Hi,
I'm trying to make a circuit that takes analog and digital signals and converts them to digital. I.e. for an input voltage of -3v<in<3v the output becomes zero and everything else leads to 5v output. I would also like to isolate the output from the input.
The absolute value of the input is supposed to be <=35v and I'm not trying to protect against input of more than 35v. What I want to make sure is that the output will never be outside 0-5v and that the circuit will accept inputs as low as 3.5v. Also, I want the circuit response to be fast, i.e. much less then 1ms.
Currently, my circuit is as attached. The problem with this is that because of the three diode voltage drops a digital signal will not be able to be passed through because a 3.5v signal will already be 0 after the drops.
I've considered putting a switch where if you know the input is a digital signal you could skip the circuit or at least the bridge rectifier. However, I'm worried that by mistake I'd connect -30v to the input when the circuit is switched to skip the protection and destroy the next circuit in line. Also, if the input ressitor is too small I'd draw too much current from the logic source.
I've considered using a pre-gain stage with this circuit, or comparator instead of this circuit, but because they are powered they'd break the isolation.
Any ideas?
Thanks,
M
I'm trying to make a circuit that takes analog and digital signals and converts them to digital. I.e. for an input voltage of -3v<in<3v the output becomes zero and everything else leads to 5v output. I would also like to isolate the output from the input.
The absolute value of the input is supposed to be <=35v and I'm not trying to protect against input of more than 35v. What I want to make sure is that the output will never be outside 0-5v and that the circuit will accept inputs as low as 3.5v. Also, I want the circuit response to be fast, i.e. much less then 1ms.
Currently, my circuit is as attached. The problem with this is that because of the three diode voltage drops a digital signal will not be able to be passed through because a 3.5v signal will already be 0 after the drops.
I've considered putting a switch where if you know the input is a digital signal you could skip the circuit or at least the bridge rectifier. However, I'm worried that by mistake I'd connect -30v to the input when the circuit is switched to skip the protection and destroy the next circuit in line. Also, if the input ressitor is too small I'd draw too much current from the logic source.
I've considered using a pre-gain stage with this circuit, or comparator instead of this circuit, but because they are powered they'd break the isolation.
Any ideas?
Thanks,
M
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