Custom nrf52832 board

[Jonaswinz]

I want to create a small bluetooth device with the nrf52823 chip. I want to use a lithium battery cell to power the whole circuit and therefore it neet to be low power. On the chip, there are two inputs: one button and the battery voltage detector. There is also a buzzer connected to the chip via a 28v boost circut. I created a schematic with easyeda, but I dont kow if I designed it propertly. Here are my questions:

- does the circuit look right?

- did I pick the right parts?

- am I able to programm the custom board via the DCLK and  SWDIO pins through the nrf52 dk?

- does the battery need a seperate protection circuit?

- how do I design the nrf and ble antenna?

 Schematic_Beep Wallet_V3.2_20191120173356.pdf

BOM_Beep Wallet_20191120173443.csv

Thank you in advice

Jonas

[Kaja]

Hi Jonas,

feedback on the circuitry:
1. There should be 4.7 uF capacitor close the the VDD pin 48.
2. Due to errata 138, and that your not using P0.25 and P0.26, you should ground those pins. 
3. C18 should be 100nF. 
4. C19 should be 100 nF. 
5. C22 must be 100 nF. 
6. Your 32.768 kHz (mark with right freq. in the schematic) has an CL = 6 pF. Therefore c24 and C23 should be = CL*2 - (~5pF) = 8 or 7 pF. 
7. Your 32 MHz crystal has an load capacitance, CL = 10 pF. Then C25 and C26  should be  = CL*2 - 4pF = 16 pF. 

The parts looks fine, we have recommendations

Yes, and with VDD and ground. Can be smart to set up an interface with pin's. See https://devzone.nordicsemi.com/f/nordic-q-a/20536/programming-external-custom-nrf52832-board-using-nrf52-dk

- does the battery need a seperate protection circuit?

 - You can have a look at this: https://devzone.nordicsemi.com/f/nordic-q-a/23534/reverse-current-battery-protection



When it comes to the design:
We have a nice guide
you have our reference design


Antenna design, if you want an easy, low cost antenna you can use our quarter printed monopole antenna for 2.45GHz guide. You can also copy our antennas form our DK's and other designs. But remember to increase the length, so that we have some length for antenna tuning. 

I'm happy to review your layout, when you get started with that. 

Best regards,
Kaja

[Jonaswinz]

Tanks for your helpfull answer. I updated my schematic...

(Schematic_Beep Wallet_V3.2_20191123005247, BOM_Beep Wallet_20191123005257) Files

Do I need a reverse battery protecten, when my battery is soldert?

I actually ment a overcharge, discharge protection. The documentation of the MCP73831 only mentions a "Under-voltage lockout". Do I still need them to protect my battery ?

I am also not sure how to design the right antennas (event though I read the documentaion). Is it ok to use these antennas:

ble: https://easyeda.com/components/2-4-GHZ-PCB-ANTENNA_5d5dd40b0303432aa7e781c8c4bf77e2

nfc: https://easyeda.com/component/NFC_Antenna_Square-b765644c71744487aa366f684ff1e6f5

I am also not quit sure how to calculate the tune capacitors for the nfc antenna.

Sorry for my many questions. Jonas

[Kaja]

Hi Jonas,

I can't see that you uploaded the new design files. Could you try uploading them again?

I have to come back to you on the battery protection. 

Have you made the antenna yourself? 

You are welcome to copy our antennas: find the antenna from the dongle in the HW files, or our quarter wave monopole antenna and our NFC antenna, you find it in the HW files on our nRF52 DK.

We have a white paper explaining tuning of the NFC antenna as well. but you do a rough calculation, and then tune the components. 

I can help you with tuning of the antennas (NFC and BLE), and tuning of the radio matching components. 

I see that this case is public, if you want it to be private, change it to private. 

Best regards,
Kaja

[Kaja]

Hi Jonas, 

when it comes to battery protection I suggest you check with Microchip since they are your PMU vendor. 

The recommendation from us, is what Stian suggested in the link I sent you. 

Best regards,
Kaja

[Jonaswinz]

I updated my circuit the second time.

This time I tried to copy the nrf circuit from the Development Kit (parts are also mostly the same). The only big different here, is the the 32.768 Mhz cristal. The Load Capacitance is 6pf not 9pf (dk). Is that a problem ?

Moreover I designed the ble antenna based on the documentations, but my pcb is only 0.6 - 0.8mm height instead of 1.6mm do I have to worry about that?

I copied the NFC antenna from the development kit.

I also added a battery discharge and overcharge protection.

What do you think about the pcb ?

v3_3.zip

Jonas