| Electronics > Beginners |
| 74LS14 testing circuit pls |
| << < (6/15) > >> |
| Ian.M:
74ACH..../74AHCT.... are excessively fast, which causes problems if you have long wires or don't have good grounding and decoupling - which is a typical problem when breadboarding. 74HC..../74HCT.... are a bit slower (similar to 'classic' or LS TTL) and more forgiving. They are far more breadboard friendly. Only get the 74xxCT... TTL logic level compatible input version if you *NEED* a low threshold voltage, either for compatibility with bipolar TTL outputs, or 3.3V CMOS logic outputs etc. Otherwise the 74xxC... families have more or less symmetrical input thresholds and significantly better noise immunity. All 74xxC... families drive rail-to-rail (except open drain parts or if excessively loaded), but for many, they are still better at sinking than sourcing, so higher current LEDs are best wired active low (between the output and Vcc, with a series resistor). |
| KrudyZ:
--- Quote from: Chriss on April 13, 2018, 05:41:31 pm ---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! --- End quote --- The rise and fall times of that purple trace are VERY slow. Look at the time base of the scope... |
| Chriss:
Yes. The purple trace is the output from the photo interrupter which is connected to the input of the gate. Sent from my GT-I8260 using Tapatalk |
| Ian.M:
So you've only got about 3V input amplitude, which means that if you are running the logic from 5V, you *NEED* real bipolar TTL or LS TTL or 74HCT not 74HC logic. It may be worth using a comparator (e.g LM339), with resistors to set the threshold and hysterisis. As that comparator has an open collector output, don't forget the output pullup resistors. |
| ebastler:
--- Quote from: Chriss on April 13, 2018, 08:53:17 pm ---Yes. The purple trace is the output from the photo interrupter which is connected to the input of the gate. --- End quote --- Huh? I thought you had a pull-down resistor and a switch to +5V connected to the input?! :-// (Your schematic in reply #5?) It's hard to do remote troubleshooting when we don't have complete and consistent information about the boundary conditions. Your photo interrupter's output might just be too weak for the LS14 input. |
| Navigation |
| Message Index |
| Next page |
| Previous page |