| Electronics > Beginners |
| 74LS14 testing circuit pls |
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| KrudyZ:
How about looking at both the output and the INPUT? LS gates need as much as 400 uA of input current when driven low. In addition this is a Schmitt trigger input with hysteresis, so your pull-pown might not be strong enough to reach a proper low state on the input. |
| Chriss:
Let's say If I set a pull-up resistor to the input pin and switch the input to low direct to ground that should deliver enough current or? But no deference, pull-up/down resistor, input signal Low or High no matter, just several of gates are working. Could it be I killed the IC's because I tested them in my breatboard but I didn't grounded all the unused inputs? I deal with such of IC's and never had this kind of problem like now. |
| StillTrying:
10k is too high to pull a LSTTL input low. Check for bad connections to 0V (pin 7) and well as 5V. As KrudyZ said, scope both the input and output of one gate at the same time, to see if you have at least one gate working. The 100u to 470u cap is to protect the IC from any voltage surges during switch on and off. |
| Chriss:
Ok, here is the working one gate of one of the two ic's. If I try all the other input to feed with the same signal and setup like this working one nothing is happening or the outputs are only HI or LOW. I assume my IC's are bad and I have one IC with only one working gate. This is what I'm think and I cant get believe this because the IC's are brand new! |
| PA0PBZ:
It wouldn't surprise me if you killed the ICs pulling too much current from the HI output. |
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