What load current is the ULN going to sink.?
0.2A
In order to sink current the pin of the MCU would have to be connected to +5V via a resistor.
why ? doesnt when i ouput zero at the pin of the MCU it doesnt act as a current sink ?
Yes its a current sink, BUT where is it going to get the current to sink if there is no current source,... the resistor to +5V supplies the current.
. OK, now this is for current sinking , what configuration should i design to let the MCU source current?
Set the MCU output pin High [+5V], BUT as 'agu' explained it can only source 60µA, which will NOT drive the ULN
I dont know really why the 74HC00 solved the problem
The 74HC00 solves the problem because its CMOS and only requires µAmps to switch it. The output of the 74HC00 has enough current to drive the ULN
i found that the ULN doesnt work with zero Input that's why i made 74HC00 act as an inverter ,would you tell me the theory behind that ?