January 2020

Audio DSP (Part 1)

This very sophisticated digital signal processor is an exciting project that can play a wide range of roles. It’s a tone control on steroids! More accurately it is an advanced Active Crossover/ DSP/ Parametric Equaliser.

Providing the ultimate in control, it’s a true high-fidelity design offering 0.001% THD+N.  The circuit uses DSP to provide an 8-channel parametric equaliser so you can adjust frequency response to exactly the way you want it with really low distortion and noise. Or use it to ‘bi-amplify’ a pair of speakers or simply experiment with any audio signal.

It has a future-friendly modular expansion capability. Features include a 128×64 graphical LCD and menu-driven interface. Software written in Microchip C. In Part One this month, the circuit diagrams are examined, and the microcontroller and front panel electronics will be described in the next two parts.

Isolated Serial Link

This nifty project allows you to transmit serial data over an opto-isolated, bi-directional link. It provides total isolation and allows mains powered or high voltage loads to be controlled in safety.

USB powered, it works with 3.3V or 5V levels at either end. Discrete, through-hole construction. Applications described in this month’s project include connecting an Arduino to a high voltage load.

Four-channel High-current DC Fan and Pump Controller (Part 2)

This multi-channel pump and fan speed controller can be used anywhere you need to adjust the speed of low-voltage DC fans or other PWM-controlled devices. It is versatile and is easy to set up using an onboard USB interface. It provides both absolute or differential control, based on either the absolute temperature of one or two sensors, or the difference in temperatures between two sensors. Up to four NTC or digital sensors can be used.

In Part Two this month, we cover PCB assembly, interwiring and adjustments.

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

Colour Maximite Computer (Part 3)

This surprisingly powerful retro 80s home computer is a lot more than a blast from the past. This month we get to grips with some programming, looking at MMBASIC and interfacing the hardware. We’ll have fun with some classic games, too!

PIC n MIX

Using a tiny PIC10F processor this month we develop a temperature and humidity sensor based around the DHT12 sensor. The design and development of the circuit is analysed followed by an tutorial about creating the PCB using EagleCAD.

Audio Out
PE Mini Monitor Crossover (Part 1)

This month we lay bare an advanced and adaptable speaker crossover suitable for the BBC LS3/5A monitor speaker project. A range of variants are also described.

Also in this issue:

• The Fox Report – is ‘sidescreen’ ScreenX all it’s cracked up to be? Possibly not, argues Barry Fox
• Techno Talk – time to debunk the claims surrounding ‘shungite’; producing electricity from differences in temperature
• Net Work – the real agenda behind the smart meter revolution; adding an SSD to a crashed PC and the latest offshore wind farm developments
• Max’s Cool Beans – Max chats with fellow electronics engineer Nick Bild
• Circuit Surgery – an in-depth explanation of logic levels (Part 1)
• Make it with Micromite (Part 12) writing serial data to external modules, using an 8×8 LED module as a demo.
• Electronic Building Blocks – build a digital mains voltmeter and ammeter using a cheap imported digital meter and current transformer

Next month

Digital Signal Processor (Part 2); Motion triggered 12V switch; Stamp-sized digital audio player; USB Keyboard and Mouse Adaptor for Micros; Colour Maximite (Part 4); Using Stepper Motors. Contents may be subject to change.