Help understanding part of a circuit

[uk.casmith]

Hi,

I'm following a book of electronics and I don't really understand what the author means:

"This arrangement works because I have used a capacitor, C4, to connect the output of IC7 to the reset of IC6. The capacitor communicates the sudden change from positive to negative, but the reset of the time it blocks the steady voltage from IC7 so that it won't interfere with IC6"

Can someone explain this further to me please.

FYI:

C4 = 0.1uF,
R10  = 1k
IC7 = 555 timer
IC6 = 555 timer.

Thanks

[xavier60]

Hi,

I'm following a book of electronics and I don't really understand what the author means:

"This arrangement works because I have used a capacitor, C4, to connect the output of IC7 to the reset of IC6. The capacitor communicates the sudden change from positive to negative, but the reset of the time it blocks the steady voltage from IC7 so that it won't interfere with IC6"

Can someone explain this further to me please.

FYI:

C4 = 0.1uF,
R10  = 1k
IC7 = 555 timer
IC6 = 555 timer.

Thanks

The words " but the reset of the time it blocks the steady voltage from IC7" are difficult to understand. I think that he is trying to tell us that the steady state on IC7 pin 3 is not continuously applied to IC6 pin4.  When IC7 pin 3 goes low, this transition is coupled by C4 to IC6 pin4 causing it to pulse low. R10 then charges the bottom end of C4 back up to + rail voltage.

[rstofer]

Looking at the pinout for a 555, we see that pin 4 (of the lower IC) is Reset.
The capacitor/resistor forms a differentiator circuit which puts out a pulse (not a level) when the input is changed.  The pulse will go high on the rising edge of a signal and low on a falling edge.  This is what we want, a brief low going pulse to reset the lower 555.  You can see that pin 4 is held high through the resistor so the only thing the capacitor can do is pull is low.  And that is exactly what it takes to reset the timer!

https://en.wikipedia.org/wiki/555_timer_IC

You can see waveforms for various ratios of R to C about half way down this page.  We're looking for the 0.1 RC or less (I'm guessing, without doing the math)

https://www.electronics-tutorials.ws/rc/rc-differentiator.html

[rstofer]

Hi,

I'm following a book of electronics and I don't really understand what the author means:

"This arrangement works because I have used a capacitor, C4, to connect the output of IC7 to the reset of IC6. The capacitor communicates the sudden change from positive to negative, but the resetREST of the time it blocks the steady voltage from IC7 so that it won't interfere with IC6"

Can someone explain this further to me please.

FYI:

C4 = 0.1uF,
R10  = 1k
IC7 = 555 timer
IC6 = 555 timer.

Thanks

I fixed a typo in the quoted text.  "...but the REST of the time..."

[uk.casmith]

Thanks for everyone's help with this. I'm going to read the link that was provided it's a little over my head but i'll try reading from the beginning.

Cheers,

[rstofer]

The short answer:  When the upper timer output drops to 0V, the differentiator generates a very brief low going pulse to reset the lower timer.  It's the falling edge that causes the pulse.

All you need to know is that the lower timer reset pin is held high by the resistor and pulled low by the pulse from the capacitor.