"John Fields" wrote in message
...
On Sat, 31 Dec 2005 17:08:31 -0500, "Henry"
wrote:


"Henry" wrote in message
...
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.)

Thanks,
Henry



Thanks every one. Okay, this seems to work so far. I have connected the
555
Reset connection to ground with a 10K pull-down resistor. Then I pull the
Reset up with a NPN transistor connected to Vcc (+5v) when I want it to
trigger (vibrate?). Anyway, seems to work so far. I tried a higher
pull-down
(100K) resistor, but there was some auto-triggering and mis-fires. Is 10K
good enough for a pull-down in this case or should I get some 20K or 50K?

---
Why didn't you use the circuit I gave you?

--
John Fields
Professional Circuit Designer

Because it took an extra 555 timer, if I understood it correctely. I only
have a couple of these and it seemed a waste to use a timer chip where a
single transistor and resistor (of which I have many) seem to do the same.
Otherwise I have used your advise in other questions. No insult intended.
But I am also tinkering and experimenting and I may not be completely
explainisg myself when I ask some of these questions. I need my last 555
timer as reset timer for something else. I have also read that 555 timers
tend to consume power and not sure how many parts I can drive from 4-AAs. Im
already using about 7 TTL logic chips, a 555 timer, (maybe another soon to
complete the auto reset part) about 6 LEDs, and 8-10 transistors. Im already
doing things like combining 2 NAND gates to make a single AND gate. Im
improvising with what I have.

Henry