Silicon ChipBiofeedback for stress management - 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.

You can view 0 of the 112 pages in the full issue.

For full access, purchase the issue for $10.00 or subscribe for access to the latest issues.

Items relevant to "":
  • Firmware (BAS and HEX) files for the DAB+/FM/AM Radio project (Software, Free)
Articles in this series:
  • Digital Radio Modes - Part 1 (April 2021)
  • Digital Radio Modes – Part 2 (May 2021)
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)
Articles in this series:
  • Digital FX (Effects) Pedal - Part 1 (April 2021)
  • Digital FX (Effects) Pedal – Part 2 (May 2021)
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 or 1010221B.HEX] (Programmed Microcontroller, AUD $10.00)
  • Hard-to-get parts for the Refined Full-Wave Motor Speed Controller (Component, AUD $60.00)
  • 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)
  • The History of Videotape – Cassette Systems (May 2021)
  • The History of Videotape – Camcorders and Digital Video (June 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 [1410221B.HEX] (Programmed Microcontroller, AUD $15.00)
  • Firmware for the High-Current Battery Balancer [1410221B.HEX] (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)
  • Simple Linear MIDI Keyboard PCB [23101213] (AUD $5.00)
  • Firmware for the 64-Key Arduino MIDI Matrix (Software, Free)
  • 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)
  • Simple Linear MIDI Keyboard PCB pattern (PDF download) [23101213] (Free)
Articles in this series:
  • Arduino-based MIDI Soundboard - Part 1 (April 2021)
  • Arduino-based MIDI Soundboard – Part 2 (May 2021)
  • Simple Linear MIDI Keyboard (August 2021)

Purchase a printed copy of this issue for $10.00.

CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. Biofeedback for stress management This circuit connects to a pair of skin electrodes on your scalp and gives you a ‘stress level’ reading. If you can see how your stress level varies immediately, it will help you to determine when you are particularly stressed and also what you need to do to relax. It measures the magnitude of the alpha waves produced by your brain, which have signal frequencies in the 4-11Hz range. A small amount of these waves (in the microvolts range) reaches the surface of your skin and can be picked up using electrodes. These signals are fed to a TL071 JFET-input op amp to be amplified to a level that can be read out on a digital voltmeter. A small bias current (less than 750µA, varying depending on skin resistance) is applied through the skin electrodes. siliconchip.com.au The AC alpha waves are coupled to the op amp input via a 1µF MKT capacitor, and they are DC-biased to around -26mV by the resistor network following that capacitor. Higher-frequency signals are filtered out using a 1kW/1nF RC low-pass filter plus a series ferrite bead. This filter also helps to eliminate any RF that is picked up by the electrode leads. The 1µF coupling capacitor and 39kW resistor form a high-pass filter with a -3dB point of 4Hz to eliminate very low frequency signals, below the range of alpha waves. The gain of this op amp stage is adjusted using trimpot VR1. It can be up to about 1000 times (1MW ÷ 1kW). The signal is then fed through a 15kW/1µF RC low-pass filter which has a -3dB point of 10.6Hz. This filters out most Australia’s electronics magazine signals above the 11Hz maximum frequency of alpha waves. The signal is then rectified by diode D3, which also reduces the reading by about 0.2V, eliminating noise from the results. A DMM set to read millivolts connected across the output terminal therefore gives a reading proportional to your alpha wave activity, with VR1 correctly adjusted. The circuit runs from a pair of 9V batteries which produce an approximately ±8.4V split supply after reverse polarity protection diodes D1 & D2. 100µH chokes reduce RF pickup from the battery leads while 47W resistors and 100µF bypass capacitors provide further supply filtering. David Strong, Penshurst, NSW. ($105) April 2021  61