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To preface, I don't come from an EE background so I'm sorry if this question is extremely simplistic.

I have a shutter controller board that allows me to open and close a shutter (optical iris) with a TTL signal. However, I want to keep things modular with a prior system that was controlling the shutter via simple power to the control board (we don't open and close the shutter often). Unfortunately, this prior system's control board has been discontinued and is no longer available.

My idea was to simply use the board's power to also provide the TTL signal. Voltage isn't a problem and I've confirmed that from lab power supply that this method should work. However, I need to introduce a delay to the TTL signal to allow the board to be powered up first.

I'd like to make this as simple as possible. I was considering doing an RC opamp delay circuit, but that seems like it may cause problems if the rising edge is too slow. Am I approaching this in a completely unreasonable way? Ideas? Thank you so much for any insight you may be able to provide!

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  • \$\begingroup\$ What is the expected value of the delay, in seconds, and how accurate must this delay value be? \$\endgroup\$ Commented Apr 29, 2021 at 21:27
  • \$\begingroup\$ Although I haven't tested it, I'd imagine the delay wouldn't need to be more than a few seconds. I'd also expect accuracy to not be needed. \$\endgroup\$ Commented Apr 29, 2021 at 21:30
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    \$\begingroup\$ No, you really need to put numbers on these requirements. What is the minimum and maximum acceptable delay, in seconds? It doesn't make sense to say that accuracy is not needed. \$\endgroup\$ Commented Apr 29, 2021 at 21:57
  • \$\begingroup\$ I see. In that case, the delay should be 2 +/- 0.5 seconds. The purpose of this is to allow the controller board to be powered on first. If I go the route of the RC opamp delay circuit, I'd choose RC values to reflect this. However, I'm not sure if this works with TTL signals. Any ideas? \$\endgroup\$ Commented Apr 29, 2021 at 23:28

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I would make it with two RS flip flops. Its a draft only, you must ensure the supply for RSs aswell as its initial reset state, proper (quick) discharging of C in case of quick re-power... After supply reaches almost full voltage fire the RS1 from zener circuit. RS2 fires after delay defined with RC constant and give you ttl signal on its output.

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