optimizing sleep mode power consumption

Hi all,

I have built an rf remote using a pic18f452, an external clock running at 10MHz with PLL, an hd44780, and an nrf24l01 wireless chip.

If the button(RB4) is not pressed within 15 seconds the pic will fall asleep. I have the lcd power and contrast wires powered from one of the pics pins. If the button is pressed while the pic is awake it will reset the 15 second timer. If the button is pressed while the pic is asleep it will wake it up and start the 15 second timer.


When the pic is asleep the circuit sucks .4mA. If I pull power and take the pic out of the circuit and then plug power back in, the circuit consumes .1mA. All measurements are taken straight off the 9V battery.

My problem is the .3mA that the pic is using while in sleep mode. The datasheet says the pic uses less than .2uA in standby mode, which I am assuming is sleep mode, no?

Before putting the pic to sleep I:

Set all of my pins to outputs and set them low.
Closed SPI.
Disabled timer.
Put the nrf24L01 in sleep mode((.13mA)(leaving .17mA))

What else can I do/disable to conserve battery life? Should I, or can I disable the external clock? If so, how? I am using C18.

Any help is much appreciated.

Thanks a lot.

These might be of some help.

https://www.electro-tech-online.com/custompdfs/2010/10/01288A.pdf
https://www.electro-tech-online.com/custompdfs/2010/10/01146B_chapter202.pdf
https://www.electro-tech-online.com/custompdfs/2010/10/00606BPDF.pdf

Thanks for the reply LTX,

I have read the tips'n'tricks. I forgot to add that I am also using a regulator that only consumes .2uA quiescent current.

I am running at 5V since my lcd is 5V. Would I save a considerable amount if I ran at 3.3V?

Thanks.

You shouldn't be connecting an external clock if you want minimum power consumption.

Can I disable the external clock while in sleep mode?

Why do you need an external clock?

The external clock was used in the nrf24l01 tutorial that I "copied". I think it is used so we can run at 40MHz. The fastes the internal clock can do is 20MHz no? I guess I could try at 20MHz using the internal. Will I save a lot of juice?

No, the PIC18F452 has no internal clock. You're intended application would be the driving factor of clock speed, use the slowest clock and voltage you can reliably get away with.

If I recall you are using an obsolete chip PIC18F452 and the one microchip suggest you replace it with PIC18F4520 does have an internal clock.

It has a 8MHz internal clock that can be used with the PLL for 32MHz or 8Mips.

Can you give me an estimate on how much current I would save using the 18f4520 with the external clock?

Thanks for sharing your expertise.