Pseudo-sine generator - part 1

Here is a new project I'm working on - a pseudo-sine wave generator.  It uses a 40106 CMOS to generate a square wave, using a B100K pot to control frequency. This is the clock-in to a 4017 decade counter.  Each output of the decade counter goes through a different resistor, which all connect together to the output.  There's an additional resistor between the output and ground -- this creates a voltage divider, between whichever of the 4017's outputs is active (which will be at 9V) and ground.

If I know what I'm doing, it should create a roughly sine waveform:

 

So, I designed a PCB and once I etch it and build, I'll be back with part 2...

Follow-up:

Doesn't seem to work quite right:(  It definitely produces a complex waveform, with multiple frequency components.  I haven't really tried much trouble-shooting, other than making sure the resistors aren't open or shorted.  Wish I had an oscilloscope!

DIY photocouplers

Here are a few pics of photocouplers I've been working with.  So far, I've only used a light sensitive resistor/LED combo, but I just ordered some photodiodes from Mouser, so we'll see...


This guy is very basic.  You can see the small (<1K) resistor on the LED's positive lead, just so I don't accidentally burn in out.

Here is a slightly more involved one.  I took a small section of toilet paper tube, glued a mirror to one side, then positioned the LED opposite the mirror and two light sensitive resistors on either side.  Then, I sealed the whole thing up with electrical tape.

Filters!

Here is a great site for designing different filters for audio signals, from very simple RC low-pass to active and notch filters.