Switching of crystals in crystal oscillator using a 74HC4316 ??

Too bad the trimmer caps are on the ground side. If they had been on the hot side you could just sequentially ground one end of the crystal with a

1N4148 and about a mil of current through it to turn each individual rock on.

Jim

--
"It is the mark of an educated mind to be able to entertain a thought 
without accepting it."
        --Aristotle


> A circuit of the oscillator is here ...
> http://www.box.net/shared/52vxldm8yl
>

Probably it won't work well; the power supply isolation of the

74HC4316 isn't great, the 50 pF/3 MHz suggests about 1k ohm impedance, and your ovenized oscillator seems to indicate the (variable, about 100 ohms) series resistance could be an issue as well as the channel capacitance (35 pF).

A bunch of reed relays driven by ULN2003 would give you logic control. Pay attention to the reed orientation, you want the long end toward the crystals.

How about a 1:10 analog data selector on the high side?

Cheers! Rich

Didnt think of reed relays. I'll have to look up what speed they can switch at. Ive got a need to switch channels sometimes at rates faster than 2Hz. Can reed relays do this? JEFF

Thanks. This was sort of the idea I had, and came up with the

74HC4316. Dont know whether a data selector would still have the problems that were mentioned for the above IC. JEFF

the

a

ck

I very much doubt that would work. Diode switching is probably the way to go.

--
http://www.wescottdesign.com

See if you can find any circuits that show such switching using diodes. I think that's your best bet.

What sort of physical constraints do you have? Do you want to just replace the switch, or can you replace the whole section of the circuit with the crystals?

Or ponder this: The '+V' is your positive supply, all resistances should be equal and enough to flow a couple of mA in the diodes, and you should ground just one of the control lines at a time. Each diode will act as a switch for RF -- no current = open, current = closed.

Plan on retuning.

+V o | .-. | | | | '-' | | ___ .-------------o-------------o------------o---|___|--. | | | | | | | === V V V GND - - - | | | | | | ___ | | o----|___|-o +V or 0V | | | ___ | o-------------+----|___|-o +V or 0V | | | ___ o-------------+-------------+----|___|-o +V or 0V | | | | | | o o o (created by AACircuit v1.28.6 beta 04/19/05

--
http://www.wescottdesign.com

BROWSER HOSTILE!

1) What is it about that reference that crashes NetScrape 7.2? 2) Why does NOTHING show even with Insanity Express 5? I have not seen any Colpitts CMOS diagrams, so i would say have N seperate Colpitts oscillators feeding CMOS transmission gates (analog gates is another term) and drive the gates as you see fit.

Reed relays take about 1mSec to "move".

Reed relay switches are available with 50 ohm specs and some seem OK to a Giggle or so.

Sure, and faster too...

Both those browsers are long past retirement age. Netscape was allways buggy and crashy. Most people stopped using it years ago. I seem to recall having to upgrade a few machines from IE5.0 to IE5.5 because microsoft could not be bothered to patch a serious security hole in 5.0 You should not be visiting any internet sites with IE5.0 Bob

Thanks for the help guys. The switch is not easy to remove, but I can un-wire it and modify as needed. Tim, I see the concept of what youre suggesting, but didnt understand your diagram if it was in relation to the oscillator cct. If R38/R39 bias point in the osc is at 10 volts (Vcc is 20V), then my understanding is that I could add separate diodes from SA4 wiper fanning off to the 4 crystal wires (anodes going to SA4 wiper), then add high value control resistors to the cathodes. Would this be sensible way to go? ALSO what do you all think of DIL relays verses the external soleniod coil types. Which would be better for this application in terms of stray capacitance, etc? Thanks, JEFF

Free. Simple to install. They work.

Ed

I do nt, except when NS7.2 crashes on same website.

Try the K-Meleon browser. Mozilla Chrome rendering engine, native Windows UI *NOT* and XUL one so it isn't resource hungry. Runs well on old machines + old windows.

*much* more stable and secure than old IEs or Netscape.

If you like it, I've got a list of extensions for it that improve security and usability.....

--
Ian Malcolm.   London, ENGLAND.  (NEWSGROUP REPLY PREFERRED)
ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk
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