April 2016

Appliance Insulation Tester

This item of test equipment can help you check that your mains-powered tools and appliances are safely insulated. It does this by applying 250V or 500V DC and measuring the resistance between mains ‘live’ and neutral to the earth (ground) on a 3-pin plug, or chassis of a suitably earthed appliance. Moving dot bargraph display shows insulation resistance in ten steps from 707kΩ to 16MΩ : too low a resistance (<1MΩ ) is a symptom of a potentially dangerous insulation fault.

Full constructional details and operating instructions are included. Not suitable for mineral-insulated metal sheathed heating elements, or portable RCDs (ELCBs) that incorporate a functional earth.

Next month we will publish a companion instrument – an Appliance Earth Leakage Tester – for use with apparatus having a ‘soft’ or non-mechanical power switch, such as most devices having remote controls (TVs, DVD players etc.). The insulation of these can only be checked when they are energised.

Low Frequency Distortion Analyser

Would you like to measure the harmonic distortion of your loudspeaker system, or maybe the AC supply?  This project will analyse the distortion of any 3-20V AC sinewave in the range of 20Hz-10kHz. It measures total distortion %, and second, third, even and odd harmonics.  THD range 0.03 – 33% with <1% error. The article includes a tutorial on calculating distortion using a Fourier transform.

Really Bright 12/24V LED Oyster Light

Adapting a commercial low-cost, 1000+ lumen LED light fitting for optional use on the mains.

Teach-In 2016 Introducing the Arduino (Part 3)
Keypads, strings and displays

Our specially-written tutorial series for Arduino enthusiasts investigates some common types of display and indicators that the Arduino can use. We interface a low-cost LCD display and check out some useful keypads and buttons. Our Coding Quickstart introduces arrays, strings and string manipulation.

Finally, this month’s Teach-In 2016 shows you how to use a low-cost matrix keyboard and LCD display to construct a simple entry/ access control system based on the Arduino Uno. If you’re wanting to climb on board and get to grips with Arduino, this series is just for you!

Also in this issue:

• PIC n’ MIX – Choosing and using accelerometers  (Part 1) – an extremely useful insight into how accelerometers work, with a view to interfacing them to a PIC microcontroller.
• Techno Talk – beware of electronic bargains bought online!
• Interface – a Raspberry Pi capacitance meter
• Circuit Surgery – Voltage References – Part 2.  Continuing an in-depth analysis of the principles and applications references including band-gap
• Net Work – news from the Internet, and a useful plug-in to help you shop smarter on Amazon
• Max’s Hot Beans –  more Nixie-tube inspired ‘steampunk’ retro designs, and (probably) the world’s finest Nixie clock.
• Electronic Building Blocks – PIR Sensor Module
• Audio Out – our column for audio enthusiasts digs more deeply into Baxendall volume circuits, offering workarounds to practical problems they sometimes pose.

Next month

4-Output Universal Voltage Regulator; Appliance Earth Leakage Tester; 2-Channel Balanced Input Attenuator for Audio Analysers and DSOs; Teach-In 2016 – our Arduino Tutorial (Part 4): interfacing to the real world.