September 2022

Touchscreen and Remote Digital Preamp with Tone Controls (Part 1)

This preamp offers audiophiles the best of both worlds, combining the benefits of digital control with the low noise and distortion of an analogue design. A classic Baxandall-type volume and tone control circuit based around op.amps is used in conjunction with high-quality digital potentiometers that provide the adjustments. The fully-featured project has a Micromite colour touchscreen and remote control and offers better than CD sound quality. Part One this month describes the circuitry with constructional details, setup and operation following in Part Two next month.

Micromite to Smartphone Connector via Bluetooth

This project offers the capability of using a Micromite at the heart of an IoT system by connecting a bare Micromite chip to an Android smartphone, to communicate and display data without needing a screen. You can even communicate  with the Micromite’s terminal output data stream using an Android app, sending it BASIC commands and so on.

20A DC Motor Speed Controller

Packed with features, this small but powerful pulse-width modulation (PWM) speed controller has a 20A continuous rating and can handle DC motors that run from near 0V up to 30V. It includes adjustable soft-start and motor load feedback control to maintain constant speed.  The article also includes very useful technical notes on PWM motor control pitfalls at higher frequencies. The circuit board uses discrete through-hole construction throughout for straightforward assembly. A PIC microcontroller project with source code available via our website.

USB-PD Triggers, Decoys and Testers

Following on from last month’s feature introducing the new standard of USB Power Delivery (USB-PD) and charging modules, this month we explore some of the many low-cost PD trigger/ decoy and tester modules that have come onto the market. These offer the prospect of using them as versatile and efficient power supplies.

Audio Out

Transformers in Audio (Part 2) – more analysis of the practical use of transformers in audio circuits

Also in this issue

• Techno Talk – an interesting look at where some common component names and types actually originated from
• The Fox Report – Barry Fox challenges the UK’s Advertising Standards Authority and the advertised role of smart meters.
• Net Work – What3Words can do for you, and electric car and e-scooter battery fires. Don’t forget to check the Net Work blog which is updated monthly to give you ready-made links.
• Circuit Surgery – our in-house ‘surgeon’ outlines the theories of electronically-controlled resistance
• Make it with Micromite – how to utilise infrared communications to synchronise time
• Max’s Cool Beans – utilising servomotors in mechatronics and robotics

Next month:

Touchscreen and Remote Digital Preamp with Tone Controls (Part 2); Tele-com traditional telephone intercom; SMD Test Tweezers; Self-contained 3.8GHz Digital RF Attenuator with OLED screen. Contents subject to change.