Capacitor Question

You'll notice that STM also recommend a 0.33uF cap on the input !

< snip elegant discourse of no practical value >

They embody knowledge about the parts directly from their designers and you ignore their advice at your peril.

You seem to reckon that you can ignore that on the basis of your theoretical analysis. I consider that very foolish.

I can tell you that prior to adopting the 'ground rules' I originally mentioned in this thread that a certain company I design for had experienced occosional trouble with 78 and 79 series regulators 'oscillating'.

Since adopting my advice, easily a hundred thousand units embodying my advice have been made without that problem.

I simply don't care how clever you think you are, I'm interested in making stable designs. At the end of the day, the cost of a small film cap easily outweighs taking chances with stability issues that'll hold up your production and require costly re-work.

Also note that every batch of ICs may perform slightly differently. Making something that works on the bench doesn't guarantee every product using that design will behave identically.

Graham

Funny then that every data sheet or app note I've ever seen for a 78 series regulator

*explicitly* states that no output cap is required for stability.

The advantage of an output cap here is enhanced transient response.

I just noticed you're from an educational institution ! No damn surprise there. Time you got out of your ivory tower and had to deal with the *real world*.

Some of the most fuckwittedly idiotic things I've heard in my entire life have come out of the mouths of so-called 'pro-fess-ors' !

Graham

: snipped-for-privacy@ccwf.cc.utexas.edu wrote:

: < snip elegant discourse of no practical value >

: Also note that every batch of ICs may perform slightly differently. Making something : that works on the bench doesn't guarantee every product using that design will behave : identically.

Therein lies your problem. You don't see the value of understanding what you work with. You simply follow "rules of thumb," or "ground rules," and make no effort to understand what is going on around you. The fact that your "ground rules" work for your specific application does nothing to demonstrate how knowledgeable you are. In this specific example, your filtering of the input signal to the regulator does not guarantee that the regulator will remain stable. Give me enough time and I will find a scenario that breaks it.

Since you want to bring numbers of successful designs into this, out of the HUNDREDS OF MILLIONS of the ICs with my regulators on them, I am not aware of a single RMA relating to those regulators. Does that, in and of itself, mean that I am correct here? No, but at least I can present my ideas elegantly (in your own words) and describe the workings of the circuits involved without (initially) resorting to name calling. What I was describing wasn't a "clever trick," but a simple mathematical truth about a simple analog circuit. Your assertion that understanding what is happening around you is of no value is just plain sad.

And you call me blind? My participation in this thread is over. I have better things to do than argue with you over simple details about simple circuits. Perhaps, one day, you will see the value of understanding the circuits that you work with, but I'm certainly not going to be able to convince you of that over the internet.

Best of Luck,

Joe

something

will behave

I don't have a problem. I solved the problem that happened before I came along and fixed it.

I understand perfectly thank you. I use rather more theoretical analysis than most engineers I know. I don't use that as a substitute for practical experience though. I combine the two.

You haven't a clue. I was writing circuit models using Mathcad back in 1989.

I don't care about demonstrating that. Engineering is about making stuff that

*works* - not arguing to the board of directors when the line is backed up that ' it shouldn't have happened ' according to some hare-brained theory.

You just said that the input *doesn't* need local decoupling !

Your university directory lists you as a student.

Where are these hundreds of millions of ICs ? They obviously aren't 78XXs.

Maybe one day you'll understand the value of making stuff that has to work in the real world rather than in academia.

Graham

: snipped-for-privacy@ccwf.cc.utexas.edu wrote:

: I just noticed you're from an educational institution ! No damn surprise there. Time you : got out of your ivory tower and had to deal with the *real world*.

: Some of the most fuckwittedly idiotic things I've heard in my entire life have come out : of the mouths of so-called 'pro-fess-ors' !

: Graham

Last, short comment: I am not a professor, but, do attend a University, as you so cleverly deduced from my .utexas.edu email address (boy, that must've been tough!) I earned my engineering degrees a long time ago, however, from a different university.

Since you like spending time checking me out, point your browser to

instead. The patents that you're likely to find aren't all mine (by some coincidence, there's someone else with a similar name that has a lot more patents than I do.)

Why did my comments bother you so much that you actually spent time "investigating" me? I could care less about you, although I DO see why you hide behind an alias (there ARE sickos like you out there that go around looking people's personal information up over a disagreement over voltage regulators!)

Successful innovation requires a thorough knowledge and understanding of what you are working with. Perhaps, unlike you, I'm not in this to slap circuits together using "ground rules" that someone else told you. I'm not denying that that's how a lot of engineering is done, but engineering needs thinkers like me, as well as followers like you. Perhaps I'm wrong and you are a world-class innovator, but your attitude doesn't show that.

Granted, this thread began about how to choose capacitors for a

7805, (hardly a problem requiring innovation,) but in my experience, your method of desinging by "rules of thumb" has gotten people around me in more trouble than my method of thoroughly understanding what I am working with has gotten me.

Joe

Hi, John (and all). I believe the signal voltage output from the transmission varies proportionately to the battery voltage, which may change with motor RPM. In that case, it might be easier for the OP to use an external reference voltage which is a voltage divider of the battery voltage, rather than using the on-board reference voltage on the PIC. Or, if the OP wants to go back to the comparator model, he could just use a voltage divider from the power supply as the reference to be divided down by the resistor divider string.

Chris

Oh Lord !

Battery voltages don't mysteriously vary with motor rpm !

Battery voltage varies with state of charge and applied load/charge current. A small battery driven from a motor driven generator will indeed vary its voltage according to the charge current ( which may vary with speed ) but not in any direct useful relationship.

It seems he was already using a 7805 regulator to drive his sensor.

If it was indeed a potentiometer sensor ( as guessed by some posters but never mentioned by the OP ) the varying output in any given gear is likely due to 'uncertainty' on the input shaft of the pot since a gear selection doesn't provide a precise mechanical input.

Graham

I agree.

There is little mystery about it. On many motorcycles, the alternator regulation is very poor, with thew alternator not keeping up at low engine RPM, and overcharging the battery at full RPM. Many don't even have a regulator, but just rely on a fair match between alternator current capability and motorcycle electrical system load.

No. He said the sensor is already connected to the electrical system, and he is just tapping into the output signal. It is a pot that senses gear shifter position and is probably part of a voltage divider across the electrical supply.

I fully appreciate the above which you have explained excellently.

It seems however that certain ppl are mistakenly associating a change in battery voltage with a direct relationship to motor rpm - which there *isn't*.

A

voltage

So where did the 7805 ever come into the equation ? I got the impression that the sensor's input was 5V.

I guessed that much, from your posts as much as anything. The 'uncertainty' about the output voltage would clearly seem to be a result of the mechnical input not being precise.

Once again I thought it was driven from 5V. Why mention a 7805 otherwise ? Of course the OP seemed to be terminally incapable of describing his setup accurately.

Graham

battery

The O.P. has stated that his electrical system voltage rises as engine RPM rises. I take him at his word, on this. This does not imply proportionality, only variation in a particular direction. You are being a bit too literal.

(snip)

the

The O.P copied a commercial circuit that has a microprocessor powered from a 5 volt regulator, and so, has an A/D converter that uses the 5 volt regulated voltage as its A/D reference voltage. It is the mismatch between the pot supply and the A/D supply that is causing trouble, in my opinion.

about the

being

There will certainly be some of that, but it doesn't explain the wrong gear position indicator flashing when the engine is revved up.

course

That may be a big part of his problem. He really doesn't understand the workings of the key pieces of his puzzle (the pot and the way it is powered, and the A/D converter and how it is powered and referenced). Rather than give him a complete course, we have sort of been hanging around, discussing various details, waiting for the various lights to come on in his mind, so he will either figure some of it out, or ask useful questions. There are no answers so useless as the answers to unasked questions. We have to be patient and wait for the questions to be asked, if we are to have any hope that the answers will not be misunderstood, or worse, ignored. We have lots of understanding and answers that the O.P. may not be ready to hear, yet.

He just wants to get this thing finished and working, so he can ride. I am interested in his electronics education, and know that frustration and desire are good motivators for learning. If we had redesigned his circuit immediately on his first post, so he could have built a perfectly working unit, without understanding anything, he would be doing something else, now, instead of building up all this new understanding. So far, we have bumped into voltage dividers, A/D converters, microprocessor programming, regulators and the electrical systems on motorcycles. How much better is that than just having a shift indicator that merely works, perfectly? I am willing to bet that his new knowledge will change his life for the better more than the shift indicator, eventually will.

Why are you taking part in this discussion? That is not sarcasm, but a sincere question.

battery

I take your point. In effect I'm being 'terribly precise' because I note that those without a formal science background are prone to 'jumping to conclusions'. But I'll bet there's a

*lag* involved in that relationship too

that the

I saw a link to a motorbike site that had some comparators driving leds. Is that the one you mean ?

about the

being

Without looking in greater detail at the comparator arrangement I'd hesitate to comment.

Of course

I admire your tenacity.

I've done this with the likes of Boki too and got a result. The thing is - Boki will actually respond sensibly when you ask a direct question. The OP here simply seems to go off at a tangent when asked for detail.

Seems to me like a classic case of the 'f*ck you' attitude. If you can't spoon-feed me the answer then screw you. The way 'education' seems to be going.

You'll note that I gave a detailed answer to the OP's original question, having had to make an assumption that he knew what 'smoothing' was about when he mentioned it. Since the original post was a complete blind alley and I had simply wasted my time I was curious to see why the OP then chose to respond with such bile to someone making an effort to provide some knowledge.

I'll bet that his guy is an utter waster frankly. His attitude ( and arrogant ignorance of technology ) speaks volumes.

Graham

those without

bet there's a

Doesn't that depend on the internal resistance of his battery? It may be a tiny thing (and he kick starts the bike).

that the one

This is the microprocessor design he is trying to copy:

He has also built a multi comparator version, so we may be talking about two different circuits.

to comment. (snip)

Boki will

seems to go

He may be having too many conversations with too many people at the same time, and getting them confused.

spoon-feed me the

I haven't gotten that impression, but we probably see people differently.

having had to make

Since the

curious to

effort to provide

Evidently, he didn't see in your response, what you intended it to contain. Communication from this distance has problems.

ignorance of

He cannot waste anything he doesn't have.

that those without

bet there's a

Internal resistance certainly plays a part.

Strange thing is - he talked about a *car* originally. I know my car's battery voltage sticks nicely at 13.8V ( typical on-charge voltage ) after a few minutes drive.

that the one

Ok. Hadn't seen that one before. Sadly doesn't show the 'gear sensor' itself.

It seems so. I have indeed seen the comparator version.

I suspect the underlying problem is the same though.

I also suspect he went to a new circuit to 'fix the problem' not realising that underlying cause.

to comment.

Boki will

seems to go

spoon-feed me the

Maybe so. I reckon I'm right though. I get the distinct impression that this is one 'cocky' guy who's happy to accept he knows little but plans to 'blag it' anyway.

I certainly wouldn't want anyone like that on any team of mine. Likely to have a net negative influence.

having had to make

Since the

was curious to

effort to provide

Given that he didn't apparently understand what his own question asked I guess so !

arrogant ignorance of

I use the term in the vernacular sense. As in 'a waste of space'.

Graham

Pooh Bear wrote: (snip)

is one 'cocky' guy

Think back. Was there a period in your life (a long time ago, I'll grant) that this description might have applied to you?

is one 'cocky' guy

No.

I might have seemed cocky to some but I *never* needed to 'blag it'. Strange as it may seem to today's kids I actually enjoyed learning and delighted in educating myself about technology.

I *still* enjoy learning too.

I've always felt confident about my work because it's backed up by a strong knowledge of the fundamentals.

Graham

is one 'cocky' guy

Perhaps I have guess wrong on the meaning of "to blag". It sounded like something I might have done in my youth.

as it may seem to

about technology.

But we are talking about teaching.

knowledge of the

And you are able to be humble about it, too. ;-)

True Love, he said "True Love", Max.

-Valerie, "The Princess Bride"

Happy Valentines day.

"He distinctly said 'to blave.' And, as we all know, "to blave" means "to bluff." So you're probably playing cards, and he cheated --"

- Miracle Max, "The Princess Bride"

Bob M.