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555 timer Stays ON after trigger

rfeyer

Mar 7, 2015
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Hi All,
I am new to this forum and new to electronics (old in life, though :) ) I started playing with components and schematics about 3 mo ago - please be gentle.

I have a 12vdc 5A source which will supply a 12VDC motor to open a small door.
Then the source is opened (i.e.: the 12VDC) I would like the stream to be intercepted by a 555 timer and Mosfet, allowing a variable (by potentiometer?) 5 to 20 seconds to elapse, then allow current to continue to motor and CONTINUE until original 12VDC is turned off. If the below is anywhere close (partially copied from online and modified) then I would like to add a buzzer as well but will try to figure out placement and resistor values.
So, does it look like the below would do/ handle the task, and, if so, what potentiometer would I purchase?
Thanks in advance


upload_2015-3-7_15-9-44.png
 

davenn

Moderator
Sep 5, 2009
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hi rfeyer

welcome to the forums :)

the way you have wired it in the circuit above ... if the 12V is turned off, then the 555 is also off ( as is the motor) as it is no longer getting any power. The 555 will start again when the power is restored

So have you physically wired it differently to the above ?
( I haven't completely checked you 555 circuit to see if it will even work correctly .... that would be the next issue)

Dave
 

rfeyer

Mar 7, 2015
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Mar 7, 2015
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Hi Dave,
thanks for the reply!!!
yes, this is part of an H-Bridge with SPDT relays - which is already working.
So, I have a MC (WebController8.0) with which I will give a TTL high to the H-Bridge and a second TTL which gives an either forward or reverse signal. In any case, once the Relays give a 12 VDC current, these two wires will then go to the delay board which I am going to place by the 12VDC motor (that way the buzzer which I will also include gives a signal just by the door).
Once the door is at either bottom or top, a limiting switch will cut the poser supply to the above delay board.

In this scenario, will the above work?

Rainer
 

rfeyer

Mar 7, 2015
6
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Mar 7, 2015
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I just ordered 100K potentiometers and 100uF Caps - hope that will work with above (if above schematic is correct) but I have not ordered the Mosfet's yet in case I am off kilter above
Rainer
 

rfeyer

Mar 7, 2015
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Could anyone tell me if the above schematic (#1) looks electronically reasonable?
TY

Rainer
 

Colin Mitchell

Aug 31, 2014
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You have the 100k and 10k in the wrong positions The 33u needs to be connected to 0v so pin 7 can be used.
You will have at least 4 "blocks" and a 74c14 will be best
 

rfeyer

Mar 7, 2015
6
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Mar 7, 2015
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TY Colin for your reply.
Is this correct:
I remove the 100k and 10k totally going to the Mosfet Gatet
I remove the 33uF before pin 6 and place it between Pin 7 and ground?

What does 'you have 4 blocks' mean?

Also, I already ordered and am awaiting the 555's - are these a deal breaker?

Rainer
 

rfeyer

Mar 7, 2015
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Mar 7, 2015
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Well,
with some help I have revamped the ciruit - does it now look liek it would work?
TY for any help,
Rainer


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