August 2013

This month’s highlights

Driveway Sentry

This interesting project detects vehicles moving (or being moved) by utilising the earth’s magnetic field. Use it to protect property, farm machinery moving through a driveway or gateway for example. False alarms caused by e.g. animals are therefore avoided.

When movement is detected by a buried sensor loop, it switches on a mains or battery-powered lighting system and activates an optional piezo buzzer alarm for a preset period of 2-25 seconds. 555/ SPST relay output is adaptable for many other applications. All constructional details are described with full colour photography showing every aspect of assembly. A unique way of safeguarding your property!

VOX Circuit

Voice-operated switches find their uses in radio transmitters to control the microphone but the same principles can be adapted to switch a light, an amplifier or even unlock a door. This sound switch uses an electret or dynamic microphone and has adjustable sensitivity and a DPDT low voltage relay output.

Milliohm Adaptor for DMMs

This low-cost adaptor will let you use almost any digital multimeter (DMM) to make accurate low-resistance measurements.

Based around an instrumentation amplifier, this design lets resistance values be read out on the DMM in millivolts. It offers a 0-0.1 ohm scale and 0-10 ohm range.

Superb Four-Channel Amplifier – on the cheap!

This high-quality home amplifier consists of a mixture of salvaged parts and pre-built modules. It follows on from the home loudspeaker project of Feb. 2013 and is not a conventional project but rather a collection of recommendations to help you build your own.

Amplifier modules can be sourced on auction websites and the author gives some useful advice on purchasing them.

Computer Error: reliable digital processing (Part 1)

Short series on high-reliability computing. Part 1 covers the start of computing’s early days, using thermionic valves (vacuum tubes).

Also in this issue:

Techno Talk – how the EU could shut down domestic appliances remotely; LED street lamps.
Max’s Cool Beans – more on radiation, particles and cosmic rays
Interface – introducing the Raspberry Pi SBC and how to interface with it.
Circuit Surgery – an in-depth analysis of dataslicing and Manchester coding.
Net Work – various Do Not Track implications and options discussed, for Internet users.