There are a
couple things you need to remember to be able to do this quiz. Luckily,
everything you need we have covered in this blog.
First: This circuit is a simple comparator,
which I have done a whole entry on in the past. The comparator will output a
high voltage when the non-inverting(+) input voltage is higher than the
inverting(-) input. When the output goes high, the LED will turn on.
Second: There are two voltage dividers
setting the voltages on both input pins of the comparator.
Third: If you watched the video on schematics I posted, please realize that wires only intersect in a schematic
where you see a dot. For instance, the voltage divider setting the voltage on
the non-inverting pin is not connected to the inverting pin in any way even
though there is a wire going from the 4.7k resistor to the mystery resistor
that passes over the negative input.
Good Luck!
5 comments:
Can you explain the number "390" on the right side of the diagram? It is confusing because it is unit-less. If I understood that, I'm sure (read- "not sure") that I can get an answer easily.
The 390 represents a 390 ohm current limiting resistor. It limits the current delivered to the LED when the output of the comparator goes high. I put it in there for completeness/correctness but it really has nothing to do with solving the problem. All you really need to care about are the 4 resistors and the voltage source.
I'm going to go out on a limb here and say 1.56k? Is that anywhere close?
Okayokayokay. I'm going to go with 7.05K volts. I hope so much that I'm correct, and my soul will be crushed if I'm wrong.
So clearly I meant ohms, not volts as I absent mindedly wrote. I was thinking about the voltage at the pins of the comparator so much I forgot the units I was actually interested in.
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