Wednesday, November 11, 2009

A Homework Assignment

In my Digital Electronics class we had to write a conclusion to a project so that someone who was not in our class and had no knowledge of DE could understand. Did I do alright? I'm posting my response - you tell me if it makes sense. (we were supposed to write to our Grandmas)

Dear Grandma,
You asked me to explain the project I did in my digital electronics class. Imagine the president, vice president, secretary and treasurer of you bingo club have to vote on a new member. I created a machine that would tally their votes and light up if the new member passed, assuming the president is a tie breaker.
The steps I went through to find which results would mean the new member passed:

I figured out every possible combination of votes by creating a TRUTH TABLE.

Wait, you don’t know what a truth table is? Well, according to, a truth table is “a table showing all possible truth-values for an expression”. That definition didn’t help much. What it means is that I take all the different combinations (All say yes, All say no, some say yes, some say no, EVERY possible outcome) and compare them by putting them in columns, one column per voter.

I figured out which of those vote combinations would equal a pass (that means I looked at how many different ways the four officers could vote and still come up with a pass by reading across the ROWS of the truth table and determining which ROWS would equal a pass. I wrote out all those combinations – each combination unique to one line in my truth table. That’s the UN-SIMPLIFIED LOGIC EXPRESSION).
Then I looked for the common patterns between the pass – the president (tie breaker) AND someone else OR the other three officers. That’s the SIMPLIFIED LOGIC EXPRESSION- where multiple combinations in my truth table can meet the requirements.
Then I figured out how to take that pattern and wire it in a circuit. That means I attached switches and wires to AND gates and OR gates to light up on a pass.

Wait, wait – you said you don’t know what gates are. Well, a gate takes in a value (like if the president said ‘yes’ the gate would take in a 1.) and compares it to another value (like if the secretary said ‘yes’). If the gate is the AND gate they both have to be ‘yes’ (aka 1) for the AND gate to be true(yes). If the gate is the OR gate only one of them has to be ‘yes’ for it to be true(yes).
I tested my pattern in the ‘Multisim’ software, which creates the wires and gates and lights virtually. That way, if I made a mistake it was easier to fix, and I could see my SCHEMATIC plan for the actual circuit. A schematic is like a blueprint – it shows all the parts you’ll need.
Then I took a BREADBOARD – not the kitchen kind, but the kind that allows for solderless wiring (that means I didn’t have to melt the wires together) and connected IC’s (tiny circuits with the gates in them), wires, switches and lights to determine if the new member passed the vote or not.

So, that was probably a much longer explanation than you wanted, but that’s what I did.
See you soon!

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