Arduino Nano as clock source

Hello everybody,

I've to deal with SM8221 (callerid ic) in order to operate, it requires to be driven by external clock of 3.57 MHz (1% tolerance,) but its datasheet forbids using a simple quartz crystal and it says clock signal need to be supplied by the microcontroller, but I don't get how to supply such a signal, I mean integer would be rather easy to supply but how to deal with this particular frequancy ?

Many thanks in advance

but its datasheet forbids using a simple quartz crystal

No it doesn’t. The data sheet says on page 3

Pin 9 OSCIN - Crystal Oscillator input. A crystal will be connected between this pin and OSCOUT pin.

SM8221 hasn’t OSCOUT pin
SM8221 is the 8 pin version, its big brother SM8220 is easier to deal with but i’m forced to use the little one

I’ve fallen for it too :slight_smile:

sm8221app.JPG

SM8221 hasn't OSCOUT pin

No but there is nothing stopping you from putting a crystal oscillator's input into that pin.

but with no OSCOUT where to connect quartz 2nd pin ? gnd ?

I did not say a crystal, I said a crystal oscillator.

well for me, this little guy is a crystal oscillator

you mean to build an entire circuit ?

That is a crystal an oscillator has extra stuff to provide a nice buffered square wave out.

No, that's just a crystal.
A crystal oscillator will usually have 4 pins, power/gnd/output and one not used, or perhaps an output enable.
Example:
http://www.digikey.com/product-search/en?pv139=5976&FV=fff4000d%2Cfff8016e&k=oscillator&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

Other frequencies close to 3.57MHz are available also:
http://www.digikey.com/product-search/en/crystals-and-oscillators/oscillators/852334?k=oscillator

ah ok so it's what i call resonator :slight_smile:
thanks

btw that also means no way to generate that frequency using nano only ?
(cause it's hard to get resonator at my place, and shipping from overseas isn't really an option :))

No, a resonator is a different animal also. It also requires an external circuit the same as a crystal - that circuit resides in the Atmega chip. With a crystal oscillator, that circuit is included in the device itself.
Nano can output 16 MHz, 8 MHz, 4 MHz, and so on dividing by 2 some more.
3.57 MHz is an awkward frequency to support with a 16 MHz clock as the source.

ok thanks so much
yeah i knew about integer clocks

so my only shot is to find a local dealer for the xo cry

so my only shot is to find a local dealer for the xo cry

No buy a crystal and make an oscillator with it.

Or just buy the oscillator online. Local shops are unlikely to have such an item.

http://www.digikey.com/product-search/en?pv7=3&pv7=2&pv7=6&FV=fff4000d%2Cfff8016e%2C22c005f&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25
(those are 3.579545mhz - that's the magic frequency used by NTSC, and I think that's probably what your device is probably expecting to use - they are much more common than 3.57 mhz crystals) Looks like ~$5 for a single one, shipped to US.

3.579545 MHz is also the magic freq sm8221 wants (and 1% tolerance allowed) :slight_smile: but i wrote 3.57 for short
and signal must be 0.3 V

in the site you suggested I found this to be a candidate ECS-2100A-035 (except need to reduce output voltage)

but shipping is about 10 times the price of the ic :confused: and take about 1 month

No buy a crystal and make an oscillator with it.

that’s not too bad, but

  1. i dunno how to build it
  2. must be very small in size, must not need another IC
  1. i dunno how to build it

Google it.

  1. must be very small in size, must not need another IC

Don't be silly you can't make a passive oscillator, you need at least a transistor or an IC.

You should say what you mean and mean what you say. 3.57MHz at 1% is a totally different thing than a colorburst crystal.

Find and old analog color TV and you can pull one right out of it. Depending on the age of the TV, it may be rather large.

@poly thats not the issue here :confused:

besides here TV before dvb was pal
in the end if i cant get the xo; the best solution (actually an overkill) seems to be ds1077

what i guessed was the possibility to generate the signal by the Arduino alone cause i read about someone who got 3.88 by portb
and stuff

thx all

agingClock:
3.579545 MHz is also the magic freq sm8221 wants (and 1% tolerance allowed) :slight_smile: but i wrote 3.57 for short
and signal must be 0.3 V

in the site you suggested I found this to be a candidate ECS-2100A-035 (except need to reduce output voltage)

but shipping is about 10 times the price of the ic :confused: and take about 1 month
that's not too bad, but

  1. i dunno how to build it
  2. must be very small in size, must not need another IC

Then buy a similar part from an online distributor in your country. w/in the USA, digikey shipping is like $2.50. Farnell is good in Europe, I hear.

Are you sure it needs to be 0.3v, not "at least 0.3v"?

You need to either build an oscillator (it does require an IC or transistor - there are various circuits available online, usually using either a transistor or one or more inverters like 74xx04 and some passives), or buy a single part that does it like the ones above (or find something you can pull one from - but I've scrapped a lot of AV equipment in USA, and I always pull crystals and oscillators, and I've never found a 3.57 oscillator, just crystals), or use the 8220 with a crystal.

You could do something with a nano, but only if you replaced the crystal with a 3.57mhz one (ofc, most nanos use smd resonator, which is very hard to replace at home - though some also have a 12mhz crystal, you don't care about that one though, it's for the USB), and enable the CKOUT fuse. This would mean creating a new board definition to run at that frequency, and running the board at 3.57mhz, which might be a problem (in terms of speed). delayMicroseconds() would not work correctly. If you could find a crystal 2x or 4x that speed, you could directly manipulate a timer to get a clock signal out via PWM, but this would also require a new board definition, and delayMicroseconds also wouldn't work. Oh, and you'd need to recompile the bootloader for that clock speed, or program via ISP and not use the bootloader. So yeah, it's possible, but it'd be a lot of work to implement :wink:

Also, re: nomenclature: "crystal" or "crystal resonator" or "frequency crystal" = crystal, with 2 pins (sometimes a third for ground, connected to case), and no oscillator circuitry. "resonator" or "ceramic resonator" = cheaper RC frequency reference with no oscillator circuitry, used like a crystal. "Oscillator" indicates that it has the circuitry - however "crystal oscillator" is very often used incorrectly to refer to a crystal with no oscillator.

Where is "here", agingClock?