Drill Speed Controller for 12V PCB Drill (Query).

[Yorkie]

Being in a hurry I got my caps the wrong way round

C3 (the output side) should be 10nF or 100nF and moved close to the 78L05 and C5 (the input side) should be 330nF.

Sigh...

No dramas Nick - I guess I should have tempered my enthusiasm with discretion, but no - I went right ahead and built it!

But the good news is that it works a treat - much better than the one I built years ago, and better than a commercial  'Como Drills' one. Like this one, they're both PWM designs, but at slower speeds they  'pulse' which isn't really much of a problem as the drill needs to run at fairly high speeds anyway. However, this design will slow right down to a stop with no jerkiness at any speed and if I apply a load to the drill, I can tell that the controller retains the full torque, whereas with simpler designs, (not that this is complex), which basically just lower the voltage to the drill, the drill loses torque and will stall under pressure.

I've attached a pic of the finished board, with the two errant caps in the wrong place, but it will be no big deal to swap them over.

In case anyone might come across the thread and decide to build it, I've updated the component overlay to correct it, and also the track layout for the mask, so the two diagrams in post #14 should be disregarded.

I've found a suitable transformer for it in my spares box, so will get on with boxing up the controller during the week to finish it off.