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| 74LS14 testing circuit pls |
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| Chriss:
Uff! Misspelled. .. it is an LS Sent from my GT-I8260 using Tapatalk |
| rstofer:
I already gave you the 'rules' for digital circuits: all inputs are terminated to appropriate logic levels, they are nexer left floating. You can tie pins to solid ground but I don't tie them to a solid Vcc, I always use a pull-up resistor. If I do the math, I can tie several unused inputs up through a single resistor. I can also tie unused inputs up to some legitimate output signal. This affects fan-out but it might not matter. For a breadboard circuit, I will probably use a pull-up between 1k and 4.7k. If I'm going to actually use the circuit, I might make certain that I always meet the VIH requirement. And then I will still use a lower value - probably between 1k and 4.7k. FWIW, it is better to use a lower value resistor when debouncing switches. Mechanical switches take a certain voltage to break through the oxide layer and a certain current to maintain continuity. 1k seems to work pretty well. Logic high input current is lower than logic low input current. In terms of power consumption, it is probably better to tie unused inputs to logic high through a pull-up resistor. |
| Chriss:
What is wrong with this circuit? I use the P832 Photo interrupter and the SN74LS14 to transform the signal from the P832 to a square signal. When I interrupt the photo signal with a card board the interrupter actually goes low aroun 0.25V but the 7414 won't invert the input. This SN74LS14 is a good one now. :D Here is my circuit what I use: I also tried the R3 to change from 1K up to 10K but no big difference... What does I miss? Thank you... |
| PA0PBZ:
What happens if you remove the P832, does the 74ls14 output go high now? Did you try to just short the 74ls14 input to ground with the P832, without using any resistors? |
| Chriss:
If I remove P832 the 7414 doesn't go high, but If I short the 7414 input to GND then the signal goes high. I also tried with a simple transistor BC337 as a switch wired up to the input of 7414 and worked fine. |
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