Need falling trigger pulse for dc time delay module.

Thread Starter

John4ll4

Joined Apr 9, 2016
6
Hi, noob here. I've got some 3-5vdc delay timer modules that require a short falling trigger pulse to activate the delay. If it is possible I'd like to use an LDR to trigger this pulse so it will only trigger when it is dark outside. The module will be li-ion powered and will be used for some 3v leds. Hopefully someone will be able to help me figure this out. Thanks in advance for any advice you can provide. John
 

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LowQCab

Joined Nov 6, 2012
4,314
This will depend upon the requirements of the Modules that You have.

Can the "Trigger" Input remain Grounded while the Timer runs-out it's time,
and then the Timer turns off, with the "Trigger" still Grounded ?,
and then the Timer only resets when the Trigger goes High again ?

If this is true,
then You don't need any extra Components,
just insert your LDR in place of the Push-Button in the Schematic.

Check the operation of the Timer with the LDR installed, then reply back.
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Thread Starter

John4ll4

Joined Apr 9, 2016
6
Put the ldr in place of the resistor like this circuit, the preset is to adjust the dark level trigger point.

View attachment 283179
Thank you so very much for your help!!! It'll be nice to have some timed led lamps.
This will depend upon the requirements of the Modules that You have.

Can the "Trigger" Input remain Grounded while the Timer runs-out it's time,
and then the Timer turns off, with the "Trigger" still Grounded ?,
and then the Timer only resets when the Trigger goes High again ?

If this is true,
then You don't need any extra Components,
just insert your LDR in place of the Push-Button in the Schematic.

Check the operation of the Timer with the LDR installed, then reply back.
.
.
.
With the trigger grounded continuously the timer never turns off the output. It would have been an easy fix it the delay didn't care if the trigger was grounded constantly. Thanks for your input!
 

LowQCab

Joined Nov 6, 2012
4,314
This means that an additional Circuit-Board will be required,
which kinda ruins the teeny-tiny one-Board format.
Is this acceptable to You ?
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.
.
 

Dodgydave

Joined Jun 22, 2012
11,375
Thank you so very much for your help!!! It'll be nice to have some timed led lamps.

With the trigger grounded continuously the timer never turns off the output. It would have been an easy fix it the delay didn't care if the trigger was grounded constantly. Thanks for your input!
As for giving a negative pulse you need another chip like a 555 or a 4093 Schmidt trigger.
 
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