NRF51822 or NRF8001 for sensor

[pascal defesche]

Hello,

For my application i need one central device collecting data from sensors. For central side i would choose for the nrf51822(s120), simply because it has high priority interrupts reserved for the radio. But i need some advice for my sensors: should i choose for the nrf51822 or nrf8001.

My sensors need to collect data with a constant rate of 125Hz. So i will need a reliable timer interrupt to collect my data. Is it correct the nrf51822 will not be able to create such realiable timer interrupt for my application as there will be LowerStack interrupts for the radio? So choosing for the nrf8001 with external MCU would be better for sensors?

Regards, Pascal

[Ole Morten]

I guess this mostly depends on how important it is that you read the sensor at exactly 125 Hz. If you can live with some jitter on the time,

The nRF51822/S110 will block the CPU for every connection event, and the time will be dependent on the number of packets transmitted. With the S120 as Central, only one packet will be sent/received every interval, and hence the blocking time should be around 1 ms. Hence, if you can live with 1 ms jitter on your sensor readings, you can do with the nRF51822.

However, if 1 ms jitter is too much, you'll have to do your sensor reading on a different CPU than the one handling the BLE communication. This can then be done either by using an external MCU and the nRF8001, or with the nRF51822 and an additional micro.

The nRF8001 is a good chip, but it's very different from the code perspective than the nRF51 series. For your use case, I would personally therefore consider to use the nRF51822 as the main MCU also in the sensors, to keep as much consistency in the system as you can. An external, very small microcontroller, could then be used to do the sensor readings and buffer them, and the main application on the nRF51 could then read out the buffer from the other micro over a serial interface, and send it over the air.

[Juliane]

Hi Ole,

I use STM32 as the main MCU in the sensor and use it to do the sensor readings and buffer them ,I want to use nRF51822 to read out the buffer from the STM32,and then send it over the air.How can I do it and wheather there a demo for it ?

Thank you for giving me a reply! Best Regards!

[Ole Morten]

This is really a very unrelated question, and would be better off on its own. You may also have use in taking a look at this question: https://devzone.nordicsemi.com/index.php/nrf51822-wired-communication

[David Edwin]

The nRF8001 has a full serial interface, which is lightweight (few hundred bytes of RAM) and 2K to 4K bytes of code, this will help you keep the sensor interfaces clean. You can also interface the nRF8001 by polling it so this does not require interrupt capability on the STM32.

You can take a look at the example STM32 + nRF8001 integration using the Maple here. The Maple is the Arduino library for STM32.

This port is based on our Arduino SDK for nRF8001. The nRF8001 serial interface is easier to integrate.

You can also use this breakout board of the nRF8001 to quickly integrate your STM32 to the nRF8001. (Note: This version of the breakout board is using the C version of the nRF8001).