Low Power SAADC

[bryanhsieh]

Hi everyone,

I am having problems in getting the low power mode in SAADC to work. If I enable it in the config file then the ADC doesn't run anymore.( Blank in the RTT viewer) I have four channels initialized in differential mode with scan, 4x Oversampling and burst enabled. I am using S132 soft device for BLE communication. Has anyone had any success in getting the low power ADC to work? I have tried following this example github.com/.../main.c but with very little success.

Here is my code for reference main.c

Thanks for the help.

Rgs, Bryan

[Jørgen Holmefjord]

Hi Bryan,

Could you check if the example in this post is working for you?

Also note that you might not want to use oversampling with scan mode, due to the reason described in this post.

Best regards,

Jørgen

[bryanhsieh]

Thanks Jorgen, I have found the problem was with how I initialized the channels. I don't quite understand why oversampling with scan mode is not a good idea, as I have burst enabled as suggested by that post and it seems to be working. What I have found is that even with low power enabled the current still increased by nearly 1.5mA with ADC on which I think is the easy DMA current. So that it makes no difference to turn on low power on not but at least the code runs now.

[Jørgen Holmefjord]

Sorry I missed that, with burst enabled, oversampling should work as expected. You are correct that the SAADC will add the EasyDMA current of ~1.5 mA when it is enabled. The point of the low power mode is to disable the SAADC peripheral between samples. If you have a slow sample rate, this can save much on the average current consumption.

[bryanhsieh]

I am guessing with a oversampling rate of 4 and 4 channels enabled, the average power would be 1.5 * 4 * 4 * total_acquisition time / 5ms if low power was working.