Instructables

Step 3: The Circuit

So now that you know what is going on, we can begin to construct the circuit. When starting the construction, I would recommend placing the NOR gate transistors on the board first. it makes things much easier as you go along. The output transistor is needed because there isn't enough power to drive the led brightly.  If you notice, it is an inverter in the circuit diagram, however, whether or not you have to invert the signal going to the led is based on which NOR gate you take the output from.  If the led's state is opposite of that of the data input, then you must either change which NOR gate you take the signal from, or change the transistor's output (inverted, or non-inverted).
 
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pyrohaz3 years ago
Surely for the output stage, using a common emitter stage would be better so it doesn't invert the output?
Teslaling (author)  pyrohaz3 years ago
I inverted the output because I accidentally connected the LED to ~Q so when D was 0, the output was 1! If you connect the LED to Q, then a common emitter stage would be better.