November 2018

Super-7 Transistor AM Radio Receiver (Part 1)

Every electronics hobbyist should build a radio receiver at least once in their lives! This modern ‘take’ on an AM (Amplitude Modulation) superheterodyne receiver is a great way of experiencing the basics of radio reception and exploring  principles that are nearly 100 years old and still relevant today.

Our radio uses standard ‘discrete’ components – no surface mount technology needed here – in a classic seven-transistor design built on a single p.c.b.   Traditional features include a volume control and speaker/ headphone jack, plus battery/ mains adapter operation.

Part One outlines the principles of the superhet receiver along with the circuit diagram and parts list, with construction following next month. It’s a great way of dabbling with radio principles and experiencing the thrill of turning on a home-built radio receiver for the first time, so tune into this project now!

6GHz+  Touchscreen Frequency & Period Counter (Part 2)

Last month we published the circuit diagram and operating principles behind this Micromite Plus Explore 100-based DFM and in Part Two this month we describe how to assemble and test the two p.c.b.s , then load the software.  Final operation and usage are offered in the final part next month.

Surface mount design needs good soldering skills

High-performance Dipole Loudspeaker

A loudspeaker without a cabinet might seem an impossible thing to create, but this open-baffle ‘dipole’ speaker is exactly that! It has no rear cabinet but offers remarkably flat response and no discernible bass roll-off in smaller rooms.

Apart from its high performance, all things considered, the open-baffle design brings constructors the added benefit of not requiring any special woodworking nor cabinet-making skills to fabricate a speaker ‘enclosure’. The design has a wide range frequency response  from 20Hz to 18kHz. We also show how to hook up power amps and the 3-Way Active Crossover featured in the September and October 2018 issues of EPE.

Full drawings are included along with plenty of practical advice to ensure you can build this interesting design with confidence.

A Build-it Yourself Software Defined Radio (SDR) Kit

Can it be true? A full SDR kit for just £16? Chinese vendor Banggood offers an SDR kit along with a DVB-T dongle which we explore in this special feature.

Kit-builders will have to strip apart the supplied dongle to couple it to the main kit’s board, but the devil is in the detail – you might need some extra help to make it workable as it involves some extremely fiddly SMD soldering. Our article shows the steps needed, along with better instructions and some close-up photos to help you build the kit successfully and run the software.

Dynamo Bicycle LED Lighting System

The traditional bicycle dynamo lighting system is given a 21st Century makeover by adding a few standard parts, a flashing tail light and the addition of a super-capacitor pack so the lights stay on when you cycle to a halt.  A great project for experimenters, just in time for those longer winter evenings.

Audio Out (Part 4) – An analogue synthesizer

If you are into electronic sound creation then this mini-series is for you! This month, as we head towards the completion of a budget analogue synth. with stylus-operated ‘keyboard’, we continue our intensive exploration of analogue music synthesis with the design and construction of more synthesizer modules including a VCA and Sample and Hold board. The importance of using matching transistor pairs is also examined.

Electronic Building Blocks
Buck/ Boost Module

This series uses ‘cheap as chips’ components bought online and adapts them into something useful. This month a buck/boost module is presented that will output 1.25V to 35V with a supply voltage anywhere from about 3 – 32V.

Also in this issue

• Techno Talk learns of a new energy storage system that could drastically reduce electric vehicle charging times. We lift the lid on the UK smart meter scandal.
• Lucy’s Lab  our Maker creates a set of #Cheerlights LED boots
• Net Work – tracing the first ever example of free downloadable music
• Circuit Surgery – introduction to Circuit Simulation with LTSpice – Part 2 – LTSpice files are included in the monthly download zip file (top right).

Next month

Touchscreen Altimeter with colour LCD; Super-7 AM Radio Receiver (Part 2); 6GHz+ Touchscreen Frequency & Period Counter (Part 3); More low-cost modules.