mvs sarma said:
How do you see logic 1? don't load the pin and have a buffer transistor to drive an LED if needed for testing
and with a diode in seires to base and a termination of sat 10K from bas to ground.
I checked only demux(decoder) and manualy changed all states.
I got this:
Vcc = 5.05V
I (all) = 17mA (7segment LED + 74ls138)
I (Yo) = 11.5mA same for other ports
Y0 0.15V(0.42V) - 3.99V(3.99V)
Y1 0.15V(0.42V) - 3.99V(3.99V)
Y2 0.15V(0.42V) - 3.99V(3.98V)
Y3 0.15V(0.41V) - 4.00V(3.99V)
Y4 0.15V(0.41V) - 4.00V(4.00V)
Y5 0.15V(0.40V) - 4.00V(4.00V)
Y6 0.15V(0.39V) - 3.99V(3.99V)
Y7 0.15V(0.42V) - 3.99V(3.99V)
Y0-Y7 are outputs, in brackets is voltage under load. Every output is connected to one cathode of LED display.
Here is how I connected it:
Click
Voltages on PIC are:
If I have logical 1, on output I see 3.49V( it stays same with and without 74ls138)
If I have logical 0, on output I see 0.00V( it stays same with and without 74ls138)
Now I know why I have 3.49V on output of PIC, I'm constantly , every 10us changing value of the port to 0V. Because I don't have oscilloscope I measure it with voltmeter, so my measured voltage is not accurate and I forgot that.
I will try to eliminate switching and post again.