# How to make momentary connection on power on?

I have a mini-computer Beelink AP34 with momentary power button and I need to simulate short pressing of this button once it is connected to the power (12V DC).

The reason is that it doesn't start automatically after power loss and does not support Wake-on-LAN or anything - I always have to physically press that button after connecting power adapter.

• Is the "mini-computer" powered by this 12 V supply? Or something else? – jonk Apr 14 at 20:16
• check the bios settings for restart on powerfail or some similar setting – jsotola Apr 14 at 20:23
• @jonk - yes it is powered by AC-DC 12V adapter. – verglor Apr 14 at 20:26
• @jsotola unfortunately BIOS does not have this setting - I believe hardware mod is inevitable. – verglor Apr 14 at 20:27
• So, all you need is a delayed power-on signal (which could start with a slow RC charging process) followed by something with hysteresis to "snap-on" a switch, so to speak. You could probably use a relay, safely. But if you want to avoid a relay then what do you know about the button? What exactly is it attached to? (You need to work out precisely the circuit connections the switch is tied to or else you may be forced to use a relay to be safer.) A latching relay would permit lower continual power consumption. But a regular relay could also be used if the power is acceptable. – jonk Apr 14 at 20:37

You wrote that, "I am total rookie in electronics, so I need it to be as simple as possible." Since none of my betters (I'm just a hobbyist without even so much as one day's class of DC electronics training) has yet bothered to provide something I'll try to follow your guiding words and provide something simple and easy and relatively available.

simulate this circuit – Schematic created using CircuitLab

Once the 555 becomes active, both the $$\\text{THRESHOLD}\$$ and $$\\text{TRIGGER}\$$ pins should be low enough (because $$\C_1\$$ is holding them both low) to start that the output will be active-HI and the relay will be engaged. I've specified one particular $$\12\:\text{V}\$$ relay you might consider using. It's a TE Connectivity IMB06CTS and is a signal relay (instead of a power relay) with a coil resistance of about $$\1\:\text{k}\Omega\$$. The 555 can easily drive it, directly.

Eventually, $$\C_1\$$ will charge up sufficiently that those two pins will be above the needed threshold and the output will go active-LO and the relay will be disabled.

I've set up $$\R_1\$$ and $$\C_1\$$ to provide about $$\750\:\text{mS}\$$ duration for the relay. That's a "long-press" of your button, so feel free to shorten that up a bit by reducing the values of either the resistor or capacitor. For example, you might use $$\R_1=270\:\text{k}\Omega\$$, instead. Or $$\C_1=220\:\text{nF}\$$, instead. Either change will probably work fine. So that gives you an idea of the range of change you might consider.

Just in case it's not entirely clear to you, the switch within the relay (shown in the diagram) should be used in parallel with your existing manual momentary switch. No need to remove the manual switch, if you want to keep it and use it. This relay switch simply bypasses it to allow for an automatic restart, as well.

• Thank You very much. This seems to be exactly what I was looking for. I am just interested if it is possible to replace IMB06CTS with any other 12V signal realy - preferably available on aliexpress or any other eshop with cheap intl shipping. Maybe something like this Omron G5V-2 ? – verglor Apr 16 at 21:32
• @verglor The 555 output can probably handle almost any small relay. Since all you are doing is emulating a switch, they don't need to have large contacts. The Omron you mentioned has about $\frac14$ the resistance and will require four times the current but the 555 can handle that, too, just fine. So I think you should feel okay with it. – jonk Apr 16 at 21:41
• Hi @jonk, I have hooked it up on breadboard and it's working prefectly. However I have some silly questions: 1) what is the purpose of C2 ? (I didn't have capacitor with so low capacity so I omitted it and it still works) 2) how can I introduce a little delay before the relay "pushes the button" ? – verglor Apr 24 at 13:08
• @verglor Add a big capacitor between ground and the reset pin. Very big, like maybe $47\:\mu\text{F}$. It takes a lot because that pin can maximally source as much as $1.5\:\text{mA}$. Adjust up or down from there, once you test it out, to get the desired delay. – jonk Apr 24 at 16:05
• @verglor $C_2$ is just a standard, recommended value to help stabilize a resistor divider inside. You could probably eliminate it if it bothers you. – jonk Apr 24 at 16:08

The 555 is a great idea, but it's worth pointing out that an arduino nano could also do the job. The power switch likely jumps a pin pulled to 5v to ground. In such case, a 5v powered arduino could do the job. It may seem like overkill, but it's a software driven solution that requires no soldering - just an arduino nano with pins soldered (around five bucks on ebay) and three conductors (for gnd, 5v, and pin) of a 40 conductor preassembled jumper. Program the arduino to pull a pin low momentarily two seconds after reset, connect that pin to the pwr_on pin on the motherboard, and there ya go. You can likely find a manual on the net that will give you the required header pins on the motherboard to provide 5v and gnd and pwr_on. This means no soldering, maybe not even needing a vom to measure things out.

Edit: apparently they have a bios revision to solve this problem. I'd suggest going to their support site and doing a bios update.

• I have found in the forum that there should be BIOS update. But it is not generally available and when I asked support to provide it, they said, that they don't have BIOS with auto start but that they support WOL. It's strange - however my current version of BIOS does not support either feature. – verglor Apr 16 at 21:22
• However your suggestion of arduino solution is interesting indeed. Thank You. I'll give it a try if I will not be able to get BIOS update. – verglor Apr 16 at 21:36