0000 0000 0001 1100

CD4026 7-segment Counter

Take two on this chip as those in the bucket originally were FAKE! So I got my money back from AliExpress and re-ordered. The wait was worth it because they turned up a few weeks later and actually worked as advertised - nice.

There was only one unanticipated problem - the outputs from the CD4026 chip are "1" for "HIGH" which turns on each segment from a common cathode 7-segment display, but sadly if you only happen to have common anode 7-segment displays in the parts bucket then the result takes a little interpretation. 

Red = what is lit, Green = what should be lit!

I have ordered some common cathode displays to make better (easier) use of the chip, but in the meantime I looked for a solution - is it possible to turn all "1" signals to "0" and vice-versa?

Well, yes! You just need an IC that has multiple NOT gates - for instance a CD4069 Hex Inverter as per last week's blog would be perfect, just add one transistor based NOT gate to complete the seven required inverters and hey presto we have a display that works on "1"s and not "0"s.

In "real life" the result is as shown in the video below.

Eagle-eyed viewers will spot a lone resistor going from the transistor not gate to segment D. There's a case to be made for resistors on all outputs as seen in many circuits shown online. I just threw one in here as the single segment output from the transistor not gate was showing up brighter on the display and it became a little distracting. A 220Ω resistor cured the imbalance and the resultant overall display was more evenly lit.