DC Current flow & Diode direction?

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cbretana

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The standard for signal pins, (like the PTT pin) on COM transceivers, which are inputs, is that the switch that opens and closes the circuit, (e. g. the normally open [NO] SPST PTT pushbutton on the control stick or yoke), is that the voltage polarity of the PTT pin/wire coming out of the transceiver is positive (12 volts), and the switch that is connected to that wire, when depressed, shorts the wire to aircraft ground, closing the circuit.
That means that although the PTT pin on the transceiver is considered an input pin, (it carries a signal in to the transceiver), the current flow, (when the PTT button is depressed), is away from the radio through the PTT switch, and then to ground. Right?

SO, If I need to add a diode to this signal wire, to ensure that no current can travel in the opposite direction (towards or into the transceiver), I need to put the diode with the arrow and black ring stripe pointing towards the ground connection, away from the transceiver. Right?

NOTE. I understand that the actual flow of the electrons is opposite the direction from higher voltage to lower voltage on any two points in the circuit. i.e., Current is considered to flow from positive to negative, even though the electrons are actually moving opposite to that.
 

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Actually, it depends on what you were taught. Most people are taught current flows from negative to positive. The cathode goes toward ground, no matter which way you were taught.

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As I thought, Thanks so much for confirming. I can imagine I am not the only one for whom that inconsistency has been the cause of confusion!
 
As Rhino said - most of us are taught in school that charge carriers are negative, and current flows from negative to positive. Today there is evidence otherwise, that charge carriers are "holes" that electrons flow into and the holes migrate toward positive just as the electrons go the other way - but either way the cathode goes to ground.

In the early 1800's it was posited that electrical energy flowed from positive (excess of charge) to negative (lack of charge), but then when the electron was discovered by Thompson in 1897 they realized that the charge was being carried the other direction, and we've rolled with that since.

It would be too hard to change all the textbooks, that's where we are.
 
As I mentioned in my question, I understand that the actual flow of the electrons is opposite the direction from higher voltage to lower voltage on any two points in the circuit. i.e., Current is considered to flow from positive to negative, even though the electrons are actually moving opposite to that.

But it is important to note that none of these actual reflect reality. They are all simply conventions. The electric charge is not positive on a proton and negative on an electron in any semantic or value sense. While true that the only thing actually moving are the electrons, (who would argue that when someone who lives in New York takes a vacation in Florida, that what is actually moving is a hole in the universe moving from Florida to New York?)

Or that a baseball doesn't move, it is the hole in the air moving from home plate to the pitcher's glove? The "hole" in the electromagnetic field that "moves" opposite to the motion of the electron when current exists is not real. It is just an abstraction that represents the absence of an electron where one might potentially be placed.

No, this issue is just one of convention, based simply by an arbitrary decision made by someone when originally defining/creating the nomenclature for electric charge. It is exactly the same as the convention that Longitude values are positive when traveling Eastwards from Greenwich England towards Europe, and negative when traveling West across the Atlantic. Another example are the vertical coordinates for a pixel on a video screen. Computer programmers have to learn that the coordinates for a pixel are defined as zero at the top of the screen, and increase positively as you move downwards, exactly the opposite from what intuition would imply.
 
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The electronics work the same either way, so it doesn't really matter much.
 
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I meant it doesn't matter which way you were taught, not which way you connect them. They still connect the same way, no matter which way you were taught current flows. So it works the same, no matter what school you went to.

On a related note, I believe the Navy still teaches positive to negative.
 
Unless you connect them the opposite way because of how or what you were taught. Inconsistencies create misunderstanding and opportunities for error.
 
They still connect the same, no matter which way you were taught. That's what I was talking about. In this case, for instance, the cathode still goes to ground.
 
If the installer, (taught in a confusing inconsistent way), connects the cathode to the positive terminal, then they are NOT connected the same.
 
cbretana said:
If the installer, (taught in a confusing inconsistent way), connects the cathode to the positive terminal, then they are NOT connected the same.
Click to expand...
That's true, but that isn't related how they were taught current flows. People who are taught current flows positive to negative still know the cathode goes to negative, and still install components the same way. They just think current flows through them in the opposite direction.
 
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The inconsistency i was talking about is the convention that the black stripe on a diode is on the end towards which the current flows. If he/she understands that the current flows in the direction that the electrons are moving, (and is nit aware of this inconsistency), then he or she will install the diode backwards.
 
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Okay. We never really thought about current flow when installing components. We just knew what went to positive and what went to negative. Current flow rarely got considered, unless we were troubleshooting some circuits where it was necessary to know. In 48 years of working electronics, I probably measured current direction less than ten times. The rest of the time, if we were concerned about current, it was just a matter of determining if it was there or not, not which way it was going. Most work surrounded voltage.
 
I understand. Given that perspective, I suppose blind adherance to convention would work, at least as long as you only execute tasks that also conform to the convention.
What I had to do was figure out how to add a diode to a circuit that controls a starter solenoid. The instructions first describe the problem the diode is there to address - the "current" that flows backwards through the coil when you close the switch to cut the motor, (collapsing the magnetic field in the coil). The voltage of that current spike can be many multiples of the voltage of the steady state flow voltage, and can damage electronics. To address this, you add another pathway for this reverse current to go directly to ground. But this pathway cannot allow normal forward current to travel on it, so you have to put a diode on it.

The instructions read like this:
the collapse of the magnetic field creates a voltage spike of opposite polarity to the voltage applied. The positive wire sees a negative spike and the negative wire sees a positive spike. The diode is wired backwards so that it does not conduct during normal forward operation. When the magnetic field collapses, the diode sees the reverse polarity spike and clamps it. This prevents the spike from possibly damaging the rest of the electronics in the car.

When used to clamp spikes in automotive circuits, connect the lead that comes from the end of the diode that has the band on it to the positive side of the circuit. Connect it the other way and you will make smoke.

Can you not see the potential for confusion here?
 
The instructions for the installation of the diode clearly call out the purpose and reason for the reverse installation, AND specifically calls the "band" to be connected to positive - no confusion there.

What did cause some confusion to me was your use "close the switch to cut the motor (collapsing the magnetic field)" - that is not CLOSING the switch. That is OPENING the switch. Again with those silly conventions, I suppose. :rolleyes:
 
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