So far I have burnt out 3 HC599 ICs. At first I thought the ICs are bad quality or factory rejects. But now I guess that I might have over driven the ICs. I skimmed through the datasheet and have the impression that the output can drive at least 3mA, and up to 6mA, but not sure if it is OK to drive all segments at the same time non multiplexingly. Anyway, I am too lazy to use buffers to off load the ICs. Instead I am using a heat sink for one of the ICs. If the other ICs burn out sooner or later, then perhaps I should redesign the circuit, or give up HC599 and use MAX7219 instead. However, one good thing about HC595 is that there is no limit on the number of digits, while MAX7219 only allows 8, if I use the fully assembled module which has no lead out for the MAX7219 serial output.
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