BLE doesn't work in the custom board of NRF52840

[salvatore_]

Hi, 

I recently started using Nordic microcontrollers and I have designed a custom board based on nRF52840 and its works except for Bluetooth.

First of all, I'm using vscode+zephyr to program the board, and the firmware I'm using is a sample firmware "peripheral_uart".

1. First I tried to upload the firmware on nrf52840DK and it works properly! - I see the device via the nRF connect smartphone app 
2. Next, I upload  the firmware onto the custom board and...
   1. The firmware is uploaded correctly.
   2. UART connection(TX[P0.14]-RX[P0.09]) OK!
   3. All other gpios are working
   4. Log print "Bluetooth initialized" - but if I try to search for the device with the nRF connect smartphone app, I can't find it

I have done several tests, both hardware(HF crystal is correctly mounted), and software. I've tried resoldering the board but nothing still doesn't work. I have been using these microcontrollers for a short time, so my little experience does not help me solve the problem.

Schematic:

[Bendik Heiskel]

Hi,

There is no antenna matching circuit in your schematic. Ignion recommends using a pi matching network for this antenna, as the antenna performance is dependent on the board size/shape and nearby components. Without this matching network the antenna may not be tuned correctly for the 2.4GHz frequency band, and the radiated power can be very low. Ignion can help you with selecting the correct components/values for the matching network.

The 32MHz crystal frequency accuracy must also be within 40ppm for the radio to be compatible with BLE. If the crystal is loaded incorrectly the frequency offset of the carrier may be outside this 40 ppm limit. What is the part number for the 32MHz crystal you are using?

 

Best regards,

Bendik

[salvatore_]

Hi, 

Thank you for your quick reply.

1. The pi network is in the updated wiring diagram and I don't think that is the problem.

2. 32MHz crystal part number: C648963 https://lcsc.com/product-detail/Crystals_HD-7D032000M01_C648963.html

Best,

Salvatore

[Bendik Heiskel]

salvatore_ said:

1. The pi network is in the updated wiring diagram and I don't think that is the problem.

Are you referring to C3, L1 and C7?

These are the radio matching/filtering circuit, they can't be used to match the antenna impedance as well.

salvatore_ said:

2. 32MHz crystal part number: C648963 https://lcsc.com/product-detail/Crystals_HD-7D032000M01_C648963.html

This crystal have a rated CL of 12pF. The correct value for C4 and C5 can be calculated using(assuming insignificant trace capacitance):
C= 2*CL - 2*Cpin

The typical pin capacitance(Cpin) for XC1 and XC2 is 3pF. Using this equation a better suited capacitance for C4 and C5 is 18pF.

[salvatore_]

I changed C4 and C5, but the problem is still there. I'm powering and programming the board with nrf52840DK, so I don't think that is the problem. I think the problem is caused by some configuration.

[salvatore_]

If it helps here are the configuration files of the board:

.dts 

// Copyright (c) 2022 Nordic Semiconductor ASA
// SPDX-License-Identifier: Apache-2.0

/dts-v1/;
#include <nordic/nrf52840_qiaa.dtsi>

/ {
	model = "custom_nRF52840";
	compatible = "custom,custom-nrf52840";

	chosen {
		zephyr,sram = &sram0;
		zephyr,flash = &flash0;
		zephyr,code-partition = &slot0_partition;
		zephyr,console = &uart0;
		zephyr,shell-uart = &uart0;

		zephyr,uart-mcumgr = &uart0;
		zephyr,bt-mon-uart = &uart0;
		zephyr,bt-c2h-uart = &uart0;
	};

	leds {
		compatible = "gpio-leds";
		led0: led_0 {
			gpios = <&gpio0 13 GPIO_ACTIVE_HIGH>;
			label = "Green LED 0";
		};
		led1: led_1 {
			gpios = <&gpio0 12 GPIO_ACTIVE_HIGH>;
			label = "Green LED 1";
		};
		led2: led_2 {
			gpios = <&gpio0 15 GPIO_ACTIVE_HIGH>;
			label = "Green LED 2";
		};
		led3: led_3 {
			gpios = <&gpio0 16 GPIO_ACTIVE_HIGH>;
			label = "Green LED 3";
		};
	};

	aliases {
		led0 = &led0;
		led1 = &led1;
		led2 = &led2;
		led3 = &led3;
	};
};

&adc {
	status = "okay";
};

&gpiote {
	status = "okay";
};

&gpio0 {
	status = "okay";
};

&gpio1 {
	status = "okay";
};

&uart0 {
	compatible = "nordic,nrf-uarte";
	status = "okay";
	current-speed = <115200>;
	tx-pin = <14>; //14//6
	rx-pin = <9>; //8
	rts-pin = <0xFFFFFFFF>;
	cts-pin = <0xFFFFFFFF>;
};

&flash0 {
	partitions {
		compatible = "fixed-partitions";
		#address-cells = <1>;
		#size-cells = <1>;

		boot_partition: partition@0 {
			label = "mcuboot";
			reg = <0x0 0xc000>;
		};
		slot0_partition: partition@c000 {
			label = "image-0";
			reg = <0xc000 0x72000>;
		};
		slot1_partition: partition@7e000 {
			label = "image-1";
			reg = <0x7e000 0x72000>;
		};
		scratch_partition: partition@f0000 {
			label = "image-scratch";
			reg = <0xf0000 0xa000>;
		};
		storage_partition: partition@fa000 {
			label = "storage";
			reg = <0xfa000 0x6000>;
		};
	};
};

_defconfig

# Copyright (c) 2022 Nordic Semiconductor ASA
# SPDX-License-Identifier: Apache-2.0

CONFIG_SOC_SERIES_NRF52X=y
CONFIG_SOC_NRF52840_QIAA=y
CONFIG_BOARD_CUSTOM_NRF52840=y

# Enable MPU
CONFIG_ARM_MPU=y

# Enable hardware stack protection
CONFIG_HW_STACK_PROTECTION=y

# Enable RTT
CONFIG_USE_SEGGER_RTT=y

# Enable gpio
CONFIG_GPIO=y

# Enable uart drive
CONFIG_SERIAL=y

# Enable console
CONFIG_CONSOLE=y
CONFIG_UART_CONSOLE=y

# additional board options
CONFIG_GPIO_AS_PINRESET=y

# CONFIG_PINCTRL=y

[Bendik Heiskel]

Since the firmware works correctly on the nRF52840 DK the problem would be with the custom hardware. As I mentioned, if the antenna is not tuned correctly the very little power will be transmitted. If C3, L1 and C7 are the only components between the ANT pin and the antenna, I expect the antenna impedance will not be tune to 50 ohm as is required for good antenna performance.