I have a very simple circuit (see below), basically a 4026BE Decade Counter linked to a 7-Seg display; when I press a momentary button to apply +ve power to the counter pin (1) it increases the 'score' on the LED by 1. No inputs are floating, I've debounced the button and it all works fine, except....
If I power it via a 9V source, either a 9V battery or a 9V adapter, the LED displays 0 (zero) when I first apply the power (momentary switch is up); pressing the switch increments by 1. Jobs a good 'un as they say and it's exactly how I want it to be.
If I power it via a 5V regulated source - i.e. the 9V source connected to a LM7805 and its 5V output routed to the momentary switch (up) the LED displays '9' usually, sometimes random segments, when I first apply the power. Pressing the button increments by 1 and it all works fine.
The counter pin is pulled low with a resistor/capacitor combination (pulls it low and debounces the button) and I've measured 0V at that pin at power on. Reset pin is pulled low as well.
I'm looking for some insights in why this might be happening: why might a lower voltage be causing output on some pins of the 4026B? Could it be because the Display Enable pin is permanently connected to source, thus 9V or 5V? I could power the circuit via 9V and be done, or use 5V and just press the reset button to set to 0, but I think I'll be missing a learning opportunity here (I'm very new to electronics.) Also, the rest of what I'm building will require 5V so I thought I'd try and keep it the same.
Thanks,
Andrew
