LPM3 and Proximity sensor

Hi,

In LPM3 the CPU and MCLK are switched off. but can be made to resume operation from ISRs.

you have not mentioned how and which type of proximity sensor is interfaced with the controller.

Hi,

if your proximity sensor only generate a pulse when it is active, you can use the LPM3. At least, this is possible in my uC, MSP430F5438A, I have enable several internal interupts while my uC,that is sleeping, consumes 4uA.

You only have to enable the external interrupt in that pin (verify that this pin/port has interrupt capabilities). So, when the interrupt enters, you can come out of LPM3 in the ISR to do the tasks in the main (when the task is completed, come back to LPM) or execute the required code in the ISR (this last option only if you have a small code to execute).

Thanks for responding 

Sorry, I forgot to mention about proximity sensor and uc. I am using capsense as a proximity sensor(MSP430G2452) and probabaly use the same.

I think the problem here is, I want to enable the proximity sensing when I am in LPM3, that means controller should scan or at least come out of LPM3 when capcitance change. I don't know is it possible or not because I am seeing in LPM3 mode is active the next instruction is nop and everything is still in that case.

Check out :

1-uA Capacitive Grip Detection Based on MSP430 Microcontrollers

This application note discusses a grip detection design using two capacitive touch sensors that utilize the PinOsc feature available on all MSP430G2xx2 and MSP430G2xx3 value line devices. The MSP430(tm) value line series of devices is well suited for ultra-low-power and low-cost applications. The PinOsc feature integrated into every MSP430G2xx2 and MSP430G2xx3 device eliminates the need for external components when implementing capacitive touch sensors and offers an average current consumption as low as 1 uA per button.

http://www.ti.com/sc/docs/psheets/abstract/apps/slaa515.htm

Also

10-cm Capacitive Proximity Detection With MSP430 Microcontrollers (PDF 1138 KB)
09 Feb 2012

http://www.ti.com/litv/pdf/slaa521

Prasun Sinha said:

I am using capsense as a proximity sensor(MSP430G2452)

MSP430G2452 is an MCU , not a capacitive sensor. which capsense are u using?

Prasun Sinha said:

I think the problem here is, I want to enable the proximity sensing when I am in LPM3

When you are in LPM3 as I have already mentioned, the CPU is literally stopped and nothing can disturb/wake it except interrupts.

and it appears from your information that , you want to enable the proximity sensing just before you enter LPM3 and once you get the signal of cpacitance change

on the MCU pin, and if you have configured that particular pin in interrupt mode, you can always exit the LPM3 mode from the ISR.