Silicon ChipControlling model railway points with a servo - December 2020 SILICON CHIP
  1. Outer Front Cover
  2. Contents
  3. Publisher's Letter: Saying goodbye to Adobe Flash
  4. Mailbag
  5. Feature: Automotive Electronics, Part 1 by Dr David Maddison
  6. Project: Power Supply for Battery-Powered Vintage Radios by Ken Kranz & Nicholas Vinen
  7. Subscriptions
  8. Feature: Making PCBs with a Laser Engraver or Cutter by Andrew Woodfield
  9. Project: Dual Battery Lifesaver by Nicholas Vinen
  10. Feature: A Closer Look at the RCWL-0516 3GHz Motion Module by Allan Linton-Smith
  11. Serviceman's Log: A brush with disaster by Dave Thompson
  12. Project: Balanced Input Attenuator for the USB SuperCodec, Part 2 by Phil Prosser
  13. Feature: El Cheapo Modules: Mini Digital Volt/Amp Panel Meters by Jim Rowe
  14. Circuit Notebook: Automated tyre inflator/deflator by Tom Croft
  15. Circuit Notebook: Infinite impedance AC source by Mauri Lampi
  16. Circuit Notebook: Controlling model railway points with a servo by George Ramsay
  17. Project: Flexible Digital Lighting Controller, part 3 by Tim Blythman
  18. PartShop
  19. Vintage Radio: 1928 RCA Radiola 60 superhet by Dennis Jackson
  20. Product Showcase
  21. Ask Silicon Chip
  22. Market Centre
  23. Advertising Index
  24. Notes & Errata: Flexible Digital Lighting Controller, November 2020; Tiny LED Christmas Ornaments, November 2020; 7-Band Audio Equalisers, April 2020
  25. Outer Back Cover

This is only a preview of the December 2020 issue of Silicon Chip.

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Articles in this series:
  • Automotive Electronics, Part 1 (December 2020)
  • Automotive Electronics, Part 2 (January 2021)
Items relevant to "Power Supply for Battery-Powered Vintage Radios":
  • Vintage Battery Radio Power Supply PCB [11111201] (AUD $7.50)
  • Pair of CSD18534KCS logic-level Mosfets (Component, AUD $6.00)
  • IPP80P03P4L04 high-current P-channel Mosfet (Component, AUD $5.00)
  • Vintage Battery Radio Power Supply PCB pattern (PDF download) [11111201] (Free)
Items relevant to "Dual Battery Lifesaver":
  • Dual Battery Lifesaver PCB [11111202] (AUD $2.50)
  • IPP80P03P4L04 high-current P-channel Mosfet (Component, AUD $5.00)
  • Dual Battery Lifesaver PCB pattern (PDF download) [11111202] (Free)
Items relevant to "A Closer Look at the RCWL-0516 3GHz Motion Module":
  • Sample audio for the RCWL-0516 radar module with frequency multiplier (Software, Free)
Items relevant to "Balanced Input Attenuator for the USB SuperCodec, Part 2":
  • USB SuperCodec PCB [01106201] (AUD $12.50)
  • USB SuperCodec Balanced Input Attenuator add-on PCB [01106202] (AUD $7.50)
  • Parts source grid for the USB SuperCodec (Software, Free)
  • USB SuperCodec PCB pattern (PDF download) [01106201] (Free)
  • USB SuperCodec Balanced Input Attenuator add-on PCB pattern (PDF download) [01106202] (Free)
  • USB SuperCodec front panel artwork (PDF download) (Free)
  • Drilling and cutting diagrams for the USB SuperCodec Balanced Input Attenuator (PDF download) (Panel Artwork, Free)
Articles in this series:
  • USB SuperCodec (August 2020)
  • USB SuperCodec – part two (September 2020)
  • USB SuperCodec – part three (October 2020)
  • Balanced Input Attenuator for the USB SuperCodec (November 2020)
  • Balanced Input Attenuator for the USB SuperCodec, Part 2 (December 2020)
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 Matix 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)
Items relevant to "Automated tyre inflator/deflator":
  • Firmware for the Automated Tyre Inflator/Deflator (Software, Free)
Items relevant to "Infinite impedance AC source":
  • Mathematical analysis of an infinite impedance AC source (Software, Free)
Items relevant to "Controlling model railway points with a servo":
  • Firmware for Controlling Model Railway Points with a Servo (Software, Free)
Items relevant to "Flexible Digital Lighting Controller, part 3":
  • Flexible Digital Lighting Controller main PCB [16110202] (AUD $20.00)
  • Flexible Digital Lighting Controller front panel PCB [16110203] (AUD $20.00)
  • Flexible Digital Lighting Controller Micromite Master PCB [16110201] (AUD $5.00)
  • Flexible Digital Lighting Controller CP2102 Adaptor [16110204] (PCB, AUD $2.50)
  • Flexible Digital Lighting Controller LED slave PCB [16110205] (AUD $5.00)
  • PIC16F1705-I/P programmed for the Flexible Digital Lighting Controller [1611020A.HEX] (Programmed Microcontroller, AUD $10.00)
  • PIC32MX170F256B-50I/SP programmed for the Flexible Digital Lighting Controller Micromite master [1611020B.hex] (Programmed Microcontroller, AUD $15.00)
  • Hard-to-get parts for the Flexible Digital Lighting Controller (Component, AUD $100.00)
  • Micromite LCD BackPack V3 complete kit (Component, AUD $75.00)
  • Si8751AB 2.5kV isolated Mosfet driver with integral power supply (Component, AUD $5.00)
  • Firmware and software for the Fiexible Digital Lighting Controller (Free)
  • Firmware and PC software for the Digital Lighting Controller [1611010A.HEX] (Free)
  • Flexible Digital Lighting Controller mains slave PCB patterns (PDF download) [16110202-3] (Free)
  • Flexible Digital Lighting Controller Master PCB patterns (PDF download) [16110201, 16110204] (Free)
  • Flexible Digital Lighting Controller LED slave PCB pattern (PDF download) [16110205] (Free)
  • Drilling and cutting diagrams for the Flexible Digital Lighting Controller Micromite master (PDF download) (Panel Artwork, Free)
  • Cutting diagram for the Flexible Digital Lighting Controller mains slave rear panel (PDF download) (Panel Artwork, Free)
  • Cutting diagrams and front panel artwork for the Flexible Digital Lighting Controller LED slave (PDF download) (Free)
Articles in this series:
  • Flexible Digital Lighting Controller, part 1 (October 2020)
  • Flexible Digital Lighting Controller, part 2 (November 2020)
  • Flexible Digital Lighting Controller, part 3 (December 2020)

Purchase a printed copy of this issue for $10.00.

A simple control loop and added synchronous rectification could make this circuit useful for driving LEDs. Other applications await. Note that another way to achieve a similar result would be to use an op amp monitoring the voltage across a shunt in series with the load, and using negative feedback to provide the required drive voltage to match the shunt voltage to a reference sinewave. However, such a circuit may suffer from stability problems, necessitating added compensation components which would reduce its precision. Mauri Lampi, Glenroy, Vic. ($90) Controlling model railway points with a servo This controller was created to operate a set of points (or turnout) on a OO/ HO model train layout using a small 9g model servo (eg, Jaycar YM2758). For simplicity, each set of points has its own small microcontroller with just three inputs. Potentiometers VR1 and VR2 set the two positions, while switch S1 selects between them. It runs from a DC supply of at least 9V and 1A. This is reduced to 5V by 7805 regulator REG1, which is adequate to operate a 9g servo. Power for the microcontroller is decoupled by schottky diode D2 and a 220µF filter capacitor, to prevent motor current surges affecting its operation. The controller should be close to the servo and the points, due to the weak drive and to minimise power losses in the wires. So switch S1 may be several metres away, and thus its wiring is susceptible to interference. Circuit Ideas Wanted siliconchip.com.au The 1kW/100nF RC low-pass filter between S1 and the GP3 input of IC1 (pin 4) reduces the effects of EMI, and it is advisable to use twisted pair wires and/or grounded shielding to further reduce the chance of interference. Potentiometers VR1 and VR2 are wired across the micro's supply, and the wiper voltages are stabilised by 100nF capacitors which perform two functions. They reduce the effects of stray electric fields and also provide the low source impedance required by the micro's internal analog-to-digital converter (ADC). The servo signal has a 330W series resistor to protect IC1 from accidental shorts at CON1. A heartbeat LED, LED1, flashes to indicate when the circuit is operational. Setup is simple. With the power off, set VR1 & VR2 to their mid positions and the points also in their mid positions. Turn the power on and adjust one potentiometer to set the points to "ahead" or "turn". Then change the position of switch S1 and adjust the other potentiometer. The points are then operational, controlled by S1. Note that if the points are hard against either end position and the servo is trying to move the points more, the servo will be destroyed in little time. To prevent this, the mechanical link between the servo and the points should not be rigid. You can use an open-coil spring or provide a U-shaped loop so that there is some compression or extension of the link. The software was written in PICBASIC Pro. The Servo_Dual_Posn_ SC.BAS and Servo_Dual_Posn_ SC.HEX files are available from siliconchip.com.au/Shop/6/5638, along with a PDF of the PCB pattern. George Ramsay, Holland Park, Qld. ($80) Got an interesting original circuit that you have cleverly devised? We will pay good money to feature it in Circuit Notebook. We can pay you by electronic funds transfer, cheque or direct to your PayPal account. Or you can use the funds to purchase anything from the SILICON CHIP Online Store, including PCBs and components, back issues, subscriptions or whatever. Email your circuit and descriptive text to editor<at>siliconchip.com.au Australia’s electronics magazine December 2020  89