Evaluate my control board, pretty please?

[Mechatrommer]

ok, so there is no user switch, just PC_USB power as signal to switch... the way i read it..
1) SWITCH_ON_SIGNAL will always 0V regardless of PC_USB level so R1, C1, Q1, R3, R12, Q4, R13 is useless. in fact if you install Q4, it will render SWITCH_SIGNAL useless, see below.
2) what makes the difference is SWITCH_SIGNAL will be pulled low whenever PC_USB is turn on. otherwise turning on relay by U3A (open collector comparator i guess) if there AMP_SIGNAL_ON is HI. but if you install Q4, it will pull the SWITCH_SIGNAL low again.
3) U2A, R2, C2 is not doing anything except wasting current, so they are useless as well. IF U2A is not open collector
4) if they are open collector, U2A and U3A will form AND circuit to RELAY_SIGNAL. you can do that with few transistors. google that in wiki.

[Otomaru]

ok, so there is no user switch, just PC_USB power as signal to switch... the way i read it..

What made you think there's a user switch?

1) SWITCH_ON_SIGNAL will always 0V regardless of PC_USB level so R1, C1, Q1, R3, R12, Q4, R13 is useless. in fact if you install Q4, it will render SWITCH_SIGNAL useless, see below.

That's some what the idea - i'm simulating a button press (press and release), so i just need pulses. Look at attachment.

2) what makes the difference is SWITCH_SIGNAL will be pulled low whenever PC_USB is turn on. otherwise turning on relay by U3A (open collector comparator i guess) if there AMP_SIGNAL_ON is HI. but if you install Q4, it will pull the SWITCH_SIGNAL low again.

So that it does not turn off the device when it's already on.

3) U2A, R2, C2 is not doing anything except wasting current, so they are useless as well. IF U2A is not open collector

The idea behind that is to power U3A (SWITCH_SIGNAL interpreter) only while PC_USB is high and shortly after it get's low. So that i can use the receiver when PC is off.

4) if they are open collector, U2A and U3A will form AND circuit to RELAY_SIGNAL. you can do that with few transistors. google that in wiki.

Yep, i got the idea when i was responding to your previous post.

After led to discovery of optocouplers and getting couple ideas while responding to your previous post - I'm pretty much redesigning majority of the circuit. Might do it this weekend. I'll post it here when i'm done.

[Otomaru]

*BUMP*

Been a while. Have vacation now. Ended up spending a lot more time on it than I thought. Works in simulation. Uses 5 mA when everything is off, 40 when idle and everything on, close to 150 when relay engages. Will update when i build it.

[Otomaru]

It's built and works perfectly.

[sokoloff]

It's built and works perfectly.

Nice!