Micropower High pin solution?

bobconan

New Member
I have a device that activates with a low pin. Any input above .18v triggers. I need the default state to be unactivated but I also need a microamp solution in the default state so keeping the pin high is not an option. I was thinking a pull up resistor but is there a way to leave the output on the m2 floating? Maybe a discreet solution?
 

Technical

Technical Support
Staff member
Pins are floating inputs by default until switched to be an output. So a pullup resistor with commands like 'low c.0' (output low) and 'input c.0' (floating input, so pulled up high) will do what you require.
 

bobconan

New Member
Pins are floating inputs by default until switched to be an output. So a pullup resistor with commands like 'low c.0' (output low) and 'input c.0' (floating input, so pulled up high) will do what you require.
This is what i was wondering. Does setting input use less power than ADC? I think I've noticed an uptick in power when reading a pin.
 

AllyCat

Senior Member
Hi,
Does setting input use less power than ADC? I think I've noticed an uptick in power when reading a pin.
Compared with what? Sleep or "normal" running?

AFAIK there is no significant (additional) power drain associated with taking an ADC reading. The FVR (which can be used as the ADC Reference) does of course drain some power when it's enabled.

However, it is "well known" that a digital input can drain more power (from the supply rail) if it is NOT receiving an input voltage close to either Vss (Ground, Logic 0) or Vdd (supply, Logic 1). Thus, it's often suggested that "unused" digital inputs should be tied to ground (preferably with a resistor), although my preference is to just enable the "Weak Pullup" resistors on any unused digital inputs (if power drain is a major concern). But if any particular inputs are receiving an "analogue" voltage (i.e. away from Vdd or Vss) then you should NOT declare them as (digital) inputs, but as an ADC input, to keep the power loss lower.

Cheers, Alan.
 

AllyCat

Senior Member
Hi,

The FVR appears to consume a typical 70 uA (at 5v) and there are other modules such as the BOR, T1OSC, A/D and WDT (the last required to time the sleep/nap period), but I would expect their current drain to change only with the respective setup commands (FVRSETUP {OFF}, ADCCONFIG, etc.) which often just write directly to the corresponding SFRs. You haven't said which PICaxe you're using, but most of the current drains can be found in the respective base PICaxe data sheets, in the "Advanced Technical Details" HERE. For M2s the "Power Down Base Current"s are around the middle of section 30 (the grey sections apply to PICaxes).

Cheers, Alan.
 
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