July 2012

“Lab Standard” 16-bit Digital Potentiometer

This design is a low-cost digital programmable voltage divider for lab or bench use. It provides an accurate adjustable output derived from a precision voltage reference input – ideal for meter or test equipment calibration and circuit prototyping or development.

After connecting a reference voltage (e.g. the 10V Precision Reference in EPE June 2011) and hooking up to an external circuit the desired voltage is keyed in through a keypad and an LCD display shows the status.  A toggle key switches the divider in or out of circuit. Accuracy is typically better than ±1mV over full range. Theory and full constructional details are included. The project is PIC  16F877 based, and free source code is downloadable from our Library.

Intelligent 12V PC Fan Controller

If your computer makes a distracting amount of fan noise then help is at hand, thanks to our 12V fan controller project. It can monitor up to four locations and control up to eight computer fans and our free Windows software configures and displays temperature and fan speeds. It works with most fan types whether 2, 3 or 4 wire and is configurable for different tachometer configurations. An audible alarm warns of fan or sensor failure.  It can also be used without software in stand-alone mode, e.g. in greenhouses or horticulture. PIC 18F2550 based, and free source code is downloadable from our Library.

Dual-Tracking PSU (Part 2)

The second part of our project deals with all assembly and interwiring of this high-quality linear ±0 to 19V bench power supply. It’s a fantastic piece of test equipment to enhance your workshop. Both the mains-powered and main adaptor versions are covered.

Also in this issue:

• PIC n MIX – producing a video library for the chipKIT Uno32 development board
• Techno Talk – trends emerging in digital billboards used in advertising
• Net Work – the Internet column – buying Internet-based printed materials, birthday cards and stationery delivered to your door (or anyone else’s); a salutary warning about taking backups look at Google’s new Drive cloud storage.
• Jump Start  – our specially written series of “design and build” projects  aimed at newcomers.  Based on Circuit Wizard, the revolutionary software that combines circuit and PCB design, simulation and CAD/CAM in one complete package. This month’s Jump Start project investigates a Battery Voltage Checker based on a popular l.e.d. bargraph i.c. and explores the foundations of software-based PCB circuit design.
• Circuit Surgery – our in-house expert explores the principles of circuit buffers, output stages and crossover distortion.
• Practically Speaking – more practical workshop advice for the electronics hobbyist.