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

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

On 2005-12-27, 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 the reset input signal and invert the output ?
have you downloaded a 555 datasheet from the manufacturer?

Bye.
Jasen

"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?

Thanks,
Henry

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

On 2005-12-31, Henry wrote:

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?

10K is fine, anything is fine long as the transistor is upto the task.

--

Bye.
Jasen

"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

On Sun, 1 Jan 2006 11:40:24 -0500, "Henry"
wrote:


"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.

---
None taken. I was wondering because you said in your original post
that you were looking for a circuit which, when triggered, would
turn another circuit on (the astable) for a fixed time and then shut
down automatically, which is what the circuit I gave you does. The
first 555 is wired to be a one-shot, with its output normally low,
and it holds the second 555 in reset. When the first 555 is
triggered, its output goes high, it pulling the second one out of
reset and allowing it to oscillate until the output of the first one
goes low, forcing the second one back into reset until the trigger
starts the first one again.
---

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.

---
You'll be able to drive them _all_ with 4 AAs, the question is, for
how long. A Duracell AA (MN1500) has a capacity of 2450mAH with a
50 mA load on it, so if you add up all your load crrents and divide
that number into 2450 you'll get hopw long the batteries will last
until their output voltage falls to 0.8V.

The supply current for the original Signetics NE555 varies from 6mA
max with a 5V supply to 15V max with a 15V supply and no load on pin
3.

7400 family TTL gates vary from about 15mA with the outputs high to
about 30mA with the outputs low. You can go to:

http://www.ti.com

Type in the part number, and a mini spec sheet will give you the
supply current. For example, typing in SN7400N for the NAND lands
you he

http://focus.ti.com/docs/prod/folders/print/sn7400.html

and if you want to you can download the data sheet.
---

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.

---
OK,

Good luck!


--
John Fields
Professional Circuit Designer

On Sat, 31 Dec 2005 17:08:31 -0500, "Henry"
wrote:


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?

---
You shouldn't be using a pull-down, you should be using a pull-up,
like this:


+V
|
[10k} +--- - - - -
| 4|_
+------O|R 555
| |
C +--- - - - -
RESET---[100K]--B NPN
E
|
GND


--
John Fields
Professional Circuit Designer

Once again I'm not sure what you want, but I've gated 2 555s together with
different pulse rates to achieve something similar to what you describe.