NEBULA BT938 Bluetooth Module Owner's Manual

1.1 Overview
The BT938 Bluetooth module is designed for BLE4.2 communication
based on the CH592 chip. It supports serial transparent
transmission and AT commands. In Bluetooth connection mode, it
operates in transparent transmission mode, while in a disconnected
state, AT commands can configure parameters like advertising
interval and device name.

1.2 Key Features
The key features include UART interface with hardware flow control,
PWM channels, and ADC support for various applications.

1.3 Application Fields
The BT938 module is suitable for IoT and HID applications in
various fields such as smart home devices, fitness equipment,
medical devices, office equipment, and automotive tools.

2. Hardware Highlights

The BT938 module features a QingKe 32-bit RISC-V4C core, GPIO
pins, UART interface, PWM channels, ADC channels, and programmable
TX output power up to +4.5dBm.

3. Electrical Parameters

3.1 Absolute Maximum Ratings

Item	Sym.	Min.	Max	Unit
Supply Voltage	VDD	-0.4	4.2	V
Voltage on input pin	VIN	-0.3	VDD+0.4	V
Output voltage	VOUT	0	VDD	V
Storage temperature range	TStr	-65	150	–
Soldering temperature	TSld	–	260	–

FAQ (Frequently Asked Questions)

Q: What are the recommended operating conditions for the
BT938 module?
A: The recommended operating conditions include a power-supply
voltage between 1.7V to 3.6V and an operating temperature range
from -40°C to 85°C.

Q: Can the GPIO pins of the BT938 module be reconfigured
for specific applications?
A: Yes, the functional pins of the module can be reconfigured
according to specific applications, allowing flexibility in
usage.

Q: What are some common application fields for the BT938
module?
A: The module is commonly used in IoT devices, smart home
applications, fitness equipment, medical devices, office equipment,
and automotive tools due to its versatile features.

Q: How can I switch the BT938 module to Bluetooth
connection mode?
A: When in Bluetooth connection mode, the module automatically
enters transparent transmission mode for data exchange with other
Bluetooth devices.

Q: What is the maximum TX output power supported by the
BT938 module?
A: The module supports programmable TX output power up to +4.5dBm
for reliable wireless communication.

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BT938 Bluetooth Specification
V1.0
1

Version Record

Version
V1.0

Date

Author

Content Initial Release

FCC Statement FCC standards: FCC CFR Title 47 Part 15 Subpart C Section 15.247 PCB antenna with antenna gain 1.2dBi A:
This device complies with part 15 of the FCC Rules. Operation is subject to the following two conditions: (1) This device may not cause harmful interference, and (2) this device must accept any interference received, including interference that may cause undesired operation. B: Any Changes or modifications not expressly approved by the party responsible for compliance could void the user’s authority to operate the equipment. C: Note: This equipment has been tested and found to comply with the limits for a Class B digital device, pursuant to part 15 of the FCC Rules. These limits are designed to provide reasonable protection against harmfu l interference in a residential installation. This equipment generates, uses and can radiate radio frequency energy and, if not installed and used in accordance with the instructions, may cause harmful interference to radio communications. However, there is no guarantee that interference will not occur in a particular installation. If this equipment does cause harmful interference to radio or television reception, which can be determined by turning the equipment off and on, the user is encouraged to try to correct the interference by one or more of the following measures:
Reorient or relocate the receiving antenna. Increase the separation between the equipment and receiver. Connect the equipment into an outlet on a circuit different from that to which the receiver is connected. Consult the dealer or an experienced radio/TV technician for help.
FCC Radiation Exposure Statement
This modular complies with FCC RF radiation exposure limits set forth for an uncontrolled environment. This transmitter must not be co-located or operating in conjunction with any other antenna or transmitter.
If the FCC identification number is not visible when the module is installed inside another device, then the outside of the device into which the module is installed must also display a label referring to the enclosed module. This exterior label can use wording such as the following: Contains Transmitter Module FCC ID: 2BAMT-BT938-2 Or Contains FCC ID: 2BAMT-BT938-2 The devices must be installed and used in strict accordance with the manufacturer’s instructions as described in the user documentation that comes with the product. Any company of the host device which install this modular with modular approval should perform the test of radiated & conducted emission and spurious emission,etc. according to FCC part15B Class B requirement, Only if the test result comply with FCC part 15B Class B requirement then the host can be sold legally. When the module is installed inside another device, the user manual of the host must contain above Paragraphs A, B, and C warning statements.

1.Introduction
1.1Overview
The BT938 Bluetooth module is a BLE4.2 module designed based on the CH592 chip. It supports serial transparent transmission and AT commands. When in Bluetooth connection mode, the module enters transparent transmission mode. When in the disconnected state, AT commands can be used to configure module parameters such as advertising interval and device name.
1.2 Key Features
Completed with Bluetooth Low Energy 5.4 standard RF power class II, ultra-low power consumption with microampere-level working current Ultra-low voltage operation, compatible with 3V button batteries Multiple interfaces: GPIO/UART/I²C/SPI/USB RoHS compliant, lead-free manufacturing process Dimensions: 16.5mm (L) × 13.3mm (W) BT938-1 module without shielding case, BT938-2 module with shielding case
1.3 Application Fields
The BT938 module is designed for IoT and HID (Human Interface Devices) applications, including but not limited to:
Smart home devices (access control, LED lighting control) Fitness equipment (treadmills, exercise machines) Medical devices (pulse meters, blood pressure monitors) Home entertainment devices (remote controls, toys) Office equipment (printers, scanners) Commercial equipment (cash registers, QR code scanners) Mobile peripherals (for phones, tablets, and computers) Automotive equipment (automotive diagnostic tools) RF and infrared remote controls
1.4 Hardware Highlights
QingKe 32-bit RISC-V4C core Supports up to 19 GPIO pins in addition to serial communication pins UART interface with hardware flow control and dual-wire debug interface 4 channels of 26-bit PWM and 8 channels of 8-bit PWM 12 channels of 12-bit ADC supporting differential and single-ended inputs
3

Programmable TX output power up to +4.5dBm
Hardware connection diagram

BTC SLEEP H Active

GPIO GPIO GPIO

The functional pins of the module can be reconfigured according to specific applications. For example, PB3 can be set as a Bluetooth control pin (BTC) to switch other devices on/off, and PA1 can be configured as a low-power control wake-up pin (P_SLEEP) to wake up the Bluetooth module or perform other functions.

2. Electrical Parameters

2.1 Absolute Maximum Ratings

Item

Sym.

Supply Voltage

VDD

Voltage on input pin Output voltage Storage temperature range Soldering temperature

VIN VOUT TStr TSld

Min.
-0.4
-0.3 0
-65 –

Max
4.2
VDD+0.4 VDD 150 260

Unit

Conditions

VDD33 and VIO33 pin V must have the same
voltage

–

2.2 Recommended Operating Conditions

Item

Sym.

Min

Typ.

Power-supply voltage Operating temperature range

VDD

1.7

3.3

TOpr

-40

–

Max

Unit

Conditions

3.6

–

2.3 Current Consumption (VDD = 3.3 V, T= 25)

Mode

Sym. Min Typ. Max Unit

Conditions

TX
RX Idle Mode Pause Mode Sleep Mode
Power Down Mode

ITx
IRx IIdle Ipause IDeep1
IDown

– 12.9 –

– 11.5

–

1.1

1.3-

– 180

–

– 0.7

–

1.7

—

4.5dBm Continuous Tx transmission

mA Continuous Rx reception
mA Clock enabled
A Clock disabled PMU+Core+PAM2K
A GPIO WakeupW/O RTC PMU OnlyReset after
A GPIO WakeuoW/O RTC

3.Module Pins and Descriptions

NO.

GND

Groud

VCC

3.3V Power Supply

General-purpose bidirectional digital I/O, RXD3 (UART3 serial data input), AIN0 (ADC

PA4

analog signal input channel 0)

General-purpose bidirectional digital I/O, TXD3 (UART3 serial data output), AIN1

PA5

(ADC analog signal input channel 1)

General-purpose bidirectional digital I/O, MISO (SPI0 serial data, master input/slave

PA15 output), RXD0_ (UART0 RXD0 mapping), AIN5 (ADC analog signal input channel 5),

sleep mode (pull high to enter sleep)

General-purpose bidirectional digital I/O, MOSI (SPI0 serial data, master output/slave

PA14

input), TXD0_ (UART0 TXD0 mapping), AIN4 (ADC analog signal input channel 4)

General-purpose bidirectional digital I/O, SCK0 (SPI0 serial clock, master output/slave

PA13

input), PWM5 (PWM output channel 5), AIN3 (ADC analog signal input channel 3)

General-purpose bidirectional digital I/O, SCS (SPI0 slave select input, active low),

PA12

PWM4 (PWM output channel 4), AIN2 (ADC analog signal input channel 2)

General-purpose bidirectional digital I/O, RXD1 (UART1 serial data input), AIN12 (ADC

PA8

analog signal input channel 12), UART programming RX

General-purpose bidirectional digital I/O, TMR0 (Timer 0 capture input 0 and PWM

PA9

output channel 0), TXD1 (UART1 serial data output), AIN13 (ADC analog signal input

channel 13), UART programming TX

General-purpose bidirectional digital I/O, TCK (two-wire emulation debug interface

serial clock input), MISO_ (SPI0 MISO mapping), SCL (I2C serial clock, master

PB15

output/input/slave input), DTR (UART0 MODEM output signal, data terminal ready),

Debug

General-purpose bidirectional digital I/O, TIO (emulation debug interface serial data

I/O with internal pull-up), MOSI_ (SPI0 MOSI mapping), SDA (I2C serial data, open-

PB14

drain output/input), PWM10 (PWM output channel 10), DSR (UART0 MODEM input

signal, data set ready), Debug

General-purpose bidirectional digital I/O, RXD0 (UART0 serial data input), PWM7

PB4

(PWM output channel 7), UART interface RX

General-purpose bidirectional digital I/O, TXD0 (UART0 serial data output), PWM9

PB7

(PWM output channel 9), UART interface TX

General-purpose bidirectional digital I/O, SCK0_ (SPI0 SCK mapping), TXD1_ (UART1

PB13

TXD1 mapping), DCD_ (UART0 DCD mapping)

General-purpose bidirectional digital I/O, SCS_ (SPI0 SCS mapping), RXD1_ (UART1

PB12

RXD1 mapping), RI_ (UART0 RI mapping)

General-purpose bidirectional digital I/O, UD+ (USB D+ data line), TMR2_ (Timer 2

PB11

TMR2 mapping)

General-purpose bidirectional digital I/O, UD- (USB D- data line), TMR1_ (Timer 1

PB10

TMR1 mapping)

General-purpose bidirectional digital I/O, TMR3 (Timer 3 capture input 3 and PWM

PB22

output channel 3), RXD2 (UART2 serial data input), UART programming Boot

4. Module Mechanical Dimensions

BT938-1 8

BT938-2

5. Module Circuit Diagram

6.BOM

Part Name Capacitor

PCB assembly parts Description
ROHS 1F/10V, 0201, X5R, ±10%

QTY. Unit 3

Capacitor

ROHS 0.1F/10V, 0201, X5R, ±10%

Resistor

ROHS 0R 0201, +/-5%

ESD diode ESD Protection Diode SESDB5V0DNG2 DFN1006-2

Bluetooth IC QFN28 4*4 CH592F QFN28

Crystal

32 MHz 12pF 20ppM 2016 Package

PCB

ROHS double-sided FR4, thickness 0.8mm, dimensions 16.5mm×13.3mm

Shielding case Nickel silver, thickness 0.2mm, laser-etched QR code 1

Remark C3,C6,C7
C8 L1 D1 U1 Y1
Main PCB
Same as BT628

7. Module Installation Requirements
The BT638 module operates at 2.4GHz, so its placement on the product is critical to antenna performance. Avoid the following: Metal enclosures can shield RF signals and prevent the module from working properly. Keep internal metal components away from the module’s RF section. Place the module around the edges of the mainboard, with the antenna part near the edge or corner. Avoid copper pours or traces under the antenna. It’s recommended to extend the antenna area outward from the main PCB to position the module as close to the edge as possible.
Module Installation Position Diagram
ABStrongly recommendedC, D, EAcceptable but not recommended FIf the main PCB lacks space, maintain a 15mm gap between the module and the main PCB
10

8Module Reflow Soldering Recommendations

Module Welding Guidance (Refer to IPC/JEDEC Industry Standard)

Preheating process Rump up rate From TS (25 Room temperature)to TL Preheating temperature
Preheating temperature TL
Preheat time Soldering Heating rate for solderingfrom (Preheating temperature) TL to TP Peak temperature) Tolerance of TP Duration of TP Duration of soldering Above 217) Ramp down rate

2/s (Max) 150 (Min.) 175 (Typ.) 200 ( Max.)
60~120 s
1~2/s 245 +0/-5
10 s 40~60 s 2.5/s (Max.)

The reflow curve recommended

Documents / Resources

NEBULA BT938 Bluetooth Module [pdf] Owner's Manual
BT938-2, 2BAMT-BT938-2, 2BAMTBT9382, BT938 Bluetooth Module, BT938, Bluetooth Module, Module

References

User Manual

NEBULA BT938 Bluetooth Module Owner’s Manual

BT938 Bluetooth Module

Specifications

Product Usage Instructions

1. Introduction

2. Hardware Highlights

3. Electrical Parameters

FAQ (Frequently Asked Questions)

Documents / Resources

References

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