Far-seeker:
To be clear, dc42, I'm not contesting the validity of your analysis or the circuitry you've suggested. It will work, and in all fairness my concerns areprobablyexcessive.Early in my career I've worked in sectors (railroad and aerospace) where electronics failure can potentially mean the loss of millions (choose your currency, at this level it doesn't really matter) or even injury and death. It has led me to internalize a stronger than average sense of risk mitigation. Therefore if an inexpensive part will prevent a one-in-a-million failure without reducing the effectiveness of the device, my first impulse is to include it. This is true even with an obivously non-mission critical application like an automobile tachometer display. Although I'm attempting to temper this impluse in the context of DIY projects.
Fair enough. I work in safety-critical software and I take a similar approach to software development.