Sinclair ZX80 / ZX81 / Z88 Forums

Does it matter which way the LED goes in (i.e. polarity before any aussie themed replies appear...)?
Which way does the diode go in? Stripe at the ‘top’?



Moderators note: The above questions were asked in the Improving Timex/Sinclair Tape Loading thread. This kicked off a discussion on the direction of current flow. I've moved those posts to this new thread. Mark

The stripe on the diode goes where the "line" is on the circuit diagram. (I think of the symbol as depicting an "arrow" hitting a "wall", showing the direction in which current can NOT flow.)

Looks like you're almost there,...
Ian

Diodes (and LEDs):-



Mark

TMAOne wrote: ↑Sun Jan 07, 2018 8:02 pm The stripe on the diode goes where the "line" is on the circuit diagram. (I think of the symbol as depicting an "arrow" hitting a "wall", showing the direction in which current can NOT flow.)

That is an interesting view. You are right and false the same regarding the difference between the technical (*) definition of current flow direction and the physical one (opposite). So to reminder, the cathode can be seen as the "cold" end of the diode to be connected to GND. Current flows to this cold end (technical definition). And the symbol (arrow) shows the direction quite obviously (arrow direction = current direction).

The technical definition let the current flow from plus to minus. In fact minus is a surplus of electrons (with negative charge) and they tend to move to places with less electrons (plus). So this is the physical dimension. Mostly people mean the technical direction when talking about current flow which is more historical or conventional but not very precise.

See here (convention section):
https://en.wikipedia.org/wiki/Electric_current

PokeMon wrote: ↑Tue Jan 09, 2018 6:56 pm Mostly people mean the technical direction when talking about current flow which is more historical or conventional but not very precise.

I wonder if it's a cultural thing which depends on which side of The Pond you're on. I was taught to think of current in terms of the flow of electrons, moving from negative to positive. Mention was made of an alternate viewpoint of current being in terms of "holes", or positive charges where an electron has been stripped from the atom. Apparently both models are valid as long as you don't try to mix and match. Perhaps I should keep my almost-forgotten early high-school perspective on diodes to myself lest I confuse folks.

How's the board coming Lardo? I'm on pins and needles here,...
Ian

Direction of current flow - Ahh, in the U.K. it depends on the level that a person has reached in their education.

In basic teaching of electricity, people are taught about conventional current flow. The history of this is that in the early days, apparently some people repeatedly made a spark jump across some electrodes. They then decided which way the spark jumped!

So with conventional current flow, electric current is said to flow from a positive terminal or point to a negative terminal or point. Hence all the various traditional symbols having arrows showing this direction of current flow (including diodes and bipolar transistors).

But of course, it was later discovered that electric current is actually the movement of electrons and that as a negative charge, they move from the negative point to the positive point. This is not normally discussed when basic electrical theory is being taught. But is taught later in the next level when electronics is the subject (rather than electricity).

Mark

Pokemon is correct.

In addition, long ago they settled on a direction of current based on lab experiments, (I suspect with batteries) before they knew there were positive and negative charges.

Positive current is defined as flowing from higher voltage or EMF to lower or GND.

Don't confuse Current with Direction of Charge Carriers.

In passive components, Current is + -> - but direction of charge Carriers (electrons) is opposite.

In a system with Plasma, you can have a flow of positive and negative charge Carriers.

In a solid semiconductor, particularly with doping you can have electrons and missing electrons as Carriers. Missing electrons are called holes.

gammaray wrote: ↑Tue Jan 23, 2018 4:02 pm Don't confuse Current with Direction of Charge Carriers.

In passive components, Current is + -> - but direction of charge Carriers (electrons) is opposite.

I don't know what you exactly mean and why you distinct between direction of current and charge carriers. Current IS the move of charge carriers and electrons are the charge carriers here. So there can not be a different direction of current and charge carriers (which is more or less the same as an electron is a kind of charge carrier - there are more existing in physics).

It was just a definition in the first steps with electronic stuff (batteries and lamps) in the very early years around 1800+ from Galvani and Volta. Later physicians found that the definition is in fact wrong because protons do not move, just electrons. I think it is that simple. Anyway too many people have been teached that current is flowing from plus to minus that it was difficult to change this new world paradigm. And I think there are many people with basic electronic education still don't know that the conventional direction is in fact wrong.

This is by the way not semiconductor stuff, even in a simple copper cable electrons are moving from minus to plus. But when you go deeper into semiconductors and the physics you will learn that the general theory of current flows from plus to minus must be wrong. The same is if you go deeper into electrochemics. Which is by the way an interesting part in electronics as well.

Pokemon,

Which way does current flow in a plasma where protons flow from higher EMF (+ ) to more negative EMF( -)and electrons flowing the opposite direction at the same time? I believe neon lights are example though AC complicates the issue.

Current is defined by charge flow from+ to -. If possible in a system, positive Carriers going from +to- is identical as same number of negatively charged Carriers going from - to +.

If only only one type of charge carrier exists in a system the direction of flow of charge particles is dependent on the type positive or negative. The current is dependent on the EMF field AKA voltage.

A similar confusion exists around the difference between speed and velocity. Velocity has direction, speed inherently does not by definition.

If I am incorrect, please take no offense, I blame the professors AND my parents for all my mistakes.

gammaray wrote: ↑Tue Jan 23, 2018 10:47 pm Pokemon,

Which way does current flow in a plasma where protons flow from higher EMF (+ ) to more negative EMF( -)and electrons flowing the opposite direction at the same time? I believe neon lights are example though AC complicates the issue.

Not sure what you mean. This isn't different in Plasma.
And how could it be opposite if outside the plasma the electrons go from more negative potential to the positive ? Current flow in a plasma need a voltage outside and current flow in the outside electronics can't be different. How could the current flow in the plasma in the other direction ?

AC doesn't complicate the situation, it changes just direction. It is not different to change polarity by hand every 10 seconds or 50 or 60 times per second in traditional AC.