# delayed 555 timer from a high trigger

#### simon_m74vr

Joined Sep 12, 2019
2
Hi,
I need to a circuit to do the following:

When input is high (power on) wait 3 seconds, then pulse an output to a relay for 5 seconds.

Its to take a TV out of standby automatically.
When its powered on, a standby LED is on.
When the standby button is pressed, the LED flashes a few times then the TV kicks into life.

The standby button does not work for the first couple of seconds - hence the 3 second delay
The trigger is going to be high - as fed from an LED
ouput to drive a relay to press the standby button for the duration of the LED flashing - that should be ignored by the input.

#### crutschow

Joined Mar 14, 2008
23,141
The standby button does not work for the first couple of seconds
First couple of seconds from what?
Are you turning the main's power on and off to the set?

#### dl324

Joined Mar 30, 2015
8,761
Welcome to AAC!

From a Signetics Linear Applications Handbook:

You need a base resistor on T1.

#### crutschow

Joined Mar 14, 2008
23,141
What is the supply voltage?
What is the trigger voltage?
Can the supply voltage be used as the trigger voltage?

Last edited:

#### simon_m74vr

Joined Sep 12, 2019
2
Thanks all.
Im changing my plan... Im going to use an arduino.

The trigger will be from the LED as soon as I turn on the mains to the TV.
Then Ill program it to wait, then output to a relay for x seconds.

Thanks tho for the 555 help - although Ill be not using it.

Joined Mar 10, 2018
3,506

#### crutschow

Joined Mar 14, 2008
23,141
Take a look at these posts -
Hooray, you found someone who wants to generate a pulse using a microprocessor instead of a 555.

Joined Mar 10, 2018
3,506
Hooray, you found someone who wants to generate a pulse using a microprocessor instead of a 555.