Silicon ChipFollow-up to 'constant' AC source - April 2021 SILICON CHIP
  1. Outer Front Cover
  2. Contents
  3. Publisher's Letter: Adobe making our lives difficult
  4. Mailbag
  5. Feature: Digital Radio Modes - Part 1 by Dr David Maddison
  6. Project: Digital FX (Effects) Pedal - Part 1 by John Clarke
  7. Project: Refined Full-Wave Motor Speed Controller by John Clarke
  8. Serviceman's Log: I hope the purists won't spit their dummies by Dave Thompson
  9. Circuit Notebook: Biofeedback for stress management by David Strong
  10. Circuit Notebook: Latching output for Remote Monitoring Station by Geoff Coppa
  11. Circuit Notebook: Alternative switched attenuator for Shirt Pocket Oscillator by Rick Arden
  12. Circuit Notebook: Follow-up to 'constant' AC source by Mauri Lampi
  13. Feature: The History of Videotape - Helical Scan by Ian Batty, Andre Switzer & Rod Humphris
  14. Project: High-Current Four Battery/Cell Balancer - Part 2 by Duraid Madina
  15. PartShop
  16. Project: Arduino-based MIDI Soundboard - Part 1 by Tim Blythman
  17. Product Showcase
  18. Review: Wagner cordless soldering iron by Tim Blythman
  19. Vintage Radio: 1948 Philips table model 114K by Associate Professor Graham Parslow
  20. Ask Silicon Chip
  21. Market Centre
  22. Advertising Index
  23. Notes & Errata: High-Current Battery Balancer, March 2021; Arduino-based Adjustable Power Supply, February 2021; LED Party Strobe Mk2, August 2015
  24. Outer Back Cover

This is only a preview of the April 2021 issue of Silicon Chip.

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Items relevant to "":
  • Firmware (BAS and HEX) files for the DAB+/FM/AM Radio project (Software, Free)
Items relevant to "Digital FX (Effects) Pedal - Part 1":
  • Digital FX Unit PCB (potentiometer-based version) [01102211] (AUD $7.50)
  • Digital FX Unit PCB (switch-based version) [01102212] (AUD $7.50)
  • 24LC32A-I/SN EEPROM programmed for the Digital FX Unit [0110221A.HEX] (Programmed Microcontroller, AUD $10.00)
  • PIC12F1571-I/SN programmed for the Digital FX Unit with potentiometer [0110221B.HEX] (Programmed Microcontroller, AUD $10.00)
  • Spin FV-1 digital effects IC (SOIC-28) (Component, AUD $40.00)
  • Firmware for the Digital FX Unit [0110221A.HEX] (Software, Free)
  • Digital FX Unit PCB patterns (PDF download) [01102211-2] (Free)
Items relevant to "Refined Full-Wave Motor Speed Controller":
  • Refined Full-Wave Motor Speed Controller PCB [10102211] (AUD $7.50)
  • PIC12F617-I/P programmed for the Refined Full-Wave Motor Speed Controller [1010221A.HEX] (Programmed Microcontroller, AUD $10.00)
  • Firmware for the Refined Full-Wave Motor Speed Controller [1010221A.HEX] (Software, Free)
  • Refined Full-Wave Motor Speed Controller PCB pattern (PDF download) [10102211] (Free)
  • Cutting diagrams and lid panel artwork for the Refined Full-Wave Motor Speed Controller (PDF download) (Free)
Articles in this series:
  • The History of Videotape – Quadruplex (March 2021)
  • The History of Videotape - Helical Scan (April 2021)
Items relevant to "High-Current Four Battery/Cell Balancer - Part 2":
  • High Current Battery Balancer PCB [14102211] (AUD $12.50)
  • ATSAML10E16A-AUT programmed for the High-Current Battery Balancer [1410221A.HEX] (Programmed Microcontroller, AUD $15.00)
  • Firmware for the High-Current Battery Balancer [1410221A.HEX] (not yet available) (Software, Free)
  • High Current Battery Balancer PCB pattern (PDF download) [14102211] (Free)
Articles in this series:
  • High-Current Four Battery/Cell Balancer (March 2021)
  • High-Current Four Battery/Cell Balancer - Part 2 (April 2021)
Items relevant to "Arduino-based MIDI Soundboard - Part 1":
  • 64-Key Arduino MIDI Shield PCB [23101211] (AUD $5.00)
  • 8x8 Tactile Pushbutton Switch Matrix PCB [23101212] (AUD $10.00)
  • Software for the Arduino MIDI Shield & 8x8 Key Matrix plus 3D keycap model (Free)
  • 64-Key Arduino MIDI Shield PCB pattern (PDF download) [23101211] (Free)
  • 8x8 Tactile Pushbutton Switch Matrix PCB pattern (PDF download) [23101212] (Free)

Purchase a printed copy of this issue for $7.00.

Follow-up to ‘constant’ AC source This circuit develops my ideas on the “infinite impedance” alternating current source concept, previously described in the December 2020 Circuit Notebook section (siliconchip.com.au/ Article/14681). That circuit used a direct digital synthesis (DDS) sinewave generator and standard op amp to drive the resonant network. The result is a sinewave at the output that delivers an essentially constant magnitude alternating current into a resistive load. To simplify the circuit, I have ditched the DDS sinewave generator and I am instead using an LM3900 dual Norton (current input) amplifier chip. The circuit snippet below is cribbed from my October 2019 Circuit Notebook submission (siliconchip.com. au/Article/12027) describing how to build a stable sinewave oscillator using a Norton amp, and also gives the formulas (in the blue box) for the oscillation condition and to derive the frequency. For the output resonant circuit, I had a 0.7mH inductor available. Using the inductance vs capacitance and frequency charts published in the December 2020 issue, that sets the capacitance required as 70nF (eg, 68nF, siliconchip.com.au 1.8nF & 200pF in parallel) for a frequency of 22.66kHz. The oscillator circuit achieves this frequency with the values shown. VR2 is used to fine-tune the frequency, with a nominal value of 4kW giving 11kW + 4kW = 15kW to set the frequency close to 22.66kHz. VR1 sets the amplitude of the input voltage to the resonant circuit and hence the value of the ‘constant’ current. IC1b buffers the oscillator’s signal and then drives a current booster circuit using NPN and PNP emitter-followers Q1 & Q2, with their base voltages biased around 0.7V above and below the oscillator signal by diodes D1 & D2. The output at the emitter junctions of Q1 & Q2 drives the resonant circuit that, in turn, drives the load resistance. I built this circuit and tested it, and the results are shown in scope grabs Scope 1-3. Scope 1 was with a load resistance of 100W, Scope 2 with 50W and Scope 3 with 200W. In each case, the oscillator’s output is the trace plotted in yellow while the voltage across the load resistance is shown in cyan. The current waveform leads the voltage waveform by 90° in all three test cases, and as expected, the voltage amplitude adjusts to supply the same current to the load. So in Scope 2, the voltage is halved as the load resistance is halved, while in Scope 3, it is doubled as the load resistance is doubled. This is not obvious from the sinewaves since the channel scaling changes in each plot; check the scale values at the bottom. Mauri Lampi, Glenroy, Vic. ($75) Australia’s electronics magazine April 2021  63