I can't find this question being asked anywhere. All the tutorials I watched and read explain how to set up an external oscillator for ATmega328, and related fuse settings.

Is the voltage rating of the oscillator important here? And why does no one mention the voltage rating of a crystal oscillator?

Can I use a 3.3 V oscillator as an external clock for an ATmega328 (pins XTAL1 and XTAL2)?

the oscillator I want to use

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    \$\begingroup\$ Provide the part number and link the datasheet to the oscillator that you are considering for use. \$\endgroup\$ Jun 27, 2021 at 14:39
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    \$\begingroup\$ Why don't you simply copy what the tutorials do? If you use an external crystal clock (containing a crystal and the electronics to make that an oscillator) and you power that by 3.3 V then the clock signal will be 3.3 V as well and you must then power your ATMega328 also with 3.3 V. Explain what you mean by "voltage rating", as it is not mentioned anywhere, why do you think it needs to be? As long as the supply voltage for crystal oscillator and ATMega328 are the same, there is no issue. \$\endgroup\$ Jun 27, 2021 at 14:55
  • \$\begingroup\$ @chris it's a chinese DIP oscillator made by SCTF. The datasheet has the ratings listed for the whole production line. (8DIP package called full package and 4DIP package called half package) the given voltage rating is 3.3v, 5v. (Both) this means the 4DIP package has these two varieties available. So does the bigger rectangle package. The iamge is added to the main question. \$\endgroup\$ Jun 27, 2021 at 14:57
  • \$\begingroup\$ @Bimpelrekkie the tutorials suggest a crystall with two 22pF capacitors. I prefer a oscillator in the package over the 3 parts method. \$\endgroup\$ Jun 27, 2021 at 15:02
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    \$\begingroup\$ the tutorials suggest a crystall with two 22pF capacitors That's not an oscillator, that's a crystal. Almost "everyone else" uses the "3 parts method" and I would say that you should too unless you have a particular reason why you would need to use an external oscillator. Generally people use the crystal + 2 loading caps as that's cheaper than a crystal oscillator. The ATMega has the crystal oscillator circuit build-in so why not use it? \$\endgroup\$ Jun 27, 2021 at 15:06

1 Answer 1


This should provide you with an answer to your question on power supply voltages of inexpensive crystal oscillator IC's :


This link provides full and complete information on inexpensive, no name, Chinese, crystal oscillators. This link, also, provides a schematics of a test circuit, the picture of the test circuit and results, measured with a multimeter.

Basically the link says this :

A 400KHz, crystal oscillator was purchased via AliExpress. The page on AliExpress did NOT say what voltage this is. I contacted the seller, who, claimed the crystal oscillator works with 5V as well as 3.3V. I insisted on a datasheet and received such. The datasheet is not written very well and says the crystal oscillator can work with 3.3V OR 5V. Different manufacturers mean different things when they say 3.3V OR 5V. Some mean 3.3V AND 5V. Other mean they have two different devices, one, which works with 3.3V and another, which works with 5V. They provide different part number for such a case.

However, the Dimensions page of the datasheet marked the Vdd pin as 5V. This is another proof the crystal oscillator can work with 5V.

Of course, the best is to test. I tested the crystal oscillator for 24 hours continuous work with 3.3V and more than 60 hours continuous work with 5V, even, with 1K resistor as a load. Worked perfectly without any warm up.

Therefore, although the crystal oscillator can work, even, with lower than 2V power supply ( although may not start up, as crystal oscillators, usually, require 2V to 3V to start up ), the manufacturer specified voltage is to be read :

3.3V +- 10% TO 5V +- 10% = 2.97V TO 5.5V

and anything in between.

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    \$\begingroup\$ Can you describe the link in the question? If the link goes die the answer will lose it's meaning \$\endgroup\$
    – Voltage Spike
    Mar 7, 2023 at 4:30
  • \$\begingroup\$ I don't see how this answer relates to the question asked. This answer is about with what voltages a specific oscillator with an ambiguous datasheet appears to work with. The question is about what kind of external clock level an AVR MCU needs, but as the AVR supply voltage is not mentioned, it can only be answered that clock signal must have same supply voltage. \$\endgroup\$
    – Justme
    Mar 8, 2023 at 15:10
  • \$\begingroup\$ The topic of this thread, which, is the main question is " Crystal oscillator voltage rating ". One of the sub questions is " And why does no one mention the voltage rating of a crystal oscillator? " I think, I have answered these questions. \$\endgroup\$ Mar 12, 2023 at 3:22
  • \$\begingroup\$ Once the original poster has this information, the original poster can read the datasheet of ATmega328 and see what voltage is allowed between XTAL1 and XTAL2. The original poster can, also, see the schematics of the oscillators, built in In microprocessors. \$\endgroup\$ Mar 12, 2023 at 3:23
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    \$\begingroup\$ However, The way I understand the question is not how to analyse the schematics of the microcontroller, but, with what voltages inexpensive, no name, Chinese oscillators work. Most likely, the original poster has figured out what to do and, just, needs the voltages of the crystal oscillators in order to find out whether the microcontroller will withstand such. \$\endgroup\$ Mar 12, 2023 at 3:24

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