[3 July 2010 – this project has been retired, but the posts left for reference]
Greeting again to followers of the bbboost journey. It has been a month since the last instalment, however the 20V DC plug pack took a long time to arrive from the land of China. Nevertheless, the project is moving forward. For my new readers, the bbboost is a power supply that can be assembled by a beginner, and can offer a smooth variable DC output voltage of between ~1.8 and ~20 volts – perfect for experimenting, breadboard, and generally saving money by not buying batteries. You can just make a PCB version, or mount it in an enclosure like a professional desktop unit. No mains voltage wiring is required, so it will fine for the younger enthusiasts. Follow the project from here.
This time I have breadboarded the power supply module, using the circuit described in chapter two. Let’s have a bit of a look:
These trimpots were ok, but it would be preferable to use the fully enclosed dustproof versions. Will order some and try ’em out.
One trimpot (the blue and white one) is 5k ohm, – to adjust between the full range, so this is the ‘coarse’ adjuster; the other trimpot is only 500 ohms and changes the voltage selected by the coarse pot by around +/- 1.2 volts. The purpose of having two controls is to make it very easy to select your required voltage down to one-hundredth of a volt. The following video clip is a rough example of this type of adjustment in action:
This power supply will also be designed for installation into a nice enclosure, so in that case one would use normal-sized potentiometers for the coarse and fine voltage adjustment.