Double 555 Timer circuit design please!

Thread Starter

Ian Barton

Joined Oct 14, 2018
6
Caravan Timers Concept resized.jpg
I used to play around with 555 timer circuits up until I retired about 15 years ago but have become a bit rusty on it now and am seeking a bit of help.
I also used to have access to bread-boarding and heaps of components to try out different things but that is not now readily available. The particular application I am putting together does not work on a pulse as such but is looking at a switch position and needs to generate a delay based on the switch position. It may be possible for some clever chap to achieve the delays simply with diodes, resistors and capacitors.
The first diagram is quite straight forward but as a possible variant it would be nice to have the 555 timers energised when the switch is closed and de-energised when the switch is open so there is no residual standby current in the open switch position. I will probably use a CMOS 555 timer so if the variant isn't possible to achieve then residual standby current won't be a huge concern.
 

Thread Starter

Ian Barton

Joined Oct 14, 2018
6
Hello Albert.
I need the input to be the opposite sense to what you have nominated as per my initial concept drawing.
Thanks
Ian
 

AlbertHall

Joined Jun 4, 2014
9,826
Hello Albert.
I need the input to be the opposite sense to what you have nominated as per my initial concept drawing.
Thanks
Ian
As the '555 needs a negative going trigger then that's the way it needs to be. You can use your positive going trigger and an inverter (chip or transistor) to drive the circuit.
 

Thread Starter

Ian Barton

Joined Oct 14, 2018
6
Hello Albert
I had a play with your suggested circuits and I am happy with your suggestion for Output 2. I have modified it slightly as per the attached file to cater for my particular needs and it works OK.
The only problem I have which you may be able to assist me with is when the circuit is powered up with S1 open the Output goes high for a second or two which means the relay it is going to control will also be energised and I don't want it to be until S1 is closed. Once the power is on and it has done it's little pulse it settles down and works as per the Input and Output diagrams.
Would you have any suggestions as to how I can hold the output low at switch on with S1 open?
Thanks
Ian
Caravan Timers Concept Output 2.jpg
 
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