Silicon ChipSmoke, alcohol or LPG alarm - August 2022 SILICON CHIP
  1. Outer Front Cover
  2. Contents
  3. Publisher's Letter: 100 years of Australian electronics magazines
  4. Mailbag
  5. Feature: IC Fabrication, Part 3 by Dr David Maddison
  6. Subscriptions
  7. Project: Wide-Range Ohmmeter, Part 1 by Phil Prosser
  8. Feature: History of Silicon Chip, Part 1 by Leo Simpson
  9. Product Showcase
  10. Project: isoundBar with Built-in Woofer by Allan Linton-Smith
  11. Review: DH30 MAX Li-ion Spot Welder by Phil Prosser
  12. Project: SPY-DER: a 3D-printed Robot by Arijit Das
  13. PartShop
  14. Serviceman's Log: Spy games and supper-villain gadgets by Dave Thompson
  15. Project: Secure Remote Mains Switch, Part 2 by John Clarke
  16. Vintage Radio: AVO valve testers, part 1 by Ian Batty
  17. Circuit Notebook: Simple mains timer/LED lamp dimmer by Hichem Benabadji
  18. Circuit Notebook: Hearing Loop (telecoil) phone headset by Anthony Leo
  19. Circuit Notebook: Smoke, alcohol or LPG alarm by Raj K. Gorkhali
  20. Ask Silicon Chip
  21. Market Centre
  22. Advertising Index
  23. Notes & Errata: Spectral Sound MIDI Synthesiser, June 2022; Digital FX (Effects) Pedal, April & May 2021
  24. Outer Back Cover

This is only a preview of the August 2022 issue of Silicon Chip.

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Articles in this series:
  • IC Fabrication, Part 1 (June 2022)
  • IC Fabrication, Part 2 (July 2022)
  • IC Fabrication, Part 3 (August 2022)
Items relevant to "Wide-Range Ohmmeter, Part 1":
  • Wide-Range Ohmmeter PCB [04109221] (AUD $7.50)
  • PIC24FJ256GA702-I/SS‎ programmed for the Wide Range Ohmmeter (0110922A.HEX) (Programmed Microcontroller, AUD $15.00)
  • 16x2 Alphanumeric module with blue backlight (Component, AUD $10.00)
  • Partial kit for the Wide-Range Ohmmeter (Component, AUD $75.00)
  • Firmware and source code for the Wide-Range Ohmmeter [0110922A.HEX] (Software, Free)
  • Wide-Range Ohmmeter PCB pattern (PDF download) [04109221] (Free)
  • Front panel label for the Wide-Range Ohmmeter (Panel Artwork, Free)
Items relevant to "isoundBar with Built-in Woofer":
  • Cutting and assembly diagrams for the isoundBar (Panel Artwork, Free)
Items relevant to "SPY-DER: a 3D-printed Robot":
  • Arduino and Raspberry Pi software plus 3D printer STL files for the SPY-DER robot (Free)
Items relevant to "Secure Remote Mains Switch, Part 2":
  • Secure Remote Mains Switch receiver PCB [10109211] (AUD $7.50)
  • Secure Remote Mains Switch transmitter PCB [10109212] (AUD $2.50)
  • PIC16F1459-I/P programmed for the Secure Remote Mains Switch receiver (1010921R.HEX) (Programmed Microcontroller, AUD $10.00)
  • PIC16LF15323-I/SL programmed for the Secure Remote Mains Switch transmitter (1010921A.HEX) (Programmed Microcontroller, AUD $10.00)
  • Firmware and ASM source code for the Secure Remote Mains Switch [1010921A/R] (Software, Free)
  • Secure Remote Mains Switch PCB patterns (PDF download) [10109211/2] (Free)
  • Front panel label and drilling diagrams for the Secure Remote Mains Switch (Panel Artwork, Free)
Articles in this series:
  • Secure Remote Mains Switch, Part 1 (July 2022)
  • Secure Remote Mains Switch, Part 2 (August 2022)

Purchase a printed copy of this issue for $8.50.

Smoke, alcohol or LPG alarm This circuit raises an alarm if it detects smoke or LPG cooking gas leakage, or even alcohol vapours. This is achieved by using the same circuit with one of several sensors designed to detect smoke, LPG or alcohol. So different alarms can be made by simply changing the sensor. For a smoke alarm, use the MQ2 sensor; to detect alcohol, use the MQ3; or use the MQ6 sensor for LPG. The MQx sensors each have six pins. The heater filament, between pins H-H, is powered from the 5V rail. Two pairs of A-B pins connect across the sensing element; it doesn’t matter which pair you use. Half of the LM358 dual op amp the lug using a screw in a hole already drilled for the purpose. The wiring is hidden under foam acoustic pads inside the ear cups. The cable connecting to the phone has two wires, pink and white, plus a screen braid, with a three-way jack plug on one end. Do not mix up the microphone’s white return wire with the white wire in the cable back to the phone. If necessary, put a label on the microphone's white wire, change its colour with a marking pen, or solder it to the common lug first. Circuit Ideas Wanted 98  Silicon Chip (IC1) is wired as a comparator. A reference voltage set using potentiometer VR1 is applied to the inverting input (pin 2) while the sensor voltage goes to the non-inverting input (pin 3). The sensor produces a current that is converted to a voltage by the 10kW resistor between the B pin and ground. Output pin 1 of the op amp swings high whenever the sensor voltage goes above the reference voltage. A small amount of hysteresis is provided via positive feedback using a 10MW resistor so that the output doesn’t vacillate when the sensor voltage hovers around the trigger threshold. When pin 1 of IC1 goes high, The centre (ring) contact on the jack plug connects to one side of the string of two induction coils and the 150W resistor. The opposite end of that string goes to the common solder lug. The third and longest contact (sleeve) at the base of the jack plug is returned via the screening braid, which you should also connect to the common lug. When finished, check for around 157W between the jack plug ring and sleeve contacts. Depending on the probe polarity, there should be around 1.2-2.5kW between the tip transistor Q1 releases the reset signal on 555 timer IC2, which is configured as an astable multivibrator, so it starts oscillating. The frequency depends on the value of the capacitor connected to pin 6 and the two resistors connected to pin 7. The resulting square wave is AC-coupled to a small 8W speaker to produce the alarm tone. After switching on the 5V supply, wait about ten seconds for the filament to heat up. Then adjust VR1 until the alarm just stops sounding. Enclose the PCB in a suitable box with vents so that fumes can circulate near the sensor. Raj K. Gorkhali, Hetadu, Nepal. ($75) and sleeve. If all indications are OK, plug your induction headset into a suitable phone and press talk to hear a dial tone. Using my Silicon Chip Hearing Loop Tester/Level Meter (November & December 2010; siliconchip.au/ Series/15), I found that the dial tone was smack bang on 0dB or 0.1A/m. The phone also has a volume control that can reduce the volume below that level. Anthony Leo, Cecil Park, NSW. ($90) 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 siliconchip.com.au