Re: Simle LED driver

On Mon, 27 Aug 2007 15:18:47 -0700, Allen Bong
<allenbsf6502@xxxxxxxxx> wrote:

On Aug 28, 6:11 am, Allen Bong <allenbsf6...@xxxxxxxxx> wrote:
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 | |<-+ | |470 |
| | .-------. | |1M '-' |
| |10k | | '-' | |
'-' | |3 | | |
| | |------------+ | |
| 2| 555 |7 | | led V -> |
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 04/19/05www.tech-chat.de)

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 | |
.------. | |1M 10k|
| )| | |470
| | '-' '-' )|
relay '-'
| |3 | |
_)| |
| |------------+ |
| |
| 555 |7 | | |
| LED V ->
| |--o----o | |
| -
| |6 | | | | | |
\ |
| |--+ | | +---+ o---|>O------

'------' | | | | | |/
|5 47u|+ | ___ |/ | |
4069
--- --- +--|___|--| | |
---10n /-\ 10k |> | +-+
| | | | |
GND GND | | |/
| +-|
| |>
| |
| |
+-------o
|
GND
(created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)

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

Allen

Sorry about the screw-up, here is the second circuit again:





VCC -----o---------o---o------------o---------o------------o
| | | | | |
| .-. | .-. | \ .-.
|8 | |<-+ | | |_ o o | |
.------. | |1M 10k| | )| | |470
| | '-' '-' )|relay '-'
| |3 | | _)| |
| |------------+ | | |
| 555 |7 | | | | LED V ->
| |--o----o | | | -
| |6 | | | | | |\ |
| |--+ | | +---+ o---| >O------
'------' | | | | | |/
|5 47u|+ | ___ |/ | | 4069
--- --- +--|___|--| | |
---10n /-\ 10k |> | +-+
| | | | |
GND GND | | |/
| +-|
| |>
| |
| |
+-------o
|
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

---
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?


--
JF
.

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