Friday 12 October 2018

BAW!! #7 Give Me Power

Sometimes it occurs that the piece of equipment that you are using could be better or have better features maybe adapted to suit your needs better.

This is my bench supply i'm currently using, it work fine on the fact that it supplies power to whatever om working on but it has a few quirks which quite frankly drive me nuts on a daily basis.

I can't set the output voltage without turning the device on, which means if you have a project wired into the terminals you have to unplug it turn the supply on set the output voltage then turn the supply of wire your project back in then you can power it at the write voltage.

The other thing I would like to have is a dedicated 3.3V supply at the moment my solution to that is using an half broken Raspberry Pi powered from a USB port as my 3.3V supply which to be honest is no the best solution. 

The easiest solution to all my problems would be to invent in a good bench power supply. But that would leave me out of pocket and there would end up being a power supply sitting on the shelf unused. 

So lets look at designing an add on board to make it more useful. 

The functions I want to add are:
  • The ability to set the voltage without having to disconnect from the supply.
  • A dedicated 3.3V supply, preferably a linear regulator of up to 1A current supplying.
  • A select-able low pass filter for low noise applications.    
  • An auxiliary channel for current measurement.
  • Hooks for attaching oscilloscope probes. 

The schematic is pretty straight forward not much in the way of active components just lots of connections.

I'm still working with KiCAD finding easier and easier to use each time I complete a board I seem to find a new feature. I this case i was coming to the end of routing the board and there seemed to be a connection missing between EarthGND terminal and a a pin header which is used to link EarthGND to supply ground if necessary. I had managed to label the pin connector as EarthGround instead of EarthGND I was on the final trace and wanted to finish routing the board. 

This is when is discovered that it is possible to change the net of the pad in the layout editor, bonus!!! It mean ti could finish the routing straight away without having to go back to the schematic and change it reexport the net list then re-import it in the board editor.

This is not the 'proper' way to do things because it them means the schematic still has the error and would have to be updated at a later date. But in a pinch it seemed to work. 

Something I have always done is to print a paper version of most boards I design and this one was no exception. As I was designing to fit to another device it was important I hadn't made a mistake.   

To my relief it appears to fit well. So it means there a high possibility the finished board will fit nicely also. 

All done and routed ready for the next one.

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