LAUNCHXL-CC1350: Clock for getting the change in time between two events

GARRET CRISLER

Part Number: LAUNCHXL-CC1350
Other Parts Discussed in Thread: CC1350, CC1310

Hi colleges,

I am using the cc1350 board to develop a wireless flow meter. One of the aspects of the flow meter is that it needs to measure the time between a electric reed switch activation to find the flow rate. To do this, I figured that I would just use a clock to measure the change in time between the two interrupts triggered by the sensor controller when the reed switch closes. However, I have spent a significant time looking and only found one clock on the chip that would allow me to capture the change in time and that is in the RTOS, which I would like to avoid for power saving reasons.

It seems hard to believe that there are no simple clocks on board in capture mode, so I think I am missing something. I am wondering if anyone knows of a clock that can be used without RTOS on board the cc1350 that would allow me to measure the change in time (interval will not be more than a second)?

Thanks for your help in advance.

over 2 years ago

0 TER over 2 years ago

TI__Guru**** 317180 points

GARRET CRISLER said:
the RTOS, which I would like to avoid for power saving reasons.

What do you base this on? TI-RTOS does not cause any power penalty. TI-RTOS ensures that the chip always is in the lowest power state possible.

For this application, the usage of the Sensor Controller will in most cases give the most energy efficient solution.

See

https://www.ti.com/lit/pdf/swra598

and

https://www.ti.com/lit/an/swra578b/swra578b.pdf

that covers some use cases. These covers how to use the Sensor Controller on CC13x2 which contains some add-ons compared to the version used on CC1310.

Look into the TDC to find the time between two pulses.

0 GARRET CRISLER over 2 years ago in reply to TER

Intellectual 520 points

Alright, I guess I was thinking that TI-RTOS would initiate a bunch of systems that I would not want, I did not know that it ensures that the chip is always in its lowest state.

However, I looked into the TDC and read that it would keep the sensor controller on while it was active, wasting battery power which would not be ideal. Is there a way to implement it and keep it low power?

0 TER over 2 years ago in reply to GARRET CRISLER

TI__Guru**** 317180 points

Any time of clock will require that the clock source and the timer are on.

You can also see https://e2e.ti.com/support/wireless-connectivity/sub-1-ghz-group/sub-1-ghz/f/sub-1-ghz-forum/1006627/launchxl-cc1310-calculate-time-between-posedge-and-negedge-of-a-button-press which is also close to what you are trying to implement.

0 TER over 2 years ago in reply to TER

TI__Guru**** 317180 points

Thinking about it, one option is to get the sensor controller count the number of events on the reed switch and check the counter value every time unit. The 32 kHz xosc is low power and controls the wakeup interval for the sensor controller. This depends on the required time resolution needed.

Sub-1 GHz

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LAUNCHXL-CC1350: Clock for getting the change in time between two events