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Topic: Transistor switch (Read 162 times) previous topic - next topic

Seabo2001

Nov 14, 2019, 09:32 pm Last Edit: Nov 14, 2019, 09:36 pm by Seabo2001
Hi, I'm trying to make a digital pin controlled switch to allow higher voltage/current power to flow, and I intend to use a 2N2222 transistor for this purpose, however the circuit I've constructed doesn't seem to be working. Rather than blinking on and off due to the transistor, the LED stays lit even with no transistor base current.

Could anyone have a look at the images to help me troubleshoot it?

Thanks so much, I'm very lost.

larryd

#1
Nov 14, 2019, 09:37 pm Last Edit: Nov 14, 2019, 09:39 pm by larryd
OP'S image.



The wires on the PCB should be soldered.

What is written on the transistor?




No technical PMs.
If you are asked a question, please respond with an answer.
If you are asked for more information, please supply it.
If you need clarification, ask for help.

Seabo2001

#2
Nov 14, 2019, 09:44 pm Last Edit: Nov 14, 2019, 09:47 pm by Seabo2001
Transistor is backwards,

Damn, I knew it was something obvious like that haha, I think i was mixing up conventional current and real electron flow.

OP'S image.



The wires on the PCB should be soldered.

What is written on the transistor?





Yes, I realise about the soldering however this was just a very quick prototyping exercise to figure out the layout and code, so I made do with just twisting the wire.


Anyway it is working perfectly now, thank you both very much.

larryd

#3
Nov 14, 2019, 09:45 pm Last Edit: Nov 14, 2019, 09:48 pm by larryd
You are not using the breadboard properly.



BTW





No technical PMs.
If you are asked a question, please respond with an answer.
If you are asked for more information, please supply it.
If you need clarification, ask for help.

raschemmel

#4
Nov 14, 2019, 09:49 pm Last Edit: Nov 14, 2019, 10:03 pm by raschemmel
Quote
Transistor is backwards,
That was incorrect. (which is why I removed that post)
I didn't look at the polarity on the pcb.
The transistor is wired correctly. (ASSUMING YOU WERE CORRECT WHEN YOU SAID YOU WERE
USING A 2N2222.
DON'T REVERSE IT !

IF , ON THE OTHER HAND , YOU ARE USING A PN2222, THEN IT IS BACKWARDS !
THEN YOU DO NEED TO REVERSE IT !


Larry was right. You're wires aren't soldered

Quote
You are not using the breadboard properly.
  
For one thing, your shoving two pins in the SAME hole ! base and base resistor , collector and resistor , and led and resistor all sharing same hole with another pin. You are going to damage your breadboard.

(just when you thought you had seen everything on the forum...)

The reason there are multiple holes in one row is so you can place a SINGLE pin in each hole.

Seabo2001

That was incorrect. (which is why I removed that post)
I didn't look at the polarity on the pcb.
The transistor is wired correctly. (ASSUMING YOU WERE CORRECT WHEN YOU SAID YOU WERE
USING A 2N2222.
DON'T REVERSE IT !

IF , ON THE OTHER HAND , YOU ARE USING A PN2222, THEN IT IS BACKWARDS !
THEN YOU DO NEED TO REVERSE IT !


Larry was right. You're wires aren't soldered

For one thing, your shoving two pins in the SAME hole ! base and base resistor , collector and resistor , and led and resistor all sharing same hole with another pin. You are going to damage your breadboard.

(just when you thought you had seen everything on the forum...)

The reason there are multiple holes in one row is so you can place a SINGLE pin in each hole.
I'm sorry, I'm new and I am trying to build a rudimentary AND gate, so I'm just trying to build up from basics.

raschemmel

#6
Nov 14, 2019, 10:12 pm Last Edit: Nov 14, 2019, 10:39 pm by raschemmel
Quote
I'm sorry, I'm new and I am trying to build a rudimentary AND gate, so I'm just trying to build up from basics.
The correct name is "Discrete transistor AND gate".

Here on the forum, we try to avoid using the word "rudimentary", as that is a concept we wish
to avoid.

Ok, here's some basics for you.

Insert ONE AND ONLY ONE pin in EACH hole in the breadboard.

Is that basic enough for you ?

Transistor AND GATE


FYI, you can replace the 4.7k collector resistor with a 220 ohm resistor and a led so the led lights
when the AND gate output is TRUE.

Seabo2001

The correct name is "Discrete transistor AND gate".

Here on the forum, we try to avoid using the word "rudimentary", as that is a concept we wish
to avoid.

Ok, here's some basics for you.

Insert ONE AND ONLY ONE pin in EACH hole in the breadboard.

Is that basic enough for you ?

Transistor AND GATE


FYI, you can replace the 4.7k collector resistor with a 220 ohm resistor and a led so the led lights
when the AND gate output is TRUE.
Thank you, this is very much my first time using a microcontroller of any kind in a project, so I'm still learning. Thanks for clarifying on the terminology I should use.

raschemmel

#8
Nov 14, 2019, 11:26 pm Last Edit: Nov 14, 2019, 11:43 pm by raschemmel
Quote
Thank you, this is very much my first time using a microcontroller of any kind in a project, so I'm still learning. Thanks for clarifying on the terminology I should use.  
FYI, the discrete transistor AND gate has been around since way before microcontrollers were invented.
Back in the day, it was called TTL (Transistor Transistor Logic), a name which was adopted for the
7400 series logic gates of the 60's and 70's.

Quote
8048 was introduced in 1976 and was the first of Intel's microcontrollers.
Quote
In 1964, Texas Instruments introduced the first members of their ceramic package SN5400 series transistor-transistor logic (TTL) logic chips, later a low-cost plastic package SN7400 series was introduced in 1966 which quickly gained over 50% of the logic chip market, and eventually becoming de facto standardized electronic components.[
7400 series logic family

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