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Never had much trouble with oscillators but can anybody help me on the oscillator part of the EE Treasure Hunter ? I am using a 32KHz cristal because I cannot get hold of a 40KHz at the moment . What are the resistors going to be ? ( now we have R6= 10 MOhm and R5= 10KOhm ) Which Capacitors should I use ? ( now we have C4=1n and C5=22p ) . Should this schematic work after all ?????? Regards and thanks . Kees
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Re: Oscillator
Well obviously nobody has the answer for me . What I got to do now is to use an IC 4060 as an oscillator . Thanks anyway ! Kees -
Re: Oscillator
Sorry for the delay...
Using a 32kHz crystal should work fine, probably no change in component values. Sure won't hurt to try.
- CarlComment
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Re: Oscillator
Thanks Carl . The oscillator with the 32KHz Xtal will not start though with components mentioned . I set up a seperate test board to check possibilities , but no dies . Has me puzzled though . I will keep trying a little longer and if no success I will use the different oscillator ( Xtal 4900.000 KHz. R = 10MOhm . C1 and C2 33p ) This will give me 38.3 KHz . Thanks KeesComment
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Re: Oscillator
Your crystal might be one meant for series resonance operation instead of parallel. Or, the required cap values might be way different than the other crystal.
- CarlComment
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Re: Oscillator
Hi,
You might want to read the information on the type of crystal you might be using at the website below. If it doesn't take you directly to the application notes, then from the home page, select the application notes under the technical info.
Then select tuning forks.
This website recommends very high values for the drive and feedback resistor for the type of crystal you are probably using if it is a watch crystal.
By the way, I found this little tutorial on crystals to be quite helpful.
One more note, a selection of a 32 Khz crystal will change the operation of the PI also. The delay will be increased so you will also have less sensitivity. You probaby will not be able detect most small gold rings or other gold jewelry very well.
Hope this helps.
Reg
Fox crystalsComment
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Re: Oscillator
Thanks Reg . Good site . KeesComment
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Re: Oscillator, & Stuart design
You have a good point about the 32kHz crystal changing the sample delay. I had not even looked at how the timing works in this circuit, so I did last night.
It appears to me that the sample delay is currently set by the Q2 tap on the dividers, meaning that the switch turns on two clock cycles after the coil turns off. Using a 40kHz crystal, this is 50us. Seems way too high right off the bat. 32kHz will put it at 62.5us.
Also, it appears that the sampling switch continues to sample at half the clock rate throughout the decay, until the coil switch turns on and disables the sample switch via D5. Am I right about this? Seems like this would decrease sensitivity as the latter part of the decay does not vary with target.
- CarlComment
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Re: Oscillator, & Stuart design
Hi Carl,
You are right, there is multiple sampling but the circuit samples and holds the peak negative value so, subsequent samples don't really do anything.
I would suspect this will be a slow decaying signal. On the bright side, there should be little or no ground effect.
The 50 usec delay is way too long for any sensitivity to gold. It would probably work for silver and copper though. It should ignore foil, but still pick up iron objects quite well.
On a different note, how is your pcb for your PI coming along?
RegComment
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PI progress
PI is built and working. I am tweaking in component values and just playing with parameters. It's on the bench right now, next step is to package it and get it away from interference.
I made one error in the layout, and have 2 other design mods I want to make. As soon as I've got a final layout, I will find someone to run off 50-100 boards for folks to play with.
- CarlComment
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Re: PI progress
Carl will this be posted on the forum or are you selling this as a kit?Comment
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Re: PI progress
I will write a complete article, including schematics and PCB artwork, free for all. I also plan to get a bunch of PC boards made up and sell them, probably close to cost. I have no plans to put together any kits, but might look into it if people are interested.
- CarlComment
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