Picaxe crystal or resonator

[JanJor]

Dear Forum,

Just an idea, but it would be nice if it works:

Many Picaxe users would like to have a very stable, reliable oscillator frequency for their Picaxe. It is of course known that it is possible to use a crystal as an external resonator instead of a standard resonator. However, even the accuracy of the crystal depends i.a. on the capacity of the capacitors used.

But: wouldn't it be possible to use one of these stable, small, ready-to-use and manufacturer-tuned inexpensive "four-legged" quartz crystal oscillators in a small metal housing instead?

However, they generate a square wave oscillating between 0 and 5 volts, whereas the Picaxe may need two opposite square waves on both pens of the resonator?

Anyone tested this? And if so: how would such an oscillator have to be connected to the Picaxe?

Thanks in advance for your thoughts/answers,

Ronald

 

[1968neil]

A crystal oscillator might be as simple as a crystal wired to an amplifier as found between OSC1 and OSC2 of the Raw PIC.
There are more complicated ones, which add temperature stabilisation (TCXO) or voltage control (VCXO), but the fundamental circuit is what you get with a PIC and a crystal. So it will be of no benefit to be honest.

A decently cut crystal will always be more stable than a ceramic resonator but if your using it for timing critical scenarios id go with a crystal and a couple of high tolerance capacitors.

Regards
Neil

 

[premelec]

With one of those capacitors variable to be able to zero the frequency to a local standard [could be radio signal etc].

 

[szd51pilot]

PIC crystal or resonator

The Microchip data sheet for PIC used for the X2 parts does describe the use of an external oscillator, although it might need an internal register change to use this. However, it could be a simple as connecting an external oscillator with a logic level output to (for example) pin 9 of a 28X2, which in the Microchip data sheet is called OSC1 and the other resonator pin left unconnected. Package oscillators will still have a tolerance and for best accuracy I would build a transistor oscillator and adjust it using a frequency counter.

16MHz crystal oscillator modules with a tolerance of 50ppm can be purchased for less than GBP 2.00 in the UK and would be well worth trying.

Richard

Dear Forum,

Just an idea, but it would be nice if it works:

Many Picaxe users would like to have a very stable, reliable oscillator frequency for their Picaxe. It is of course known that it is possible to use a crystal as an external resonator instead of a standard resonator. However, even the accuracy of the crystal depends i.a. on the capacity of the capacitors used.

But: wouldn't it be possible to use one of these stable, small, ready-to-use and manufacturer-tuned inexpensive "four-legged" quartz crystal oscillators in a small metal housing instead?

However, they generate a square wave oscillating between 0 and 5 volts, whereas the Picaxe may need two opposite square waves on both pens of the resonator?

Anyone tested this? And if so: how would such an oscillator have to be connected to the Picaxe?

Thanks in advance for your thoughts/answers,

Ronald

 

[inglewoodpete]

simple as connecting an external oscillator with a logic level output to (for example) pin 9 of a 28X2, which in the Microchip data sheet is called OSC1 and the other resonator pin left unconnected.

In a nut shell.

The PICAXE (PIC) will not know that its output is not being used to excite the crystal. After attaching the crystal-generated, TTL level clock signal, you need to need to tell the PICAXE what speed it is running at, noting that the chip is locked in to a frequency 4 times the crystal frequency. Eg, with a 16MHz clock input use the command SetFreq EM64.

 

[JanJor]

Dear All,

Thanks for looking at my question, and for your comments. @Richard: thanks Richard, this was actually what I was looking for. I'll give it a try.

Thanks again.

Ronald