I need help! Trying to use 555 timer to pulse but input will be steady state.
Michae...@gmail.com
to imitate pressing of a button when I turn the ignition on. I want the
pulse to be about one second long.
The thing is, when I start the car the trigger will always be at a
steady state, not a pulsed input.
I have tried this, but the output just stays low, if the trigger is
steady state low.
I was thinking I could use the momentary position of the ignition
switch which turns the motor and it would be like an trigger pulse, but
I wish to use he same circuit more than once , and when the car is
already running.
Anyone any ideas on this?
Thanks.
D from BC
Thanks.
.
-------------
Oh no..hope you're not making a car bomb :(
See 555 app notes.. You're looking for positive edge triggering.
Or...just skip that boring way and use a microcontroller :)
D
------
jasen
> I am trying to figure out a cct which uses a 555 timer to send a pulse
> to imitate pressing of a button when I turn the ignition on. I want the
> pulse to be about one second long.
> The thing is, when I start the car the trigger will always be at a
> steady state, not a pulsed input.
> I have tried this, but the output just stays low, if the trigger is
> steady state low.
tried what?
> Anyone any ideas on this?
just one: (view with fixed font)
ign
|
.--------------------+
| |
| . . . .|. . . .
| . VCC(8) .
| . .
+--------------RES(4) OUT(3)------ out
| . 555 .
+--[100K]--+---TH(6) DIS(7)--
| | . .
`--|<----+-+---TR(2) CV(5)--
| . .
|+ . GND(1) .
10uF=== . . . .|. . . .
| |
--+-----------+--------- ground
Bye.
Jasen
ehsjr
Here's one way:
Ignition
Switch
/
+12---o o-----+------+
|+ |
[100uF] |
| [10K]
[Rly] | |> |
| | | |
Gnd -----------+------+---o o----> To 555 pin 2
That will give you a trigger pulse to the 555,
rather than a steady level. You'll likely get
several pulses due to relay contact bounce, but
the bouncing will be finished in less than .1
seconds, so it's irrelevant.
Ed
default
The datasheet for the standard 555 shows a circuit that capacitive
couples the trigger in on pin 6 (I think that's it) of the mono
stable. Cap is .01 uf and there's a 10 K pull-up resistor on either
side of the cap.
The low trigger toggles the mono stable through one timing cycle and
the input trigger on the cap can remain low thereafter.
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Michae...@gmail.com
Thanks everyone, although, I cannot read those ccts even with a fixed
font. I know it took a lot of work to type them in, and I am grateful.
Where do I find the standard 555 datasheet so I can look at this
capacitative coupling cct.
Thanks again.
default
>
>Where do I find the standard 555 datasheet so I can look at this
>capacitative coupling cct.
>Thanks again.
http://www.williamson-labs.com/555_apps.htm has it first example on
the page
http://www.doctronics.co.uk/pdf_files/555an.pdf pretty pictures has
it on page 3 Two pull up resistors and a .001 uf cap
National Semiconductor has their data and applications on searchable
CDrom for free, and on line. Too lazy to look it up so I picked the
first hit that matched my search terms <555 application notes >
FYI - all this stuff is on line - goggle for it
Winfield Hill
> Michae...@gmail.com wrote:
>> I am trying to figure out a cct which uses a 555 timer to send a pulse
>> to imitate pressing of a button when I turn the ignition on. I want the
>> pulse to be about one second long.
>> The thing is, when I start the car the trigger will always be at a
>> steady state, not a pulsed input.
>>
>> I have tried this, but the output just stays low, if the trigger is
>> steady state low.
>>
>> I was thinking I could use the momentary position of the ignition
>> switch which turns the motor and it would be like an trigger pulse, but
>> I wish to use he same circuit more than once , and when the car is
>> already running.
>
>
> Ignition
> Switch
> /
> +12---o o-----+------+
> |+ |
> [100uF] |
> | [10K]
> [Rly] | |> |
> | | | |
> Gnd -----------+------+---o o----> To 555 pin 2
>
> That will give you a trigger pulse to the 555,
> rather than a steady level. You'll likely get
> several pulses due to relay contact bounce, but
> the bouncing will be finished in less than .1
> seconds, so it's irrelevant.
Thanks Ed, but that's rather painful with the relay...
jasen showed an attractive approach, using switched
power. That's a good idea, and should be considered.
We usually use continuously-powered circuits, maybe
because they're easier to think about. In the case of a
555 timer chip, we need to AC couple the trigger signal.
Here's an example:
battery
|
,------+---+--------------+----------,
| | | | 555 |
| | | . . . . . . . . . |
| | 100k . VCC(8) . |
| | | .___ . |
IGN | | +------.DIS(4) OUT(3).--| ---- out
| 22k 22k | . ___ . |
| | | +------.THRES(6) RES(4).--'
| | 0.01 | | .____ .
22k +-||---+-- | -----.TRIG(2) CV(5).--
| | | . .
| |/ _|_+ . GND(1) .
'----| --- . . . . . . . . .
|\v | 10uF |
| | |
---+----------+--------------+------- ground
The Ignition signal is positive going, but the 555 wants
a negative trigger, so we have to add an inverter. This
makes this approach less attractive than jasen's circuit.
ign
|
.--------------------+
| |
| . . . .|. . . .
| . VCC(8)
| . .
+--------------RES(4) OUT(3)------ out
| . 555 .
+--[100K]--+---TH(6) DIS(7)-
ehsjr
Yup, it's ugly. :-)
>
> jasen showed an attractive approach, using switched
> power. That's a good idea, and should be considered.
His stuff is always good, as is yours, of course.
Thanks,
Ed
Michae...@gmail.com
Is there any chance one of you guys could elaborate or draw a proper
pic and put a link to the photo site where the picture would be located
so I could look at it?
Thanks again.
Winfield Hill
>> Winfield Hill wrote:
>>> ehsjr wrote:
>>>>
>>>> Here's one way:
>>>>
>>>> Ignition
>>>> Switch
>>>> /
>>>> +12---o o-----+------+
>>>> |+ |
>>>> [100uF] |
>>>> | [10K]
>>>> [Rly] | |> |
>>>> | | | |
>>>> Gnd -----------+------+---o o----> To 555 pin 2
>>>>
>>>> That will give you a trigger pulse to the 555,
>>>
You can easiiy see ASCII drawings if you tell your viewer
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I've shortened the text above to just the three drawings.
Michae...@gmail.com
Hey, that 2nd example works a treat.
Thanks very much.
JeffM
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