What does this 555 Circuit do? Its for sale as a kit on Ali Express but I cannot see what its for? I used to be into electronics in my teens and have recently started to look at taking this up as a hobby once more. Last time I used 555 was in the 80s and I was saddened to hear its creator passed away in 2012

https://www.aliexpress.com/item/Hig...-occupation-Evaluation-Kit/1000001959223.html

The circuit diagram and PCB photo show a relay and LED probably the output.

There are 2 variable resistors so I'm not sure what they are doing in the configuration shown.

I wanted to build a circuit for a paper shredder that I normally forget to turn off. I've a couple of options

1) Use a PIR and relay and set the duration / detection on that so I just walk up to the shredder it powers up and will run for a set period after I've left say 30s to a minute

2) Build a 555 circuit with a relay that is monostable and use a push button (low voltage isolated from the mains power)

I thought this 555 option on AliExpress might be a cheap way of trying option 2 or this premade unit https://www.aliexpress.com/item/Fre...Delay-Turn-off-Switch-Module/32454773989.html

Prebuild items for option 1 include https://www.aliexpress.com/item/Fre...Motion-Sensor-Detector-Module/1874938103.html with a relay perhaps like this https://www.aliexpress.com/item/Hot...sehold-Appliance-Control-for/32316656858.html

 

There are 2 variable resistors so I'm not sure what they are doing in the configuration shown.

The pots let you adjust on and off time independently.

 

The pots let you adjust on and off time independently.

Ok thanks so its in astable mode. I think I need a monostable set up. I could modify the circuit accordingly.
Thanks - I'll take a look at how to add a trigger input by comparing a typical monostable 555 setup with this astable one.

 

Its an Astable circuit with separate on off times...
Scroll to the third image for circuit diagram.

 

On and off times separately adjustable from 15 to 45 seconds.
Operates from 14V to 32V DC or 10V to 22V AC.

 

I think I need a monostable set up. I could modify the circuit accordingly.
Thanks - I'll take a look at how to add a trigger input by comparing a typical monostable 555 setup with this astable one.

You just need to disconnect the trigger input. Seems to me that building the circuit from scratch would be less bother than buying something that isn't what you want and modifying it.

 

This block diagram might be helpful:


The timer is triggered when the TRIGGER input is taken below 1/3Vcc. When THRESHOLD gets to 2/3Vcc, the DISCHARGE transistor is turned on to discharge the timing cap.

And a belated Welcome to AAC!

 

Do you want to build a circuit from scratch, or wire up an ali or ebay timer module? Many PIR modules are built to run directly on line voltage and switch an AC load, so that way probably is the least effort.

ak

 

Its an Astable circuit with separate on off times...
Scroll to the third image for circuit diagram.

Looks like a handy little board - there's a lot you can do with that with very simple modifications.