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I'm trying to achieve something seemingly simple. I have a contact (button) that I upon pressing should wait a few seconds before actually allowing current to flow through. For this purpose I'd need some expensive button that I'm not really sure I will find, or I need to just put another component after the button that does the delay part. I searched for such components but without luck.

Is there any component that will allow me to delay current flow by couple seconds and then conduct as if it were just an ordinary conductor?

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  • \$\begingroup\$ Why? Is this a safety function with a minimum "hold to start" time? Otherwise you could just press the button a few seconds later. Normally you need to add a timer module. \$\endgroup\$
    – Transistor
    Oct 19, 2017 at 13:53
  • \$\begingroup\$ @Transistor I need something else to be powered on first in the circuit but I'd like to avoid having 2 buttons. \$\endgroup\$
    – php_nub_qq
    Oct 19, 2017 at 14:02
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    \$\begingroup\$ Is there a contact on the other device that can be used to indicate that it has powered up. This would all be much easier if you explain the problem and not your solution! \$\endgroup\$
    – Transistor
    Oct 19, 2017 at 14:20
  • \$\begingroup\$ @Transistor that's what I thought myself but not really, it's a replaceable device and there is no easy way to detect it has powered on (without modifying it). I've been researching timer modules since your first comment and I'm trying to work something out but it appears to get much more complicated than the task would suggest to a hobbyist like me. \$\endgroup\$
    – php_nub_qq
    Oct 19, 2017 at 14:23
  • \$\begingroup\$ Try looking for "Time Delay Relays" with "On Delay" functionality such as macromatic.com/products-main/time-delay-relays \$\endgroup\$
    – Tut
    Oct 19, 2017 at 15:08

1 Answer 1

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One way to handle this is have the button be a input to a tiny microcontroller, then have that micro control a relay. The micro does the timing and possible de-glitching of the button.

The cheap and tiny PIC 10F200 can do this easily. It comes in a SOT-23 package, which is the same package individual transistors come in. The button can be wired to a input pin directly, since some pins can be configured with internal weak pullups. The output could drive something like a logic-level N channel FET, which would enable the relay.

All together, the total parts would be:

  • Pushbutton.

  • Microcontroller.

  • Bypass cap for the micro, like 1 µF 10 V ceramic.

  • N channel logic-level MOSFET, like IRLML2502.

  • Relay.

  • Reverse diode across the relay coil, like 1N4148.

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  • \$\begingroup\$ Thia gets way too complicated for me, guess what I envisioned is too far from reality. Will have to just go with 2 buttons \$\endgroup\$
    – php_nub_qq
    Oct 19, 2017 at 15:35
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    \$\begingroup\$ @php: If you consider 5 parts beyond the button "complicated", then you are very severely limiting the possible solutions. \$\endgroup\$
    – Olin Lathrop
    Oct 19, 2017 at 15:41
  • \$\begingroup\$ Depending on what this needs to power, it's possible you could eliminate the relay and the diode. For this to work, you'd need to be powering a small load (i.e., something that doesn't draw much power) that's close to a purely resistive load (i.e., little or nor reactive component to its impedance). Even if this is the case, eliminating them is a poor idea, but you might (just barely) be able to get by with it. \$\endgroup\$
    – Jerry Coffin
    Oct 20, 2017 at 5:30

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