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Topic: Why 5V??? (Read 622 times) previous topic - next topic

larryd

In the good old days, just after they came out with TTL, they offered Hi Noise Immunity.

This was 12 volt logic with similar construction as TTL.

This made speeds slow but was popular in high noise environments.


No technical PMs.
The last thing you did is where you should start looking.

AWOL

The Intel 8080 had a 12V clock signal, I seem to remember.
"Pete, it's a fool (who) looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.
I speak for myself, not Arduino.

1steve

In some less enlightend countries perhaps, here in the UK we had access to the  from 1951 onwards;

The instrument has an accuracy of ±1% of FSD on DC current ranges, ±2% of FSD on DC voltage ranges, ±2.25% of FSD on all AC ranges and ±5% of reading (at centre scale only) on resistance ranges.[11] Its maximum current draw of 50 μA at full-scale deflection (corresponding to 20,000 ohms per volt) is sufficient in most cases to reduce voltage measurement error due to circuit loading by the meter to an acceptable level.

Had mine around 25 years, still works well.
How many people remember why there was a mirror strip on the label with scales behind the pointer.
Do you remember the cost of one? What would that be in today money?  I can remember a Electronic calculator being chained to a deck in early  60's in the engineer Dept, all it did was +-/*.

larryd

No technical PMs.
The last thing you did is where you should start looking.

Wawa

You're amongst geriatric friends Larry.
I build my Heathkit valve voltmeter more than 50years ago.
The high impedance of a valve voltmeter was a big improvement over the one my dad was using.
Still working, and sitting on my shelf, with a high voltage probe.
Leo..

AWOL

Quote
How many people remember why there was a mirror strip on the label with scales behind the pointer.
'O' level optics
"Pete, it's a fool (who) looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.
I speak for myself, not Arduino.

SamR

Discrete logic powered by batteries?  No, that was never the expected thing, early logic families are
very power hungry, bulky and non portable - mains power was assumed(*).  5 is a nice round number,
I suspect its as simple as that.

(*) These chips were developed for mainframe computers, for instance.
The driving force behind 7400/5400 IC development was military dollars.  The US was locked into a Cold War and a Space Race with USSR and was spending enormous  sums on rocket guidance systems and other avionics which required small lightweight *battery* powered electronic parts.  I think you may be right as to 5V being a SWAG.  "Hey 5V looks about right and there is enough voltage overhead to cover the series voltage drops when we daisy chain a few together."  Computers of that time were power hogs and quickly took advantage of this new low powered technology.  When I was in engineering school in the 60's the Xerox Sigma 7 computer took up an entire floor.  Keypunch card decks, card readers and chain printers.  Put your punched card deck into the in box and come back tomorrow to see if it ran or not.  I still have my slide rule...
Electrons can neither be created or destroyed, however I can excite them and they excite me.

MarkT

#22
Feb 14, 2019, 06:05 pm Last Edit: Feb 14, 2019, 06:06 pm by MarkT
Also, old valve (tube) heaters ran on 6.3V (why 6.3?  :o   ) - it was relatively simple to build 5V supplies with the transformers. (BT,DT)
6.3 is a standard value in the Renard R5 series. https://en.wikipedia.org/wiki/Renard_series#ISO_3

This series lives on in capacitor working voltage standard values.  10, 16, 25, 40, 63, ...
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

polymorph

Zener action and avalanche have opposite temperature coefficients. It just happens that it zeroes out pretty well at about 5.6V.

A very simple regulator can be made with a 5.6V zener diode and an NPN transistor. The transistor BE junction drops out about 0.6V, leaving 5V.

I've always wondered if that was the real reason for 5V Vcc for TTL ICs.

https://en.wikipedia.org/wiki/Zener_diode

Quote
Another mechanism that produces a similar effect is the avalanche effect as in the avalanche diode.[1] The two types of diode are in fact constructed the same way and both effects are present in diodes of this type. In silicon diodes up to about 5.6 volts, the Zener effect is the predominant effect and shows a marked negative temperature coefficient. Above 5.6 volts, the avalanche effect becomes predominant and exhibits a positive temperature coefficient.[2]

In a 5.6 V diode, the two effects occur together, and their temperature coefficients nearly cancel each other out, thus the 5.6 V diode is useful in temperature-critical applications.
Steve Greenfield AE7HD
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