Long time since I`ve been writing something here, but I`m reading at the forum almost every day. Thought I could ask you guys if you have som experience with the shiftregisters, 74HC165 and 74HC595. I`m using those registers for inputs and outputs in my Propeller 1 controller for my hydro power station. Been running for about 3 years now, but almost everytime we have thunderstorms and lightning in the area, some of the shiftregisters brake down and has to be replaced.
I`m running the registers at 3,3v. At the 165-registers (inputs), all inputs are pulled up to 3,3v by 10k. Grounding the input = activate the input. All inputs are mainly from the switches in the front of the controller box, abt 0,7m cable.
At the 595-registers (outputs), each output goes to the base of a transistor (via 2k2) that drives the relay.
I`ve also sometimes seen broke transistor and relay coil afther a lightning stroke. But it seems like the registers itself brake down first.
So, my main question is: Do you know about similar shiftregisters (same funktion and layout) that can resist high voltage spikes better than the 74HC165 and 595 ?
I`ve attached the schematic for the project. (expressPCB)
Here is the link to the project: arnevik1.no/Kraftverket.htm
Maybe this is a dumb question at the forum, but I will appreciate some thoughts from you about what to do.
One strange thing; the main board with the Propeller onboard is never ruined by the lightning. It survive every time.