Which resonator is best

[The Master]

Hi. Sorry if this is a daft question but what are the reasons for using small resonators? Lets say a chip supports both 5mhz and 10mhz. Why would you choose a 5mhz over a 10mhz? I can see that there is a slight cost difference but is there more to it? Would the chip only last half as long with a 10mhz because its working twice as hard? Does it use twice as much power?

Just another little question. If the datasheet says "DC - 20MHz clock input". That means 20MHz is the highest resonator that can be used on the chip right? Its not the rating of the internal one is it?

[mister_e]

In theory lifetime have to be the same, but yes the power consumption would be higher @10MHz than 5MHz.

Which speed to choose... Yikes.. hard to tell... and it's different from project to project. For low current, lower the crystal(resonator) better it is. Lower frequency will also produce less EMI/RF noise... and so on.

If your application is not timing critical and if your PIC have an internal OSC, just use it... it save PCB space and free up 2 I/O. Newer devices have better internal OSC accuracy .. 1% if my memory serves me well. So for many Serial Comm, this might work pretty well. Keep in mind it's a RC OSC and it will shift will temperature.

Some PIC18F can run up to 32MHz using the internal OSC with internal PLL... that's pretty fast.(Yeah i know PIC32 run up to 80MHz now)

All PIC have their own external OSC limit. Some can run @48Mhz... but with a 4 MHz external osc.

Loads of different PIC, each have their respective datasheets. In case of doubt, just post your PIC model and we may have a look at it.

[The Master]

I dont really have a specific model. I was looking at a datasheet for PIC16f84A just now but im not garunteed to be using that.

Having the extra I/O pins sounds like a good idea. I might be doing a few things where that would be helpfull. I like saving on PCB space too. What about with PWM though? I guess that is timing critical and i had to use a 16MHz resonator before. Im not sure that the small PICs i use would have above 4MHz built in.

Whats and "RC" osc?

80MHz :O wow! Heres me never gone above 16MHz before.

What about these 2 pin ones i keep seeing on rapid. Do they work in the same kind of way?

[mister_e]

My favourite 8 pin is the PIC12F683.. it has the PWM module built-in and can run up to 8MHz internal OSC... really nice device.. ADCs, comparator as well.

Forget the 10+ years obsoleted PIC16F84A device , use his big brother 16F628A (even if almost obsolete as well) or 16F88, PIC18F1320.. oh well so much in the list I keep 50 different model for 10f to 18F, 'round 20 for DsPIC and PIC32.

I suggest you to have on hand both 16F88 and 18F1320.

PWM.. not as this critical.. unless you REALLY need it accurate, the internal OSC worked for me pretty well in the past.. and still. My PICMultiCalc could be handy, just go on my website to download it.

RC osc. it's an oscillator built with Resistor and Capacitor. Knowing their temperature variation, you may use it or not. It always depend where and how you will use it. As i said, some, see most, newer device says to be 1% accurate... erm... look the whole datasheet and make your own conclusion. To me accuracy=crystal... but as i said... many application will run anyways with the internal OSC.

Just post your part# and we will have a look at.

[The Master]

Ive never used the 2 pin resonators before but some can be found here http://www.rapidonline.com/Electroni...5/kw/resonator. Why do some have 2 and some have 3 pins?

I dont really have any PIC chips that arnt in use. Just a few 16F84As and some 40 pin ones (cant remember the number). I should get a few in i suppose.

PICMultiCalc. Sounds familiar. I remember downloading something from your site that deals with baud rates (proably the same thing).

I think it depends what you mean by "Critical". I took it to mean it has to run at a certain speed or it wont work as intended. It will just be fading bulbs though. Its not like anyones life depends on it.

I had no idea that a PIC16F84A was so obsolete. Everywhere still sells them round here. Usually as soon as something new comes out you can never find the old ones

[mister_e]

Most of those 3 pins ceramic resonator i know have built-in capacitors. Those you post above don't, so you'll have to add 2 extra capacitor to make it work.

16F84(A) is popular 'cause it's the first Flash one (16C84). Many code example here and there in ASM. But you don't want to use it for a new project unless you don't have access to something else. Most newer model are also cheaper... see WAY cheaper. Good enough for a pin board

16C54 have been popular as well.. now they have 16F54

[skimask]

As i said, some, see most, newer device says to be 1% accurate...

Just a 2nd opinion...
All of my 18F4620's, when running on the internal 8Mhz & 4xPLL (giving 32Mhz on the chip) are well within 1% and have always worked well when using a serial interface. The datasheet says +/- 10% over the full voltage/temp range, but again, at least 1% for the 100-ish I've used so far (maybe one or two of those have been a bit out in the weeds and needed tweaking, but I don't remember any off the top of my head).

[T.Jackson]

In theory lifetime have to be the same, but yes the power consumption would be higher @10MHz than 5MHz.

In theory it's quite the opposite actually. More power being consumed equates to higher thermal dissipation, heat is what kills components.

[mackrackit]

In theory it's quite the opposite actually. More power being consumed equates to higher thermal dissipation, heat is what kills components.

With PICs I think the max life is calculated on the max speed.

My first industrial application with a PIC (BS2 actually) was back in 2000. The control panel is out side in the ambient Temperatures of SW Arizona. 120 F in the shade in the summer. The machine runs 6 days a week for 10 to 12 hours a day. Still going strong.

The only time I ever had a hot PIC was...well I do not like to talk about it

[T.Jackson]

You'll become a guaranteed billionaire if you can come up with a way to control the flow of electrons without wasting them (given off in the form of heat) -- which is once again what kills components. Many argue that it's not possible I don't know enough about science to give an opinion. But then again it is said that if anyone ever does it then most of the theories will need to be rewritten.

[mackrackit]

You'll become a guaranteed billionaire if you can come up with a way to control the flow of electrons without wasting them (given off in the form of heat) -- which is once again what kills components. Many argue that it's not possible I don't know enough about science to give an opinion. But then again it is said that if anyone ever does it then most of the theories will need to be rewritten.

My point was that if a PIC will last whatever the advertised time frame is at max speed. Then we say double that by slowing it down. I know I will not be around that long. So if the only reason to slow it down is to get more life, then why bother.

[T.Jackson]

You're absolutely correct bud. I think mister_e needs to go back and hit the books on some relatively "simple" stuff.