What is the correct external crystal for Bluefruit LE Sniffer?

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sofakng
 
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What is the correct external crystal for Bluefruit LE Sniffer?

Post by sofakng »

Can anybody tell me what is the correct crystal for the Bluefruit LE Sniffer? (#2269)

I know it's 32.768 kHz but what is the correct load capacitance? The schematic doesn't show any load capacitors and I can't find any crystals with the exact footprint on the PCB.

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mikeysklar
 
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Re: What is the correct external crystal for Bluefruit LE Sniffer?

Post by mikeysklar »

You can see the crystals digikey part# and specs in the *.sch files from the github repo.

https://github.com/adafruit/Adafruit-Bl ... niffer-PCB

Code: Select all

$ grep 32.768 *.sch | grep -i digikey
Adafrruit Bluefruit LE USB Friend CP2102N.sch:<li>32.768 KHz 12.5pF 20ppm 4.9 x 1.8mm Crystal [Digikey: SE2415CT-ND]</li>
Adafrruit Bluefruit LE USB Friend CP2102N.sch:<li>32.768kHz 12.5pF 20ppm -40°C-85°C [Digikey: 535-9166-2-ND]</li>
Adafrruit Bluefruit LE USB Friend CP2102N.sch:<li>32.768KHz Cylinder Crystal (2x6mm body) [Ex. Digikey: 300-8341-2-ND]</li>
Adafruit Bluefruit LE USB Friend Rev I.sch:<li>32.768 KHz 12.5pF 20ppm 4.9 x 1.8mm Crystal [Digikey: SE2415CT-ND]</li>
Adafruit Bluefruit LE USB Friend Rev I.sch:<li>32.768kHz 12.5pF 20ppm -40°C-85°C [Digikey: 535-9166-2-ND]</li>
Adafruit Bluefruit LE USB Friend Rev I.sch:<li>32.768KHz Cylinder Crystal (2x6mm body) [Ex. Digikey: 300-8341-2-ND]</li>
Adafruit Bluefruit LE USB Friend.sch:<li>32.768 KHz 12.5pF 20ppm 4.9 x 1.8mm Crystal [Digikey: SE2415CT-ND]</li>
Adafruit Bluefruit LE USB Friend.sch:<li>32.768kHz 12.5pF 20ppm -40°C-85°C [Digikey: 535-9166-2-ND]</li>
Adafruit Bluefruit LE USB Friend.sch:<li>32.768KHz Cylinder Crystal (2x6mm body) [Ex. Digikey: 300-8341-2-ND]</li>
The crystal should not be necessary unless you wanted to running firmware direct from Nordic (non-Adafruit) releases.

The Adafruit board has a small difference compared to the original Nordic HW that Nordic wrote their sniffer firmware for. To keep the cost as low as possible, we don't populate the optional 32.768KHz RTC crystal on our boards, whereas it is present on the more expensive Nordic development kit.

Because the startup code in the sniffer firmware from Nordic uses this crystal, we had to request a custom version from Nordic that uses the internal 16MHz RC oscillator instead. When providing us the custom firmware, they changed the version number slightly, which is the reason for the warning message.

You can safely ignore the firmware update warning and use the device as normal, and in fact updating to a firmware from Nordic won't work unless you also solder the optional 32.768KHz crystal on the bottom of your PCB as well.
https://learn.adafruit.com/introducing- ... aq-2317994

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sofakng
 
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Re: What is the correct external crystal for Bluefruit LE Sniffer?

Post by sofakng »

Thanks for the reply!

Yes, I'm looking to use other firmware besides the one included which is why I'm trying to find it.

However, your listing above shows several different crystals and strangely none of them seem to have the same footprint that's on the PCB unless I'm missing something?

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mikeysklar
 
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Re: What is the correct external crystal for Bluefruit LE Sniffer?

Post by mikeysklar »

Okay, new approach.

The schematic shows Y1 / DNC as the add-on crystal.

Looking at the latest BRD file I see it is a 6mm / 2mm radial design and we know the 32.768 frequency. That makes it pretty easy to narrow things down to two crystals from digikey.

Code: Select all

Adafrruit Bluefruit LE USB Friend CP2102N.brd:<element name="Y1" library="microbuilder" package="CRYSTAL_CYL_2X6MM_SMT" value="DNC" x="3.302" y="23.622" smashed="yes" rot="MR90">
Adafrruit Bluefruit LE USB Friend CP2102N.sch:<part name="Y1" library="microbuilder" deviceset="CRYSTAL" device="2.0X6.0_32.768" value="DNC"/>
Adafruit Bluefruit LE USB Friend Rev I.brd:<element name="Y1" library="microbuilder" package="CRYSTAL_CYL_2X6MM_SMT" value="DNC" x="3.302" y="23.622" smashed="yes" rot="MR90">
Adafruit Bluefruit LE USB Friend Rev I.sch:<part name="Y1" library="microbuilder" deviceset="CRYSTAL" device="2.0X6.0_32.768" value="DNC"/>
Adafruit Bluefruit LE USB Friend.brd:<element name="Y1" library="microbuilder" package="CRYSTAL_CYL_2X6MM_SMT" value="DNC" x="3.302" y="21.082" smashed="yes" rot="MR90">
Adafruit Bluefruit LE USB Friend.sch:<part name="Y1" library="microbuilder" deviceset="CRYSTAL" device="2.0X6.0_32.768" value="DNC"/>

https://www.digikey.com/en/products/det ... C/10499214

https://www.digikey.com/en/products/det ... C/10500011

The only difference between the two is 7pF vs 12.5pF which based on the forum posts I doubt matters much.

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