SparkFun Forums

[timeforlife]

I'm building a LED watch using a PIC16F684, all SM components, and I'm looking for an appropriate SM crystal. ~32MHZ. Any suggestions?

[Philba]

no offense, but did you actually try looking? try the distis I pointed out in the other posting.

[noptical]

I guess you mean 32.768kHZ? because thats what you use for clocks.

Ebay is the place to look for common things like this unless you want to pay more for shipping than for your overpriced components.

[timeforlife]

Philba, I have looked. I am not actually involved in the design of this circuit, I'm helping to source out these components so I'm a newcomer to this. I re-read your post and you didn't specifically mention any particular crystals. I was hoping there existed some common 32.***Mhz Surface Mount crystal for 3.0V circuits that I was unaware of.

[emf]

Digikey seems to have a pretty good selection of 32MHz surface mount crystals in stock... 4 pages of results. But the PIC you're using only accepts clocking up to 20MHz, so you might want to double-check the MHz/kHz thing with the circuit designer. As noptical said, 32kHz would make a whole lot more sense for a watch.

[Philba]

yeah. good point, KiloHertz.

look for watch crystals. note that if this is the primary crystal, you won't have a lot of cpu cycles to use (8K instructions per second).

[noptical]

For watch applications you don't actually use the 32,768khz crystal as the main oscillator, but you connect it to the pins that are tied with e.g. tmr1 which is a 16bit timer (in this case it operates as a counter) so that an interrupt is flagged on overflow, which in that case is exactly every 2 seconds. You can also set the timer to 10000000 00000000 so that it interrupts every 1 second instead and you get yourself a very precise clock.