Noggin
Member
I have a GPS that uses RS-232 signaling that I need to communicate to a microcontroller. According to the specs, the inputs are compatible with a 0 to 5v signaling (though it can accept -15 to 15v) and the outputs swing from -5 to +5 volts.
The +5 isn't a problem, but the -5 is as my microcontroller can only handle down to 0v. Since the microcontroller can drive the input but can't take a -5v signal (rated for a minimum voltage of -0.5v) would it be safe to use something like in the drawing below?
The leakage on the MCU is about 8 uA... I don't know how much the GPS unit can source/sink though, but it does say in the paper that an "output driver is available."
I'm not sure exactly what type of diode I'd need, I just need something that can switch faster than a 4800 baud (which I don't think would be a problem). Schottky has low forward drop right? I'm looking on digikey and there are a LOT of packages... what kind of package is a through hole with two leads like just a run of the mill diode? Or does a schottky need more connections? I've never used one before.
I think we can ignore the MCU input current, so I'd need to find a diode with V(forward) drop of about .5v or less, then the resistor would be (5v-V(forward))/I
Edit: And of course the GPS and MCU share a common ground
The +5 isn't a problem, but the -5 is as my microcontroller can only handle down to 0v. Since the microcontroller can drive the input but can't take a -5v signal (rated for a minimum voltage of -0.5v) would it be safe to use something like in the drawing below?
The leakage on the MCU is about 8 uA... I don't know how much the GPS unit can source/sink though, but it does say in the paper that an "output driver is available."
I'm not sure exactly what type of diode I'd need, I just need something that can switch faster than a 4800 baud (which I don't think would be a problem). Schottky has low forward drop right? I'm looking on digikey and there are a LOT of packages... what kind of package is a through hole with two leads like just a run of the mill diode? Or does a schottky need more connections? I've never used one before.
I think we can ignore the MCU input current, so I'd need to find a diode with V(forward) drop of about .5v or less, then the resistor would be (5v-V(forward))/I
Edit: And of course the GPS and MCU share a common ground