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can I get a lower current with this pic and setup

 
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Nick
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can I get a lower current with this pic and setup
PostPosted: Mon Aug 09, 2004 9:08 am     Reply with quote
I'm down to

1-1.4ma @ 6volts.
.9- 1.0 ma @ 5volts.


Here is a dumb question, why when I raise the voltage does the current used go up?


Here is the setup

24LC32a (only powered when used, I'm powering directly from pic without a pull-up resistor, is this a bad idea?)
pic16f876 @ 4mhz(this is the smallest clock I have)
DS1307 Dallas RTC


When the pic is turn off the current from the DS1307 is .1ma. The PIC sleeps most of the time.


right now I dont have a voltage regulator, the lowest voltage I can use is ~4.1 volts, otherwise the pic doesnt come on. Shouldnt the pic run on less than that?

Which battery would give me the longest life at 1.0 @ 5volts?

maybe 4 AA 1.5v batteries in series would be 6, they are around 1100mah

1100/1 = 1100hours/24 = 43 days, thats not long enought. I need atleast 4-6 months.


Is the A/D turned off by default? I dont need it and a search result said if I disabled it I could lower my current.

Thanks
Nick
valemike
Guest
Re: can I get a lower current with this pic and setup
PostPosted: Mon Aug 09, 2004 9:23 am     Reply with quote
Nick wrote:
I'm down to

1-1.4ma @ 6volts.
.9- 1.0 ma @ 5volts.

Here is a dumb question, why when I raise the voltage does the current used go up?


Ohm's Law says I = V/R

Assuming your impedance/resistance stays the same: the bigger your voltage, then current will go up
Ttelmah
Guest
Re: can I get a lower current with this pic and setup
PostPosted: Mon Aug 09, 2004 10:03 am     Reply with quote
Nick wrote:
I'm down to

1-1.4ma @ 6volts.
.9- 1.0 ma @ 5volts.


Here is a dumb question, why when I raise the voltage does the current used go up?


Here is the setup

24LC32a (only powered when used, I'm powering directly from pic without a pull-up resistor, is this a bad idea?)
pic16f876 @ 4mhz(this is the smallest clock I have)
DS1307 Dallas RTC


When the pic is turn off the current from the DS1307 is .1ma. The PIC sleeps most of the time.


right now I dont have a voltage regulator, the lowest voltage I can use is ~4.1 volts, otherwise the pic doesnt come on. Shouldnt the pic run on less than that?

Which battery would give me the longest life at 1.0 @ 5volts?

maybe 4 AA 1.5v batteries in series would be 6, they are around 1100mah

1100/1 = 1100hours/24 = 43 days, thats not long enought. I need atleast 4-6 months.


Is the A/D turned off by default? I dont need it and a search result said if I disabled it I could lower my current.

Thanks
Nick

The PIC should operate to 4v. remember though, you need to be measuring the voltage at the chip, not the supply, so 4.1v is not far off.
Have you got brown out reset enabled?. This typically resets the chip at around 4v, and could be why yours is failing here. It also draws about 150uA, so is another option that should be disabled. To go to lower voltage, you need the LF version at 4MHz, this will operate down to 2v, making it possible (for instance), for you to run the circuit on a 3.3v lithium battery, without regulation.
You should turn off _all_ peripherals not in use. The 'classic' ones are the ADC, the watchdog timer etc..
6v, is _above_ the maximum voltage rating for the PIC...
At 5.5v, and 4MHz, the F876, typically draws about 1.6mA, with the watchdog enabled, so you may allready have the watchdog disabled to get down to the current you are seeing. The LF typically draws about half the current at this voltage. If though, you go down to 3v, and get a slower crystal at say 33KHz, the consumption falls into the 50uA range...

Best Wishes
Nick
Guest
PostPosted: Mon Aug 09, 2004 10:58 am     Reply with quote
Ttelmah,

thanks for the help. Basically what help me the most is saying that I have about got hte pic16f876 as low as it will go.

I'm going to look into the nanowatt chips, the Pic16f373 looks like a good fit.

http://ww1.microchip.com/downloads/en/DeviceDoc/30498b.pdf
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