# Make half and full adder without chips

UppercaseQ
Could some one recommend a good kit to build a simple half adder and full adder with breadboard, wires, transistors and diodes?

We understand how diodes and transistors work. We may not get beyond the full adder.
We really do not want to use a chip at this point because we can not see inside it to know where all the electrons are moving to and from.

You might also just give me the approximate costs if you don't mind. Well if not too much , maybe we would consider getting a chip kit for us to grow into as long as it includes the individual transistors and diodes needed for the full adder.
We need to keep the cost down as much as possible.

Wait, I forgot. Couldn't we actually build a half adder without diodes and transistors?
Thanks.

## Answers and Replies

Mentor
You mean something like this?

Merlin3189 and UppercaseQ
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We really do not want to use a chip at this point because we can not see inside it to know where all the electrons are moving to and from.
I'm curious to know why this is important to you. I can see why you might want to see how individual gates work at the transistor level, but once you know that, it seems like gate-level abstraction is more useful for implementing an adder.

Merlin3189
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. Couldn't we actually build a half adder without diodes and transistors?

What would it use instead?

Mentor
What would it use instead?
Maybe little bistable teeter-totters and a Mousetrap Game-like mechanism?

Vanadium 50 and DaveE
UppercaseQ
You mean something like this?

Yes! Exactly.
I'm curious to know why this is important to you. I can see why you might want to see how individual gates work at the transistor level, but once you know that, it seems like gate-level abstraction is more useful for implementing an adder.
As a teacher on the rez, my students and I need to see things as close to the concrete level as possible - to limit as much mystery as possible. It is similar to the acceleration labs, where we like the old style clapper that makes the dots every 0.017 seconds or so. We like the to get the period of the simple pendulum to within a hundredth of a second using the wall clock that ticks every second.

Staff Emeritus
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What would it use instead?
Gears

Vanadium 50
Mentor
As a teacher on the rez, my students and I need to see things as close to the concrete level as possible - to limit as much mystery as possible.
Seems like a good theme. But keep in mind that for some subjects, it's better to approach it in a hierarchical way. It can be easier to understand some subjects if they are broken down into the building blocks, and then the contents of the building blocks are discussed as well (but separately).

So for the Full Adder, you can show the logic of the FA and discuss the Truth Table, and then you can discuss what the transistor circuit looks like to form the logic gates (AND, OR, NOR, etc.). Of course, that assumes that the students know how transistors work at a simple level.

I can pretty much guarantee you that if you want to teach your students about the circuitry inside an Arduino microcontroller, you will lose them if you only show it at the transistor level...

https://theorycircuit.com/wp-content/uploads/2018/07/full-adder-circuit.png

https://www.electrical4u.com/wp-content/uploads/What-is-an-AND-Gate.png

UppercaseQ
UppercaseQ
"logic gates (AND, OR, NOR, etc.). Of course, that assumes that the students know how transistors work at a simple level. ..."

I have students who remember how transistors work at the "simple level," but many do not. So when I draw the circuit, I include the the Si and P or N and electrons in the diagram. So yeah, it would get to be a big diagram with various colors of side-walk chalk on the board. Now, I often have to write my own computer diagrams to show on the smart board because so many educational programs seem to assume all students made the jump from several components to a chip. I feel like every step along the way needs to be described in a concrete way from beginning to end - especially while introducing a new concept (half-adder, itc).

Well, I suppose what we are talking about is trying to teach students who were passed along without really learning the prerequisites - including how to study. I have to tell you that for some reason, in a certain school, all ninth graders had to take chemistry. I think that school might have been kind of affected by the middle college high school philosophy. Q:?)

Science Advisor
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This might be a good use of simulators, if they can handle that. Something free like LTSpice, perhaps with some guidance from you to limit their choices?

UppercaseQ
UppercaseQ
Maybe little bistable teeter-totters and a Mousetrap Game-like mechanism?

I am pretty sure my students got bored with these games and actually have rejected them a long time ago. So I suspect they would not feel ownership of their learning if we started at the level of the bistable teeter-totters and a Mousetrap Game-like mechanism. I suppose I could give a project requiring them to start with such games and build from there. Projects are good for ownership, so yeah, I'll give it some more thought. Q:?)

UppercaseQ
This might be a good use of simulators, if they can handle that. Something free like LTSpice, perhaps with some guidance from you to limit their choices?
Thank you. That would be good. My students learn most by hands-on activities, so I'll probably start with labs. Then we will see if we can transfer to simulators.

Gold Member
I feel like every step along the way needs to be described in a concrete way from beginning to end - especially while introducing a new concept (half-adder, itc).
Then I would go with what @vela stated in post 3.

There are several families of semiconductor that can produce the gates.
Which one, or all perhaps, would you teach, and spend time on before introducing the logic gates.
Bipolar( NPN, PNP) or MOS, or Cmos( PMOS, NMOS) technology
RTL, DTL, TTL, ECL use bipolar junction transistors.
While RTL is basically obsolete, it does give one more additional insight on to how discrete components can be parts can be combined to produce logic gates.
( Maybe you want to add in some sub families such as low power Schottkey as a bonus. )

These all work differently with different basic power consumption, fan out, propagation delay, noise, basic circuit ( NOR or NAND ), ... To fully understand all that in itself is a whole course, and would take time away from learning how logic gates ( along with Boolean logic ) can be combined to produce something such as an adder.

It all depends upon what your final goal is - how discrete components can be combined to make a logic gate, or how logic gates can be combined to make a useful digital circuit.

https://digitalbyte.weebly.com/logic-families.html
https://nscpolteksby.ac.id/ebook/fi.../Chapter 10 - Digital Integrated Circuits.pdf

UppercaseQ
Science Advisor
Gold Member
Logic is all MOS now. You could teach the BJT stuff as history, I guess, but I would use the time to teach more fundamental, durable concepts.

In fact, most logic these days is inside a programmable device (FPGA, CPLDs, etc.). The design is done in SW with some HDL. I would still teach digital design concepts, like Karnaugh maps, for example, but I bet they will rarely be used.

UppercaseQ
UppercaseQ
Thank you. I like the idea of teaching it as history - I guess helping students know where things come from.

UppercaseQ
Then I would go with what @vela stated in post 3.

There are several families of semiconductor that can produce the gates.
Which one, or all perhaps, would you teach, and spend time on before introducing the logic gates.
Bipolar( NPN, PNP) or MOS, or Cmos( PMOS, NMOS) technology
RTL, DTL, TTL, ECL use bipolar junction transistors.
While RTL is basically obsolete, it does give one more additional insight on to how discrete components can be parts can be combined to produce logic gates.
( Maybe you want to add in some sub families such as low power Schottkey as a bonus. )

These all work differently with different basic power consumption, fan out, propagation delay, noise, basic circuit ( NOR or NAND ), ... To fully understand all that in itself is a whole course, and would take time away from learning how logic gates ( along with Boolean logic ) can be combined to produce something such as an adder.

It all depends upon what your final goal is - how discrete components can be combined to make a logic gate, or how logic gates can be combined to make a useful digital circuit.

https://digitalbyte.weebly.com/logic-families.html
https://nscpolteksby.ac.id/ebook/files/Ebook/Computer Engineering/Digital Design/Chapter 10 - Digital Integrated Circuits.pdf
Thank you. I will try to look into these components.