Fisher CZ crystal replacement

[ETEXHunter]

Seems that some time back I saw someone suggest an L/C (R/C) circuit to replace the 'impossible to find' tuning fork crystal in the Fisher CZ series of detectors. The crystal frequency is 60.12 KHz which is divided down to the 5.1 KHz operating frequency.

Any help would be greatly appreciated.

[Carl-NC]

For the production CZ21 I recently replaced the crystal with a small PIC module. It uses a 12F1840 running at 16MHz and the PWM is set up for 60.15kHz. You could use something as simple as a 555 timer if you are not concerned about high frequency stability.

[ETEXHunter]

Thanks Carl..a little more complicated but should be a lot more stable.

[dbanner]

Maybe this is what you need but maybe not, it seems close enough?https://mt.rsdelivers.com/product/epson/c-2-600000k-ppbfree/epson-60khz-crystal-unit-100ppm-2-pin-2-dia-x-6mm/1849185

[Skippy]

I would recommend a 'regular' frequency quartz crystal oscillator circuit, followed by a binary divider, then feed that into the appropriate place in the existing circuit.
A Xtal in the 3-12 MHz range would be the range to consider. 4000-series components for the divider, maybe oscillator/divider in one, eg. CD4020, CD4040

[kt315]

buy timing generator on ne555. it will be costing you kopeiki.

https://www.banggood.com/DIY-Digital...r_warehouse=CN
https://www.aliexpress.com/item/3301...chweb201603_55

[Skippy]

If you use a "555" timer, I recommend the Lin-CMOS versions, like the TLC555. Don't use the bipolar NE555, as it's not temperature stable, and avoid the regular low-power CMOS types, like the ICL7555, as they have unstable characteristics. Make sure your timing capacitor is a stable low-temperature-coefficient type, not polyester, not most ceramic types. Choose polypropylene, polystyrene.

[kt315]

you can put gen pcb in a fridge, get out and measure the frequency. after put under hot lamp and do measure.
you will see the frequency floating away from cold point to hot one. then do experiment with cap changing, there are with + and - temperature coefficient caps.

[ETEXHunter]

Thanks folks...all good suggestions. I think I will try the 60Khz tuning fork crystals suggested above. Hopefully it won't throw it too far off frequency in the count down to 5KHz to prevent the circuit from working. I let you know.

[Skippy]

If you do use that tiny Epson crystal, check the datasheet for recommended oscillator circuits. They are very low power devices, and using the regular CMOS inverter type circuits can damage them, or result in odd oscillation, like 3rd harmonics etc. The usual circuits for these crystals have resistors in series with the gate output, to reduce signal strength.
Some mention of the circuit I had in mind:
https://www.eevblog.com/forum/beginn...lator-circuit/