I'm trying to connect a 3-wire NPN inductive sensor, 10 to 30v, and I need to get a 5v output. If someone has an idea on how to do that or a schematic showing how to wire it.
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Thank you for your help.
It is quite possible that all you need to get a 5 volt output from this thing is to connect a pull up resistor (say, 4.7k) between a 5 volt supply and the output. You will also need a DC supply voltage between +10 and +30 volts applied to its power wire and a common (to both the supply voltage and the +5 logic supply). When the NPN output transistor is on, the output voltage will be a fraction of a volt. When it turns off, the pull up resistor will provide the logic high to the 5 volt logic it is connected to.
Most of the time, Mr. Popelish's suggestion will work well (view in fixed font or M$ Notepad):
| | (+10-30VDC) | VCC +5V | + | | | .-. | .---o---. 1K| | | | | | | | | | '-' | | |Out | | | .-o-------o-- | | | | | | |/ | | | -| | | | |> | | | | | | | GND| | '---o---' | | | === | GND (created by AACircuit v1.28.6 beta 04/19/05
However, a few NPN industrial sensors have a weak current source in parallel with the NPN transistor output, to help with noise immunity when they're OFF. If your sensor has one (read the data sheet on the sensor), you might get an input voltage significantly greater than +5V with the above.
If your sensor has the supplemental weak current source, just use a zener with your resistor like this (view in fixed font or M$ Notepad):
| | (+10-30VDC) | VCC | + | | | .---o---. VCC (10-30V) | | | + | | _ | | | | /|\\ | .-. | | ( | )| | | | | \\v/ | | | | | | | '-' | | | |Out | | | 'o-o-------o-- | | | | | | | |/ | /-/ 1N4732A | | -| | ^ Vz = 4.7V | | |> | | | | | | === | | GND| GND | '---o---' | | | === | GND (created by AACircuit v1.28.6 beta 04/19/05
This will keep the voltage from exceeding 5V if you have one of those current-sinking sensors with the internal weak current source pullup.
There is one other element to consider -- that is whether there is protection circuitry built in to the sensor which might bring up your ON output below what you would consider a minimum logic low (more of a problem with TTL). Many of the circuits are proprietary, and are not covered in the data sheets. This may be an issue, particularly if you're interfacing to logic which requires a TTL-level logic "0" (
Alternatively, just use 74HCxx or CD4xxx logic instead of 74LSxx, etc, for the I/F stage.
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