Thingy91 Power consumption

Question

Hi Dev team, 
 I am working around with the Thiny91 and wanted to have more information regarding the power consumption characteristics of the board. 
 I have a program running on the Thingy91 that connects to my server to send sensor data through MQTT, every 5 mins. In the meantime, I want to go into the lowest power consumption mode and wake up only to send data and then back to the low power mode in between. 
 I currently have a power consumption of around 1.5 mA in the low power mode and I want to reduce it further to the datasheet values. I also have enabled PSM mode with : 
 CONFIG_LTE_PSM_REQ_RPTAU="10101010" CONFIG_LTE_PSM_REQ_RAT="00000001" 
 and I see that it is configured by the network correctly as well. 
 
 I had a few questions regarding the power consumption of the Thingy91 board : 
 (1). I get sensor data through my UART every 5 mins, so I cant have CONFIG_SERIAL = n in my prj.conf . That maybe 1 cause for this significantly high power consumption. Can I enable and disable the UART in runtime and will that make any difference to the power consumption in this case. 
 (2). The Thingy91 user guide says that , the 3.3V power domain can be powered down to save power when Thingy91 is in sleep mode. How can this be done ? 
 (3). Will it be logical to turn off the modem in order to save power during the sleep mode ? 
 (4). Does modem firmware affect the power measurements ? 
 (5). To measure power power consumption, I use Joulescope and remove the USB power to the Thingy91. Thus, I am unable to view the logs in my link monitor when measuring power. Is there any other way to view the logs while measuring current (like Segger RTT Viewer) and how do I enable that . 
 (6). Any other power saving tips that could help reduce power for the Thingy91. 
 Regards, 
 Adeel.

Stian Røed Hafskjold · Accepted Answer

Hi,

(1). I get sensor data through my UART every 5 mins, so I cant have CONFIG_SERIAL = n in my prj.conf . That maybe 1 cause for this significantly high power consumption. Can I enable and disable the UART in runtime and will that make any difference to the power consumption in this case.

Yes, you can enable and disable the UART at runtime. One way to do it is to use the power management API in zephyr. This will make a difference in power consumption. The UART consumes about 4-600 uA. By turning it off you should ideally get down to 3-4 uA (unless something else is consuming power as well of course).

#include <device.h>
#include "power/power.h"

const struct device *console, *uart1;

void main(void)
{
  // Turn off logging (which is using UART0):
  console = device_get_binding(DT_LABEL(DT_CHOSEN(zephyr_console)));
  device_set_power_state(console, DEVICE_PM_OFF_STATE, NULL, NULL);
  
  // Turn off UART1:
  uart1 = device_get_binding(DT_LABEL(DT_NODELABEL(uart1)));
  device_set_power_state(uart1, DEVICE_PM_OFF_STATE, NULL, NULL);
  
  .......

}

and in prj.conf:

CONFIG_DEVICE_POWER_MANAGEMENT=y

(2). The Thingy91 user guide says that , the 3.3V power domain can be powered down to save power when Thingy91 is in sleep mode. How can this be done ?

Yes that is correct. I see that you already figured this out in your previous answer. You can use the adp536x library functions

adp536x_init(ADP536X_I2C_DEV_NAME);
adp536x_buckbst_enable(false);

(3). Will it be logical to turn off the modem in order to save power during the sleep mode ?

Usually you would just send the AT+CFUN=0 command to disconnect from the network and let the modem stay in idle mode. You can then issue new AT commands for reconnecting. Or you can use the LTE link control API. Something link this:

#include <modem/lte_lc.h>

void main(void){
  int err;
  err = lte_lc_offline();
  
  ......
  
}

And in prj.conf:

CONFIG_NETWORKING=y
CONFIG_NET_SOCEKTS=y
CONFIG_NET_SOCKETS_OFFLOAD=y

CONFIG_AT_HOST_LIBRARY=y
CONFIG_BSD_LIBRARY=y

CONFIG_LTE_LINK_CONTROL=y
#do not automatically connect to the network:
CONFIG_LTE_AUTO_INIT_AND_CONNECT=n

You should get a current consumption of 2.2uA in this mode.

Alternatively, if the network supports it, you can use PSM mode. In PSM mode the modem is in sleep, but you are still attached to the network, meaning that the energy needed to reconnect to the network is minimal, since it does not have to do the scanning procedure etc. The idle current in PSM mode is 2.7uA.

(4). Does modem firmware affect the power measurements ?

The modem FW should not affect the power measurements when the modem is turned off. If the modem is turned on and connected/trying to connect to the network it will affect the current consumption.

(5). To measure power power consumption, I use Joulescope and remove the USB power to the Thingy91. Thus, I am unable to view the logs in my link monitor when measuring power. Is there any other way to view the logs while measuring current (like Segger RTT Viewer) and how do I enable that .

If you want to measure current at the same time as you see the logs you should leave the USB cable plugged in and use the default UART logging module. You can still measure current to the nRF91 and nRF52 through the current measurement headers. However, this is not very useful for debugging current consumption, since the UART module is consuming current. You can turn off RX in the logging module to save some power. NRF_UARTE0->TASKS_STOPRX = 1; And the UART will consume about 50uA instead of 600uA.

You can use RTT as well if you have a debugger that supports RTT, and connected it to the SWD header. The problem is that in order to use RTT the chip has to be in debug mode, which is consuming 3-4 mA. So it's not that useful at all when measuring current.

(6). Any other power saving tips that could help reduce power for the Thingy91.

You should start with a simple project where you get the 3-4 uA idle current, and then add one peripheral/feature after another.

You can also try System OFF mode which will completely shut down the nRF91 and then see what floor current you are able to achieve, and use that as a base line for later measurements.

Remember that on the thingy91 there are both a nRF91 and a nRF52. If you are not going to use the nRF52 you might want to consider putting this to system OFF mode to save current. Check out the thingy91 schematics to see which external sensors are connected to which nRF chip.

Stian Røed Hafskjold · Answer

Hi, 
 What kind of 3.3V driver is this? There can be leakages through the GPIOs if not initialized correctly. The text you pasted is for peripherals running in the nRF91 core. You have to make sure that they are stopped when in idle so they don't keep the HF clock running, which will consume current 
 Stian

Thingy91 Power consumption

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