September 2018

3-Way Stereo Active Crossover (Part 1)

This stereo 3-way active crossover is not only a fantastic tool for loudspeaker design and development, but it can also be integrated into a 2-way or 3-way (powered) loudspeaker in its own right. The crossover points and levels are fully adjustable and overall volume and balance controls are incorporated. Optional bass limiter.

In Part One this month, the circuit description is provided, with constructional details following next month.

Surface mount components are used. Good soldering skills are needed to complete this project successfully.

Dead-Easy Superhet IF Alignment using DDS

This project is based on the touch-screen Micromite DDS Signal generator project (see April 2018 issue).  It makes aligning the IF stage of superhets – whether valve (vacuum tube) or transistorised – a real snap!

It also enables examination of the IF stage bandwidth, which gives a good indication of the set’s selectivity, as well as the shape of the IF curve. Its interactive colour touch-screen module makes for simple, intuitive use.

Touchscreen Appliance Energy Meter (Part 3)

Previously we described the design and construction of this sophisticated piece of test and measurement equipment. This final part describes some programming considerations and how to calibrate and use it.

Ultra-Low-Voltage Mini LED Flasher

Using just a handful of components on a tiny (15 x 19mm) printed circuit board, this ingenious circuit can deliver a high-power flash yet it will run from a single 1.5V cell. It’s ideal for toys and models, railroad setups or warning signals and consumes very little power when the LED is off.

Ambient light monitoring can switch the LED off during the day. Supply voltage 0.8 – 3.3V, up to 50 days battery life (alkaline AA), variable duty cycle.

Experience useful – Surface mount design.

Using Cheap Asian Electronic Modules – Part 9

The AD9850 DDS Module – In the April 2018 issue we covered the AD9833 Direct Digital Synthesis (DDS) chip. This month we’re looking at its big brother, the AD9850 which typically can generate sinewaves to 40MHz controlled via an SPI serial interface.

Audio Out – Analogue Synthesis – Part 2

Continuing an in-depth exploration of the intricacies of analogue synthesiser circuitry and hardware, our expert demonstrates his hands-on knowledge of the operating principles of ‘synths’ in this class-leading series.

Electronic Building Blocks

More practical examples to try based on very cheap imported modules – a waterproof voltmeter, an LED display temperature switch and an ATX-based benchtop PSU adaptor.

Also in this issue:

• Lucy’s Lab – the true meaning of ‘Wi-Fi’
• Net Work – How Google’s Chromecast  lets you enjoy YouTube (and more) on the big screen
• PIC n’ MIX –  PICMeter Part 1 – The start of a new project, the PICMeter multimeter. Voltmeter principles are introduced this month.
• Circuit Surgery – our in-house ‘surgeon’ explores differentiator circuitry and offers LTSpice simulator files too. LTSpice files now available for download – see above.
• Techno Talk –African drumbeat messaging is more sophisticated than you might think.

Next month

6GHz+ Touchscreen Frequency & Period Counter (Part 1); 3-Way Fully Adjustable Stereo Active Crossover for Loudspeakers (Part 2); Low-Cost Electronic Modules (Part 10); PIC n’ MIX.