-> If so that means there have to be a 2V swing...
The difference between VIL and VIH is dependant upon the type of circuitry involved...generally speaking:
CMOS: 0= <1/2 Vdd, 1= >1/2 Vdd
TTL: 0= <.8v, 1= >.7Vdd
-> the pulse width is no where near even half a volt.
Pulse width is measured in time, not in quantity. If you are putting a meter on a line with a signal meant for a servo, what you are actually reading is the average DC voltage on that line. And 300mV seems about right consider that the signal isn't constant (50hz give or take) and is only around 1.5ms during those times.
-> I have done this with a 270mV signal on over 50 chips so im either really lucky or something else.
You probably haven't been measuring a 270mV signal. As stated in the paragraph above, you've probably been measuring a signal that swings from 0v to 5v, with an average DC value of 270mV.
-> Again im new to all this but like I said I have never had any problems reading a pulse width off a rc receiver and thats at 270mV
Again, R/C receivers don't output a signal that's around 270-300mV. It's definetely a signal that's repeating at a rate of 50hz, for about 1.5ms for every repitition. So if we do a bit of math on that...
50hz = one signal every 20ms. A centered servo wants a signal of around 1.5ms, generally between 1-2ms. Therefore, over a second, the total amount of time, on average, with a pulse width of 1ms, this signal is reaching 5v is about 20ms.
20ms out of 1000ms = (5v * 20ms) + (0v * 980ms) = .25V on average.
Does that work for you?
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