NoobMan:
Actually I aim for 12V tolerance as I hope 12V will be enough for my purposes. I agree you have to be careful with diodes and that is why I removed any part info in the schematic as I want to measure and verify the part first. They are intended to clamp at VDD and be sized to handle the current if you source 12V at the connector.
I realise that the pictures are to small to be of much use. I´ll fix that. The schematic shows what is intended to be a first step developement board to play around with MCU and hopefully avoid most pitfalls before it is time to proceed with a fully functional controller board. You could consider the pin protection components as placeholders for series and/or parallell components to be determined when they are assigned their function later on. The default configuration I consider will be 1k series resistance and 3V3 zeners wich I think is pretty good protection to start with and remove them when neccesary. The capacitors will be omitted on signals who needs it but I try to always limit the bandwith of signals just enough to fulfill its intended use. I will probably have to use gate drivers for FET switching as this MCU have to weak drive to start with even without any limiting components.
Cefiar:
Can you elaborate or point to a thread where this problem has been investigated? I am curious to see under what circumstances these problem shows up and if it is absolutely determined that it is a ground loop problem and not interference that causes this behavior. Many, if not most, dev boards are also missing filtering that is commonly used in commercial products to pass EMC compliance tests. I want to try making this board as reliable as I can and that is why it is going to be limited in functionality so I can put more effort in verifying and testing, hopefully. I am aware it is not a trivial task to make a board with an MCU working at its limits, communicating over USB while switching the currents involved here on the same board so I hope I am not percieved as critical, I just want to try to understand and learn.
Traumfug:
Can you elaborate too please? This USB reliability issues is one of the main reasons I am doing this. It is very frustrating for me trying to learn and set up my first printer when the communication with the host keeps crapping out on me. :(
Actually I aim for 12V tolerance as I hope 12V will be enough for my purposes. I agree you have to be careful with diodes and that is why I removed any part info in the schematic as I want to measure and verify the part first. They are intended to clamp at VDD and be sized to handle the current if you source 12V at the connector.
I realise that the pictures are to small to be of much use. I´ll fix that. The schematic shows what is intended to be a first step developement board to play around with MCU and hopefully avoid most pitfalls before it is time to proceed with a fully functional controller board. You could consider the pin protection components as placeholders for series and/or parallell components to be determined when they are assigned their function later on. The default configuration I consider will be 1k series resistance and 3V3 zeners wich I think is pretty good protection to start with and remove them when neccesary. The capacitors will be omitted on signals who needs it but I try to always limit the bandwith of signals just enough to fulfill its intended use. I will probably have to use gate drivers for FET switching as this MCU have to weak drive to start with even without any limiting components.
Cefiar:
Can you elaborate or point to a thread where this problem has been investigated? I am curious to see under what circumstances these problem shows up and if it is absolutely determined that it is a ground loop problem and not interference that causes this behavior. Many, if not most, dev boards are also missing filtering that is commonly used in commercial products to pass EMC compliance tests. I want to try making this board as reliable as I can and that is why it is going to be limited in functionality so I can put more effort in verifying and testing, hopefully. I am aware it is not a trivial task to make a board with an MCU working at its limits, communicating over USB while switching the currents involved here on the same board so I hope I am not percieved as critical, I just want to try to understand and learn.
Traumfug:
Can you elaborate too please? This USB reliability issues is one of the main reasons I am doing this. It is very frustrating for me trying to learn and set up my first printer when the communication with the host keeps crapping out on me. :(