Not gate troubleshooting 74LS06N

holz1100

Joined Apr 27, 2016
18
I am having troubles with the 74LS06N not gate.
An input of 5v gives an output of 0.05v (correct).
However, an input of 0.128v gives an output of 1.350v (not high enough)
I am powering the gate with 5v. Any advice on troubleshooting?

bertus

Joined Apr 5, 2008
21,057
Hello,

Are you using pull-up resistors on the outputs?
The 7406 is an open collector device:

Bertus

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dl324

Joined Mar 30, 2015
12,269
However, an input of 0.128v gives an output of 1.350v (not high enough)
As @bertus mentioned, that device needs a pull-up resistor. The value depends on what the output is driving.

holz1100

Joined Apr 27, 2016
18
As @bertus mentioned, that device needs a pull-up resistor. The value depends on what the output is driving.
The output is just fed into another logic gate (an AND gate). Any help in the way of how to calculate the pull up resistance value if i'm feeding into another and gate?

The switch by the not gate represents the input being either high or low

dl324

Joined Mar 30, 2015
12,269

Assuming the AND gate is 74LS08, the maximum high level input current is 0.1mA and the minimum high level input voltage is 2V. The largest pull-up you can use is R = V/I = 3V/0.1mA = 30KΩ, but you could only drive 1 LS TTL load. LS gates have a fanout of 20, so I'd use nothing larger than 1.5KΩ.

hp1729

Joined Nov 23, 2015
2,304
The output is just fed into another logic gate (an AND gate). Any help in the way of how to calculate the pull up resistance value if i'm feeding into another and gate?

View attachment 105666

The switch by the not gate represents the input being either high or low
You need a pullup resistor on the output of the NOT gate to +V. 1K to 10K. The voltage you are reporting (1.35 or whatever it was) is the floating input of the next gate.