Resistor & Capacitor Values; Engineering Notation

A guy from Europe here.

I don’t find the SI rules suitable for a schematic. At least for my schematics.

For caps and resistors I use the R_small and C_small symbols, so there is not too much room for the value fields.

I use:
10u for a 10 µF cap. The F is implicitly understood.
3k3 for a 3.3 kΩ resistor
10R for a 10 Ω resistor
Never came across a 1 F cap :wink:

I’m better :slight_smile: I use 10 for 10 Ω resistor.

I don’t think you can get everyone else to follow such rules. Of course you might say the same regarding engineering notation. Simplis/Simetrix simulator always uses a lower case “k”.

At least in the USA mho was replaced by Siemens during my career; the last 45 years. It may be a little newer than that. I think the change was 5-10 years more recent than replacing Kilocycles with KiloHertz.

In my opinion, the 50 mil default text size in the KiCad symbol library is too large. I use 30 mil text and I find it to be very readable as I work on schematics with my 1080 x 1920 monitor. I have also used 15 mil text when I need to shrink it further. I guess the question is whether it can be read on a printed page, and how necessary is this?

According to:

mho was replaced by S in 1881.
If it is true - I don’t know. For me since always conductance was in S but before 1977 I probably didn’t hear about conductance (I used only resistance).

I have a 1977 edition of Reference Data for Electrical Engineers. In the chapter on units, mhos and Siemens appear to have equal footing. If you look up either one, they say it is equal to the other and did not mention one replacing the other.

At least in the U.S., those of us who first learned electronics on radios that glowed in the dark always saw “millimhos” or “micromhos” as the unit for vacuum tube transconductance. And it was usually spelled out - the inverted omega symbol seems to have been rare among typography fonts. I believe I first encountered “Siemens” in a classroom circa 1968 - 1970, either High School or early college, with a comment to the effect that “Siemens” was used in some European technical literature.

I don’t know when a professional organization or standards body proclaimed that “Siemens” was the proper unit, but it took a while to be accepted and catch on. (My impression is that the change to “Hertz” happened quickly, in just a year or two circa 1967 - '68.) I have some preliminary product data for International Rectifier’s “HexFET” power mosfets, circa 1977 - 1980, that uses “mhos” and “millimhos”. Several years later the 1982 Databook shows transconductance units as “S” (Siemens), but with the inverted omega symbol in parentheses beside the “S”.


The first book about electronic I have read was “ABC Radioamatora” There I have first time read about Hz. I had the 1953 edition (older then me):

I found the scan of edition from 1964:

At bottom of page 41 there is 50Hz and 60Hz.
I don’t wont to give my head but I’m sure in 1953 edition there were also Hz.
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Hi, Piotr

I had a quick look at that book. I cannot read Polish but (seriously) those illustrations.are great. On a lighter note, the illustrations towards the front remind me of this:

I committed an error in my previous post. The correct book title is Reference Data for Radio Engineers.

Since I read it the frequency filtering pictures (page 129) left in my head for always.
When I was 9 according to page 92 I wind my first trafo (7 turns primary, 1 turn secondary) and connected it to 220V AC expecting to get 31V output but not got it :frowning:
When I was 10 I’ve build my first radio receiver using the schematic at page 326. Were surprised hearing the same station independently of Cs knob position.

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Did we walk the same path? About age 12 or 13 my father made me purchase, with my own money, a supply of fuses for the household electrical system because my experiments were consuming too many fuses.

And a simple crystal radio receiver (and long-wire antenna) confirmed that an entire world existed on the MW band, far beyond where I could go on my bicycle!


As a teenager I almost electrocuted myself with the valve amplifier I had built. I was holding the chassis and my thumb touched the live contact on the power toggle switch at the front of the chassis. I dropped the chassis. Miraculously I didn’t break the valves (2xEL84?) because the transformers were taller. I had a burn scar on my thumb for a long time. I did get the amplifier working.

The worst part was when I later wrote about the experience for a school composition, the teacher picked out my essay from the marked pile and ridiculed it in front of the class, calling it a fantasy. :angry:

That’s awful! :frowning: The teacher did not appreciate that truth can be stranger than fiction. But your original tale was not even that strange. I was building a 750V powered amateur transceiver kit when I was 13.

Regarding teachers: As a child I once had a substitute teacher who told us that we sway our arms when we walk to push air out of the way. I did not know why we sway our arms when we walk but I was pretty sure that it was not to push air out of the way.

Fortunately we had an automatic fuse :slight_smile:
But when I connected my trafo I didn’t noticed any spark. Seeing no output voltage I concluded “They had to switch off power just when I wont to do my experiments”. Those time switching off power for few hours was frequent in Poland. I was doing it being alone (ill in bed). When my mother came and I told - there is no power she just looked into fridge to take a water off. When my father came he just pushed the button at fuse and asked me what I was doing :slight_smile:
When I was 4 years and 4 months old I liked very much to switch on and off the lights at Christmas tree by taking off and inserting the plug into socked. I keep plug handful (not sure how to say it - plug surrounded by my hand). The sockets were very shallow and it happened that my figer was touching both plug pins while they get contact with 220V. Typically adults don’t remember what was before they were 6, but I remember few second with my loud cry looking at red line on my finger.
Very shallow means like this:

And a plug like this:

When I was a boy, I used a 120VAC light to read at night. But my mama wanted me to sleep, not read. So I unscrewed the lightbulb from its socket when mama was in the hall. And then screwed it back into the socket when she was in the kitchen or in the living room. (All to avoid the audible click of the light’s switch.) One night, I forgot I had unscrewed the lightbulb completely from its socket. When I reached inside to screw the lightbulb back into the socket, my fingers instead went into the empty socket and I felt 110VAC. Spasms in my hand caused me to let go.
Once bitten, twice shy.

I’m not sure if I have written at forum that when doing final calibration of my scope I was shocked by 1100V DC hand to hand (anoda voltage for scope bulb). I was 24 years old so in theory should be not as stupid as child. But only in theory :slight_smile:
As I have never done anything with electron tubes I was not used to be care when device is powered.
When shocked I was thrown at chair (I was standing), lost completely my eyesight for 10…20s, and my hands and legs were trembling for next few hours.

To not say again the same:

The use of the upper case letter “R” comes from International Morse Code and stands for a decimal point in a series of numbers. This is the way the radio operators of the sinking Titanic would have sent their latitude and longitude location. For a capacitor with a part number of “…4R7…” this would be “4.7” of whatever capacitance.

Hi, 9V1MI

I cannot say for certain that you are wrong, however I am a former amateur radio operator who used Morse Code. In fact I built an Iambic keyer which worked properly unless it was actually keying the transmitter. :frowning: (I guess there was too much “RF in the shack.”) I do not remember anything about “R” being used to indicate a decimal, and the Wikipedia page has no reference to that. But in electrical engineering an “R” suggests a resistor, so that 4R7 brings to mind a 4.7 ohm resistor. It seems there are so many different options which all have some reason behind them. My father thought of “M” standing for “mil” meaning “thousand” (think Roman numerals); of course to me “M” indicates “Meg” for million. As a non-programmer user of KiCad and Microsoft office, I find that the ease of importing from a text field into Excel (and then sorting) to be a compelling advantage of scientific notation.

@BobZ, @9V1MI, 73/51

I did an internet search “decimal point in morse code”. There is a difference between “full stop” (a period) di-dah-di-dah-di-dah and a “decimal point” di-dah-dit. But the decimal point is inferred from the context, which would be numbers. A number like 99.9 (ninety-nine point nine) would be sent dah-dah-dah-dah-dit dah-dah-dah-dah-dit di-dah-dit dah-dah-dah-dah-dit. The ARRL bulletins, Morse Code practice, and the old satellite equator crossings sent over W1AW by CW (Morse Code) use/used the abbreviation “R” as the decimal marker. The callsign of 9V1MI I obtained when I lived in Singapore for four years.
–73 de WN8P, Larry

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