I'm designing a circuit based on arduino using EasyEDA program. By following the schematic of arduino nano I finished designing all my circuit. But in case to get PCB assembly service I need to find an equivalent part to 16MHZ resonator crystal.
So, based on what I have to pick another part? keeping in mind that all the other parts that I found are with 2 or 4 pins. But the default 16MHZ resonator crystal in arduino schematic has 3 pins.
The one that is listed in the official schematic of Arduino nano is not available in the assembly service, there are another 16MHZ crystals available in the assembly service. But I don't know if they will work fine or I have to use the same crystal listed in the official schematic of Arduino nano!
Because its a billion times too slow... m = milli, M = mega.
A 16MHz crystal would be good though - but crystals need load capacitors, whereas 3-terminal resonators
do not. And crystals need the right load capacitors as per the datasheet for the crystal and the MCU,
so you need to check what the load capacitance is for the crystal, and what the stray capacitance is
for the MCU oscillator, and calculate the load crystals so that they make up the difference.
Crystals are way more accurate timekeepers than resonators, normally you'll want a crystal if anything
needs accurate timing.
Be careful with your EasyEDA design. I found an error in the Nano V3 footprint where pin 16 is listed twice and there is no pin 15. The problem affects D12 and the track snaps to D13 instead. I have reported the issue, but doubt that anyone is the slightest bit bothered!
As far as the crystal is concerned, bear in mind that you can either draw the component of your choice yourself, or just manually place pads for it. I am going to have to do that for an Amphenol 12 pin box header with ejectors. Not sure about how easy it will be, but needs must.
You can pick any 16MHz crystal and use two 22pF capacitors . The capacitance is not super critical and no calculations are needed ( the data sheet lists 12-22pF for 16MHz). The crystal and capacitors or indeed a resonator should be placed close to the 328.
My suggestion was based on if you can’t find a resonator do the job and fit with your PCB designer.
[The comments on my typo for “m” although amusing, maybe, to someone, are just likely to confuse the OP. I’ve edited that anyhow ]
hsalame:
The one that is listed in the official schematic of Arduino Nano is not available in the assembly service, there are another 16MHZ crystals available in the assembly service. But I don't know if they will work fine or I have to use the same crystal listed in the official schematic of Arduino Nano!
Almost any of the available crystals will be fine, "16 MHz" is the complete specification (well actually, it includes "parallel mode", you do not want a series mode crystal but they are pretty uncommon).
The crystal will have a "load capacitance" specification. To obtain the value of each of the two capacitors, you take the specified crystal load capacitance, double it and subtract any stray capacitance of the ATmega328 oscillator pin. If you select the Low Frequency Crystal Oscillator mode for a 32.768 kHz "clock" crystal, the ATmega328 switches in internal 18 pF capacitors.
For a crystal that requires a 10 pF total load, use two load capacitors, each about 18 pF (to take into account stray trace capacitance), from each leg of the crystal to ground.
jremington:
For a crystal that requires a 10 pF total load, use two load capacitors, each about 18 pF (to take into account stray trace capacitance), from each leg of the crystal to ground.
That's not taking the pin capacitance into accound of the Arduino chip - probably only need 10pF load capacitors
or so - check datasheets to be sure how much the chip provides.
Its likely to work, but the frequency tolerance spec on the datasheet depends on the load capacitance being
the right value.
MarkT:
That's not taking the pin capacitance into account of the Arduino chip - probably only need 10pF load capacitors
or so - check datasheets to be sure how much the chip provides.
I spent considerable time trying to find such a specification.
Could only find the reference to switching in internal 18 pF capacitors if you select the Low Frequency Crystal Oscillator mode for a 32.768 kHz "clock" crystal.
That's not taking the pin capacitance into accound of the Arduino chip - probably only need 10pF load capacitors or so - check datasheets to be sure how much the chip provides.
When using the external crystal oscillator on non-PB AVR devices, crystals with a nominal frequency
range starting from 400 kHz can be used. For the standard high-frequency crystals, the recommended
capacitor value range is in the range of 22 pF - 33 pF. For the newer AVR PB, the recommended
capacitor value range is 12 pF - 22 pF, the total capacitance (Ce + Ci + Cs) for each pin must not exceed
22 pF.
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