nrf52832 system off design issue

[bevis]

Hi:

When I use DK PCA1004 to debug the system off function, I add a shake sensor to the hardware. At rest, the sensor has two states, on or off. When shake occurs, the resistance of the sensor itself will be changed, 0 - > infinite ohm. With this feature, I can easily wake up Bluetooth.

But there is one problem. I set up a pull-up input for the sensor, and the sensor connects to GND. my VDD is 3V,  Electrical specification said V_{IH = 0.7*VDD = 2.1V, I used nrf_drv_gpiote_in_is_set to detect that 1.9-2V still returns true. This is not serious, more serious is when the MCU enters the system off when the sensor is off. Because of the pull-up input, the power consumption of the whole system is 100 - 200 ua. I use the keys on the DK52 development board, and often press the keys to simulate the situation of the sensor off. The result is still 200ua.It has been confirmed that all GPIO ports are set to default, except the wake-up port.} 

_{On the other hand, if the series pull-down resistance is increased, the leakage current can be reduced, but this will not produce detectable logic level.} 

_{Can the wake-up system off only use nrf_gpio_cfg_sense_set?} 

[haakonsh]

From System OFF mode: 

When in System OFF mode, the device can be woken up through one of the following signals:

1. The DETECT signal, optionally generated by the GPIO peripheral
2. The ANADETECT signal, optionally generated by the LPCOMP module
3. The SENSE signal, optionally generated by the NFC module to “wake-on-field”
4. A reset

I suggest you try the LPCOMP — Low power comparator peripheral instead of the GPIO peripheral as the wake-up source.

By using an external reference you can use a pull-up of much higher resistance:



You can probably use 10M or higher resistance pull-ups, you'll have to try it out.