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