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Circuitbenders Forum => Circuitbending discussion => BENDING TIPS => Topic started by: LoFi-Ninja on July 23, 2009, 07:30:30 PM

Title: Crystal clock replacement
Post by: LoFi-Ninja on July 23, 2009, 07:30:30 PM

Hi..

Simple Q.. I have a cute drum/beat box that has a 16MHz crystal clock of the two pin type.

I've tried replacing it with various variable oscillators but it just won't work.. Can you guide me to a schematic that you know works for replacing crystals... ?

Thanks alot !

Title: Re: Crystal clock replacement
Post by: Gordonjcp on July 23, 2009, 08:37:25 PM

One of the crystal pins will be an output, and one will be an input.  You may need to try both the pins to see which works.  Start with your oscillator set to 16MHz first.

Title: Re: Crystal clock replacement
Post by: LoFi-Ninja on July 24, 2009, 01:09:58 AM

Are you sure they're "polarity oriented" ??? I've never had this problem before.. I'm pretty sure it's only the four legged ones that got a specific pinout..

Title: Re: Crystal clock replacement
Post by: MAGTIG on August 09, 2009, 08:36:39 AM

Anyone happen to know if Radioshack or Fry's Electronics (US) stock crystals?

If not, I'd really like a nice handy link of where to order them online. I've yet to replace one, but I've studied the SA series schematics over at casperelectronics.

Title: Re: Crystal clock replacement
Post by: Matt the Modulator on August 09, 2009, 12:09:05 PM

this link has some info on using osc to replace resonators http://www.sailormouth.org/index2.php?pg=addingosc.inc (http://www.sailormouth.org/index2.php?pg=addingosc.inc)

Title: Re: Crystal clock replacement
Post by: Gordonjcp on August 09, 2009, 11:14:17 PM

Quote from: LoFi-Ninja on July 24, 2009, 01:09:58 AM

Are you sure they're "polarity oriented" ??? I've never had this problem before.. I'm pretty sure it's only the four legged ones that got a specific pinout..

The crystals aren't, but the chip will have one of the pins acting as an output that drives one end of the crystal and the other as an input from the crystal.  Which way round you connect the crystal isn't important (except maybe aesthetically) but if you're driving the chip from an oscillator it matters which pin you connect it to.

Title: Re: Crystal clock replacement
Post by: MAGTIG on August 11, 2009, 06:42:32 AM

Ok, I'm on Futurlec.com adding stuff to my shopping cart. I figured I'd pick up an assortment of crystals to try in various spots.

But do I want these: http://www.futurlec.com/ICCrystalsMain.shtml (http://www.futurlec.com/ICCrystalsMain.shtml)
Or should I be getting crystal oscillators? http://www.futurlec.com/ICCrystalsOscillators.shtml (http://www.futurlec.com/ICCrystalsOscillators.shtml)

Sorry for all the hand holding and whatnot, I've only been doing this a couple months. I've read a ton of stuff, but this is my first time buying crystals/oscillators... which reminds me, should I grab an assortment of oscillators too? Which ones?

Thanks for your patience, guys. I'm totally loving this stuff, I'm just getting a bit confused with so many options. haha

Title: Re: Crystal clock replacement
Post by: Circuitbenders on August 11, 2009, 12:52:33 PM

probably the first one, although you might be better off just buying parts to build your own variable oscillator using a 555 timer. Just search for '555 oscillator crystal' or something and there should be details of how to do it somewhere

Title: Re: Crystal clock replacement
Post by: Tyler1144 on August 14, 2009, 05:56:25 AM

So with a 555, you will be able to adjust the mhz? So it would be like an actual pitch bend then, right?

Title: Re: Crystal clock replacement
Post by: Circuitbenders on August 14, 2009, 12:57:29 PM

thats the theory, yes.

Title: Re: Crystal clock replacement
Post by: Tyler1144 on August 14, 2009, 08:23:02 PM

So with a 555, im guessing the device needs a square wave?

Title: Re: Crystal clock replacement
Post by: Sam_Zen on September 17, 2009, 05:11:04 AM

A clock signal always has to be a symmetrical square wave.
Most processors have two clock lines : one input, one output, both connected to a crystal.
If the crystal is replaced by another clocksignal, only the input line is used.

The 555 is quite unstable and noisy, but it has the advantage of a wide power supply range.
If you happen to have + 5v, it's much better to use the 74LS624 of the TTL series.
A HF VCO, having two analog inputs, so lineair pots can be used between V+ and V-.

Title: Re: Crystal clock replacement
Post by: noystoise on September 17, 2009, 08:18:20 AM

i agree, 74624 is a good way to go. the 555 cant even go high enough to reach the original clock speed of most devices. the only problem i have with the 74624 is the range. you cant go from inaudibly high all the way to a grinding halt with one sweep. i still need to try out that 1799 chip thats been getting so much attention lately. looks like theyre a little cheaper than the 74624 too.

Title: Re: Crystal clock replacement
Post by: Sam_Zen on September 18, 2009, 04:09:52 AM

You can have a preset range with one pot, and a finetuning with a second pot (to 'R'):

(http://www.xs4all.nl/~samzen/synth/ttl624.png)