originator
Industrial
- Dec 12, 2004
- 71
Can any one please give a logical answer for this behavior:
Using a 555 with reset(pin 4) going to +V
4.7 mic to GND from pin 6/7(thresh/discharge)
10k to +V off 6/7
Input to the 555 trigger is from an OR gate, and the 555 is normally sitting at LOW in- gives HIGH output Hi in gives LOW out
Same circuit, BUT run the OR output into a 4050 non inverting buffer, then to the 555 trigger, gives oposite results: 555 LOW input results in LOW out, and HIGH in gives HIGH out
In either case, the inputs to the 555 are LOW In whether straight off the OR, or through the 4050, since the 4050 is just a buffer.
I am looking to use the circuit with the 4050 with the results as described, LOW in/LOW out as that is the requirement, but it just doesn't make sense that the 555 sees LOW from 2 different devices and gives different responses.
Part 2:
In most circuit books I see, the input to the 555 is usually held HIGH and triggers on the going low edge, whereas the output goes high on a low going trigger in. However, I am using it in the oposite mode, low-going-high is the trigger. Is there any particular reason not to use low going high for the trigger? Seems there is a difference in the output pulse duration between the two methods of trigger, but that is managable. It also appears that LOW-HIGH trigger gives a fixed pulse duration which is what I am after to begin with. Is possible to think of the 555 as a pulse stretcher and a pusle length fixer determined by the method of triggering(hi going low or low going high)?
Thanks!
Using a 555 with reset(pin 4) going to +V
4.7 mic to GND from pin 6/7(thresh/discharge)
10k to +V off 6/7
Input to the 555 trigger is from an OR gate, and the 555 is normally sitting at LOW in- gives HIGH output Hi in gives LOW out
Same circuit, BUT run the OR output into a 4050 non inverting buffer, then to the 555 trigger, gives oposite results: 555 LOW input results in LOW out, and HIGH in gives HIGH out
In either case, the inputs to the 555 are LOW In whether straight off the OR, or through the 4050, since the 4050 is just a buffer.
I am looking to use the circuit with the 4050 with the results as described, LOW in/LOW out as that is the requirement, but it just doesn't make sense that the 555 sees LOW from 2 different devices and gives different responses.
Part 2:
In most circuit books I see, the input to the 555 is usually held HIGH and triggers on the going low edge, whereas the output goes high on a low going trigger in. However, I am using it in the oposite mode, low-going-high is the trigger. Is there any particular reason not to use low going high for the trigger? Seems there is a difference in the output pulse duration between the two methods of trigger, but that is managable. It also appears that LOW-HIGH trigger gives a fixed pulse duration which is what I am after to begin with. Is possible to think of the 555 as a pulse stretcher and a pusle length fixer determined by the method of triggering(hi going low or low going high)?
Thanks!