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Stretch 0.5sec pulse to 6sec

J

Jamie

Jan 1, 1970
0
Fred said:
George Herold a écrit :


I just mentioned jameco because the OP seems to be an hobbyist, but have
a look at the datasheet. It's a pretty interesting son of a ...555

The timer has been one of the most versatile IC's made that i've
worked with. I've used that for various applications including those
that had nothing to do with timing but to do with using the Trigger and
threshold as window comparators, one time even trigger latch,etc...

The Cmos version brings an interesting batch of applications with it
since it can operate on a single cell. THe ICM7555 Cmos timer is an
interesting package, too.

Jamie
 
J

Jamie

Jan 1, 1970
0
John said:
I have a 4 volt pulse that is 0.5 sec long.
I need a 6 sec pulse that will switch a 2n3904.
The 4 volts has about a 400 ohm source impedance.

I could use a 555, but first I need to invert the signal then
drive my 2n3904 switch, so I have 2 transistors and a 555. Oh yes I
could probably differentiate the 0.5 sec pulse to trigger the 555, so
maybe only 1 transistor and a 555.

Could someone help with a pulse stretcher circuit.
Maybe an RC, transistor, or, I have some FETs, J301 or 2N3819, probably
a diode. That will drive my final 2N3904 switch.
The 2N3904 switch is across the alert button on a Walkie Talkie and
shorts about 3.5v to ground.


---
View using a fixed-pitch font:
WALKIE-TALKIE
Vcc-----------------------+-------+ +-------------+
| | | Vbat+ |
[R] | | | |
| | | [R] |
0.5S>--[1N4148>]--+---+---|----+-|-\U1A | | |
| | | | | >-+-->|>--+ |
| | +--+-|-|+/ | | | |
| | | | | | | O | |
| | | | | | | |<-PTT |
[Rt][Ct] | | | | | O | |
| | [R] | +-|-\ | | | |
| | | | | >-+ | | |
| | | +---|+/U1B | +--Vbat- |
| | | |LM393 | | |
GND>--------------+---+---+-------+------>|>--+ |
+-------------+





555 Inverted PTT, non resetable


.---------------.
| |
| 4V TX SIG > -----THRESHOLD |
=== | |
GND | |
--- | |
--- | |
|---+---+------+----TRIG |
.-. + | |
| | - | |
| | ^ | |
'-' + |OUT |
+---+---+------+---- Discg ---------- PTT LINE
| |
| |
VCC | |
-+ |Vcc |
|---- |
5 VOLTS | | RESET |
| '--|---------|--'
| | |
| | |
| + |
+------+ GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Try this one. I see yours work but it has more parts than this one
does and this is non-resetable, which means the first pulse will
set it to exactly what time window is needed with out any other
pulses resetting the time constant before expiration.

Now It could be that the resetting of the time constant before
expiration of the 6 seconds maybe more desirable but with this one,
the first pulse will start it and any remaining pulses will be ignored
with in the time frame.

Jamie
 
G

George Herold

Jan 1, 1970
0
  I remember having a few of those too, and the voltages were all over
the place. I don't remember where I got them from but it would appear to
me they may have been seconds that I got from some surplus dealer.

  Sometimes you never know.

Jamie- Hide quoted text -

- Show quoted text -

These had a problem with turn on. Sometimes V+ would turn on before
V- and then sometimes the 7912 would *not* turn on. PITA, when it only
doesn't work sometimes. I was pulling out my hair, until my boss
suggested ordering new parts. No problems since then.... Well, not
the same problem anyway.

George H.
 
J

Jamie

Jan 1, 1970
0
George said:
These had a problem with turn on. Sometimes V+ would turn on before
V- and then sometimes the 7912 would *not* turn on. PITA, when it only
doesn't work sometimes. I was pulling out my hair, until my boss
suggested ordering new parts. No problems since then.... Well, not
the same problem anyway.

George H.
Never had that problem, sounds like protection coming in too soon do
to inrush from the caps.

You must remember when those were originally made, ESR worries wasn't
so much the rave as they are today. Crappie high ESR caps most likely
would work just fine if that is the issue.

Jamie
 
G

George Herold

Jan 1, 1970
0
  Never had that problem, sounds like protection coming in too soon do
to inrush from the caps.

   You must remember when those were originally made, ESR worries wasn't
so much the rave as they are today. Crappie high ESR caps most likely
would work just fine if that is the issue.

Jamie- Hide quoted text -

- Show quoted text -

Well in this case it was just bad parts. The same circuit has been
working of years now... I just copied whatever was in the app note/
spec sheet. Both ceramic's and tant's cap-wise. 0.1 of this, 10uf of
that.

George H.
 
A

amdx

Jan 1, 1970
0
---
I don't think so since, from his post, he wants a 1/2 second pulse
(ostensibly detected from a remote transmission) from the receiver to
be stretched into a pulse long enough to allow three "alert" signals
to be generated by the receiver.

Since the stretched pulse is DC, the implication is that as long as
it's active the receiver will continue to generate the "alert" signal
in the form of tone bursts.

If that's true, then the frequency of the "alert" tone will be
irrelevant, while the number of tone burst packets - counted using
your idea - will be important.

Well said John, and also correct.

Mikek
 
A

amdx

Jan 1, 1970
0
Is there a counter chip that has hysteresis on the CLK input? Main
problem I see on a one-chip solution is counting the packets due to
ratty risetime.

...Jim Thompson
The walk/talk has (ICs) on the board that have potting over them.
Mikek
 
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