Very simple problem with transistors

Thread Starter


Joined Oct 28, 2017
I've just got into electronics about three days ago and started reading the tutorials on this website (best one I could find!) and yesterday I bought what I wanted and started trying to make something. I made a simple LED switch but then wanted to make logic gates with transistors. So I first tried something really simple, and surprise-surprise, it didn't work. I did look up information of what resistors etc. to use for the transistors, but I guess I did something wrong (my bet is that there's a too weak wrong resistor for the base current or something even more stupid).

Here's a picture of what I tried:


And a crappy drawing:


I have a 9V battery, from the negative pole come two resistors. One is 4.3KR (base) and other is 360R. The transistor is 2N3904. More details in bottom picture. I know I probably just a made a stupid mistake or perhaps pretty much the whole thing is a disaster.

Thanks ahead!

Moderators note: uploaded images


Joined Mar 30, 2015
Welcome to AAC!

The base of the transistor is connected to ground, so it can never turn on.

The picture of your breadboard is less useful than the drawing you made. I can't tell which terminal is the cathode on the LED. If I hadn't been using a 2N3094 recently, I probably wouldn't have remembered the pinout.

Your schematic is drawn upside down. Normal convention is to have it flow from left to right and top to bottom:
You want something more like this:
I changed R2 to limit current in the LED to about 10mA; 20mA is usually near the max allowed continuous current.