[SOLVED] problem to activate tansistor drive circuit....with controller pin

[vijay satija]

tranisitor drive cicuit is connected to controller pin
its not working
when i connected supply to trasistor its working .....
whats the problem

 

[KerimF]

My Atmel C51 MCUs have I/O pins with open collector as output. To give the pin a high state, a weak pull-up resistance is added internally (equivalent to 50K approximately).

So, if your MCU pin has also an open collector with a weak pull-up internal resistor, you can add an external pull-up one (from pin to Vcc) of value 4K7 for example. In this case, when the pin is set to low, its voltage will be close to 0 volt and it sinks about 1 mA via 4K7 (Vcc = 5 V). When the pin is set to high, the 4K7 resistor will drive the base of your external NPN transistor. If necessary, you can lower the value 4K7... down to 470 Ohm. Please note that for 470R, I_sink would be equal about 10 mA when the transistor is off (MCU pin is low).

 

[Mithun_K_Das]

first of all, post your diagram. It will help finding the error.

 

[vijay satija]

a new problem arise on ma lcd show different character but yesteray its working ........