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Crystal Tester (Tony van Roon)

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aljamri

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Has problem to check my crystals, search for a simple circuit to use, I found the a circuit from:

**broken link removed**

I used 2N3904 instead of the proposed 2N3563 transistor, as per the designer recommendations. After constructing the circuit using bread board, the LED is always ON even when the crystal is not connected.

any idea for the reasons ?
 
Has problem to check my crystals, search for a simple circuit to use, I found the a circuit from:

**broken link removed**

I used 2N3904 instead of the proposed 2N3563 transistor, as per the designer recommendations. After constructing the circuit using bread board, the LED is always ON even when the crystal is not connected.

any idea for the reasons ?

hi aljamri,
My guess would be that you have the 2N3904 wired incorrectly, check the pin out.:)
 

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You are absolutely RIGHT !!!

up side down and it is working.

Thanks for you and for this great forum. But how you guessed it ?
 
You are absolutely RIGHT !!!

up side down and it is working.

Thanks for you and for this great forum. But how you guessed it ?
hi,
As there is no other path to switch ON the 2N3904, it meant the 2N3904 must be conducting for the LED to light, so its reversed...;)
 
O.K. I would like to go a step further and make the circuit to check my 20 MHz crystal ( It is desigened to check xtls with frequency range 2 MHz upto 8 MHz ). What part to modify, is it the transistors or the capacitors also.
 
First, just try it with 20MHz crystal. It may work.

If it doesn't work, try changing C1 and C2 to lower values. Try 100pF.
 
It's possible to make an oscillator using a CMOS gate, maybe this is a better solution?

Here's an idea. I haven't tested it so I can't promise it works.
 

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Just for a matter of curiosity, why is the last three inverters ? and why not one instead of one ?!
 
A single CMOS inverter has a weak output with barely enough current to light an LED brightly so three are paralleled to make the LED light brightly, besides there are six inverters on a CD4069 so you might as well use them all.
 
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CD4069 can be found in many of my old junkyard, but 10M resistor is very high value that I dont remember if I came across an time. But no problem my supplier have it for $0.10 each.

Thanks
 
It's not important, any high value resistor will do, you could try 1M, if you don't have 10M.
 
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