PJ:
If you feel that there arguments are superstition, you obviously have not read most of this page of posts. They show, without 'taking it on faith', the reasons for there statements. It sounds to me that you are searching for evidence to support your hypothesis, and often when we search for that type of thing we over look what is actually being said, instead seeing what we want to.
PJ, Yes, the relay coil is isolated from the contacts so we do not have to worry about the load circuit voltage and current. Of course relay coils, diodes, and drive transistors never fail either, and even if they did what possible harm could 12 volts do when applied to the prop pin through a resistor. So nothing to worry about there either. Please forgive me for being an obsessive superstitious fool. It must be the huge advertising campaign the opto isolator manufacturers put on to brainwash us.
kwinn, 13 posts I ago I posted, "You WIN, kwinn." You should've quit while you were ahead. davidsaunders, There's no hypothesis, an opto-iso was/is unnecessary in/for the OP's situation - and practically every other that I've ever seen on this forum.
In Propeller-Land people oscillate between hyper-inflated, paranoiac needs for "protection" from any and all remote catastrophe viz opto-isolators galore on the one hand and the absence of good sense on the other with simple things like resistors being deemed "optional" and the desire for liberation from the shackles of datasheets and voltmeters, proclaiming the Propeller's unique, amazing, though formally unspecified, quality to withstand the absurd (ask the Pre-eminent Propeller Prophet about that.)
PJ
And they SAID that it is UNNEEDED for THIS application, in the same post as noted that there is also no good reason to change the design not to include it. And I still believe that you are looking for evidence to support your hypothesis that they are working on a blind faith and not fact, and using pushing unneeded precautions. If I am wrong, Why did you completely ignore the posts that said that it is indeed unneeded, as well as the ones that say that each has there own way of doing things, before you gave rebuttal to my statement? For your rebuttal completely ignores there statements, essentially saying that they are trying to say that the optical coupling component is needed, when in fact they have made it clear that that is NOT there stance. It really does seem as if you are not seeing what is actually being said.
PJ:
I just reread this thread and I do NOT even see ANY THING that says that optical coupling is needed for THIS circuit, though I do see a couple of places where it is said that it is NOT needed for THIS circuit.
david,
That's just not the case, whereas there was a certain retraction by kwinn there followed a re-entrenchment/s by kwinn.
There's no "they", it's just kwinn.
The likelihood of relay coils shorting, drive transistors failing catastrophic, ad nauseam are remote in the extreme.
Others' padding their kit based on bizarre assumptions as a would-be prophylaxis, a precautionary talisman , because that's what it all amounts to, is senseless, pointless, obsessive.
PE - But, hey, don't mind me - if a belt ain't enough, get a pair of suspenders, and some super-glue, too. Good Night!
PJ:
To verify I JUST REREAD the posts by KWINN and he did NOT SAY that it is NEEDED for THIS circuit. He did say in post #17 of this thread:
I agree with pretty much everything posted here except the "I don't get the obsession with "optos" and "isolation" and "protection"; it's like a lot of stuff around here, superstitious behaviour.".
Witch can only be interpreted as (exactly what he says) meaning that he disagrees with there being an obsession, or superstitious behavior.
If it is similar things that you are interpreting as recommendations, or professions of necessity in other threads, then I would have to question weather you have a predisposition based on a malformed hypothesis of believed superstitious behavior.
A hypothesis is just a theory that does not yet have reliably reproducible confirmation. Unfortunately we do tend to be tainted by our hypothesis, no matter how strongly we wish not to be (or even how strongly we feel we are not). Your belief of consistent superstitious behavior amongst the members of this forum is thus a hypothesis. If it were both accurate and consistently repeatable, from the view of multiple observers, then it would be a theory, though at this time those requirements are not met.
PJ also if you wish to site the remainder of post #17 as evidence, he did not say, or even imply that his statements apply to this situation, he only implied that he was giving an example to answer when an optical coupling device may be useful.
The original question had to do with reasons and techniques for protecting a Prop I/O pin when you're driving some kind of moderate voltage / moderate current load, more than a Prop I/O pin is designed to handle. Like a lot of these situations, there's no magic solution. You have to have some understanding of your system and maybe the most likely failure modes. You have to consider the costs of the various solutions, particularly vs. the various risks. Are you going to be protecting against lightning? What about someone spilling a Coke on your robot? What about static electricity in a carpeted home in winter? What about the old electric dryer or the air conditioner on the same circuit on the other side of the house? What about that old X-ray machine in the office on the other floor of your building?
A well filtered power supply with a fused built-in or external surge suppressor is a good idea. A series resistor appropriately chosen on all input leads that'll tolerate them is a good idea. You can add ferrite beads or chokes to leads carrying relatively slow signals. Remember that the differences between noise and data may be more a matter of what you want than the characteristics of the signals. Appropriate output drivers with protective diodes for non-resistive loads is important. Avoid ground loops. Avoid wiring setups that allow noise to be coupled into sensitive input leads or into grounds or low voltage supplies. The list goes on. Optocouplers provide high voltage isolation and potential separation of ground loops, but they introduce signal degradation and sometimes a false sense of security.
Beau did some experimenting with Propeller I/O pins and found that they could withstand a short circuit to ground or +3.3V. CMOS transistors have a negative temperature coefficient in terms of output current. The Prop output pin circuitry tends to current limit over roughly 30mA which is the maximum load on them. I don't know where the Prop pins hit their limit, but it's before the point of damage. They're not officially rated above this and I wouldn't design something that depends on this, but it's nice to know that they're capable of holding up under some kinds of abuse.
PJ:
All I am asking is that you allow this thread to return to its intended topic. Ever since post #20 you have effectively taken over this trying to find evidence to support your belief that superstitious behavior is common on these forums, as well as attempting to convince others of your belief, this debate is counterproductive. Since you have not responded to the 4 polite requests I have made to this effect, nor have you responded to the requests along the same line I am being more direct, PLEASE ALLOW THIS THREAD TO RETURN TO ITS ORIGINAL TOPIC.
Comments
If you feel that there arguments are superstition, you obviously have not read most of this page of posts. They show, without 'taking it on faith', the reasons for there statements. It sounds to me that you are searching for evidence to support your hypothesis, and often when we search for that type of thing we over look what is actually being said, instead seeing what we want to.
PJ, Yes, the relay coil is isolated from the contacts so we do not have to worry about the load circuit voltage and current. Of course relay coils, diodes, and drive transistors never fail either, and even if they did what possible harm could 12 volts do when applied to the prop pin through a resistor. So nothing to worry about there either. Please forgive me for being an obsessive superstitious fool. It must be the huge advertising campaign the opto isolator manufacturers put on to brainwash us.
davidsaunders, There's no hypothesis, an opto-iso was/is unnecessary in/for the OP's situation - and practically every other that I've ever seen on this forum.
In Propeller-Land people oscillate between hyper-inflated, paranoiac needs for "protection" from any and all remote catastrophe viz opto-isolators galore on the one hand and the absence of good sense on the other with simple things like resistors being deemed "optional" and the desire for liberation from the shackles of datasheets and voltmeters, proclaiming the Propeller's unique, amazing, though formally unspecified, quality to withstand the absurd (ask the Pre-eminent Propeller Prophet about that.)
And they SAID that it is UNNEEDED for THIS application, in the same post as noted that there is also no good reason to change the design not to include it. And I still believe that you are looking for evidence to support your hypothesis that they are working on a blind faith and not fact, and using pushing unneeded precautions. If I am wrong, Why did you completely ignore the posts that said that it is indeed unneeded, as well as the ones that say that each has there own way of doing things, before you gave rebuttal to my statement? For your rebuttal completely ignores there statements, essentially saying that they are trying to say that the optical coupling component is needed, when in fact they have made it clear that that is NOT there stance. It really does seem as if you are not seeing what is actually being said.
I just reread this thread and I do NOT even see ANY THING that says that optical coupling is needed for THIS circuit, though I do see a couple of places where it is said that it is NOT needed for THIS circuit.
That's just not the case, whereas there was a certain retraction by kwinn there followed a re-entrenchment/s by kwinn.
There's no "they", it's just kwinn.
Re-read #33.
Others' padding their kit based on bizarre assumptions as a would-be prophylaxis, a precautionary talisman , because that's what it all amounts to, is senseless, pointless, obsessive.
PE - But, hey, don't mind me - if a belt ain't enough, get a pair of suspenders, and some super-glue, too. Good Night!
To verify I JUST REREAD the posts by KWINN and he did NOT SAY that it is NEEDED for THIS circuit. He did say in post #17 of this thread: Witch can only be interpreted as (exactly what he says) meaning that he disagrees with there being an obsession, or superstitious behavior.
If it is similar things that you are interpreting as recommendations, or professions of necessity in other threads, then I would have to question weather you have a predisposition based on a malformed hypothesis of believed superstitious behavior.
A hypothesis is just a theory that does not yet have reliably reproducible confirmation. Unfortunately we do tend to be tainted by our hypothesis, no matter how strongly we wish not to be (or even how strongly we feel we are not). Your belief of consistent superstitious behavior amongst the members of this forum is thus a hypothesis. If it were both accurate and consistently repeatable, from the view of multiple observers, then it would be a theory, though at this time those requirements are not met.
The current through the infrared LED is about 20 mA.
It's a wonder the pin isn't already dammaged.
Duane
A well filtered power supply with a fused built-in or external surge suppressor is a good idea. A series resistor appropriately chosen on all input leads that'll tolerate them is a good idea. You can add ferrite beads or chokes to leads carrying relatively slow signals. Remember that the differences between noise and data may be more a matter of what you want than the characteristics of the signals. Appropriate output drivers with protective diodes for non-resistive loads is important. Avoid ground loops. Avoid wiring setups that allow noise to be coupled into sensitive input leads or into grounds or low voltage supplies. The list goes on. Optocouplers provide high voltage isolation and potential separation of ground loops, but they introduce signal degradation and sometimes a false sense of security.
Beau did some experimenting with Propeller I/O pins and found that they could withstand a short circuit to ground or +3.3V. CMOS transistors have a negative temperature coefficient in terms of output current. The Prop output pin circuitry tends to current limit over roughly 30mA which is the maximum load on them. I don't know where the Prop pins hit their limit, but it's before the point of damage. They're not officially rated above this and I wouldn't design something that depends on this, but it's nice to know that they're capable of holding up under some kinds of abuse.
All I am asking is that you allow this thread to return to its intended topic. Ever since post #20 you have effectively taken over this trying to find evidence to support your belief that superstitious behavior is common on these forums, as well as attempting to convince others of your belief, this debate is counterproductive. Since you have not responded to the 4 polite requests I have made to this effect, nor have you responded to the requests along the same line I am being more direct, PLEASE ALLOW THIS THREAD TO RETURN TO ITS ORIGINAL TOPIC.
Who died and made you God?
Take a Midol.
The thread was OVER at #16.
Paul