To the OP: The site linked in your first post has a fundamental design flaw that stresses the 4026 chip beyond its specified operational limits.
spec - depends on what you mean by complex. First, the circuit in posts #1 and #6 are missing 21 current limiting resistors to protect the 4026 output stages. They depend on the the P-channel output transistors to act as both current limiting and balast resistors for the individual display segments, something they never were intended to do. Second, the outputs are rated for under 5 mA per segment max and 3 mA typical, which will limit significantly the display brightness. Third, at those output currents the output voltage will not be close to the rail, which will decrease display brightness even more. There are five different display applications in the 4026 datasheet, and *none* of them have the device directly driving anything except other display driver devices. Why do you suppose that is?
Fourth, what is the purpose of R1 at each display? If it is meant to be an overall current limiter, that will not work. There are several threads on this and other sites that explain why driving LEDs that are connected in parallel will not work, and that is essentially what you are trying to do. The display brightness will vary greatly depending on how many segments are lit. Also, when multiple segments are lit they will not be at the same brightness because the LEDs will not have perfectly matched forward voltages. Separate from that, with 6 V Vdd and 2.0 V Vf for an LED display segment, then a perfectly saturated output limited by only 100 ohms would have to supply 40 mA, while all of the charts for the high output condition quit at 30 mA. More importantly, while there is no plot for Vdd = 6 V, at 5 V the device can supply less than 5 mA. Most importantly, that is at an output voltage of zero volts, the exact opposite of saturated. In other words, the device cannot directly drive the display effectively or reliably, with or without current limiting resistors to keep it from burning up.
OTOH, the 4511 suggested in post #11 is designed from the ground up to be an actual display driver, and can source 25 mA while maintaining a terminal voltage high enough to drive an LED display with headroom to spare. This is more than enough current for visibility in anything other than direct sunlight.
When comparing different designs, one way to judge the complexity of a project is by the total number of soldered device pins; another is by the total circuit power. For anything with a multi-digit display, multiplexing wins every time.
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