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Simle LED driver

Hi,

I have a simple 555 delayed timer and I wish to light up a LED when the timer starts and a relay off. At the end of the interval the LED should be off and the relay on. I made a simple circuit as follows:

+------------+---+---------+---+------------+---------+-- VCC | | | | | .-. | | | | .-. | | | | .-. |4 |8 | | | o----------| |--o----o | - | | | |6 | | | | | \\ |+ | |--+ | | +---+ |_ o o === '-------' | | | | )| /-\\33u |1 |5 47u|+ | ___ |/ | )| relay | | --- --- +--|___|--| | _)| | | ---10n /-\\ 10k |> | +-- | | | | | | | GND GND GND GND | | |/ | +-| | |>

| | | | +-------o | GND (created by AACircuit v1.28.6 beta 04/19/05

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But the LED stays ON at the end of the interval when the relay is switched ON. I have to add an iverter and modified the circuit as below:

VCC -----o---------o---o------------o--------- o------------o | | | | | | | .-. | .-. | \\ .-. |8 | | | |--o----o | | | - | |6 | | | | | | \\ | | |--+ | | +---+ o---|

O------

'------' | | | | | |/ |5 47u|+ | ___ |/ | |

4069 --- --- +--|___|--| | | ---10n /-\\ 10k |> | +-+ | | | | | GND GND | | |/ | +-| | |>

| | | | +-------o | GND (created by AACircuit v1.28.6 beta 04/19/05

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Is there any way not to light up the LED when the relay is switched on with just the two transistors?

Allen

Reply to
Allen Bong
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Sorry about the screw-up, here is the second circuit again:

VCC -----o---------o---o------------o---------o------------o | | | | | | | .-. | .-. | \\ .-. |8 | | | |--o----o | | | - | |6 | | | | | |\\ | | |--+ | | +---+ o---| >O------ '------' | | | | | |/ |5 47u|+ | ___ |/ | | 4069 --- --- +--|___|--| | | ---10n /-\\ 10k |> | +-+ | | | | | GND GND | | |/ | +-| | |>

| | | | +-------o | GND (created by AACircuit v1.28.6 beta 04/19/05

formatting link

Reply to
Allen Bong

You can get a lot simpler:

+12 ------------------+------+ | | [Relay] [D2] D1 | |a 555 pin3]----+---|
Reply to
ehsjr 

--
So, it looks like you want the relay to be ON and the LED to be OFF
when power is down, and then when power comes up you want the relay
to turn OFF and the LED to turn ON for a certain amount of time and
then when that time expires you want the relay to turn ON and the
LED to turn OFF for as long as power is up?
Reply to
John Fields

o---|>O------

No, when the power is up the led will be ON and relay is OFF for a time determined by the 1M preset. When the time expires, the LED will be off and the relay turns ON. It operates exactly like a delay timer for electrical controls except that I have to put 8 of them on a PCB.

When the power is off everything turns OFF.

Allen

Reply to
Allen Bong

Thanks Ed, that seems to have solved all but one of my problems. Based on circuit #1, do you think the 555 would kick start reliably every time the power is switched ON?

Regards,

Allen

Reply to
Allen Bong

--- With RESET- tied to Vcc, in order to do that you'll have to make sure that the TRIGGER- input stays below 1/3Vcc until after the RESET- input rises above 1.0V.

Additionally, the TRIGGER input must rise to >= 2/3Vcc before the one-shot times out.

-- JF

Reply to
John Fields

Thanks very much John,

I'll recalculated the values of the components on pins 2, 6 and 7 to make sure the interval of the TRIGGER is shorter than the minimum time interval of the one-shot.

Allen

Reply to
Allen Bong

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