Hi try this:
very cheap external variable oscillator with logic IC 74HC14 (or 74HCT14)
Frequency range 0.1Hz to 10MHz (should be enough for most toyz)
You can build 6 oscillators with one IC.
Most toys use a crystal for the microcontroller/CPU clock generation. (4MHz,6MHz or so)
It's difficult to change a crystals frequency with an resistor (should not work)
With 4 parts you can build your own cheap variable oszillator (for pitch shift or overclocking/clock glitches)
Parts needed:
- 1 capacitor 100nF
- 1 capacitor [C]
- 1 potentiometer (linear) [R] ~ 4.7kOhm ... 100kOhm
- 1 logic IC 74HC14 or 74HCT14
http://www.ortodoxism.ro/datasheets/philips/74HC_HCT14_CNV_2.pdfRemove the crystal and check out which pin works (only one pin of the two is needed)
Leave the other one open (unconnected)
Works fine I've tested it with a kids toy "my speaking ABC soup" very very funny stuff
the IC contains 6 of the "inverting schmitt triggers" what means that you can build 6 osciallators with one single IC !! that's really cheap isn't it.
For example you can setup the other 5 ones on lower frequencies (replacement for the NE555) to do modulating stuff (with an vactrol - light depending resistor with an LED)
I think the 74HC14 is much cheaper than the 555 (not to say the 74HC14 is 6x555 in one package)
Frequency f=1/(0.6*R*C) R in Ohm and C in Farad
http://www.jz-server.de/forum2/e107_files/public/1159546388_13_FT0_7414_osc.jpghttp://www.jz-server.de/forum2/e107_files/public/1159546804_13_FT362_7414_osc2_.jpg(also posted in Casiobend Forum)