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Electronic knowledge wanted: Transistor/Transistor logic Answered

Hi all. I am embarking on an electronics project and I was hoping to gain some info on using transistors as logic gates in a circuit. I searched both the interwebs and instructables extensively, but all the info I could find was either outdated or was in a level of techno-babble my Noobish hardware skills could not comprehend (been programming for years; Just recently decided to dabble in hardware).

To summarize: I want to know how to construct AND, OR, NOT, XOR and the like and integrate it into my circuit using primarily transistors, and maybe some capacitors. Is there something I have gotten mistaken in this premise? Is this really the proper use for a transistor? Should I use something else, is there a better method? Please note that I have little experience in non-software areas (I understand what voltage and amperage is (kinda) and what serial and parallel circuits are, and the proper configurations of positive and negative). I also do not want to use a microcontroller for this; Just me and my wires.

I would be immensely thankful for some help. I apologize in advance if I have gotten anything wrong here.



Best Answer 8 years ago

Using transistors in your own hand constructed logic gates is easy but very outdated in and of itself.  Since the IC was invented they have been using them and constructing the gates that way for years now.

Constructing them by hand is a great learning experience but extremely inefficient.

Google "diy logic gate" and see what you get.  Most of what you will see is going to be outdated since the whole process is "outdated" now.

Also try googling the specific gate you are looking for.

Most of what I've found in the past gave general circuits but didn't give any part numbers so you might have to do some research to find which transistors work best.

Good luck.

New problem: I need some non-volatile storage. A hard drive is out of the question because they are extremely complex to work with at the lowest level and can be disasterous if you don't know what you're doing. I'm considering using flash memory, although I still need to know how to interact with it at the lowest level possible.


8 years ago

 To make a NOT gate:
Connect a big resistor (so it doesn't draw much current) between the collector of an NPN transistor and +ve power supply rail. Connect the emitter to the ground rail. The output from the NOT gate is the collector of the transistor, it is normally held high by the resistor but when you apply a voltage to the base of the transistor, the collector is pulled low.

Some info on AND and OR gates www.play-hookey.com/digital/electronics/dl_gates.html 

Some info on transistor logic hyperphysics.phy-astr.gsu.edu/hbase/electronic/trangate.html

Any problems let me know.
It would probably be easier for you to use CMOS logic gate chips though although it depends on what you're doing.

Hmm, I would appreciate an enlightenment towards these CMOS chips. What are they (I'm quickly starting to disregard TTL as an option).

I concur that TTL logic is very old hat that has, for the most part, been surpassed by chips that do the same function in way much less space and at a much lower cost. Since you are a programmer, you know how thesefunctions work. Just search for the TTL logic gate (such as "TTL logic XOR")and you will see most links run to Wikipedia. Most pages there do have some simple schematics. As an alternative, you could join the Nuts n Volts forum at www.servomagazine.com/forum/., where I am a member. There a number of professionals there who would be willing to help you learn what you need.


Thanks, Re-Design for the immense help (This is more to learn than anything; Although, if what I have planned gets going you can expect an instructable soon) and I also appreciate the great insight, seandogue.


Sorry, but your nest source for that information WILL be those outdated links. Just don't expect the polished look to the websites that offer information on transistor logic, since the kind souls who keep paying for the sites are usually older folk who feel an altruistic bent for maintaining information that the younger, more myopic set doesn't think is necessary any longer (until they need it, at which point they'll gladly whine about the lack of information)