Why are the trimmers in the Tapanator wired this way?

[WormBoy]

I am planning to build the Tapanator(ator), trying to undertand the schematic, and was wondering about the wiring of the trim pots 1-3. I was expecting a variable series resistor (to limit current) or a voltage divider with the LED on the wiper, but instead the 5V supply is on the wiper. If a trim pot is set to its minimal position, that would mean that there is only 330 Ohm resistance between 5V and ground. Seems like a waste of current ... So, is there a need for wiring the trimmers this way in this circuit?

[madbean]

I don't remember the exact circumstance which led to that but IIRC I didn't like the way the LED's behaved when the pots were wired as variable resistors (maybe as they are turned down some?? not sure). I agree it would be better to have at least some stopper resistors between the pots and ground. However, space was really limited on the board and pretty much all of the time those pots are going to be turned 2/3rd up or more to work well.  But you are right it's not ideal.

[WormBoy]

Thanks for the explanation. I might experiment with this part a bit, as I will probably not build it entirely standard anyway  . You're right that the bottom half of the trimmer is unlikely to be used in practice. In any case, with this setup, it's a good idea to keep the trimmers up for any unused outputs.