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).

[The Master]

What do those codes actually mean? Is the first number and letter like a version number and the second number like the type?

Sorry to get back into this one again but how do i know what type of chip to use? The main reason im using a PIC16F84A is because ive used it in the past and its always worked fine. I dont like thinking that way. Im all for changing to make things better but here i dont know what to change to. You have given me a few examples but how did you know which ones do the same thing? I know the datasheets tell you but i dont believe that you sit there reading every possible datasheet to find the chip you want

I think ill stick with 3 pin ones then. I dont want any extra components taking up room/money.

[The Master]

What kind of temperatures affect them? Are we talking 1 or 2 degrees could alter it or like 20-30 degrees? Most of my stuff would remain at more or less the same kind of temperature give or take a few degrees.

[mister_e]

PIC16F84 don't do much and absolutely need an external crystal+MCLR connection.. 16F628 have comparator, MSSP, USART, no real must for external MCLR (this gives 1 i/o for free), can use it's own internal osc (that's 2 more i/o for free) and so on. More with PIC16F88, and a bit more with 18F1320. and there's still the codespace...

There's some temperature curves in the datasheet you can refer to. I still repeat, unless you need a real timing accuracy (e.g. high speed asynch serial comm), internal osc may be just fine. 16F88 one can run up to 8MHz, 18F1320 up to 32MHz!

[mackrackit]

This is the quick way to start picking PICs.
http://www.microchip.com/ParamChartS...g=en&pageId=74
http://www.microchip.com/stellent/id...PAGE&nodeId=74
And I do read many many data sheets. Not that it helps much Always fall asleep.

[The Master]

Ive seen that site before but i had trouble using it. It looks like all the information is there but searching and displaying it could be improved a bit.

In the second link (and the dropdown on the first). Should i always pick PIC16MCU? I dont get that bit and there doesnt seem to be any description of whats different between them

[mackrackit]

The 16MCU will take you to the 16C/16F chips. 18MCU will take you to the 18C/18F chips etc.

[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.

[mister_e]

Feel better now ?

[T.Jackson]

Feel better now ?

It's hard to argue that one isn't it? I don't go out of my way looking to pick people up on their errors, but I just couldn't ignore your comment, because it goes against the very foundation on which electronics is taught. You will never have a true appreciate of electronics without it. Just tell yourself that is was a typo -- because I do indeed believe that you are crafted with this "appreciation" and just happened to have overlooked it this time. My reasoning for saying this is because you haven't argued it.

[paul borgmeier]

Dave, I have never seen a max life value from Microchip for a PIC - do you have a reference for this?

Trent, I have never seen reference to microchip PIC life reduction if run at the high end of datasheet-listed allowed speeds (or voltages for that matter). Can you provide reference to this?

Trent, Would Einstein not have been correct with his theory of relativity if he had been challenged and had not replied? (ref: TRENT - My reasoning for saying this is because you haven't argued it.)

[T.Jackson]

Trent, I have never seen reference to microchip PIC life reduction if run at the high end of datasheet-listed allowed speeds (or voltages for that matter). Can you provide reference to this?

You sound like my university tutor marking me down in an assignment for not referencing something in an essay. Best I could do is hand you a 300pg text book on basic electronics and let you decide for yourself as to whether or not there is questionable truth in what I'm saying. I say this because there is no one paragraph, or even just a couple of pages that could be used to support it. You need the whole book, even then you may not conclude that what I'm saying is true.

Trent, Would Einstein not have been correct with his theory of relativity if he had been challenged and had not replied? (ref: TRENT - My reasoning for saying this is because you haven't argued it.)

I know it's besides to the point, but Einstein was actually challenged in his younger years.

[mackrackit]

http://ww1.microchip.com/downloads/e...cs/00097AB.pdf
Not max life values. Just the reliability report.

[The Master]

In the kind of things ill be making (disco lights / pinball machines etc) i would be happy if the chips lasted 10 years. The biggest heat problem i have will be my pinball machine. There are so many lights under the playfield and in the ones ive done in the past it gets quite warm in there but i dont think its enough to harm anything. The drive chips got hotter than the bulbs and they still work fine... except that one that was connected to the wire i accidentally shorted out :P The new one will be slightly ventilated anyway.

Is it just heat that makes a higher speed shorten the life? Could it be possible that doubling the speed doesnt make it heat up too much and so it doesnt shorten the lifespan much? (just a thought)

So, as long as theres no power issue (like running from a battery) and the lifespan isnt critical then using a faster resonator doesnt really make any difference? I suppose it does give you the chance to use that speed in the future though without having to solder a new resonator in

[Acetronics2]

Hi,

The main problem is not run time, but ON/OFF powering count and "violence" ...

design carefully your power supplies, take care of your I/Os , use the "cool startup" features now provided, and your Pics will last ... How much is the MTBF given in Dave's document ???

LOL !!!

Alain

[mackrackit]

The biggest heat problem i have will be my pinball machine. There are so many lights under the playfield and in the ones ive done in the past it gets quite warm in there but i dont think its enough to harm anything.

If you are worried about heat, get the industrial version. The 16F877A for example will handle 85C. Check the end of the data sheet for the PIC you plan to use.

And like Alain, design carefully.

[T.Jackson]

The difference is negligible, but it is important to be aware that a difference does exist. We're talking nano watts of power with many integrated circuits, (increased thermal dissipation is negligible) but if we were to turn the subject into say watts then difference could become very significant.

[The Master]

Whats MTFB? Im guessing mean time before failure and yeah, they seem to last quite a long time.

Im not that concerned about heat. My pinball is probably the hottest place they will go and that should never go above about 30 degrees even on a hot day (yeah, our hot days are about 15 degrees!)

The on/off count i expect to be high while testing things. I always put safety switches on to cut the power to the whole playfield as soon as you lift it up and i do tend to turn things on and off a lot when im testing (maybe a few times a minute). Once everythings up and running i expect they will stay on most of the time (might turn it off at night).

How do i take care of I/Os? All my outputs will go directly into some driver chips and the inputs will go to switches with a 10K grounding resistor. Is that fine?

Whats cool startup?

[T.Jackson]

Trent, Would Einstein not have been correct with his theory of relativity if he had been challenged and had not replied? (ref: TRENT - My reasoning for saying this is because you haven't argued it.)

An unsupported argument against the claim that Einstein was a poor student: http://www.abc.net.au/science/k2/moments/s1115185.htm

An unsupported premise for it: http://findarticles.com/p/articles/m...57/ai_68648469

I think the truth is somewhere in between.

[mister_e]

Area: PICmicro Products
Product Group:
Product: Date Created: 4/2/2008 6:48 PM
Issue: Reliability Specification Date Resolved: 4/10/2008 5:30 AM
Description: Hi,
i've a small question for you. Is there any kind of relationship between the OSC speed and the PICMicro lifetime?

Will a PIC running, say @20Mhz, have shorter lifetime than another running@4Mhz assuming they both running the same program, same voltage, ambient temperature etc etc.

Just curious to know.

Thanks for any doc and/or tips.

This is what Microchip told me

Resolution: Hi Steve,

There is no relation between the OSC speed and the PICMicro lifetime.

The device gets into shorter life span conditions only if operated higher (over and above) the absolute electrical conditions as specified by the specific device datasheet.

Hope the information helps you. In case you need further assistance please let us know.

Thanks and Regards,

[mackrackit]

Well that clears that up!

[skimask]

I agree completely with the Microchip reply...
However, doesn't it looks too much like a 'canned statement'?
I wouldn't doubt that, all other things being equal, a PIC running at 20Mhz would fail sooner than that exact same PIC running at 4Mhz.
But how much sooner? What kind of time scale are we talking about here? Would any of us, or our offspring be around to mark the time at which one or the other failed? Kind of like measuring how long an EEPROM will hold data. EEPROMs haven't been around for the 100's of years it would take for one to supposedly degrade and lose data.

[The Master]

For the things im making at the moment i have no need for them to continue working longer than i do. If i will not live to see my devices fail with either osc then it doesnt bother me which i use.

I would have thought that a higher speed would shorten the lifespan but i think it depends on what actually fails. If the inner workings of the chip will only last for a certain amount of switching (like some relays can only switch 100,000 before they are due to break) then it would shorten the lifespan (twice as many switches, half the length of time).

That reply suggests that the lifetime doesnt have anything to do with that and it may be something else. Maybe something inside degrades over time?

Just my thoughts anyway

[precision]

I always use MAX7375AXR805+ , Where xtal failed and serial data disrupt at 80 degr.C.

Great performance. Try it with two free sample order.


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