| ??? 03/17/09 18:14 Modified: 03/17/09 18:23 Read: times |
#163541 - Sorry, Bing, but what you plan is nonsense! Responding to: ???'s previous message |
Bing said:
I tried to control(turn on/off) the output of uln2803 with 8051 via the ground, i connected the GND of ULN2803 to pin P1.7 of 8051, I am able to turn on/off ULN2803, is this circuit safe enough? No, it is not, and it will not work either! You mean to connect the GND pin of this chip to P1.7 of micro? 
Well, you can make the 2803 turn-off, somehow, but you cannot make the 2803 turn-on by emitting low level at P1.7, on the other hand, because all the 2803's ground currents have to flow into P1.7 then. So, one single general purpose output of 8052 would have to withstand the same current as 8 high current outputs of 2803, which is only thinkable if the ground currents are very very little. But in this case it would be better to sink the currents directly by the micro. Bing, what you try to fabricate is an "newbie's solution", which is entirely contrary to well established design practice!!! Stop planning to float any GND pin of any chip because this is nonsense! It would be much wiser to strobe the anode drivers, like shown in the following scheme snippet: 
Kai |
