Re: Simple Count down Timer Project! New post!

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Why not simulate before you build?

On a sunny day (Mon, 14 Feb 2011 06:33:58 -0600) it happened John Fields wrote in :

555 is only partly analog :-)

solution.

Apart from flexibility there is the issue of part count and accuracy. A 8 pin PIC running from internal oscillator will do the most complicated stuff with an accuracy of about +-2 %, with ZERO external parts, apart from a 100 nF decoupling cap.

solution.

And 5V power supply. 555 can run over a much wider supply range.

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Actually, if you want to split hairs, it's _all_ analog.

So is your pic.

solution.

Nope. The PICs with internal shunt voltage regulator can safely run over a much wider range than the 555.

- they won't drive hundreds of mA from the output

- using a pot to set things over a wide range might be more problematic (or not- you could turn a linear pot into a log pot by using the 10-12bit ADC and a LUT or equation)

On a sunny day (Mon, 14 Feb 2011 08:09:53 -0600) it happened John Fields wrote in :

Well, OK, if you go a bit deeper it is all quarks and stuf :-)

555 is not very sensitive to Vcc, but neither is the PIC internal osc.

For a 16F628A, quoting: F13 IOSC Oscillator Stability (jitter) -- -- ±1 % VDD = 3.5 V, 25°C -- -- ±2 % 2.0 V VDD 5.5V 0°C TA +85°C -- -- ±5 % 2.0 V VDD 5.5V -40°C TA +85°C (IND) -40°C TA +125°C (EXT)

The +-2% is over the full supply and temp range, there usually also is an oscillator software calibration, factory set, but you can change it a bit.

solution.

But that is not as simple as it sounds.

There are very few versions of the PIC with internal shunt regulator.

You have to be careful with power dissipation of the internal regulator. Not an problem with the OP's circuit but for example if you are driving LEDs from the PIC the variation in regulator current can become an issue.

solution.

Nah, they all have that. Some of them won't work anymore after you try using it, though. ;)

I really don't understand why using or not using 555s is such an emotional issue. The folks making the running in small electronic gizmos these days are the Chinese, and they have absolutely no hangups about using the cheapest thing that will work. (Some use even cheaper things that don't work, but that's beside the point.)

If an engineer is going to become obsolete, it's far more likely to be because he focuses on whatever is the latest thing when he's in school, and neglects breadth and flexibility.

Back when we had the thread about what a new grad's engineering library should look like, I gave a list that emphasized old books full of fundamentals and lore, both, in fields that aren't commonly emphasized in school at present. I think that's the right answer--maintaining intellectual flexibility and being able to derive things on one's own rather than looking them up. Both of those things require playing around with stuff for fun.

The one thing that won't broaden _anybody_ is spending energy rooting out evil infidel 555s and forcing people to sign PIC loyalty oaths and pledge not to use 4000-series CMOS or any op amp more than 10 years old.

Use what works, folks, and spend the energy on dreaming up the next cool project. And now, back on your heads. ;)

Cheers

Phil Hobbs

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Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
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email: hobbs (atsign) electrooptical (period) net
http://electrooptical.net

a

Because I started doing analog design well before I had access to a simulator :)

I only used the LTC one after reading this newsgroup, so I'm hardly proficient with it, to my mind it takes as much if not more effort than programming a microcontroller.

But that might be because I spent over a decade programming little micros for work. Before the PIC came along -- well, it was here, but in the days when OTP

6805 parts were being used, and after the mask program type effort I did in '84.

There, that should place how far behind the times I am? When I quit design in '93, we were looking to change from OTP 68hc05 family to PIC around then for small stuff, also stop using the 8048 mask chip after a decade, in favour of PICs.

Grant.

a

Because that doesn't do anything to eliminate such boo-boos?

ts on

, some

using a

Actually that is exactly the kind of obvious drop-off that simulation does find.

Simulation is a mixed blessing, but it can be handy - if imperfect - checking mechanism.

-- Bill Sloman, Nijmegen

some

using a

Demonstrating a working simulation frees one's mind to pay attention to other stuff.

some

using a

You're an idiot, Slowman. No simulation under the sun is going to correct a misteak in the schematic symbol or a wiring error.

It doesn't do a damned thing to catch schematic or layout errors. It certainly would *not* have caught my most recent (74LV1G123) goof.

elds

ng

iest solution.

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The 555 is a bad solution for a lot of problems because it puts a not- very-high-current switch in the same package and on the same ground return as a not-all-that-good monostable. Even I admit that there are jobs where its cheapness and wide availability compensate for its numerous defects.

4000-series CMOS isn't anything like as bad - it is slow, but that isn't always a disadvantage, since it makes somewhat less sensitive to narrow glitches than more modern logic.

And there are some decades-old op amps which are very hard to improve on. The 741 isn't one of them, but the LM308 and the LM11 are roughly as old and both are cute. If you were to reject anything more than a decade old, you couldn't even use the ON-Semiconductor MC33201/2/4 single dual and quad rail-to rail parts - not all that fast or precise, but with a very nice output stage

The problem with the 555 is that there's almost always a solution that works better.

-- Bill Sloman, Nijmegen

nputs on

PIC, some

han using a

ect a

You are the idiot krw, as we are all aware.

The simulation doesn't correct the mistake. The fact that the circuit simulation doesn't do what it was expected to do makes it obvious that a mistake has crept into the circuit diagram, and once you are aware that the circuit diagram contains a mistake, the way the simulation goes wrong can help you to find it.

Not in your hands, obviously ...

-- Bill Sloman, Nijmegen

inputs on

some

using a

You really are a clueless asshole, Slowman. Simulation CANNOT FIND A FOOTPRINT OR SYMBOL ERROR. It really is that simple, though not as simple as you, evidently.

Good god, you're stupid!

inputs on

PIC, some

using a

It's not BSs fault. You didn't take 3 pages with references and have it peer reviewed. Therefore his mega brain could not cope.

It's amazing he comes slumming here with mere engineers. Feel good, he has honoured you by acknowldeging your existance.

Remember him in your prayers.

Slowman isn't slumming. He's desperately seeking respect. What Slowman (like all pansies on the left) doesn't understand is that respect isn't an entitlement, it has to be earned. ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
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      Remember: Once you go over the hill, you pick up speed

John Fields expounded in news: snipped-for-privacy@4ax.com:

...

And some folks like AVR better (like me).

Warren