December 2014

PortaPAL-D (Part 1) Portable Public Address Amplifier

PortaPAL-D is a high quality powerful, portable public address loudspeaker system combining the best of several earlier EPE projects with a design that is right up to date. It features a class-D high power amplifier delivering up to 100W short term (50W continuous). It has battery operation thanks to a 12V Lithium-Polymer battery and has twin 200mm loudspeakers with integral tweeters.

Our PortaPAL-D offers two mic inputs, a guitar input, line input and line out. Individual level, bass and treble control are incorporated and it’s designed to conserve battery power, with standby indication and low-battery shutdown. A thermostatic fan circulates air inside.

We reckon a commercial equivalent would be £500-£600 so PortaPAL is a brilliant  investment for the keen audio electronics constructor looking for a high-quality portable speaker-amp. Part 1 this month describes the circuitry.

Electronic Bellbird novelty sound effect

A great school project or something for Christmas, this PIC-powered (PIC 16LF88) novelty simulates the tinkling bell sound of the elusive Bellbird (or Bell Miner Manorina Melanophrys), a charming inhabitant that feeds in the eucalyptus forests of Australia and New Zealand.

The realistic ‘ting’ sounds have randomised spacings and repetitions and, like the real thing, it only sounds during the day or when there is good ambient light. For added effect an LED chaser effect is built in. It has low current drain and is powered by a 3V coin cell. A wonderful novelty for the festive Christmas tree.

Why not check YouTube for sounds of Bellbirds?

SiDRADIO (Part 3)

This month’s closing instalment explains how easy it is to convert your PC or laptop into a software-defined radio receiver (SDR) with a cheap USB DVB-T dongle.  The software application is explained along with antenna requirements.

50 Golden Years of Practical Electronics
(Part 2)

Our follow-up feature celebrating the golden anniversary of  Practical Electronics magazine looks at events from the 1970s to the present day, charting the evolution of EPE from a number of British titles including Hobby Electronics, Electronics Monthly and Electronics Today International. A range of evocative cover shots of the era are included in this colour feature to celebrate Britain’s last remaining electronics hobbyist magazine.

PIC n’ MIX

Our in-house PIC expert dedicates this month’s column to fine-tuning our ADC skills, adding an analog input to the PIC development board.

Make Your Own PCBs (part 4)

Typical steps for using EagleCAD when creating a more complex design, and outsourcing the manufacture, are outlined by our industry expert this month.

Also in this month’s issue:

• Special Review RPIADCISOL – a look at the first available optically-isolated 24-bit ADC board for the Raspberry Pi
• Techno Talk and the origins of the ‘hash’ #
• Net Work – Virus Vigilance – free anti-virus programs, Shellshock and understanding secure certificates
• Interface – the column popular with PC users investigates the updated Raspberry Pi B+ A/D
• Circuit Surgery – an in-depth look at Power MOSFET failures