pitch bending and crystals

[gmeredith]

I've just bought a Casio DH100 horn (being delivered now!). It hasn't got a pitch adjustment for tuning it to other instruments, according to the service manual, just a fixed crystal and cap network to set the processor clock.

Can you tweak the caps around the crystals to change pitch, or are the crystals unaffected and so won't change the clock speed?

Below is the crystal circuit.

Cheers, Graham

[catweazle]

Hi,
you can't (and shouldn't) change the capacitors ar the crystal, that wouldn't change the crystals frequency.
Remove the crystal and use a variable (square wave) oscillator.

For example  Linear Technologies   LTC1799   
Or...
A voltage controlled oscillator  0.12Hz to 60MHz

74xx124 , 74xx624, 74xx628 or 74xx629   TTL VCO   (xx stands for  HC, AC, HCT ...)

search for the datasheet at google for the device you get (pinout and maximum frequency can be different)...

Schematic:

[catweazle]

....
Remove the crystal and the capacitors.
connect the "clock output" from the VCO to the  CPU pin  X1 (pin 25)   
leave pin 26 on the CPU open

[gmeredith]

Hi Catweasle!

Thanks! I thought it might not be as easy as just fiddling with the caps.

Re: "leave pin 26 open" - are you sure you you don't mean pin 24 (x2)? - pin 26 is the Vss gnd for several CPU pins.

Cheers, Graham


P.S. - how did your work go on the MIDI OUT board for the SK-8? Last I heard you had a prototype board going. Did you ever get it finished to your satisfaction?

[catweazle]

you are right! it should be pin 24 of course    sorry about that

here is the datasheet for the 74LS624 from www.TI.com
http://focus.ti.com/lit/ds/symlink/sn74ls624.pdf
[urlhttp://focus.ti.com/docs/prod/folders/print/sn74ls624.html][/url]
The  74LS624  can only be used up to max. 20MHz

if you need higer frequencies use the  74LS124  instead  (up to 60MHz)
and this one is a dual VCO , what mean you have two seperate VCOs in one IC.
So you can use one for the Clocksource and the other as LFO for modulations
FM is possible or Ringmodulation with an XOR logic gate (CMOS 4030 or TTL 74xx86)
http://focus.ti.com/lit/ds/symlink/sn74s124.pdf
http://focus.ti.com/docs/prod/folders/print/sn74s124.html

Be aware that the TTL 74xx Logic series ICs can used 2..6 Volt power supply.
CMOS 40xx Logic Series can used 5..15 Volt power supply.

after reading the datasheet more exactly I saw it is better to use other capacitor C2 values (in my schematic)
try values around 15pF to 1nF somewhere between.


The MIDI thing lies on ice, a lot of ohter work have to be done
(I need 48 hours a day...)

[gmeredith]

The 74LS624 should be fine, as I only want a pitch bend of a couple of notes, for tuning adjustment.

Actually, I've just thought of an idea that might be interesting to try. Looking at the schematic you provided of the circuit, I presume you control the frequency by the input CV voltage from 1-5V, controlling it by a pot from a 5V DC source - basically using a resistor to control the CV.

If I can get pitch bend control using this, perhaps I can control the pitch bend using pressure. For example, using a pressure/resistance device on the mouthpiece that could bend the pitch the harder you squeeze, if you clamp down on the mouthpiece with your lips. Are there any of these things available? - I'm thinking maybe a semi-conductive rubber strip on the outside of the mouthpiece, that changes resistance as pressure is applied - is there such a thing? It would need to be made slobber-proof as well

Cheers and thanks for your help

Graham

[catweazle]

As I've seen the CPU uses a 12MHz crystal, so 20MHz will be adequate.

There are two cv controls one is for the range (maybe it sets the maximum frequency)
the other controls the frequency. The capactior sets also the maximum frequency,
high values results in lower maximum frequency (for LFO for example).

You can control the CV control inputs via a potentiometer voltage devider of course for pitch bend.

Check  www.FreeScale.com   they have pressure sensors (you can ordder free product samples there)
MPX2010: Compensated Pressure Sensor for example.
http://www.freescale.com/webapp/sps/site/overview.jsp?nodeId=0112699036

Slobber protection would be neccessary I think 

Gtz
Eric

[catweazle]

Additional information about the pressure sensor idea:

First of all you have to know is the maximum pressure a human can "blow" into the pressure sensor.
Then select a suitable pressure sensor.
Compensated pressure sensor selection list (sorted by maximum pressure)
http://www.freescale.com/webapp/sps/site/taxonomy.jsp?nodeId=01126990368710#2

- MPX pressure sensors need a 10..16 Volt power supply.
- MPX pressure sensors have an analog output corresponding to the pressure
  0..~40mV (yes, milli Volts -> 0.04 Volt)   0.2V/kPa 

mmmh, 40mV that's not a lot ...
That means you have to amplify the analog sensor output x100 
to get a usable control voltage for the VCO  1..5V   (with offset off 1Volt you can get it  40mV*100 +1V)
This can easly done with an "non inverting operational amplifier (OPV)"  LM358  for example
http://www.technologystudent.com/elec1/opamp2.htm

http://www.national.com/mpf/LM/LM358.html

[catweazle]

Or ...
I think you meant something like this
http://shopping.msn.co.uk/results/shp/?bCatID=23,av=2-46228,layout=list

[gmeredith]

Yeah, that last one is what I had in mind - perfect! Thanks for the link! These also look easy enough to "slobber-proof, just by sticking them to the mouthpiece with sticky tape. Price is affordable, too.

Thanks for the info!

Cheers, Graham