From voltage to bits: a signal on a wire
Two voltage levels, an agreed moment to look, and suddenly a wire can carry ones and zeros.
A wire can only be at one voltage at a time. That is enough to carry a bit: agree that a high voltage means 1 and a low voltage means 0. For example, 3.3 volts is a 1 and 0 volts is a 0. Nothing about the wire is digital — the sender and the receiver simply agreed on what the levels mean.
The sender has to hold each level long enough for the receiver to notice it. If the voltage flips faster than the receiver can sample, bits are lost. So both sides agree on a rate: one bit every so many nanoseconds, and the receiver looks in the middle of each slot, where the level is stable.
Frequency is how many times per second the signal repeats, measured in hertz. A clock of 1 MHz means a million slots per second, so one bit takes one microsecond. Double the frequency and each bit gets half the time — more data, but less room for the signal to settle.
Practice
Order the stages of sending a single 1 over a wire.
Hints
- Nothing can be read before the voltage has actually changed.
- The low part finishes the bit; the next bit starts after that.
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The clock runs at 1 MHz, so one bit takes one microsecond. What happens if the clock is doubled to 2 MHz?
Hints
- Frequency counts how many times the voltage goes up and down each second.
- Twice the frequency means half the time for each bit.
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Match each stage of sending a single 1 with what it does.
Hints
- Pick the tool by the job: many bits quickly, or a small number of very reliable bits.
- The classic telephone network was built for voices, not for wiring your house.
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