do using them. The 4017 Light Chaser which could be integrated into a ‘wearable’ project – perhaps a Light Chaser tie, badge or broach. For those who are familiar with Kraftwerk, such a tie was featured in their music video The Robots, and this tie was so brilliant that, when it was introduced in the music video, the cameraman zoomed in on it! See: https:// youtu.be/D_8Pma1vHmw The Traffic Light is a great kit for those involved with model railways and dioramas, especially for those who reside in the UK. While not quite the correct scale for all models, it can easily be modified to work with pre-existing traffic light designs if the separate traffic light PCB is removed and wires connected to existing LEDs. Finally, the Electronic Dice is a good option for those who want to replace the mechanical dice found in popular board games. It is possible for two to be mounted in an enclosure with the first dice connected to the second via some extra wires so that the second dice continues to roll until the first one has finished (we won’t tell you how this could be done, that’s a challenge for you to figure out). Our dice only has six faces so it’s not ideal for games such as Dungeons and Dragons, which use a 20-sided dice. Remember, if you want to help support our work at MitchElectronics in designing kits for makers and engineers along with educational articles, blogs, and video content, then head over to the MitchElectronics store where you can get all kinds of kits, components, and resources that can help you with your next wonderful project. In the next article, we will look at a collection of related circuits that measure physical parameters, such as light, sound and temperature. Plus, we will introduce you to the most important class of analogue ICs – the operational amplifier, or ‘op amp’ for short. Partnership with PE MitchElectronics Ltd is an independent UK company. These articles are not ‘advertorials’, PE does not pay for the articles and MitchElectronics does not pay for their publication. Fig. 24. This month’s collection of kits available from: https://mitchelectronics.co.uk All the kits/parts described in the series are available from: https://mitchelectronics.co.uk 62 Practical Electronics | January | 2024 AOShop Small-signal PNP transistors NKT214F, OC57, OC59, 2N1377, 2N525 £1.00 5534H metal-cased op amp LM384, TDA2030A, TDA2050V TAA435 (Mullard power amp driver) Low-noise PNP transistors GET106 £2.50 Synthesiser ICs Ge semiconductors The home for specialist audio, analogue and historic components – provided by Jake Rothman, PE’s Audio Out columnist. The AOShop is your best bet for classic analogue ‘NOS’ (new old stock) components, including all parts for Audio Out projects and designs. £3.00 £1.50 £1.20 Small power NPN transistors AC176, AC176K, AC187K, AC141K £2.00 That/dbx 2180 VCA/VCF £6.00 CA3080 VCA/VCF (vocoder) £2.80 CA3280 VCA/VCF £4.00 LM13600/ LM13700 VCA/VCF £2.00 CA3086 transistor array £1.00 PT2399 echo/delay £1.50 High-voltage PNP transistors OC77, CV7001 £1.50 Dual transistors Small power PNP transistors AC153, AC153K, AC188, AC188K £1.50 TO3 PNP power transistors OC22, CV7054 (OC23), OC25, OC35, OC36, AD143, AD149, AD161, AD162 £2.00 AD140 £3.50 AD149, AD161/2 matched pair £5.00 RF PNP transistors OC41, OC42, 2SA12, 2SA53,AF124, AF178, GET872A £1.50 NPN transistors OC139, OC140, ASY73 £2.00 Diodes CV7049 (OA10), CG92 (OA91) £0.50 Si semiconductors Diodes ZC5800 RF Schottky £0.20 Low-noise silicon transistors BFW16A, 2SC3071, 2SC3068, 2SA1016K, 2SC2362K, 2SA970BL £1.50 2SC2204, 2SD655, BC550C £0.50 ZTX651 £0.30 ZTX751 £0.50 RF transistors (suitable for Theremin) BF199 £0.50 Audio power MOSFETs Exicon 10N20, 10P20 Hitachi 2SJ99, 2SK343 Hitachi 2SJ56, 2SK176 £6.50 £3.50 £8.50 JFETs BFW11, BFW10, TIS73L, J177, J113, U1994, U1898, 2SJ176, J201 £1.00 J175, J176, J112, J111, 2N3820, 2N5467, BF244, 2N5460, J230 £0.60 Small power output/driver transistors 2SB649A, D669A, 2SA1208, 2SC2910, MJE253G, MJE243G, 2SA1725, 2SC4511 £1.20 BD139,BD140, BD135, BD156, BD435, BD436, MPSA63, BCV46 £0.50 MOSFETs ZVP2106A Dual-gate 3SK45, BFS28 £0.30 £1.50 Metal-cased transistors BC143 2N1711 BCY71 BC109C £0.35 £0.50 £0.30 £0.60 Amplifiers LM318 high-speed op amp µA709 metal-cased op amp £0.35 £2.00 2N2639, 2N2223, 2N2910 (NPN) £4.00 E401 (JFET Moog) £4.00 2SK2145-Y dual JFET £0.80 2N5564 JFET £8.00 HN3C51F, HN3A51F £1.00 DMMT3904/6, HN1A01F, HN1C01F £0.50 Loudspeakers PE Mini-Monitor Volt PE165 6.5-inch woofer (each) £85 Morel MDT29 tweeter (each) £25 Kit pair of PE165/MDT29 plus Volt crossover parts and PCBs £299 Monacor DT-28N tweeter (each) £35 Vifa 19mm BC20SC15-04 tweeter (each) £15 Volt crossover inductors 1.2mH, 1.5mH, 2mH, 2.7mH, 0.5mH (tapped at 0.3mH) (each) £5.85 Fully assembled and tested high-quality speaker prototypes – ask for details LS3/5As and other similar speaker systems (pair) £200-£350 Fully tested reclaimed speakers Vifa BC14 5-inch woofer (each) £10 Vifa TC26 1-inch tweeter (each) £10 Low-price speakers Philips 4-inch 4070 £2.00 EMI 10x6-inch, 30Ω Alnico £7 64mm 64Ω neodymium £1.20 5x3-inch elliptical 50Ω or 80Ω Alnico £3.50 1.65x2.75-inch 8Ω £1.50 Capacitors Note ‘10/63’ denotes ‘10µF 63V’. Polyester 3.3/100, 4.7/250, 4.7/63 £1.00 5.6/63, 8.2/63, 10/63 £2.00 Mullard ‘Mustard’ C296 0.22/400 £2.00 Polycarbonate Axial 2.2/63 1%, 4.7/160, 6.8/63 £1.00 Radial 6.8/160V, 10/63 Reclaimed 22/63 £2.00 £2.00 Polystyrene Philips 1% 4.7nF/160, 6.2nF/500, 12nF/63, 22nF/63, 110nF/63, 24nF, 2nF £1.00 RIFA 1% 100nF/100, Suflex 90.9nF 0.5% £2.00 Suflex 2.5% 10nF/63 (rad. or ax.) £0.50 Practical Electronics | January | 2024 Radiation resistant Siemens cellulose acetate MKL 2.2/25 £0.80 Electrolytic – Mullard blue 017 series 10/25, 22/25, 100/10 £0.50 150/40, 470/40, 1000/40 £1.00 Tantalum – axial metal cased 22/50, 47/35, 68/25, 100/20, 120/10, 150/16, 220/10, 330/6 £2.00 22/35, 33/35, 47/20, 68/15, 100/10, 150/6 £1.25 4.7/50, 6.8/35, 10/25, 10/35, 22/15 £1.00 Axial moulded-case tantalum Kemet axial 6.8/10 £0.30 Kemet radial 33/10 £0.40 STC radial 100/20 £1.50 Tantalum bead 22/50 470/3 680/6.3 £1.00 £2.00 £3.00 Wet tantalum 220/25 axial £3.20 Castanet button 140/30, 470/3 £3.20 Hughes 540/10 £3.20 Bipolar Hermetic bipolar tantalum 16/35 £3.20 Elcap axial 10/50 £0.50 Generic radial 100/16, 470/35, 100/ 63, 22/35, 4.7/35, 220/16 £0.50 Philips solid-aluminium (axial) 121/123 47/16 £1.00 330/6.3 £2.00 100/35 £4.00 Philips Pearl 122 series (radial) 10/16 £0.30 Silvered mica (radial) 1nF/500 1% £1.00 Trimmer capacitors Vishay plastic-film 4-40pF Vishay plastic-film 5.5-45pF Vishay plastic-film 5-80pF Vishay plastic-film 10-250pF Mica 1-12pF, 2-40pF £0.80 £1.00 £1.20 £2.00 £1.00 Audio transformers and inductors Eagle transformers LT44, LT722 driver, LT700, LT723 500Ω output £2.50 LT30 500mW output £3.50 5:1 interstage £1.50 Repanco T/T3 splitter transformer CH2 5mH RFC £4.00 £2.00 Balanced output transformer Vigortronix 600Ω VTX-101-007 £10 Vigortronix 600Ω VTX-101-3001 £10 Vigortronix 600Ω VTX-101-3002 £15 Gardners 150Ω £10 Reclaimed BBC LL74/MPC nickel core 600Ω £12 Reclaimed mic input transformer £15 Inductors 82µH, 4.7mH, 100µH, 270µH, 10µH, 14µH (low Z) 7-inch ferrite rod with MW and LW windings £0.50 £3.00 Special resistors Bourns wire-wound trimmer 5kΩ 3059 JM panel-mount £2.00 Thermistor RA53, R13 £4.00 A13 £2.00 Thermistor CZ1, CZ6 £1.50 Holco H2 2.2MΩ 1W, 1% £1.00 Welwyn 1GΩ 2W £1.00 5k Bourns 3321H cermet trimmer £0.50 Potentiometers Bourns 81 25kΩ lin cermet £2.00 25kΩ lin, 5kΩ lin conductive plastic £3.00 Bourns 91 10k dual-gang lin or log £10.00 Plessey moulded-track 5kΩ log with switch 50kΩ A/log Mil 250kΩ lin dual £3.00 £3.00 £5.00 Alpha 16mm 4.7kΩ A/log £0.80 220kΩ A/log £0.80 10kΩ lin centre-detent dual-gang £1.50 Allen Bradley J series/Honeywell 10kΩ lin 1 million cycles £5.00 Blore Edwards AB 45 dual 5kΩ A/log with switch £3.50 Alps RK9 dual-gang 5kΩ RD law £4.00 Alps 50k log tapped motorised stereo £5.00 BI P260 500kΩ log conductive plastic 1 million cycles £2.00 Colvern wire-wound 100kΩ or 50kΩ dual-gang 3W £5.00 Mil Spec hermetic 10Ω £8.00 Miscellaneous Theremin Clearance Sale! Elysian Theremin MIDI box £300 PCBs Pocket Theremin (EPE, 1996) £2.00 Elysian Theremin (EPE, 1996) £6 Synth VCF, VCO (EPE, 2017) £3.00 48V PSU (EPE, 2019) £3.00 SMT dual transistor adapter £0.40 Contact Jake Rothman The Old Rectory, Arlais Road, Llandrindod Wells, Powys LD1 5HE (visit by appointment) +44 (0)1597 829102 jrothman1962<at>gmail.com Minimum order £5.00 inc post Quantity discounts negotiable Payment PayPal, cards (via phone), bank transfer, cheques (payable to ‘J Rothman’, UK pounds only) No VAT payable Postage Small Jiffy bag £2.99 Small package £4.99 Big boxes and overseas at cost – ask for a quote 63 AUDIO OUT AUDIO OUT L R By Jake Rothman Discrete audio op amp – Part 4 for my signal generator. This was needed for testing the high-voltage buffer amps that we will start describing next month. Next, I need to make some little additions to the component list in last month’s Part 3. For the high-power version, R10 is 5.6kΩ to make the Iq preset more likely to be in the middle of its rotation. R27 is 75Ω and C14 is 100µF, 35V to provide higher headroom. This was the biggest capacitor I could find to fit on the PCB and I used a Panasonic ECA1VAM101X (Farnell 876-7254, costs a very reasonable 15p). Note the voltages across the 2.2Ω resistors R11 and R12 are 70mV for optimum Iq of 32mA, the same voltage as the low-power version. For the low-impedance version, R10 is 6.2kΩ. Also, PE reader Les Wolstenholme noticed on the Fig.42 circuit diagram that TR10 should be labelled BC327, not BC337. Mullard muddle Fig.57. The new Discrete Op Amp PCB as supplied by the PE PCB Service. It has a new orange colour with some minor modifications. Note the fully insulated ST BD139/40 output devices must have their writing facing outwards from the board. N o circuit design is ever finished – there’s always something to change, add or improve – and with that in mind I have a few updates for the Discrete Audio Op Amp. First, there is an updated batch of PCBs, which are a new orange colour with locations for the extra R27 resistor, C15 capacitor and input earth pin shown in Fig.35 (Part 3). It’s pictured in all its glory in Fig.57. After building 20 boards, it became apparent that some 2SB649AL (TR13, PNP) and 2SD669AL (TR14, NPN) transistors did need C15 for stability, so I recommend always including C15. The high-power version using the BD139/40 NPN/PNP pair and the above transistors will go up to a frequency limit of 130kHz without problems. I made myself one as a booster amplifier 64 I wrongly castigated the BD139/40 transistors for having higher distortion than other pairs. When I Fig.58. Distortion curve for high-power non-inverting discrete op amp shown in Fig.57 using new ST BD139/40 output transistors and with standard BC546B/556B small-signal devices. For this version, the output is 6Vpk-pk, gain of 6, driving 180Ω load and supply of ±25V. Practical Electronics | January | 2024