* sheepsint in radio / toy piano keyboard

things that would make life easier
* badnop over ICD2 compatible connector

for when i get bored:

* christian's lcd screens
* bitbanged serial / midi
* bd led (icomm)
* isa bus <-> spi interface using spare 452 (vga card interface)
* fatman mcu replacement
* msx serial + rom interface
* serial switch / usb multi serial io
* cheap wireless/irda


PIC TIPS & TRICKS
-----------------
* pic counters are asynchronous (during sleep) and can count faster than cpu
* use pic output pin to power peripheral devices (i.e. opamps, line drivers)
* protection diodes can take quite a lot of current. add a large enough 
  capacitor between VDD and VSS and you can steal power from a digital 
  input that has a usable duty cycle.



LED DISPLAYS
------------

maxim makes display drivers that can probably be sampled. this is
a lot easier than wiring up to microcontroller and writing controller
software for it.. for max brightness, high current sinking transistors
are necessary, so an IC is a lot easier. to bad only QSOP.

serially controlled (SPI)
MAX7219	(MAX7221)   8 x 8 segment - using 8+8 pins (PDIP)
MAX6950 (MAX6951)   5 (8) x 8 segment - using 9 pins (QSOP)
MAX6960             8 x 8 matrix driver - 2color / 4steps (MQFP)



ANALOG
------

i'd like to get into some digitally controlled analog synth/filter
projects. these might be interesting toys:

MAX274		4x 2nd order section (PDIP)
MAX265		2x switched cap (PDIP)
AD633		4 quadrant analog multiplier (PDIP)
SSM2164		quad VCA (PDIP)
CS3318		8 channel volume control 

one of the things i've been breaking my head over is how to build a
decent sawtooth oscillator with controllable frequency and amplitude
using digital tricks only. this is basicly a current DAC charging a
capacitor. how to make a current DAC?


VIDEO
-----

AD723		rgb to ntsc/pal encoder (TSSOP)



POWER
-----

i have some old crappy speakers and PC power supplies lying around,
maybe they can be recycled as a crude class D power amp? if not for
general purpose things, then for one bit sound experiments. as long as
you don't go poking in the insides, and make sure they are always
loaded, PC power supplies are fairly safe to toy with. they can
provide a lot of power, so can and will destroy components if wired up
incorrectly. the one on my desk is a 300W version, rated

+12V  15A
+5V   30A
+3.3V 20A

using a full bridge (H bridge) 4 transistor configuration is probably
best, since it allows a capacitorless operation. the most useful is
probably the +12V one. a full range square wave can dump about 18
watts into a 8 ohm speaker, and 36 into a 4 ohm one.



binary FSK/PSK
--------------

i'd like to give this a try with minimal electronics. mainly in the
spirit of MSX tape format:

http://www.terra.es/personal7/miguel.colom/msx/codif_en.htm

one thing i don't understand about this format is that the high
frequency is used as pilot tone, since it requires one more phase
correction once the data starts.

to do proper demod, you always need to extract a clock to determine
the sampling. after that, it's simple matched filters and error
correction and resynchronization state machines. so, i work on the
binary sampled stream. algorithm is:

1. use preamble to synchronize clock frequency and phase
2. use matched filters to extract one bit for 2 sampled bits

for BPSK, using 10 for one and 01 for zero, a preamble could be a
series of ones, where the first data bit follows a zero start bit:

10101010101001xxxxxxxx
p p p p p p s d d d d

this would enable to detect the frequency and phase by synchronising
on the rising edge, and averaging the time to determine the sample
frequency. if you get the edge right without phase mismatch, sampling
at 4x the baud rate should be enough. during sampling, one can lock on
the mid-bit transition.


AUDIO
-----

- adaptive filters



SKIN SIGNALS
------------

apparently it's possible to transmit signals over human skin through
capacitive coupling. frequencies upto about 100kHz are possible, above
that energy will start to radiate.


CIRCUITS
--------

some things that might come in handy for wearables
* 3 opamp measurement amp
* charge pumps for higher voltages
* upconverters: run off a single 1.2 battery
* battery chargers: charge the battery when power is available
* battery monitoring
* A/D stuff