Experiment #2: Power supply


Following the decision to power the diorama using 9V DC, the next step was to design a power supply with the following features:

  1. To enable either centre positive or centre negative power supplies to be used - implying the use of a bridge rectifier.
  2. To have an output for a “power-on” LED.
  3. To have a tap making available the full voltage after rectification.
  4. To have a tap for a 5V supply to power the microcontroller(s) and (probably) the LEDs.

Testing was done with both centre-positive and centre-negative 9V DC supplies. In fact the same centre negative supply was used for both tests using an adapter cable to swap polarity as required.


The following circuit was drawn up:

Power supply schematic

It was tested on a breadboard:

Power supply test breadboard layout

Since the voltages obtained were as expected, a trial circuit was constructed on perf board that replicated the breadboard design. A bank of 8 pins were provided for external connection, as follows:

Given that this was my first ever soldered circuit there were some problems and the circuit wasn't as tidy as it could be!


Evaluating the soldered circuit led to a redesign of the layout of the board along with some changes in functionality. These changes were incorporated in a second version of the board. The functional changes were:

This final version of the circuit board is pictured on the main project page.

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