December 2019 Issue

A summary of this month's contents.

Extremely Sensitive Magnetometer

A truly fascinating project, this super-sensitive dual-channel design detects magnetic field strength changes of as little as 3nT (nanoTeslas).


It is completely immune to stationary magnetic fields and has high immunity to magnetic noise. Separate handheld controller for sensitivity adjustment. It’s so sensitive that we’ve found it can find ferrous objects smaller than the head of a pin!


Easy to use, it has both a simple LED and relay switch output. Straightforward to build, using discrete through-hole components.


Useless Box

A take on the original ‘Useless Box’ electro-mechanical novelty, it’s a simple box with a switch marked ‘Do Not Switch Off’ – but what happens if you do switch it off?


It’s used along with our Super Digital Sound Effects Generator (PE, Aug-Sept 2019). A great Christmas gift or surprise for youngsters, for use under adult supervision.  This design uses two PIC microcontrollers requiring downloadable .hex files; the separate Sound Board is PICmicro based and also requires a downloadable .hex file.

The Useless Box uses standard discrete through-hole components but note that the Sound Effects Generator board is a miniaturised circuit using surface mount devices and good soldering  skills are required to complete it.



Four–channel High-current DC Fan and Pump Controller

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. Four independent 10A MOSFET outputs provide 4 x 10A or 2 x 20A, or 2 x 10A and 1 x 20A output. Many uses in automotive and control technology.

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


Colour Maximite Computer – Part 2

This month we cover the constructional details for building this retro 80s home computer. It contains surface mounted devices and good soldering skills are needed if you decide to assemble everything from scratch yourself. (Pre-populated boards are also available from  This article provides all the information you need to identify parts and install them correctly. In Part 3 next month, we’ll explore some applications, including having some fun and retro games with your Maximite!


Using Stepper Motors (Part 3)

In this part we explore the essential electronics needed to drive stepper motors efficiently, looking at driver circuitry for common types.


Audio Out

A plethora of practical hints and tips for building and using  loudspeakers are given this month, also examining the physics behind the moving coil itself and a detailed examination of common loudspeaker terminals and connection types. Plenty of hands-on advice and hints and tips for audio enthusiasts, not to be missed!


Also in this month’s issue:


  • The Fox Report – an update on Huawei and Oppo, the latest Chinese smartphone maker hoping to hit the big time.
  • Techno Talk – the implications of the expected changeover from analogue to VoIP telecoms.
  • Net Work – Freeview channel anomalies; an inexplicable Ethernet port on an LG TV; the changing face of UK power consumption over the past 50 years; the unspoken features of smart meters.
  • Circuit Surgery – common emitter transistor amplifiers examined
  • Max’s Cool Beans -  Max eggs us on with more insightful news about the HRRG, or Heath Robinson Rube Goldberg 4-Bit Mixed-Technology Computer
  • Make It with Micromite (Part 11): serial data communications


Next month

Digital Signal Processor; Zero-Risk Serial Link; Four-channel Fan and Pump Controller (Part 2); Colour Maximite Computer (Part 3); Using Stepper Motors (Part 4). Contents may be subject to change.


There’s more in PE than ever before! PE is packed with practical electronics projects and theory for the hobbyist. You can order a printed copy of PE for delivery to your door (worldwide), or try the PDF Version (needs Adobe Reader for Windows), or the Pocketmags for your mobile device. Subscribe now!



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