I have the book Getting Started In Electronics, by Forrest M. Mims III, and it has an RTL NOT gate schematic that looks pretty much the same as this:

RTL Not Gate
(source: electronics-tutorials.ws)

About a month or two ago, I was starting to get into RTL logic (had already done logic in video games like Portal 2 (2-bit adder I built using laser logic) and Minecraft (lots of little redstone things, some 8-bit like an 8-bit ALU)). Anyways, a while back ago, with RTL I got a NOT gate working, and even an AND gate using 3 not gates and some sort of OR gate (can't remember how I built any of them). Recently I peered into my book, built the gate, then connected my battery pack that I got from RadioShack (two AAs, 3 volts total in the pack) aaand...nothing. The red LED did not light up, even if I switched on the input.

Yes, the batteries are working and contain plenty of charge, as I changed them and then connected a plain LED and a resistor to test them and the LED lit up as expected.

The resistors I used were 10k ohm, and the transistor an NPN 2N3904. Can someone direct me maybe what I did wrong (maybe a clear picture or video of this on a breadboard)? I am highly confused.

EDIT: I figured it out! Don't really know what I was doing wrong at first (probably grounded something wrong) but it is working now.

  • \$\begingroup\$ Also, yes, I understand logic very well (that's why I included the video game part). I understand how to build gates from just NOT and OR, like XOR, AND, XNOR, etc. and even how to use XOR and others to make adders, so don't say I don't know about logic, I just don't know about electronics! haha \$\endgroup\$ Mar 21, 2015 at 18:43
  • 1
    \$\begingroup\$ I suspect that the 10k collector resistor may be too high, given the collector supply is only 3V. \$\endgroup\$
    – Chu
    Mar 21, 2015 at 19:23
  • \$\begingroup\$ I tried replacing it with a 1k resistor, which some websites said to use a 1k for the collector. Nothing changed. Maybe I am not correctly grounding or connecting something? I disconnected everything from my breadboard already, but if someone could link me to a diagram with - and + labeled on every single input and output, and the resistor values and transistor EBC labeled, then maybe I could do it. Ugh, I hate it when things don't work. Persistence! \$\endgroup\$ Mar 21, 2015 at 19:27
  • \$\begingroup\$ Wow I feel so dumb right now. I wish this would work! Have tried using a 2n2222 also, but that didn't work either. I have also tried using a different 2n3904 thinking the first one I used might have been messed up by something else, but again, nothing changed. \$\endgroup\$ Mar 21, 2015 at 19:29
  • \$\begingroup\$ ooops, 10mA and a 1k drops 10V! You need higher Vcc and lower collector resistor. \$\endgroup\$
    – Chu
    Mar 21, 2015 at 20:08

1 Answer 1


A 10 K ohm resistor, as a collector resistor, with a 0.7 Volt drop VCE, with a 3.0 Volt source, will result in a 230 microamp flow, aka 0.23 milliamps. With a hfe gain of 100 as ideal, that's 2.3 milliamps at best VCE. But a 10 K ohm resistor as R2 would only allow a few micro amps through a led, not lighting it up. Try replacing both R and R2 with larger resistors and it will work. Try 470 to 1000 ohm.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.