Hello all. I’m working on a simple oscillator circuit that I’d like to run at 455khz and switch to 1500Khz as well. I have the 455 running great but would like to know the resistor and cap values required for it to run with a 1500 crystal. I have attached a photo of the 455 circuit. BTW, I’m using a fixed 100pf cap and not the trimmer. Thanks for any assistance.

 

Hello all. I’m working on a simple oscillator circuit that I’d like to run at 455khz and switch to 1500Khz as well. I have the 455 running great but would like to know the resistor and cap values required for it to run with a 1500 crystal. I have attached a photo of the 455 circuit. BTW, I’m using a fixed 100pf cap and not the trimmer. Thanks for any assistance.

There are no absolute answers with lack of information. You simply have to try it with the new crystal.
I would reduce both capacitors to 22 or 33 pF fixed capacitors.

 

Hello,

What is the load capacitance for the crystals?
Have a look at the attached pdfs.

Bertus

 

My first thought is to simulate a known ltspice pierce tuning fork oscillator using crystal equivalent circuit. Use one that is known to work that is much than fishing through endless web pages of odd ball crystal circuit (having unknown parts). One such known crystal is an Epson C-001R 12.5pF, simulates nicely. If you work without known values it is possible to oscillate your thinking instead of facts.

There are simulations for Pierce crystal oscillators with 32.768 kHz tuning fork crystal. The 2 resistors Rf called feedback resistor and Rs series resistor. This variety of crystal must be driven at very low currents. It is useful to study a circuit that is well documented such as the garden variety tuning fork crystal even though you might have some rare old crystals, it is more difficult to develop a circuit from and having little or no documentation as a guide making a steep learning curve even steeper. A picture of the crystal might give some indication of drive level but not always. It is better to start low and increase patiently.

Using the 32.768 kHz tunnig fork must apply current below the maximum drive level. The 4069UB known as an unbuffered cmos hex inverter can be used to make a Sine Pierce oscillator with it's many gates. A Pierce oscillator is used to nearly approach the parallel resonance of the crystal. The resistor found in series with the crystal is sometimes Rs 300k or 100k. Rf can be 15M But is not always the case as you can see in references below.

MSP430™ 32-kHz Crystal Oscillators (Rev. C)

Pierce Oscillator