The 1 Hz output from the Timebase stage provides the clock signal for the CD4518 (synchronous) counting that can be switched on or off.ICD2O Minute Minder Project: BCD Counter
IC Pinout images from https://www.build-electronic-circuits.com/4000-series-integrated-circuits/The 1 Hz output from the Timebase stage provides the clock signal for the CD4518 (synchronous) counting that can be switched on or off.
As a DUAL BCD Counter the two counters of the CD4518 can be chained together to synchronize both the units and tens digits of the counting. See this reference for a description of this variant wiring strategy.
Once the tens digit reaches 6 (2 & 4) momentarily, the tens count must be reset to 0. The familiar CD4081 AND logic IC is used for this purpose as shown in the schematic below.
Temporarily place LEDs (8 of them) on the BCD outputs to confirm the counting. Take great photos for your DER before removing them for the next stage.
