On Mon, 26 Dec 2005 16:31:40 -0600, John Fields
wrote:

On Mon, 26 Dec 2005 16:19:06 -0500, "Henry"
wrote:


"John Fields" wrote in message
news
On Sun, 25 Dec 2005 05:55:22 -0500, "Henry"
wrote:

Hi, dabbling with some TTL stuff that I dug out of storage. Im about 25
years rusty since I tinkered with this stuff all those years ago. Anyway,
working on a project where it would be deal to have a 555-timer based
monostable multivibrator (with retrigger ability.) Is that possible with
the
555? I have found many circuits online (actually mostly the same one over
and over again) but they dont seem to support re-triggering with the 555.

---

Try this: (view in Courier)


+V-----------------------+--------------+-------+
| | |8
[1K] [Rt] +---+---+
| | 2|_ Vcc |3
+--------------|--O|T OUT|-- OUT
| | 6| |
C +---|TH |
IN-------+-[0.1µF]--+--B NPN | 7|_ 7555|
| | E +-----+--O|D |
| | | | +| | GND |
| | | D [Ct] +---+---+
[10K] +-----------G NCH | |1
| | | S | |
| [10K] | | | |
| | | | | |
GND-----+----------+----+--------+-----+-------+

The input is a positive-going pulse or edge.


--
John Fields
Professional Circuit Designer

Thanks, I will give it a try. One question. I am uncertain what the NCH
component is. I assume its not hydrogen cyanide as that would be HCN. :-)
---
It's a nitrogen carbon hydride switch.

Actually, it's an N-Channel enhancement mode MOSFET with a channel
resistance which will discharge Ct sufficiently close to ground
before the input pulse goes away so that you can predict the
increased length of the output pulse. If you don't have any
MOSFETS, an NPN transistor will work if Ct isn't too big.

---
Aarghhh!!!

There's a gross error in the circuit which I'll fix tomorrow...

Hint: Vbe of the NPN won't allow the MOSFET to turn on, duh...

--
John Fields
Professional Circuit Designer