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--- projects:snap_circuits [2013/12/19 21:39]
mcieminski
+++ projects:snap_circuits [2013/12/20 09:43] (current)
rifkinni
@@ Line 23: / Line 23: @@
 The input column shows what you give it, and the output column shows what it gives you.
+{{:projects:img_20131219_215919_029.jpg|}}
+The snap circuits kit comes with multiple NOT gates, because they're quite important.
@@ Line 35: / Line 37: @@
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-You will notice that your snap circuit set does not come with an And gate, but rather a Nand gate. This is because in a computer, And gates are often constructed using a Nand gate and a Not gate.
+You will notice that your snap circuit set does not come with an And gate, but rather a Nand gate. This is because in a computer, And gates are often constructed using a Nand gate and a Not gate. You can see a demonstration of this particular mini-project [[http://youtu.be/RrZ79l9zpmw|here]].
 **NAND:**
-{{:projects:nand.png?300|}}
+{{:projects:nand.png|}}
 A Nand gate is the exact opposite of an And, and means Not Input 1 and Input 2. Therefore, a Nand gate has a true output except for when Input 1 and Input 2 are both true. It is very easy to create the truth table for Nand, because we already have the truth table for And. In the output column, whenever And has a 0, Nand has a 1, and vice versa. The input columns stay the same.
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+{{:projects:img_20131219_215754_779.jpg|}}
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 | 1    | 0     | 0        |
 | 1    | 1     | 0        |
+{{:projects:img_20131219_215831_224.jpg|}}
 **XOR:**
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+{{:projects:img_20131219_215700_492.jpg?300|}}
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 As you may have realized, what you have just built is a half adder.  A full adder has three inputs. 2 are meant to be added, and a third is a carry in. This input is always wired to the carry out of the adder before it. By putting 4 full adders, one after another, you can add a 4 bit binary number.
+You can see an example of the half-adder project [[http://youtu.be/O5cXm81vWpM|here]].
@@ Line 162: / Line 166: @@
  As you can see, if the input is zero, the output will always be zero. If the input is one, the selector determines which output is also one. This is useful for sending information only to the specific place that it is needed. You build it by creating two And gates, with a Not gate in front of one of them. The selector input should get wired to both the first Not gate and the And gate. The data input should be wired to both And gates. The diagram below shows this visually. See if you can predict which red LED will light up!
+**PERSONAL REFLECTIONS:**
+One of the biggest challenges of this project was thinking about ways to make it user friendly and accessible to others. I think in a lot of ways we succeeded in making a toy that is tangible and can visually show the behavior of logic circuits. However, they are not safe for children to use because there are so many exposed wires, even though it would be a great resource for them. In addition, there is a bit of a learning curve that goes along with them; it requires knowledge of how a breadboard works, and is only intuitive if you are familiar with electrical conventions, such as red wires getting power and black wires getting grounded. It was also very difficult to put together a manual that contained enough information to be useful but not so much to become a textbook. For example, currently, it puts a black box around the binary number system. It is still possible to use and enjoy the Snap circuits without knowledge of binary, but the user will not understand the adder as well. I could imagine that it would be intimidating or turn the user off to the user if they did not understand large parts of it, but at the same time, it would not be helpful to have 20 pages of documentation. We would really appreciate feedback on what parts of the manual were clear and intuitive and what parts were confusing or intimidating, because this was a part that we definitely struggled with.
+We also had a lot of debate on what features the actual snap circuits should include. We decided to go with nand gates rather than and gates because it is a more accurate representation of real logic gates in processors, and took fewer transistors to build. However, it was more of a challenge to explain them in our documentation. We discussed including an exaggerated propagation delay, but chose not to for a number of reasons. In a circuit of several logic gates, it could take several seconds to see the final output, which can be undesirable for the user. In addition, we tried to keep each circuit as small as possible, and ran out of physical space for an RC time delay.
+The most challenging part about this project was to go all the way back to the beginning of the semester when we were first learning this material, thinking about how we could have learned it better, and then trying to implement that.
+In terms of timing, I think we had a fairly accurate prediction of the number of hours that we were going to put in to this project. We did not keep to our schedule, but had a good idea in mind of how long each step would take, and ended up finishing when we expected to. The timing reflections for every lab have definitely given us a better intuition collectively on how long an assignment will reasonably take.

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