Thursday, November 1, 2012

555-Based Dimmer 3D Circuit

I built this 3D, freeform circuit as a test project. I've seen a few lately and love the way they look, and after making this circuit, I'm excited about this method as an alternative to point-to-point soldering or etching for small, one-off boards.

It's a dimmer circuit: a 555-timer-based PWM generator driving a high power MOSFET.  I kept it simple and focused on a method, not on making anything particularly fancy.

Here's a video walk-through of the circuit:

I edited a schematic for a board I'd built earlier, adding a scrounged 10k audio potentiometer with switch.  The parts list was short:
  • 10k potentiometer with switch,
  • 2 2-pin screw terminals (input and output),
  • NE555 8-pin chip,
  • fat npn MOSFET,
  • 2 1N4148 diodes,
  • 2 capacitors: .1uF and 1uF,
  • 330 ohm resistor
The first step was the Eagle board layout.  With air-wires I moved things around for a while to get things close, and routed and rerouted a few times before setting some guidelines:
  • Put the major components where you want them first.
  • Pack the rest of the components in paying attention to keeping traces short.
  • Small 2-lead components can fit later, with one lead overlapping its signal, the other reached by a branch made from its lead.
  • Lay out a few long traces that hit the most pins and cover the most ground first.  Try to get those traces in a straight line or aligned in an L- or S- or U- arrangement, more or less.
  • Avoid branching, unless the branch can be a component's lead.
  • Small kinks and zig-zags are OK and may be built with straighter wire segments later, with pins bent to get where they need to be. 
  • Don't think much about top/bottom layering and about crossing lines.  There will be room to cross a wire here or there.  Try not to cross, but you can worry about top and bottom later.
Then on to building, which breezed by.  Pre-bent wires made it a straightforward, by-numbers sort of thing, and I used the components' leads instead where I could,  reducing the number of parts.  Building notes:
  • Print out a sheet to see the circuit different ways, to use as a pattern.  Run the same sheet through the printer, taking advantage of the print options:
    • Aligned top center, scale 2 or 3 (what will fit), with all layers drawn.
    • Aligned lower left, scale 1, with all layers,
    • Aligned lower right, scale 1, just the traces.
    • Note: also print scale 1 mirrored versions too, of all layers and traces only, to see things from the bottom, which is how things are soldered.
  • In the trace-only print-out, number the longest traces to make wires for them.
  • Strip a length of stripped solid-core wire for each long trace.  Bend them to shape with pliers, clipping to length, using the trace-only print as the pattern.
    • Small kinks in the pattern don't generally need to be bent-- wires and pins will bend during soldering.
  • Clip leads after soldering, unless it has to butt up as a T.  It's easy to clip after soldering, and wires can shift during soldering.
I kept it simple and methodical so I could scale it up to bigger circuits.  I have to say that the result surprised me in how quickly and easily the board came together.

I'm looking forward to using this on a few other cicruits, maybe a PIC-based USB-serial converter, or a multichannel MOSFET-based switcher or SSR or... good stuff from this :) Then there's the question of how to mount this, or cast it in some material.


  1. Just a small remark: A TIP121 is a Darlington and not a Mosfet.
    Here is an interesting read, I found a bit ago:

    1. Thanks, good link! I'll edit the text, I'm using a MOSFET.

  2. Do you have the schematic for it?

    I am looking for a nice simple, small sized PWM circuit to control LEDs

    1. Sorry I don't have it handy now, but it's nothing fancy-- just a schematic I found that looked like so many others :) This looks similar: