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The mistake a number of people make is thinking that an open circuit/unconnected input from of an opamp is zero volt.
Floating inpit/Open circuit doesn't imply zero volt.
In practice, without the pulldown resistor, a number of factors will contribute toward the voltage on that node...
How can a 50Hz and 50.5Hz signals be in phase.
And even if the frequency is equal, crossing zero point at the same time doesn't imlply being in phase either. Could be 180 out of phase.
Being in phase means the average of the difference will always be zero at all points, not just at a point.
As smijesh mentioned, that is exactly what you might do. But sometimes, this is one of the case where we overestimate the power of software on microcontrollers. Well depending on the frequency of your AM signal, you may be better off with an hardware demodulator, followed by a zero crossing...
What you want is feasible, I just don't think this simple rc will do. Since you can't wait for the charging cycle of the capacitor to complete, say you have a semiconductor spdt switch which of course must be able to handle the required current by the module. NC to the 4.3V and NO to the...
Your cir uit looks good. Only that trying to charge the capacitor from 4V supply through a diode may not be a too good idea. Increase the charging voltage to 4.3v so you don't have to use a too hefty capacitor
Re: Simple 7805 regulator circuit is flaky
Yeah seen that before. One damaged pin or a damaged diode within the bridge rectifier is certainly the cause. Change your rectifier friend
The 12v and -12v connected to the circuit. Are they defined in the power configuration. I would rather place a voltage generator and change the magnitude to 12v and -12v. I am guessing proteus is applying 5v to your IC and not the 12v you labelled it
It's obvious you have more fault than just the fet and resistor. If this is driven by an spms IC, you may have to check that too
Either way, watch out for where the pwm signal for the fet is supposed to come from
As long as you are not withdrawing much current from the gpio, you should be fine without a buffer. I will suggest a resistor greater than or exactly 2.2k in series with the LED as this brings the current sourced by the pin to about just 1ma
Motorboating
The vref labelled from your circuit is from where?
Is this 1hz signal present on the first and second stage amplifier?
PCB layout?
There is just a lot that can cause this
It wasn't doing a perfect job. I said it has a faulty card.
That was just an instance, not the question I asked
And reliability? Yes it has been running over two years now and still is. If two years is enough of that claim, though.
I have always wondered why commercial circuits are overly complex with a lot of ICs.
Take for instance a client brought in a display controller with a faulty card. Looking on the board with about 200mm x 200mm size, I notice nothing less than 10 ICs, a lot of discreet component. We eventually...
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