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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.

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  • \$\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\$
    – Cello Coder
    Commented Mar 21, 2015 at 18:43
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    \$\begingroup\$ I suspect that the 10k collector resistor may be too high, given the collector supply is only 3V. \$\endgroup\$
    – Chu
    Commented 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\$
    – Cello Coder
    Commented 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\$
    – Cello Coder
    Commented Mar 21, 2015 at 19:29
  • \$\begingroup\$ ooops, 10mA and a 1k drops 10V! You need higher Vcc and lower collector resistor. \$\endgroup\$
    – Chu
    Commented Mar 21, 2015 at 20:08

1 Answer 1

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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.

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