deskthority

This is where the foolish habit of calling earth "ground" instead leads to confusion! They are separate things: like neutral and earth on a mains plug. Or ground and ground as I guess you could say!

Ground goes to Teensy. Earth goes to the plate. Some IBM keyboards even have an earthed space bar (I don't know why, as the space bar is still plastic, but maybe it helps prevent static shocks somehow) which is wired to the plate. My 122 key Model M is like that, so I earthed its plate with the appropriate shield on the cable, and my Soarer box uses its conductive metal shell to do the same and hook earth all the way back to the host computer.

Muirium wrote:This is where the foolish habit of calling earth "ground" instead leads to confusion! They are separate things: like neutral and earth on a mains plug. Or ground and ground as I guess you could say!

Ground goes to Teensy. Earth goes to the plate. Some IBM keyboards even have an earthed space bar (I don't know why, as the space bar is still plastic, but maybe it helps prevent static shocks somehow) which is wired to the plate. My 122 key Model M is like that, so I earthed its plate with the appropriate shield on the cable, and my Soarer box uses its conductive metal shell to do the same and hook earth all the way back to the host computer.

Thanks, Mu, for being so grounded and bringing this discussion back down to earth. However, I am still somewhat confused. It would be helpful to see a diagram illustrating these concepts and seeing how they are implemented in practice. Partially toward this end, here is a quote from the present definition of "ground" from Wikipedia:

"Voltage is a differential quantity. To measure the voltage of a single point, a reference point must be selected to measure against. This common reference point is called "ground" and considered to have zero voltage. This signal ground may not be connected to a power ground. A system where the system ground is not connected to another circuit or to earth (though there may still be AC coupling) is often referred to as a floating ground."

Wikipedia presently defines Ground and Neutral as follows:

"Ground or earth in a mains (AC power) electrical wiring system is a conductor that provides a low impedance path to the earth to prevent hazardous voltages from appearing on equipment (the terms "ground" (North American practice) and "earth" (most other English-speaking countries) are used synonymously here). Under normal conditions, a grounding conductor does not carry current."

"Neutral is a circuit conductor that carries current in normal operation, which is connected to ground (or earth)."

"In a polyphase or three-wire (single-phase) AC system, the neutral conductor is intended to have similar voltages to each of the other circuit conductors. By that definition, a circuit must have at least three wires for one to serve as a neutral."

"In the electrical trade, the conductor of a 2-wire circuit connected to the supply neutral point and earth ground is also referred to as the "neutral.""

"The United States' National Electrical Code and Canadian electrical code only define neutral as the first of those. In North American use, the second definition is used in less formal language but not in official specifications. In the United Kingdom the Institution of Engineering and Technology defines a neutral conductor as one connected to the supply system neutral point, which includes both these uses."

"All neutral wires of the same electrical system should have the same electrical potential, because they are all connected through the system ground. Neutral conductors are usually insulated for the same voltage as the line conductors, with interesting exceptions."

I had been laboring under the misconception that there was a single symbol for "ground", but the one I had been using is the symbol for "earth ground".

Annoying, right? We have three words for two concepts, and the remainder is expressed in confusion!

Digital electronics uses GND as 0 V (versus VCC for +5 V or whatever value) ubiquitously. But ground is the American name for Earth, not Neutral. Ugh!

The shielding on cables, and especially metal exteriors themselves, is earthed. Do *not* confuse with "ground" / GND / 0V, which is an internal connection with just as little to do with static electricity as VCC. Simple! (Yet unfortunately not.)

Muirium wrote:Annoying, right? We have three words for two concepts, and the remainder is expressed in confusion!

Digital electronics uses GND as 0 V (versus VCC for +5 V or whatever value) ubiquitously. But ground is the American name for Earth, not Neutral. Ugh!

The shielding on cables, and especially metal exteriors themselves, is earthed. Do *not* confuse with "ground" / GND / 0V, which is an internal connection with just as little to do with static electricity as VCC. Simple! (Yet unfortunately not.)

Small wonder I remain at least somewhat confused.

Part of the problem is the US/UK dichotomy of definitions. I studied for a year in England. On my first day in the lab, my supervisor sat me down, pulled out a sheet of UK foolscap, which was in reality a piece of A4 paper, and set about writing two columns, British and American, under the general heading of Glossary.

"Right," he said. "It has been said that we are two nations divided by a common language. This is true; therefore, I hope that this glossary will be of some help."

Despite this exercise, I am still a bit fuzzy about "ground" and "earth", but your explanations are helping.

It gets even more complicated when you are dealing with analog/digital mixed circuitry. You have analog ground, digital ground, single-point ground, chassis ground, etc. Then there's RF. You can short the far end of a wire to ground and have it appear as an open circuit at the near end if the frequency and wire length are just right.

Hypersphere wrote:"Right," he said. "It has been said that we are two nations divided by a common language. This is true; therefore, I hope that this glossary will be of some help."

He wasn't the first, and he won't be the last… The Office. (No, not that one.) And a saturnine fellow in an Ali G costume, who will always be more famous here than his brother Borat.

Muirium wrote:This is where the foolish habit of calling earth "ground" instead leads to confusion! They are separate things: like neutral and earth on a mains plug. Or ground and ground as I guess you could say!

Ground goes to Teensy. Earth goes to the plate. Some IBM keyboards even have an earthed space bar (I don't know why, as the space bar is still plastic, but maybe it helps prevent static shocks somehow) which is wired to the plate. My 122 key Model M is like that, so I earthed its plate with the appropriate shield on the cable, and my Soarer box uses its conductive metal shell to do the same and hook earth all the way back to the host computer.

I thought you might enjoy this inscription on a metal badge affixed to an IBM Selectric typewriter: The Selectric will be a keycap donor for my IBM Displaywriter. The Selectric has beautiful spherical double-shots -- white legends on a black background that looks almost like a dark olive green.

If this typewriter were in the UK, I suppose the badge should say, "earthing not required" (?)

Everything mains powered, at least computer wise and I expect electric typewriters too, is double earthed by convention over here. So I heard in "tech" class back at school. No, not high tech, it was what you guys call "shop", I think. We were usually playing with saws and sanders!

Today I finished installing a Teensy in a refurbished XT keyboard. I used a USB B panel mount connector with a cable to a mini-USB connection to the Teensy. However, I am dissatisfied with the panel mount USB B connector for the external cable -- it sits a bit too high on the rear of the case and at too high an angle, so that the connection to the external cable is overly conspicuous. I think it would be better to devise a way to use the opening that is already in the case for the original cable and to use a micro or mini USB receptacle. In addition, the solution I used provides no obvious way to connect a 5th earth wire to the metal part of the case and to a shield on the USB cable, which is separate from the ground that is connected to the Teensy. What are others doing for their USB connections from their Teensy-equipped XT keyboards?

USB B ain't great. It's bulky and not especially reliable. I'd go with something similar to what Quantal did, in the original cable exit hole:

http://deskthority.net/post164995.html#p164995

I'd have to take a close look at my XT, but my guess is micro USB would fit there just fine.

As for earthing: the exterior of all USB connectors and sockets is earth. This is also true for PS/2, AT, XT, and ADB. I have my converter box act as a conductor between all the sockets, and that way the earthing chain runs right from the host computer to the keyboard, no matter the switch position. With a simpler setup like yours, all you need to do is attach a wire on the outside of your USB socket (sometimes they have a little tag to help you fit it, but not always) and then run it to the plate or whatever you want earthed.

I haven't forgotten my promised howto guide, by the way. It's stalled temporarily while I prepare work on a new box for Facetsesame, which will have better pictures of the work in progress. There's only so much you can see from pictures of the final product, as I've about 20 wire connections inside mine thanks to that dial!

Muirium wrote: ↑USB B ain't great. It's bulky and not especially reliable. I'd go with something similar to what Quantal did, in the original cable exit hole:

http://deskthority.net/post164995.html#p164995

I'd have to take a close look at my XT, but my guess is micro USB would fit there just fine.

As for earthing: the exterior of all USB connectors and sockets is earth. This is also true for PS/2, AT, XT, and ADB. I have my converter box act as a conductor between all the sockets, and that way the earthing chain runs right from the host computer to the keyboard, no matter the switch position. With a simpler setup like yours, all you need to do is attach a wire on the outside of your USB socket (sometimes they have a little tag to help you fit it, but not always) and then run it to the plate or whatever you want earthed.

I haven't forgotten my promised howto guide, by the way. It's stalled temporarily while I prepare work on a new box for Facetsesame, which will have better pictures of the work in progress. There's only so much you can see from pictures of the final product, as I've about 20 wire connections inside mine thanks to that dial!

I like the panel-mount usb connectors that have a short cable attached, terminating in either a micro-usb or mini-usb male connector. With a mini-usb male connector, you can connect this directly to the mini-usb receptacle on the Teensy. Unfortunately, this setup does not provide an easy way for making an earth connection.

However, instead of the convenient and rather inexpensive panel-mount usb connectors with a cable, you can use a panel-mount usb connector that has soldering pins on the back. One of these pins would be connected to the shield and would provide an earth connection. This solution is more expensive and requires more soldering.

I like the panel-mount solutions, because they provide a very solid connector that is screwed into the case. The downside is that you need to drill mounting holes in the case.

There are other solutions, such as cutting a usb adapter to fit through the existing cable hole in the case, but this does not work well with the XT case.

Despite my somewhat botched job on my first real mod of an XT, I find that it makes quite a difference to be able to detach the keyboard from the computer without having the awkwardness of an attached cable.

For my next XT mod, I think I will use the panel-mount micro-usb connectors with the attached cable. This will fit nicely in the XT case and the center hole is significantly smaller than was needed for a full-size usb B connector. However, this solution will not provide for an earth connection to the shied and case, but only a ground connection to the Teensy. In fact, this is the situation I have now with the usb B connector; I am typing on it now and it works fine, but I would feel better having a proper earth connection.

Looking forward to seeing the forthcoming illustrated guide to making a universal converter box. I think if you were to take the time to photograph each layer of wires (and we know that you are an excellent photographer), and if the wires are color coded in a consistent way, it will be intelligible even with the number of connections that you have. The end result will be like focusing up and down on a CT scan of your switch box.