On Tue, 27 Dec 2005 14:09:25 -0500, "Henry"
wrote:

Looking for a way to make a 555 timer astable circuit "triggerable." Seem
all the circuits I see (I think the some one over and over again) show an
astable 555 rigger to run constantly as a "clock." Right now I am using a
transistor to power up and down the 555, but it seems there should be a
better way. Basically I want "bursts" of pulses based on a trigger. (And it
needs to reset itself, not needing any manual reset.)

--- _____
Use one 555 as a monostable with its output going to the RESET pin
of another 555 wired as an astable. when you trigger the first one
it will enable the second one, which will put out a signal for as
long as the output of the first one is high. Like this:


+V---+---------+----+-------+-------------------+-------+
| | | |8 | |8
[10K] [10K] [Rt] +---+---+ [RA] +---+---+
| | | 2|_ Vcc |3 | 7|_ Vcc |3
+-[0.1µF]-+----|--O|T OUT|--+ +--------+--O|D OUT|--OUT
| | 6| | | | 6| |
| O +---|TH | | +--[RB]--+---|TH |
| O S1 | 7|_ 7555| | | 2|_ 7555|
| +--O|D | | +--O|T |
| | |_ | | | |_ |
| +V---|--O|R | +------------|--O|R |
| |+ | GND | |+ | GND |
| [Ct] +---+---+ [Ct] +---+---+
| | |1 | |1
GND-+--------------+-------+-------------------+-------+


--
John Fields
Professional Circuit Designer