Silicon ChipAutomated tyre inflator/deflator - 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.

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. Automated tyre inflator/deflator ing winter, then as the ambient temperature increases going into summer, they can become overinflated, which could lead to the tyre popping in extreme cases or suffering excess wear. This circuit takes the guesswork out of the equation; rather than letting the air out, then re-inflating them to the correct pressure, it does it all for you. The main components are a microcontroller, 0-100PSI pressure sensor, solenoid driver, motor driver and LCD screen. Pushbuttons S1 & S2 are used to set the desired pressure, which is shown on the LCD screen. It then checks the tyre pressure and if it is higher than the set pressure, actuates the pressure release valve solenoid until the tyre pressure drops to the set pressure. Alternatively, if the tyre pressure is too low, the motor driver is activated to power up a 12V compressor which then raises the pressure until it reaches the set point. The motor is then switched off. The prototype was built on a Curiosity development board. ► The 0-100PSI pressure sensor is connected directly to the pipes near the hose connection point, although an onboard sensor can be used instead. ► siliconchip.com.au Australia’s electronics magazine ► I decided to build my own digital tyre inflator, mainly because pretty much all the affordable ones I found online could only increase the tyre pressure, not decrease it. Sometimes you just want to dial in a pressure value (in PSI, kilopascals or bar) and let the device do all the work for you. It runs off a 12V battery, so it could even be kept in your car and used on the road. Keep in mind that if you keep your tyres inflated to the right pressure dur- The final build uses a custom PCB design and a significant heatsink. This all mounts closely to the motor, pipes and valves. December 2020  85 In either case, when the tyre pressure reaches the target, the piezo buzzer sounds to let you know. In terms of the air plumbing (not shown), the following are all connected together via threaded pipes and joiners: the air hose, 12V compressor, pressure sensor and pressure release valve. Make sure all the pipes and connectors are gas-tight; use yellow Teflon tape on each set of screw threads. The air release valve is not shown on the circuit; it is a readily available type and connects to the terminal marked “VALVE” near the bottom. 86 Silicon Chip The output from the absolute pressure sensor at upper left is 0.5V at 0 PSI, 2.5V at 50PSI and 4.5V at 100PSI. This signal is reduced via a resistive divider to be within the 0-3.3V range that the PIC24 micro can handle, then filtered and buffered by IC3a, part of an MCP6004 quad rail-to-rail op amp. It is then fed into one of the PIC24’s analog input pins, AN6 (pin 25). The output from an optional second pressure sensor (eg, ambient) goes to AN7 (pin 24), while the output of an analog temperature sensor (IC4) is similarly fed to AN8 (pin 23). Australia’s electronics magazine This could be used to compensate the pressure setting for variations in ambient temperature, but you would need to change the software. Analog input AN9 (pin 26) is used to sense the battery voltage, for the under-voltage cutout to protect the battery. The air release valve is powered by Mosfet Q4, which is controlled via an opto-isolator for simplicity. It is driven from one output of MCP23S08 I/O expander IC2, as many of IC1’s pins are occupied driving the display. Similarly, the motor is driven by a parallel pair of high-current Mosfets siliconchip.com.au (Q2 & Q3), which are in turn driven by Mosfet Q1. It is controlled by another opto-isolator, this time driven from the RA0 output of IC1 (pin 2). There is no need to reverse the motor, so this part of the circuit acts as a switch. The I/O expander (IC2) also handles sensing when pushbuttons S1 and S2 are pressed, along with controlling the air release valve, piezo buzzer, some of the low-speed LCD signal lines plus indicator LED2. Circuit power comes from a 12V battery which must be able to supply a siliconchip.com.au substantial amount of current to drive the compressor motor. Power for the rest of the circuit goes via protective fuse F1 and reverse polarity protection diode D1, with the piezo and pressure relief valve running off that 12V rail (it’s also fed to IC3d for battery voltage sensing). The rest of the circuitry runs off 5V or 3.3V, derived from the 12V supply by low-dropout linear regulators REG1 & REG2. An in-circuit serial programming (ICSP) header is provided to allow microcontroller IC1 to be re-proAustralia’s electronics magazine grammed in-circuit, while the COM1 serial port header is provided for debugging purposes. The original prototype was built by hanging the various modules off a PIC24FJ256GA7 Curiosity development board from Microchip, while my final version uses a custom-designed PCB. The PIC24 firmware files (source code and HEX file) are available for download from siliconchip.com.au/ Shop/6/5637 Tom Croft, Sunnybank Hills, Qld. ($150) December 2020  87