08M2 - Minimum current

#1
Hello. I'm looking for the option to minimise the current. I have a picaxe 08M2 which drives a piezo by TUNE with a pot (volume) from C.2 (also a led). The supply is 9v (by 7805 - 5v). The program is a TUNE (every 20minutes) and I finish by END after 3 hours. The cell drops to 6v after 2 days :) I checked and only the piezo in PAUSE (20 minutes between TUNE) draws the current. For the 08M2 is there any solution to have no current in PAUSE or after the END. Thank you
 

AllyCat

Senior Member
#2
Hi,
The supply is 9v (by 7805 - 5v).
Welcome to the forum. A "quiescent" (unloaded) 7805 (or even a 78L05) draws much more current (several mA) than a PICaxe (which draws about 600uA at 4 MHz, excluding any external loads). A few "Ultra Low Quiescent current" regulators do exist (do not confuse with Low Dropout types) but a physical switch on the regulator input is the normally-adopted solution.

The PICaxe has SLEEP and NAP commands which can reduce its power drain to almost nothing (a few uA), so it's mainly a matter of how you design the external circuit.

Generally, PP3 type cells are a poor (and expensive) battery for most PICaxe projects. They only have a capacity of a few hundred mA.hrs whilst AAA cells are nearly 1,000 mA.hrs and AAs over 2,000 mA.hrs. For many applications a "regulated" supply is not needed, so 3 (or even 2) alkaline cells in series can be a better solution.

Cheers, Alan.
 
#3
To add to what Alan says - Yes 2 x AA cells will easily run an 08M2 for an extended period. The batteries are not much larger and a 9v "PP3" type.
 

Hemi345

Senior Member
#5
My automated window blinds have been averaging about 10 months on a single set of 4x AA alkaline batteries, opening/closing the blinds and reporting in over WiFi to log battery, temperature, & blind position at least twice a day. An efficient MC78LC33 voltage regulator is always on and powers the PICAXE 20M2 which is sleeping a vast majority of time but wakes about every 5 seconds to check the pin tied to SRLATCH to see if anyone pressed the button to open/close the blinds and to also check the ambient light sensor (to automatically open/close the blinds in the morning/evening). A TPS27082L load switch controls the 6V power to the servo so it's only powered when the blinds need to move. The PICAXE also switches an LP38692SD-3.3 1A regulator to power up the ESP8266 ESP-01 module when it needs to transmit the stats. Average current consumption is <10uA!
 

hippy

Technical Support
Staff member
#6
If one makes a rough guesstimate that the 9V battery has a 100mAh rating and it's going flat after two days; that's about 2mA used per hour. That wouldn't be surprising for a PICAXE which is mostly idling with PAUSE.

Replacing the PAUSE with SLEEP would likely reduce the current considerably, and replacing the 9V and regulator with 3 x AA batteries would extend their lifetime considerably.

Doing that would likely extend operation from a couple of days to around a month and possibly longer.
 
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