Circuitbenders Forum

Circuitbenders Forum => Circuitbending discussion => Topic started by: the_zombiest on July 21, 2006, 01:57:52 AM

Title: external oscillators
Post by: the_zombiest on July 21, 2006, 01:57:52 AM

I'm trying to replace a 3.29mHz ceramic resonator with an oscillator.  I'm fairly sure that a 555 based osc won't make that frequency so i'm trying a 4011 IC.  does anyone know what cap/resistor values i need to get in the 2 - 6 mhz range, if it's at all possible?

I've tried sourcing the LTC1799 chip and they are really hard to find, really small and really expensive...well, over 2quid...

Any help would be much appreciated and for the record, it's to mod my matchbox edition Talking Teacher.  It's been gathering dust for a while and i need to give it a purpose.

Title: Re: external oscillators
Post by: the_zombiest on July 24, 2006, 02:44:25 AM

well, after 3 hours of arse-numbing, brain-hurting tedium... I did it!  it may not seem like that big a deal but i'm happy.  There is one problem though,  the pitch change is really high and i'm not sure how to alter that.  I'm not entirely sure how i got the damn thing working full stop!  But it does (kinda) work.

If anyone's interested at all in a matrix board layout (i hate schematics) for a 4016/4011 oscillator that's identical to this one (http://www.sailormouth.org/index2.php?pg=alphadesk.inc) (at the bottom of the page) minus the amp meter... then let me know and i'll try draw it up for you.

Title: Re: external oscillators
Post by: catweazle on September 30, 2006, 10:24:15 AM

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.pdf

Remove 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.jpg
http://www.jz-server.de/forum2/e107_files/public/1159546804_13_FT362_7414_osc2_.jpg

(also posted in Casiobend Forum)

Title: Re: external oscillators
Post by: merry1shah on August 15, 2012, 11:44:13 AM

Thanks for sharing. Sorry i do not have any idea about this topic.

Title: Re: external oscillators
Post by: Circuitbenders on August 15, 2012, 07:22:54 PM

thanks for digging up a six year old thread for that post.  ::)