Silicon ChipDiscrete microamp LED flasher - November 2023 SILICON CHIP
  1. Outer Front Cover
  2. Contents
  3. Publisher's Letter: Computer keyboards need an update / Australia Post wants to put prices up again!
  4. Mailbag
  5. Feature: The History of Electronics, Pt2 by Dr David Maddison
  6. Product Showcase
  7. Project: Pico Audio Analyser by Tim Blythman
  8. Feature: 16-bit precision 4-input ADC by Jim Rowe
  9. Project: K-Type Thermostat by John Clarke
  10. Review: Microchip's new PICkit 5 by Tim Blythman
  11. Project: Modem/Router Watchdog by Nicholas Vinen
  12. Project: 1kW+ Class-D Amplifier, Pt2 by Allan Linton-Smith
  13. Serviceman's Log: Charge of the light yardwork by Dave Thompson
  14. PartShop
  15. Circuit Notebook: A minimal WiFi water tank level gauge by Mohammed Salim Benabadji
  16. Circuit Notebook: Magnetic levitation demonstration by Les Kerr
  17. Circuit Notebook: Discrete microamp LED flasher by Russell Gurrin
  18. Subscriptions
  19. Vintage Radio: Recreating Sputnik-1, Part 1 by Dr Hugo Holden
  20. Ask Silicon Chip
  21. Market Centre
  22. Advertising Index
  23. Notes & Errata: Watering System Controller
  24. Outer Back Cover

This is only a preview of the November 2023 issue of Silicon Chip.

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Articles in this series:
  • The History of Electronics, Pt1 (October 2023)
  • The History of Electronics, Pt2 (November 2023)
  • The History of Electronics, Pt3 (December 2023)
Items relevant to "Pico Audio Analyser":
  • Pico Audio Analyser PCB (04107231) (AUD $5.00)
  • 1.3-inch blue OLED with 4-pin I²C interface (Component, AUD $15.00)
  • 1.3-inch white OLED with 4-pin I²C interface (Component, AUD $15.00)
  • Short-form kit for the Pico Audio Analyser (Component, AUD $50.00)
  • Pico Audio Analyser firmware (0410723A) (Software, Free)
  • Pico Audio Analyser PCB pattern (PDF download) [04107231] (Free)
  • Pico Audio Analyser box cutting details (Panel Artwork, 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)
  • PAS CO2 Air Quality Sensor (July 2022)
  • Particulate Matter (PM) Sensors (November 2022)
  • Heart Rate Sensor Module (February 2023)
  • UVM-30A UV Light Sensor (May 2023)
  • VL6180X Rangefinding Module (July 2023)
  • pH Meter Module (September 2023)
  • 1.3in Monochrome OLED Display (October 2023)
  • 16-bit precision 4-input ADC (November 2023)
Items relevant to "K-Type Thermostat":
  • Thermocouple Thermometer/Thermostat main PCB (04108231) (AUD $7.50)
  • Thermocouple Thermometer/Thermostat front panel PCB (04108232) (AUD $2.50)
  • PIC16F1459-I/P programmed for the Thermocouple Thermometer/Thermostat (0410823A.HEX) (Programmed Microcontroller, AUD $10.00)
  • MCP1700 3.3V LDO (TO-92) (Component, AUD $2.00)
  • K-Type Thermocouple Thermometer/Thermostat short-form kit (Component, AUD $75.00)
  • K-Type Thermocouple Thermometer/Thermostat firmware (0410823A.HEX) (Software, Free)
  • K-Type Thermocouple Thermometer/Thermostat PCB pattern (PDF download) [04108231] (Free)
  • K-Type Thermostat panel artwork (PDF download) (Free)
Items relevant to "Modem/Router Watchdog":
  • Modem Watchdog PCB (10111231) (AUD $2.50)
  • Modem/Router Watchdog kit (Component, AUD $35.00)
  • Modem/Router Watchdog Software (Free)
  • Modem Watchdog PCB pattern (PDF download) [10111231] (Free)
Items relevant to "1kW+ Class-D Amplifier, Pt2":
  • 1kW+ Mono Class-D Amplifier cutting and drilling details (Panel Artwork, Free)
Articles in this series:
  • 1kW+ Class-D Amplifier, Pt1 (October 2023)
  • 1kW+ Class-D Amplifier, Pt2 (November 2023)
Items relevant to "A minimal WiFi water tank level gauge":
  • Firmware for the Minimal WiFi water tank level gauge (Software, Free)
Items relevant to "Magnetic levitation demonstration":
  • Magnetic levitation demonstration PCB (AUD $5.00)
  • PIC12F617-I/P programmed for the magnetic levitation demonstration [jumping ring.HEX] (Programmed Microcontroller, AUD $10.00)
  • Magnetic levitation demonstration software (Free)
  • Magnetic levitation demonstration PCB pattern (PDF download) [levitation] (Free)
Items relevant to "Discrete microamp LED flasher":
  • Discrete microamp LED flasher PCB (AUD $2.50)
  • Discrete microamp LED flasher PCB files and LTspice model (Software, Free)
  • Discrete microamp LED flasher PCB pattern (PDF download) [LED_Flasher_1uA_V2] (Free)
Items relevant to "Recreating Sputnik-1, Part 1":
  • Sputnik design documents and Manipulator sound recording (Software, Free)
Articles in this series:
  • Recreating Sputnik-1, Part 1 (November 2023)
  • Recreating Sputnik-1, Part 2 (December 2023)

Purchase a printed copy of this issue for $12.50.

Discrete microamp LED flasher This LED flasher has an average current of less than one microamp and flashes the LED roughly once every two seconds. The low current means it can be used as an ultra-low-power indicator in places where an indicator is not normally possible, such as a power-on indicator in devices powered by lithium watch batteries. A CR1620 cell has a usable capacity of about 70mAh, which will power this flasher for eight years. The component values in the circuit are for use with a 3V or 3.3V supply. Higher supply voltages can be used, but the average current will increase, and the flash rate will also increase. To use a higher supply voltage while keeping the supply current low, increase the value of all four 2.2MW resistors; for example, 3.9MW will work well for a 4.5V supply. The circuit is basically a relaxation oscillator. It charges a capacitor, then discharges the capacitor through the LED. There are three main sections in the circuit: • A trigger circuit, which detects when the capacitor reaches full charge. • A monostable, which generates a fixed-length pulse. • A power stage to drive the LED. The trigger circuit starts the monostable and the monostable’s output drives the power stage. The 1μF capacitor is charged over time, then powers the LED for each flash. It is charged mostly through 2.2MW resistor R1 and partially through Q2’s emitter and base resis- tors (and its emitter-base junction). PNP transistors Q1 and Q2, and the resistors around them, are the trigger circuit, which monitors the voltage across R1. As the 1μF capacitor charges, the voltage across R1 drops. When it’s below approximately 0.6V, the two transistors act as a Schmitt trigger, turning the gradually changing voltage across R1 into an abrupt signal at the collector of Q1 to start the monostable. NPN transistor Q4 and PNP transistor Q5, along with the resistors around them and the 100nF capacitor, form the monostable circuit. The 100nF capacitor charges through R6 at the same time as the other capacitor. Q4 and Q5 are wired as a discrete thyristor (SCR); once it gets the trigger signal, Q4 starts to switch on, which makes Q5 start to switch on, and they hold each other on. The monostable is powered by the 100nF capacitor, so while it is on, this capacitor discharges, ultimately Above: a 3D render of the Flasher PCB. Left: a plot of the current through LED1 (green) and R1 (blue) for the Flasher. 96 Silicon Chip Australia's electronics magazine dropping to a voltage too low to keep the transistors on, at which time the monostable turns off. NPN transistor Q3 is the power stage. While the monostable is on, the voltage across Q4’s emitter resistor is high enough to drive hundreds of microamps into the base of Q3, which goes into saturation and permits current to flow through the LED. The current through the LED discharges the 1μF capacitor, creating a flash that lasts a fraction of a millisecond. The LED choice is critical in this circuit. As the amount of power available to drive the LED is tiny, an ordinary LED will produce a barely-­visible flash. You need a wide-angle super bright LED; if the angle is too narrow, the flash won’t be visible when your eye is not on-axis with the LED. One suitable LED is Jaycar’s ZD0040 2mm red LED, rated at 600mcd with a 60° viewing angle. Although the circuit shows BC846 (NPN) and BC856 (PNP) surface-mount SOT-23 transistors, it works equally well with BC547 (NPN) and BC557 (PNP) transistors with leads. After building this circuit, clean off all solder flux residue, as flux can absorb moisture from the air and become conductive. Even a fraction of a microamp leaking through flux can prevent the circuit from working! I have designed a small SMD PCB for this circuit, shown in the 3D rendering (siliconchip. au/Shop/6/284). The accompanying LTspice simulation shows the LED current in green and the supply current in blue. We will also be selling a PCB at siliconchip.au/Shop/8/6868 Russell Gurrin, Highgate Hill, Qld. ($100) siliconchip.com.au