Hi everyone. I am conducting a blinking LED experiment by using a basic astable multivibrator oscillator circuit. The problem I am having with it is that one LED is staying on for longer than the other LED even though both individual circuits should be identical. What could be the reason for this?

Component used:

• 2 x 230 ohm resisters
• 2 x 100k ohm resisters
• 2 x white leds
• 2 x 10uF capacitors
• 2 x npn transistors 2N 2222 A331
• 5V DC supply

Notes:
Both sides of breadboard power rail set to 5V. The uneven blinking still occurs when I attach all wires to only one side of the rail.


Video of blinking using 100k Ohm resisters for charging capacitors.

http://imgur.com/a/sQJsY9v

Video of blinking when using 10k Ohm resisters for charging. (not uneven blinking is only noticeable with 20k ohm and above for charging path

http://imgur.com/a/ShgY0BQ

 

Ahh sorry figured it out. I had transister on the wrong way once again

 

Ahh sorry figured it out. I had transister on the wrong way once again

Next time, post a clearly focused picture of the breadboard and make sure the components are exposed enough for us to be able to see details. Also be certain to give correct part numbers. 2N2222A should be in metal packages. PN2222A are in TO-92.


If you want us to be able to talk intelligently about your circuit, use component designators (e.g. R1, R2, R3).

 

Ahh sorry figured it out. I had transister on the wrong way once again

Don't feel bad, we've all done that and worse.

 

Next time, post a clearly focused picture of the breadboard and make sure the components are exposed enough for us to be able to see details. Also be certain to give correct part numbers. 2N2222A should be in metal packages. PN2222A are in TO-92.
View attachment 308507View attachment 308508

If you want us to be able to talk intelligently about your circuit, use component designators (e.g. R1, R2, R3).

Ok, noted. Im pretty sure my part number is correct by the way its this transistor. Package TO-92 according to that site.
The PN2222 variation seems to have the pins in the opposite order.

 

The "2222" transistor goes by many aliases with various prefixes and suffixes... In several various packages from metal cans to surface mounts. Never really understood how the 2N2222 got to be the de facto beginner's transistor as I usually use the 2N3904 as my general-purpose transistor... They were both introduced by Motorola in the early 60's but the 2N2222 gets used in many introductory circuits instead of the 2N3904 for some reason. Probably pricing and availability although both are now cheap and plentiful.

 

The "2222" transistor goes by many aliases with various prefixes and suffixes... In several various packages from metal cans to surface mounts. Never really understood how the 2N2222 got to be the de facto beginner's transistor as I usually use the 2N3904 as my general-purpose transistor... They were both introduced by Motorola in the early 60's but the 2N2222 gets used in many introductory circuits instead of the 2N3904 for some reason. Probably pricing and availability although both are now cheap and plentiful.

Interesting. I've seen some of the beginner kits in my country use the BC548 & BC338 npn transisters. The 2N3904 is nearly double the price of the BC548 & BC338 here in Australia

 

Im pretty sure my part number is correct by the way its this transistor. Package TO-92 according to that site.
The PN2222 variation seems to have the pins in the opposite order.

I am of the opinion that some manufacturers are labeling their parts incorrectly. 2N2222A has always been in TO-18. Any device in TO-92 needs to be labeled PN2222A or P2N2222A. The aforementioned parts in TO-92 have the opposite pinouts. The P2N2222A has the same pin order as BC547, and similar European style transistors.

This is from Texas Instruments. Note the March 1973 date which is probably earlier than any you'll find from the newcomers.

 

Interesting. I've seen some of the beginner kits in my country use the BC548 & BC338 npn transisters. The 2N3904 is nearly double the price of the BC548 & BC338 here in Australia

I think it's a regional preference. US, and maybe Canadian/North American, designs prefer 2N transistors. Europe, and apparently Australia, prefer BC. Japan, and maybe other Asian countries, prefer 2S.

 

Additionally, 2N2222A has a higher continuous collector current and power dissipation than the similar parts in TO-92:

TI:


On Semi:

 

the 2N2222 gets used in many introductory circuits instead of the 2N3904 for some reason.

The 2N2222 has triple the max current rating of the 2N3904, so perhaps was considered more "universal" in its application.

2N3904--

 

The hFE of a transistor part number has a wide range. Some are weak (minimum) and others are powerful (maximum).
If you want even blinking, in addition to correctly wiring the transistors, you must test many transistor and select matched hFEs for them. ICs usually have matched transistor hFEs.

 

The hFE of a transistor part number has a wide range. Some are weak (minimum) and others are powerful (maximum).
If you want even blinking, in addition to correctly wiring the transistors, you must test many transistor and select matched hFEs for them. ICs usually have matched transistor hFEs.

Except that the hfe does not strongly effect the time constants, which are set by an RC combination.