Having Trouble With 2N2222

Other Hardware General Electronics
1

I bought a bag of 2N222 transistors more than 5 years ago but didn't use them then. Now that I'm using Arduino I got them out. I have been having problems with them. I tried a simple circuit from a video today with a couple of them. If they worked they were very erratic, the blink rate kept changing and the rate seemed too fast for the capacitor I was using. Could it be I have a bad batch?

This Is the first video I tried and it didn't work. https://www.youtube.com/watch?v=tpKssr9p2rc

This is the second one I followed, I it to work sort of. https://www.youtube.com/watch?v=49V7xdpgenk

I switched out the 2N2222 for a BC547 on the first one and it worked., I had to turn the 547 to face the other way.

2

Show us a schematic (hand drawn is fine).

Show us a good image(s) of the actual wiring.

Show us your current sketch, use:
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3

Do you have the 2N2222 or the P2N2222.
The 2PN is the same pinout as a BC547, the 2N is reversed.
Leo..

4

It's a 2N2222.

5

I bought a 100 count pack of 2N2222 from Amazon a few years ago. They are clearly marked 2N2222, see below. They are actually P2N2222. Pins C and E are swapped. I guess that's why i got them so cheap

20230210_184017
20230210_184017494×561 44.9 KB

6

Show the circuit wiring.

7

Hi, @jonny6363

Do you have a DMM?

Thanks.. Tom.. :smiley: :+1: :coffee: :australia:

8

That won't tell you of it's a 2N or a P2N.
Because the BE and BC diodes measure the same.

A transistor Beta tester would be handy for this.
Leo..

9

Google;

simple dmm trick to find e b c

Tom... :smiley: :+1: :coffee: :australia:

1 Like
10

I doubt that 0.25% difference in BE or BC diode drop is a reliable indicator.
That drop is also temp dependent, and likely transistor type dependent.

60 years ago finding the base with a multimeter was a common test. I didn't have any other tester.
To find the collector I connected the meter to collector and emitter, and connected the base with a wet finger to the red lead. It was correct when there was some meter movement.
This was the time you made a power amplifier with an AC187/AC188 pair :slight_smile:
Leo..

11

That is after the OC era ...

12

I've still got some of them!

13

It is an odd schematic with the base unconnected....
But if it works it works...
My guess you have the same transistors as @2112

14

Every maker needs todays newfangled inexpensive component tester similar to these:

71IY5P3dujL.AC_SX679
71IY5P3dujL.AC_SX679679×695 48.9 KB

s-l500

1 Like
15

Hi,
image
The circuit work because of the 2N2222 reverse bias Emitter Base voltage, Vebo, being only 6V.
image

The Base Collector is in this circuit forward biased, so conducts all the time.
The power supply charges the electro capacitor up, when the voltage on the capacitor reaches the voltage == (the base emitter reverse bias voltage)+( the forward drop collector to base)
The base-emitter junction breaks over and conducts.
The capacitor discharges through the transistor and the LED.

As the charging current is much lover than the discharge current, the voltage on the capacitor will decrease and the base-emitter will cease conduction and then allow the capacitor to charge back up.
I hope that is clear, not enough caffeine in the coffee stream today.

Tom.. :smiley: :+1: :coffee: :australia:
PS. Tweaking the resistor and capacitor values will help to get good operation.

4 Likes
16

As I recall, Vebo means voltage between emitter and base with the collector open, the collector is not connected and the reversed emitter - base junction acts as a zener diode.

17

I stand corrected.... :+1: :+1: :+1: :+1:

Tom.. :smiley: :+1: :coffee: :australia:

18

This is my tester. I have two wires with alligator clamps on them so I can put on on the ground of a transistor and the other on either outside wire.

IMG_20230211_152738435_HDR
IMG_20230211_152738435_HDR1920×1440 209 KB

2112

Your image of the transistor is what mine looks like, it's too small to get an image of. I turned it both was in the circuit and it lights up but doesn't blink.

I am using a 9v power supply right now with a 2k resistor and the circuit with a BC547 is working fine.

19

I got some new 2N2222s today and it's the same thing.

20

Let’s start afresh.

Always show us a good schematic of your proposed circuit.
Show us a good image of your ‘actual’ wiring.