Multiple buttons on 1 analog VS one digital per button:Power Consumption

Projects General Guidance
1

hi everybody,
im working on a bluetooth watch project.
You may have already seen it on hackaday

i kinda need to add some buttons onto the watch
and power efficiency is really important in this project.
So im wonder which method consumes less power?
Multiple buttons on 1 analogRead like here: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1267115381
or 1 digitalRead for each button

1 DigitalRead per button:
Cons:
each Pulldown resistor will always be spending power even while the button is not pressed.
Pros:
no hardtime tweaking pwm interval

Multiple buttons on 1 analog:
Cons:
each button pwm has to be defined.
Pros:
Less power consumption "i think"...

im not very good with electronics...
please guide me which method i should use to add buttons onto my watch
Thanks :slight_smile:

2

There is not really a rule of thumb here.
Both methodes have, like you wrote, their pro's and con's.
You can use whatever solution works best for you.

The powerconsumption can be calculated using ohms law and will show what ever solution is the most power efficient.

3

Multiple buttons on 1 analog:
Cons:
each button pwm has to be defined.
Pros:
Less power consumption "i think"...

PWM is an output function. Analog pins are input only. So, this statement does not make sense.

The only time power is being consumed is when the switch is pressed, completing the circuit. It makes no difference if that circuit goes through the ADC or straight to a digital pin.

4

For lowest current consumption for digital input pins, I would just enable the internal pull up resistors and wire the normally open switch contacts to ground. Current flow would only happen while switch was pushed and would be very low.

Lefty