I'm building a small touch screen which will sport a Raspberry PI Zero inside the monitor. The screen is powered by a 12 V external power supply.

To power the RP Zero I use an L7805ACV voltage regulator. However, when I plug my device in, only the screen starts and it shows no signal message. I have to unplug the RP Zero and plug it in again to make it start.

My idea is to make a RP power supply which will wait 2 seconds before it turns on (start 2 seconds after screen). Unfortunately I have no idea how to do it. Can anyone give some advice here?

Here is the schematic:

enter image description here

  • 5
    \$\begingroup\$ It might be easier to fix the underlying issue than to design a workaround to provide a startup delay. I think you have an X-Y problem. You have problem X, the startup problem, and with no other info what else to do, you are trying to solve it with Y, a delay circuit, and therefore you are asking how to do Y. I suggest you provide more info and try to solve the actual problem, X. \$\endgroup\$
    – Justme
    Commented Jan 5, 2023 at 0:09
  • \$\begingroup\$ and what is the problem X in your opinion ? \$\endgroup\$
    – smoczyna
    Commented Jan 5, 2023 at 10:50
  • 1
    \$\begingroup\$ The problem of the system not starting without a MCU reboot. But with no info we can't help solving it. For example, incorrect power up sequencing of devices may damage them, so it is worth to figure out why you have the problem, before either the display or MCU damages. It also may be a software issue, if you try to communicate with the display before it is ready. But without info on the hardware or software, we can only guess why it does not work. \$\endgroup\$
    – Justme
    Commented Jan 5, 2023 at 11:57
  • \$\begingroup\$ OK, I added the block schematic of the the project. Both display and RP are powered at the same time and this is the issue I think. That's why I thought about "delayed powering" of RP. \$\endgroup\$
    – smoczyna
    Commented Jan 10, 2023 at 23:24
  • \$\begingroup\$ When your rpi doesn't want to start, measure voltage on 12V and 5V pins to check if maybe your power circuit on display board goes into some kind of protection mode \$\endgroup\$
    – floppydisk
    Commented Jan 11, 2023 at 13:20

1 Answer 1


I found the solution I'm going for (due to lack of other options), it is: Time-based Switch Using a Real Time Clock. Basically it is using clock Alarm function to turn on/off things.


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