Pic Based Pitch sequencer for Toy Keyboard

Over the past few weeks I’ve been tinkering with PIC Microcontroller programming and hardware development ( ie: Stringing things together with clip leads DIY style ) .The result of the initial trials turned out quite nicely. Based on a simple premise of taking a toy with a pitch resistor and varying the value of that resistor sequentially. This creates note strings and also at higher tempo frequencies more modulated sounds. Unfortunatelyy PIC 16F627 does not have a DAC that would output specific voltages, but it does have plenty of PINs that can be turned OFF and ON, the easy way to create some cascading variations is to use something called a resistor network and in this case I took advantage of parallel resistor properties while keeping things isolated with a 4066 quad switch IC for building the resistor ladder. When all the switches are ON the resistance is least compared to when all of them are OFF. This coupled in parallel with a 1Meg Pot provides for some nice variations. The sequencer program running on the PIC has 16 steps and each resistor has its own channel of ONs and OFFs that can be “Muted” if needed. The controller has only4 buttons and 4 LEDs, however many buttons are overloaded with functions so different combinations do various things like speed up and slow down the tempo, randomize patterns, randomize step lengths to create “Swings”, and also edit patterns in a special mode. As a bonus MIDI out port sends out the 4 note patterns than be mapped to Samples, Drums, or Synth sounds. All that functionality really maxed out the massive 1K of Program space, granted the code is not the greatest and was written in PICClite, but the DSI keyboard turned out quite nicely and is lots of fun to play around with. There is also new blog which will have more tips and tricks of the MIDI and PIC programming located at PIC4MIDI.blogspot.com, contributors will include myself and Electrokraft. A schematic of my circuit is posted as a general idea. Actual circuit is a little different, but if anyone has suggestions please let me know.
Video of the keyboard in action as well as some prototype photos are available.