Computing stuff tied to the physical world

New Dimmer Plug

In Hardware on Feb 17, 2010 at 00:01

One last plug… who knows, with a bit of luck, some of them might just work on first try?

The Dimmer Plug controls up to 16 LEDs or other lamps, and is based on the PCA9635 chip:

Screen shot 2010-02-16 at 21.29.21.png

It’s driven from the I2C bus, with a couple of jumpers to allow daisy-chaining up to 8 plugs on a single port:

Screen shot 2010-02-16 at 21.46.19.png

Here’s an extract of the datasheet, showing the different ways to hook up LEDs:

Screen shot 2010-02-16 at 02.04.23.png

Basically, you can drive one LED directly per pin, or add a transistor to drive many more in parallel or in series. The chip just does the PWM part, with various blinking options and more, all from an I2C bus.

To drive high-power displays, the outputs can be tied to darlington arrays such as the ULN2803, or to MOSFETs. There are no drivers on the plug because there are too many different usage scenarios. It all depends!

Originally, I wanted to make this plug also fit on a the back of a display such as this one:


That pressure plug on the photo was added for size comparison. It’s the same size as this Dimmer Plug, which happens to allow daisy-chaining two such displays tightly next to each other when you include the headers.

But I can’t make it fit without widening the plug and mounting components on both sides. So I’ll leave it as is – it could still be mounted on the back by adding lots of little wires and 16 resistors, but it will take some more work. Or one could add a little board to sit in between, with 16 resistors and pins to stick into the 3×6 headers.

Now I’ll stop with this plug madness. Need to finalize all the layouts and traces, send the designs off, and then the waiting starts. Luckily, there’s still enough other stuff left to do around here :)

Update – there are some errors in the schematic. I’ll fix them before sending off this board.

  1. Ah, something like this was the last piece I needed to make the radio-synchronised clock(s) I’ve been meaning to make the last several years. Thank you very much Jean-Claude. Now I just have to get off my arse and do it…

    But why limit them to eight per port when the chip supports 126? Power?

  2. Very nice. Whish I hand knewn this, before I started my moving led display. :)

  3. Yes, yes, yes! I want this one! But take your time, we don’t want to have bugs in the first version ;-)

  4. Very interested in this one. The TLC5940 is long in the tooth.

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