C
CFoley1064
- Jan 1, 1970
- 0
Subject: Switch de-bounce circuit questions.
Hi, Andrew. The 555 trigger input is level-triggered rather than
edge-triggered. That gives you some options, depending on how your circuit is
built.
Here's the worst choice (view in fixed font or M$ Notepad):
T .---------.
--- | |
..--o o-----o-----|2 |
| | |
| | |
'----------o--. | 555 |
| | |
| | |
=== | |
GND | |
'---------'
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de
A standard 555 has an input that may permit this, but it will false trigger all
over the place.
This setup is somewhat better:
VCC
+
|
1K.-.
| |
| |
T '-' .---------.
--- || | | |
..--o o---o--||-o--o2 |
| || | |
| .01uF | |
'--------o--. | 555 |
| | |
| | |
=== | |
GND | |
'---------'
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de
The lower value you can make the pullup resistor, the better. The cap keeps
the input signal from exceeding the length of the one shot.
A 555 is very sensitive to false triggering. This will help some. If this
doesn't do it, and you are still getting false triggering when you bring the 1K
resistor down to 150 ohms or so, you might have to add further input signal
conditioning.
Good luck
Chris
From: (Rubicon)
Date: 11/7/2004 1:19 AM Central Standard Time
Message-id: <[email protected]>
Hello,
I have put together a switch circuit using two tactile switches with
555 de-bouncers to a positive edge triggered flip-flop controling
transistors/mosfets.
The on-board tactile switches work fine but I have also added pins for
off-board switches.
With off-board switches what do I need to do in addition to using
shielded wires to prevent false triggering? Twisted wires caused the
switch circuit to flip-flop when a fluorescent light was turned on.
In addition I have LEDs indicating the flip-flops output ON state but
how do I indicate the OFF state with LEDs? Formerly I used a double
pole switch.
Cheers,
Andrew.
Hi, Andrew. The 555 trigger input is level-triggered rather than
edge-triggered. That gives you some options, depending on how your circuit is
built.
Here's the worst choice (view in fixed font or M$ Notepad):
T .---------.
--- | |
..--o o-----o-----|2 |
| | |
| | |
'----------o--. | 555 |
| | |
| | |
=== | |
GND | |
'---------'
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de
A standard 555 has an input that may permit this, but it will false trigger all
over the place.
This setup is somewhat better:
VCC
+
|
1K.-.
| |
| |
T '-' .---------.
--- || | | |
..--o o---o--||-o--o2 |
| || | |
| .01uF | |
'--------o--. | 555 |
| | |
| | |
=== | |
GND | |
'---------'
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de
The lower value you can make the pullup resistor, the better. The cap keeps
the input signal from exceeding the length of the one shot.
A 555 is very sensitive to false triggering. This will help some. If this
doesn't do it, and you are still getting false triggering when you bring the 1K
resistor down to 150 ohms or so, you might have to add further input signal
conditioning.
Good luck
Chris