Dear sir,
I need to design a circuit with the following requirements,
1) I will get 2 types of inputs to my card which are +15V,-15V.
2) When i will get +15V, micro controller should read 1,if i get -15V it should read 0, can u please suggest me how to Sense these two Signals.



Regards,
Venkatesh N

 

A diode would turn +15V into about +14.3V and -15V into 0V. Then a voltage divider (resistor ratio of 5.7 to 8.6) would turn 14.3V into 5.7V. Then a voltage follower to buffer the output wouuld turn 5.7V into 5.0V.

An op-amp circuit could be simpler depending on what supply voltages you have available.

 

The following works only if the input impedance of the uC is high, if it isn't put a noninverting voltage follower at the output.

EDIT: Just saw it was already posted by Bretm

 

He specified TTL, and TTL requires a lot smaller impedence on its inputs. For logic-low level the input circuit will need to sink current from the TTL's input pin, and a 5k resistor may drop more than allowed.

 

what speed?
you can use also use devices designed for that like MAX232