With the analogue board completed, it's now time to build out the digital and power management sections.

Digital Section

The digital section is built on to standard perfboard, there's nothing much to see here other than marvel at the poor quality of the construction. At one point, I had power and ground backwards leading to some exciting choices but that's what happens when building out on the fly without a plan. Memo to self, draw a diagram first.

Breakout pins were added for ground and the PPS signals from the 555 and GPS; these facilitate connecting the TICC for doing measurements.

Power Section

So far the prototypes have been running from my bench power supply, but I wanted a bit more flexibility on the power source, allowing the board to run from a standard 12v wall adapter to be a bit more efficient on longer runs.

Each of the sections has their own 5v LDO voltage regulator to avoid coupling noise between the digital and analogue components. This presents two challenges:

• avoiding adding noise from using a cheap wall wart

• dropping 12v to ~7v to supply the voltage regulators

Whilst the boards use a tiny amount of power and the heat would probably be manageable, it seemed unwise to feed a potentially noisy 12v straight to the LDOs

The power section uses a small buck converter to initially drop from 12v (or more) down to ~9v. This is then followed by an LM317 adjustable regulator to clean the input and drop the voltage again to 7v. The LM317 provides the analogue and digital sections with a relatively clean 7v which is then tidied up again by the section LDOs.

The Big View

Here's an annotated view of the final configuration