Drops will have their PCB !

Hey !

I have good news ! Our PCB is ready for production ! You can find the final electrical schematic : PCB_DROP.
We chose to use internal LDO with our nRF51822. Since last time, I added a kind of connector which is similar to SWD debugger to be able to connect an external circuit with a minimum place. With Alexis, we added ground planes in top and bottom layers. Moreover, we had to add a lot of via. Thanks to that, the ground would be equipotential. We also change the width of some path such as alimentation, or for the antenna, because there are some important constraints on them.
When we were done, Alexis said that we have to wait almost one night, to check if we had not done any mistake. And he was right ! Yersterday, I realize that since the beginning, I have wrong connections for the 16Mhz quartz ! It would have been a desaster if we send earlier the PCB to production ! But now, all issues are fixed.

I have taken a screenshot of our PCB top layer. The bottom layer only include our battery mount, and a few electrical path.
So… our drop circuit will not be any larger than 3 cm * 3 cm.

Capture d'écran 2014-03-26 18.44.31Capture d'écran 2014-03-26 18.43.56

I hope we will receive the 30 of them really soon. But we probably will have to wait around two weeks, maybe more.

Yersterday, I also worked on the nRF51822 eval kit with Matthieu while Lau was doing the Android application. I was in charge with the drop program which has to create a table of messages, and to write the callback functions of a new BLE service for exchanging message. That is to say I write the processing part, while Matthieu wrote the BLE Service part (much more complicated). After that, we wanted to test our new service on our eval kit… but for a weird reason, when we should receive “message 1”, we only receive 4 characters “mess” and then, we was disconnected. We looked for the problem. I think we found it, but there was no more time to change the code and check it.

Then, I decided to update a little our website. If you are reading this blog with attention, their are not a lot of things you will learn, but elsewhere, it would help you to follow us 🙂

See you !


5 comments to Drops will have their PCB !

  • So sad that your Drop doesn’t allow to monitor the battery level… 🙁

    • Blyste

      Actually, our drop allows to monitor the battery level…
      As you see on the screenshot, we have the possibility to link various components thanks to our connector. So, we can for example link VCC of the connector to another pin, which is linked to a ADC pin of the nRF.
      It should work, shouldn’t it ?

  • OK, I meant “natively”! 🙂
    But yes, it should work as long as you ensure that the ADC prescaling is at most 1/2. Which will make the firmware update a little bit difficult, we’ll talk about it this afternoon.

  • Florent

    Well, actually I think you can monitor the battery level without external connection: if you select VDD / 3 or 2 * VDD / 3 as ADC input and VBG (internal 1.2V) as ADC reference, you should be able to get battery voltage. As far as I understand, you don’t use any voltage regulator, so it should be enough to get an estimation of battery level, right?

  • Well actually you’re right, you can indeed select VDD/2 or VDD/3 as ADC input. Thanx for pointing it Flo 🙂