Please explain 'no' current to PNP transistor

[james_s]

I think in a lot of cases they were scraping the bottom of the barrel in order to come up with as many circuits as possible that could be built using the limited selection of components. It's hardly surprising that some of them are not as well designed as others. In this case it's the way the schematic is drawn and the lack of description of how it works that is the biggest issue.

[IanB]

How dare you all criticise my 130 in 1 Maxitronix kit!   

I’ll order some breadboard and bits. The kit isn’t visual as components are so spread out. If I stick them on a breadboard and lay then out in a… better manner, it may help me understand better…

The attached picture may help to explain the behaviour of NPN and PNP transistors when used in a switching configuration. Using a breadboard you should be able to lay things out so that the arrangement follows this diagram.

(If I somehow have a mistake here, I'm sure someone will correct me.)

[EPAIII]

Yes, the jackass who drew that schematic did not know how to draw schematics. A schematic should be drawn in a manner that makes the operation of the circuit as plain and understandable as possible. That one fails miserably.

And the jackass who wrote the text is equally bad. It states that a "Voltage" applied to the base of what are apparently BJTs is what controls them and causes them to conduct. BJTs are current operated devices, not Voltage. I don't care if there is 1,000,000 Volts on the base of a transistor, if there is no current flowing, it is not going to conduct. Except by turning to carbon.

I would toss that book in the fireplace and look for a better source of electronic knowledge.

flip the picture upside down then it is much easier to understand

[IanB]

And the jackass who wrote the text is equally bad. It states that a "Voltage" applied to the base of what are apparently BJTs is what controls them and causes them to conduct. BJTs are current operated devices, not Voltage.

The equations that describe the operation of a BJT have the base-emitter voltage v_BE as the primary variable, so saying this voltage is what controls the transistor is entirely reasonable:

https://leachlegacy.ece.gatech.edu/ece3050/notes/bjt/thebjt.pdf

[magic]

I have seen several old schematics with negative supply and ground at the top; it seems to be the way things were done in germanium era.

I don't care if there is 1,000,000 Volts on the base of a transistor, if there is no current flowing, it is not going to conduct. Except by turning to carbon.

If there 1,000,000 V on the base and no current flowing then there is 1,000,000 V on the emitter too - of course not going to conduct.
And if it isn't conducting, it isn't turning into carbon either

[m k]

Maybe the maker has thought the straight through schematics is too obvious.
Was there somewhere that transistor is not Ge?
Though "NPN is turned off because negative voltage is applied" and "through the diode" is a bit off, for today.

Much better explanation, for today, since turning on and off 7-segment parts was the thing, would have been explaining things towards Common(25) level.
Then one threshold voltage needed over the diode vs. two, and then some, needed over transistor and LEDs is also eminent.
No current to PNP is also eminent then, since Common is floating, since LEDs are in opposite direction.

[ledtester]

I have seen several old schematics with negative supply and ground at the top; it seems to be the way things were done in germanium era.

Related thread:

https://www.eevblog.com/forum/projects/old-schematics-positive-rail-at-the-bottom/

[magic]

Did I really write this?
Yes, that's what I meant, negative rail at the top. Contrary to modern convention.

[Zero999]

Yes, the jackass who drew that schematic did not know how to draw schematics. A schematic should be drawn in a manner that makes the operation of the circuit as plain and understandable as possible. That one fails miserably.

To be fair the verbal description of the circuit is fairly good. It's possible there was a reason for the odd schematic. The original poster has stated it came with a kit. Perhaps it matches the layout of the components attached to the unmodifiable breadboard, thus making it easier to build.

I have seen several old schematics with negative supply and ground at the top; it seems to be the way things were done in germanium era.

Related thread:

https://www.eevblog.com/forum/projects/old-schematics-positive-rail-at-the-bottom/

Except, the circuit discussed in that thread made sense, with a negative rail. The only thing they got wrong was not denoting the 0V reference, which should be the +V of the battery in that case.

[floobydust]

This is how you explain electronics... it actually saved me as a kid from disliking the whole thing. I was too young for the kit but got into it due to the cartoons.

[james_s]

I would toss that book in the fireplace and look for a better source of electronic knowledge.

Once again, that book is part of a collectible vintage circuit lab kit which is useless without the book so it is not helpful to suggest throwing the book away. These "xx in one" things were toys for young children, not serious educational sets.

[james_s]

This is the one I had when I was a kid, it came from a garage sale, I must have been around 6 years old.

https://medium.com/@rxseger/electronic-project-kits-hands-on-with-a-vintage-160-in-1-eea39e6193f4

It was much more nicely made than the newer ones, having a wooden case. I had several others over the years, eventually I got the 200 in 1:
https://www.petervis.com/electronics-lab/200-in-one-electronic-project-lab/200-in-one-electronic-project-lab.html

I don't know that they were all that educational really, but it was fun to build the circuits and see them do something.

[james_s]

I have seen several old schematics with negative supply and ground at the top; it seems to be the way things were done in germanium era.

The earliest transistors were all PNP, circuits that would normally be built today with NPN used PNP instead and were drawn upside down by modern conventions. This was also the era of transitioning from vacuum tubes to solid state so most engineers were used to working with tubes. You saw a lot of vestiges of the tube era, such as output transformers used in solid state amplifiers. The electronic kits in question were popular from the early 70s into the late 80s.

[Zero999]

I would toss that book in the fireplace and look for a better source of electronic knowledge.

Once again, that book is part of a collectible vintage circuit lab kit which is useless without the book so it is not helpful to suggest throwing the book away. These "xx in one" things were toys for young children, not serious educational sets.

I agree. I was too hasty to support the idea of throwing it out.

It would be better to try to understand it, by redrawing the schematics in a more legible manner and ask more questions here.

[floobydust]

This is the one I had when I was a kid, it came from a garage sale, I must have been around 6 years old.

https://medium.com/@rxseger/electronic-project-kits-hands-on-with-a-vintage-160-in-1-eea39e6193f4

It was much more nicely made than the newer ones, having a wooden case. I had several others over the years, eventually I got the 200 in 1:
https://www.petervis.com/electronics-lab/200-in-one-electronic-project-lab/200-in-one-electronic-project-lab.html

I don't know that they were all that educational really, but it was fun to build the circuits and see them do something.

100-in-1 $21.95 New for 1972 ($150 in today's dollars) ran until 1976. I still have that one but can't pinpoint the year I got it. Guessing '73. Really expensive with a family income median $11,500/year back then.
150-in-1 $29.95 New for 1977 ($135 in today's dollars)
source: Radio Shack Catalogs

I think RS and Science Fair Kits shaped a nation of kids learning electronics. We'll never see a two transistor VCO or RF Wireless Burglar Alarm again. I don't know who designed these kits.

[IanB]

I remember really wanting one of those kits in the mid-70's, but the price was out of reach 

[floobydust]

The entire family pitched in, I think it was my uncle that actually wanted it for himself. Weren't rich, it covered a birthday present as well.
60, 75, 100, 150, 160, 200-in-1 there was a craze about having more circuits, every year as part of the competition.
I remember the rich kids got the 150-in-1's and rubbed it in my face, and then they didn't build more than a few circuits and shelved it. To get the circuit count up there, it became a game of just adding many useless builds, circuits that were boring and or useless. Too bad it was a number race.

Sadly I see Elenco discontinued all their project lab kits: the 500-in-1, the 300-in-1, 200-in-1, 130-in-1 etc.  I wonder if these are still made or kids have any interest.