# Series Time Delay circuit question

Discussion in 'The Projects Forum' started by zcream, Feb 21, 2009.

1. ### zcream Thread Starter Member

Feb 21, 2009
20
0
Hi! I am connecting 30 devices in series. I am trying to delay the input pulse 4-10ms for each device. Thus Device 1 is 4ms delayed from Device 0, Device 2 is 8ms delayed from Device 0 etc.

Since the delay is small enough and does not have to be precise I am thinking of using a simple RC delay.
However, I am unsure what happens when you connect 30 RC delay circuits in series.
There is probably feedback, and due to capacitances in parallel the net capacitance will reduce..
How can I add a "buffer" so that once a signal progresses from Device 0 to 1 to 2, it is unaffected by the R and C values "behind" it ??
I hope its clear - I can add more details if its not..

In summary, a circuit where various points in series need an increasing time delay from the origin..

2. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
What does your input pulse look like? Do you need to have fast risetimes at each delay point?

3. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
I made a 3 phase square wave generator using 3 inverters with a 10k from output to input, and a .1μF to ground, with output of 3rd going back to the first. It ran around 400Hz, each is 50% duty 120 degrees apart. Output wasn't exactly square, but didn't need to be for the application.

Adding an additional buffer between input (R/C) and output would give a clean square wave at the inverter output if you use Schmidt Trigger inverters (74xx14 or 40106).

4. ### zcream Thread Starter Member

Feb 21, 2009
20
0
Hi Ron. I dont need fast rise times - the trigger is essentially a Voltage rise upto 3V.
I am using a 3.6V Lithium battery for sending the pulse..

5. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
How precise does your delay have to be?
How wide is the pulse?
Does the pulse repeat?
If so, what is the frequency (repetition rate)?