Electronics > Projects, Designs, and Technical Stuff

Need some help with a 555 timer circuit

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Pizzashape23:
So as a "conclusion" to the question, which circuit should I use in the final build? Noting that I have no preference in regards to complexity and number of components as long as it does the job and does so safely and reliably. One point in favour of Ian.M's circuit is that it does not cause an activation on power up.

Ian.M:
Before you make a decision, breadboard the contenders with grounded foil under the breadboard and about 30cm of switch wiring, lay that switch wiring next to a mobile phone and dial that phone from another.  Mobile phones cause a lot of EMI when they go active, and this crude suceptability test is to get some idea what could happen if someone with a mobile phone on a belt clip is right next to your device.  You can also try the effect of a Pizeo lighter (for gas - not the sort that makes its own flame), to simulate a strong  ESD discharge.  Ground its shield and extend the electrode so you can bring it close enough to the button to spark to it. 

Pizzashape23:
While I do plan to breadboard both, as stated I don't currently have access to the components required to do so. Realistically, a better question would have been; at first glance which circuit would you implement yourself (If you couldnt do a real world test)?

Ian.M:
Neither.  Analog RC timing is so '80's!

Assuming a requirement *NOT* to use a MCU, I'd probably go for an Analog Devices LTC6993-3 TimerBlox  one-shot,  supplied by a dropper resistor and a 4.7V Zener, driving a low threshold (so-called 'logic level') MOSFET gate via a 100R resistor. It also needs enough decoupling to supply the MOSFET gate charge without a significant V+ voltage drop.  The TimerBlox trigger input has hysteresis so is directly compatible with RC debouncing / ESD protection, and with one more resistor added to the debounce circuit to make a potential divider, you can also level shift from 12V or even 24V levels at the button down to the logic level input the TimerBlox chip needs.   You only need enough debouncing to cope with button release bounce as that specific TimerBlox is non-retriggerable.

An introduction to TimerBlox can be found [here].

Pizzashape23:
 :-DD :-DD
In one post you managed to show up both circuits and completely defeat the purpose of my question.

In all seriousness though, if you had to pick between either circuit in this topic which would it be? I think i have learned more than enough and don't really feel like opening another can of worms, as interesting as it seems.

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