Silicon ChipRadiating test antenna for AM radios - January 2021 SILICON CHIP
  1. Outer Front Cover
  2. Contents
  3. Publisher's Letter: More articles than space - a good problem to have!
  4. Mailbag
  5. Feature: Automotive Electronics, Part 2 by Dr David Maddison
  6. Project: AM/FM/SW Single-Chip Digital Radio by Charles Kosina
  7. Review: Altium 365 and Altium Designer 21 by Tim Blythman
  8. Project: MiniHeart: A Miniature Heartbeat Simulator by John Clarke
  9. Feature: How to use the MPLAB X Development Environment by Tim Blythman
  10. Serviceman's Log: One good turn deserves another by Dave Thompson
  11. Project: The Bass Block Subwoofer by Nicholas Dunand
  12. Circuit Notebook: A reliable solar lighting system by K. G.
  13. Circuit Notebook: Converting a cheap welder to a high-current battery charger by John Russull
  14. Circuit Notebook: Radiating test antenna for AM radios by Ian Batty
  15. Project: Busy Loo Indicator by John Chappell
  16. Feature: AVR128DA48 and Curiosity Nano Evaluation Board by Tim Blythman
  17. Product Showcase
  18. Vintage Radio: 1963 Philips Musicmaker MM1 mantel radio by Associate Professor Graham Parslow
  19. PartShop
  20. Feature: El Cheapo Modules: Mini Digital AC Panel Meters by Jim Rowe
  21. Ask Silicon Chip
  22. Market Centre
  23. Advertising Index
  24. Notes & Errata: Balanced Input Attenuator for the USB SuperCodec, November-December 2020; Two LED Christmas Stars, November 2020; D1 Mini LCD BackPack, October 2020
  25. Outer Back Cover

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Articles in this series:
  • Automotive Electronics, Part 1 (December 2020)
  • Automotive Electronics, Part 2 (January 2021)
Items relevant to "AM/FM/SW Single-Chip Digital Radio":
  • AM/FM/SW Single-Chip Digital Radio PCB [CSE200902A] (AUD $10.00)
  • Pulse-type rotary encoder with pushbutton and 18t spline shaft (Component, AUD $3.00)
  • PCB-mount right-angle SMA socket (Component, AUD $3.00)
  • 16x2 Alphanumeric serial (I²C) LCD module with blue backlight (Component, AUD $7.50)
  • Firmware for the AM/FM/SW Single-Chip Digital Radio (Software, Free)
  • AM/FM/SW Single-Chip Digital Radio PCB pattern (PDF download) [CSE200902A] (Free)
  • Cutting diagrams and front panel artwork for the AM/FM/SW Single-Chip Digital Radio (PDF download) (Free)
Items relevant to "MiniHeart: A Miniature Heartbeat Simulator":
  • MiniHeart PCB [01109201] (AUD $5.00)
  • PIC12F617-I/P programmed for the MiniHeart [0110920A.HEX] (Programmed Microcontroller, AUD $10.00)
  • MiniHeart SMD parts (Component, AUD $7.50)
  • Firmware for the MiniHeart [01109201A.hex] (Software, Free)
  • MiniHeart PCB pattern (PDF download) [01109201] (Free)
  • Cutting diagrams and front panel artwork for the MiniHeart (PDF download) (Free)
Items relevant to "The Bass Block Subwoofer":
  • Cutting diagrams for the Bass Block (PDF download) (Panel Artwork, Free)
Items relevant to "Busy Loo Indicator":
  • Busy Loo Indicator PCB [16112201] (AUD $2.50)
  • Busy Loo Indicator PCB pattern (PDF download) [16112201] (Free)
Articles in this series:
  • El Cheapo Modules From Asia - Part 1 (October 2016)
  • El Cheapo Modules From Asia - Part 2 (December 2016)
  • El Cheapo Modules From Asia - Part 3 (January 2017)
  • El Cheapo Modules from Asia - Part 4 (February 2017)
  • El Cheapo Modules, Part 5: LCD module with I²C (March 2017)
  • El Cheapo Modules, Part 6: Direct Digital Synthesiser (April 2017)
  • El Cheapo Modules, Part 7: LED Matrix displays (June 2017)
  • El Cheapo Modules: Li-ion & LiPo Chargers (August 2017)
  • El Cheapo modules Part 9: AD9850 DDS module (September 2017)
  • El Cheapo Modules Part 10: GPS receivers (October 2017)
  • El Cheapo Modules 11: Pressure/Temperature Sensors (December 2017)
  • El Cheapo Modules 12: 2.4GHz Wireless Data Modules (January 2018)
  • El Cheapo Modules 13: sensing motion and moisture (February 2018)
  • El Cheapo Modules 14: Logarithmic RF Detector (March 2018)
  • El Cheapo Modules 16: 35-4400MHz frequency generator (May 2018)
  • El Cheapo Modules 17: 4GHz digital attenuator (June 2018)
  • El Cheapo: 500MHz frequency counter and preamp (July 2018)
  • El Cheapo modules Part 19 – Arduino NFC Shield (September 2018)
  • El cheapo modules, part 20: two tiny compass modules (November 2018)
  • El cheapo modules, part 21: stamp-sized audio player (December 2018)
  • El Cheapo Modules 22: Stepper Motor Drivers (February 2019)
  • El Cheapo Modules 23: Galvanic Skin Response (March 2019)
  • El Cheapo Modules: Class D amplifier modules (May 2019)
  • El Cheapo Modules: Long Range (LoRa) Transceivers (June 2019)
  • El Cheapo Modules: AD584 Precision Voltage References (July 2019)
  • Three I-O Expanders to give you more control! (November 2019)
  • El Cheapo modules: “Intelligent” 8x8 RGB LED Matrix (January 2020)
  • El Cheapo modules: 8-channel USB Logic Analyser (February 2020)
  • New w-i-d-e-b-a-n-d RTL-SDR modules (May 2020)
  • New w-i-d-e-b-a-n-d RTL-SDR modules, Part 2 (June 2020)
  • El Cheapo Modules: Mini Digital Volt/Amp Panel Meters (December 2020)
  • El Cheapo Modules: Mini Digital AC Panel Meters (January 2021)
  • El Cheapo Modules: LCR-T4 Digital Multi-Tester (February 2021)
  • El Cheapo Modules: USB-PD chargers (July 2021)
  • El Cheapo Modules: USB-PD Triggers (August 2021)
  • El Cheapo Modules: 3.8GHz Digital Attenuator (October 2021)
  • El Cheapo Modules: 6GHz Digital Attenuator (November 2021)
  • El Cheapo Modules: 35MHz-4.4GHz Signal Generator (December 2021)
  • El Cheapo Modules: LTDZ Spectrum Analyser (January 2022)
  • Low-noise HF-UHF Amplifiers (February 2022)
  • A Gesture Recognition Module (March 2022)
  • Air Quality Sensors (May 2022)
  • MOS Air Quality Sensors (June 2022)

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Converting a cheap welder to a high-current battery charger I modified a low-cost Kenstar 200A IGBT inverter welder so that it can be used as a welder or a battery charger. An added switch and relay allows either of the two functions to be selected. The circuit uses the common UC3846 switchmode controller chip. Its output voltage can be varied from 11-22V, with the typically ~14.4V charging voltage for 12V lead-acid batteries well within this range. Generic IGBT or Mosfet welders are cheap to buy and usually easy to repair or modify. If they fail, it is often the auxiliary ±24V power supply module that is faulty. I bought my welder for $7 in a nonworking condition and repaired it for a few dollars. For any engineer used to working on mains-powered equipment, it is easy to modify it to charge a car battery. The high-voltage side does not have to be changed – only the lowvoltage control board. I purchased a low-cost LED voltage/ current meter online to display the battery voltage and charging current (see our article on these meters in the De- cember 2020 and this issue on p102; siliconchip.com.au/Series/306). It is necessary to add a current shunt resistor to sense and display the charge current; most meters come with the shunt. Both are shown in my circuit diagram. The modifications for switching between charging and welding are as follows. I added a 12V regulator on the +24V rail which generates a voltage to switch the coil of the added relay via the charge/weld switch. I cut the connection between pins The modifications marked on the welder – remember to be careful when working on mains-powered equipment. Radiating test antenna for AM radios Most transistor radios, and many later valve models, use ferrite rod antennas. While some of these provide external antenna/Earth connections, most don’t. While it is possible to connect a signal generator directly to sets that do have antenna connections, proper alignment demands the use of a ‘dummy’ antenna to mimic the capacitive nature of the few metres of wire typically used. This radiating antenna solves several problems. It will work with all sets using ferrite rod or wire loop antenna circuits, needs no electrical connections to the set being tested and, for ferrite rod antennas, gives an actual 76 Silicon Chip sensitivity calibration in microvolts per metre (µV/m). The antenna uses an ordinary 200 x 9.5mm ferrite rod. The coil is seventeen turns of wire, 0.4-0.65mm diameter (22~26 B&S gauge), spaced over 100mm. The two resistors, 100W and 82W, are carbon types. The antenna can sit in a simple non-metallic cradle of timber or plastic. Placed close to the set under test, it’s possible to inject IF signals at a high enough level for IF alignment, even for the low-sensitivity Regency TR-1 with its unusual intermediate frequency of 262kHz. This eliminates the difficulties of injecting to the converter base in compact sets. Australia's Australia’s electronics magazine For broadcast alignment, set the radiating antenna 600mm from the receiver’s antenna and parallel to it, and align at the usual frequencies of 1610kHz for the oscillator trimmer, 600kHz for the local oscillator coil and antenna and 1400kHz for the antenna trimmer. Once you have completed alignment, you can easily determine your set’s sensitivity for 50mW output. With the radiating antenna 600mm from the set’s antenna rod, divide the generator output by 20 to get the field strength at the receiver. For example, a signal generator output of 20mV RMS gives a field strength of 1mV/m at the receiver. The radiating loop gives useful results on sets with frame antenna loops, but the radiating loop must be aimed perpendicularly at the frame antenna for measurement results. This design is based on information in Mingay’s Electrical Weekly, October 18, 1963: Pye Caddy Transistor Portable Receiver Service Data Sheet. Ian Batty, Rosebud, Vic. ($80) siliconchip.com.au