Heyo! I've done quite a bit of googling on this subject but I'm relatively new to concept of physical electronics as a whole and was curious if there was any simple way to make sure that I could take an input voltage and make sure to just clip off negative voltages and anything above 5v to protect my microcontroller. The reason I ask this is so that I can use it with CV coming from my modular and similar things such as that. I also imagine I could use it if I applied DC bias to a audio signal as well.
I tried a regular diode and that worked fairly well for removing the negative voltages, but I couldn't figure out how to remove anything above 5v. I'm aware that diodes also have some amount of a forward voltage, but it seemed like the minimum of -.3 volts I was getting from my negative clipping circuit wasn't enough to bust my Arduino as I have read the pins can technically support voltages up to -.5 volts.
In terms of >5 volts mitigation, though, I have run into some issues figuring it out. The best shot I've seemed to have so far is Zener diodes, and to be fair they do seem to be pretty good, however I have also heard they slightly attenuate your signal and I was having issues getting it to fit somewhere within the 5v-5.5v range that would make it fully accurate while also not so much as to blow out a pin.
My new theory is that maybe I should use an op-amp, but it seems like from what I've read (or rather, lack of what I can find) that this might not be the best idea, and not really something that op-amps are meant for. I did find out also that most op-amps tend to also somewhat limit the signal slightly below their supply voltages, which would cause problems. I have also heard that "rail to rail" op-amps exist, but I still don't know if using an op-amp purely to clip voltages without doing any actual amplification is a good idea or not.
So that's why I'm here. I feel like this is a very hyper-specific question or maybe I'm not using the best words when trying to google it. I imagine it probably the ladder. If anyone could help me out with the practical theory on this, it would be GREATLY appreciated. Huge thanks!
The inputs are already protected by diodes. What you need to do is limit the current into or out of each diode to below 1 mA.
A 10K resistor in series with the input will protect it in a range from about -10 to 10 V.
I can use it with CV coming from my modular
Many forum members, including me, have no idea what that means.
Oh. That makes my job much easier LMAO. Thanks so much!
Sorry, I should have clarified. I am referring to a modular synthesizer which typically outputs voltages ranging from -5v to 5v. Thanks so much!
EDIT: For more clarity, CV stands for Control Voltage.
As I’m not an hardware guy I’m willing to trust you on that but I’m very surprised that a resistor in series (agree on current limiting) would protect an input pin for 10V when it’s rated at 5.5V max for example
Use a voltage divider with three resistors if you want to read that range.
One from pin to ground, one from pin to VCC, and one from pin to input.
With the right values, you can convert -5volt +5volt to 0-1023.
Google "clamping diodes" (images) to see the basics of pin protection.
Don't believe half of the advice there. Zeners and common diodes won't work.
Schottky diodes are commonly used to keep the pin within 0.4volt of VCC/GND.
Leo..
Given the voltage drop across the series resistor, the voltage on the (internal) input will be at most one diode drop above Vcc, so possibly 5.6V for positive input on a 5V Arduino, or one diode drop below GND, for reverse input polarity.
I think that that particular specification from the data sheet assumes no resistance in series with the input, so the real point is to avoid excessive current flow burning out the protection diode.
Ok. Thx
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