EasyVR 3 User Manual Release 1.0.14 www.veear.
www.veear.eu Table of Contents EasyVR 3 Module ............................................................................................................. 5 Product Description ........................................................................................................5 EasyVR 3 Features .......................................................................................................5 Technical specifications ..............................................................................
www.veear.eu Use custom sound playback .......................................................................................... 40 Read sound table ...................................................................................................... 40 Built-in Command Sets ................................................................................................... 41 Error codes .................................................................................................................
www.veear.eu Document History Information Revision Date Description 1.0 2015/01/27 Initial draft 1.0.3 2015/02/09 New drawings and updated descriptions 1.0.4 2015/03/19 Added new pictures and minor updates 1.0.5 2015/03/25 Updated pictures and quick-start sections 1.0.6 2015/03/30 Added programming and library chapters Added PC software description Updated pictures and layout 1.0.7 2015/03/31 Minor corrections 1.0.
www.veear.eu EasyVR 3 Module Product Description EasyVR 3 is a multi-purpose speech recognition module designed to easily add versatile, robust and cost effective speech recognition capabilities to almost any application. The EasyVR 3 module can be used with any host with an UART interface powered at 3.3V – 5V, such as PIC and Arduino boards.
www.veear.eu Technical specifications MIC R4 D2 GPIO IO1 IO2 IO3 IO4 IO5 IO6 SP+ SPVM MIC RET VDD XM DE TX RX RST MIKROBUS 3V3 GND AUDIO SPEAKER MISC MIKROBUS CABLES 5V GND 6 4 2 5 3 1 PWR SEL QUICK USB D1 MISC ADAPTER MISC The outer headers J1 and J2 are the mikroBUS™ interface connectors, providing selectable 3.3V/5V power input to the module and voltage translated digital I/O lines, including: UART receive/transmit lines and control pins.
www.veear.eu Pin assignment Group Name J1 ● MIKROBUS J2 ● ● ● GPIO AUDIO J3 J4 J5 CABLES J6 ● ADAPTER User Manual (1.0.14) J7 Number Pin Type Description 1 - - (Not connected) 2 RST I Active low asynchronous reset (internal pull-up) 3-6 - - (Not connected) 7 3V3 I 3.3V DC power input 8 GND - Ground 1 XM I Boot select (internal pull-down) 2 DE O (Reserved) 3 TX O Serial Data Transmit 4 RX I Serial Data Receive 5-6 - - (Not connected) 7 5V I 5.
www.veear.eu Note: The General Purpose I/O lines (J3.1-6) are at nominal 3.0VDC level.
www.veear.eu Recommended Operating Conditions Symbol 5V 3V3 5V_P Ta Parameter DC Power Input (Host) = VSEL DC Power Input (Programming cable) Ambient Operating Temperature Range Min Typ Max Unit 3.15 5.0 5.5 V 3.15 3.3 5.5 V 4.0 5.0 5.5 V 0 25 70 °C Min Typ Max Unit Power Supply Requirements Symbol Parameter ISLEEP Sleep current (VSEL = 5.0V) 6 mA IOPER Operating current (VSEL = 5.
www.veear.eu These are applicable to pin RX_P. Symbol Parameter Min Typ Max Unit VOH Output High Voltage (IOH = -5 mA) 2.4 3.0 V VOL Output Low Voltage (IOL = 8 mA) 0.0 0.6 V These are applicable to pins IO1 – IO6. Symbol Parameter Min Typ Max Unit VIH Input High Voltage 2.4 3.0 3.3 V VIL Input Low Voltage -0.1 0.0 0.75 V IIL Input Leakage Current (0 < VI < 3V, Hi-Z Input) <1 10 µA RPU Pull-up Resistance VOH Output High Voltage (IOH = -5 mA) 2.4 3.
www.veear.eu Microphone The microphone provided with the EasyVR 3 module is an omnidirectional electret condenser microphone (Horn EM9745P-382): Sensitivity -38dB (0dB=1V/Pa @1KHz) Load Impedance 2.2K Operating Voltage 3V Almost flat frequency response in the range 100Hz – 20kHz The microphone circuit is optimized for use at ARMS_LENGTH (default, about 60cm) or FAR_MIC distance settings. If you use a microphone with different specifications the recognition accuracy may be adversely affected.
www.veear.eu Examples 1) The optimal gain resistance for the bundled microphone at ARMS_LENGTH distance is: – Use the closest standard 5% resistor to Rs. In this example, it would be 1.1 kΩ. The EasyVR uses a 1.2 kΩ resistor to allow use of “FAR” settings without replacing the internal resistor. Sometimes you might also need to compensate some gain loss for a voltage lower than the microphone ratings (using a larger resistor value sets a higher input gain).
www.veear.eu auditory noises produced by handling or jarring the device from being “picked up” by the microphone. Such extraneous noises can reduce recognition accuracy. GOOD BAD absorbent material fastened directly 4. Distance - If the microphone is moved from 15 cm to 30 cm from the speaker’s mouth, the signal power decreases by a factor of four. The difference between a loud and a soft voice can also be more than a factor of four.
www.veear.eu General Purpose I/O Since the EasyVR communication interface takes two pins of the host controller, a few spare I/O pins are provided, which can be controlled with the communication protocol, to get those pins back for basic tasks, such as lighting an LED or reading a switch. The six I/O pins IO1–IO6 are connected directly to the embedded microcontroller on the EasyVR module, so they are referenced to the internal 3.0V regulated power supply VDD.
www.veear.eu IOn IOn optional filter Isolated IN IOn SWITCH 5V IN optocoupler I/O pin connected to a switch (or switching sensor) I/O pin connected 5V source (such as MCU output pin) I/O pin with isolated input (for safety circuits) All these circuits assume the EasyVR pin has been configured with an internal pull-up (passive components value can be adjusted to account for weak or strong pull-up).
www.veear.eu Quick start for using the module EasyVR 3 as a Development Board The QuickUSB serial adapter cable can be used to program voice commands and sound outputs into an EasyVR 3 module and quickly test it from your PC. Just connect the microphone and an 8Ω speaker to the module, plug-in the adapter cable and you are ready to go. The EasyVR 3 boot mode is managed automatically through the serial handshake lines, so you don’t need to set any jumper. How to get started 1. 2. 3. 4.
www.veear.eu Serial Adapter Interface Connector J7 is a 6-pin socket specifically designed for the QuickUSB serial adapter cable, but another adapter may also be used provided that it uses the same connector type, pin assignment and electrical specifications. Pin Name Type Notes 1 RX_P I Adapter should have TTL/LVTTL compatible inputs (VIH = 2.0V) 2 RTS_P O Adapter outputs can have 3.
www.veear.eu EasyVR Shield 3 for Arduino Product description The EasyVR Shield 3 is an adapter board for the EasyVR 3 module, designed to simplify its use among the Arduino community. The Shield is compatible with any Arduino board using UNOR3 Shield headers, running at either 3.3V or 5V levels, by using the IOREF pin to select the EasyVR operating voltage. It is also backward compatible with earlier Arduino boards that don’t have the IOREF pin, which are using 5V I/O levels by default.
www.veear.eu Technical specifications Board overview MODE JUMPER ARDUINO ANALOG IOREF RESET 3V3 5V GND GND VIN A0 A1 A2 A3 A4 A5 3.5mm JACK LINE OUT MIC SDA SCL AREF GND 13 12 11 10 9 8 7 6 5 4 3 2 1 0 ARDUINO DIGITAL IO1 IO2 IO3 IO4 IO5 IO6 ARDUINO DIGITAL ARDUINO POWER EASYVR GPIO LED SW HW PC UP LEO PROG SPEAKER EASYVR AUDIO TX – D13 D9 – TX RX – D12 D8 – RX SW SERIAL PINS SW SERIAL PINS (Top View) (Detail – Bottom View) User Manual (1.0.
www.veear.eu Pin assignment Group Pin Description ● ARDUINO HEADERS - Arduino UNO-R3 Shield interface, pass-through connectors (Pins 0-1 are in use when J12 is set to UP, PC, HW or LEO) (Pins 12-13 or 8-9 are in use when J12 is set to SW) ● ● EASYVR AUDIO - Audio cables connectors of the EasyVR 3 module (microphone and speaker) LINE OUT - 3.
www.veear.eu Mode Jumper settings This jumper selects the operating mode of the EasyVR Shield and it can be placed in one of four positions: o o o o o SW – Software Serial mode Use it for controlling the EasyVR module from your Arduino sketch through a software serial port (using pins 12-13). You can also connect the EasyVR Commander in this mode, provided that the running sketch implements bridge mode (see the Arduino library examples).
www.veear.eu Quick start guide for using the Shield Follow these few steps to start using your EasyVR Shield 3 and Arduino: 1. Insert the EasyVR Shield on top of your Arduino board 2. If you want audio output, either wire an 8Ω speaker into the SPEAKER connector (J5) on the EasyVR module or connect headphones or amplified speakers to the LINE OUT 3.5mm audio jack on the Shield 3. Connect the supplied microphone to the MIC connector (J6) on the EasyVR module 4.
www.veear.eu Figure 2 - Finding example sketches for the EasyVR With Arduino 2009 – Uno – Mega Test the Shield with Arduino 1. 2. 3. 4. Set the Mode jumper (J7) in the SW position Open the example sketch TestEasyVR from your IDE menu “File” > “Examples” > “EasyVR” Upload the sketch and open the “Serial Monitor” window See comments on top of the sketch for usage details Test the Shield with the EasyVR Commander 1. Make sure the Mode jumper (J7) is in the PC position 2.
www.veear.eu EasyVR Programming Communication Protocol Introduction Communication with the EasyVR module uses a standard UART interface compatible with 3.3-5V TTL/CMOS logical levels, according to the powering voltage VCC. A typical connection to an MCU-based host: EasyVR Host MCU VCC GND ERX ETX 3.3V – 5V GND TX RX The initial configuration at power on is 9600 baud, 8 bit data, No parity, 1 bit stop. The baud rate can be changed later to operate in the range 9600 - 115200 baud.
www.veear.eu Arguments Mapping Command or status messages sent over the serial link may have one or more numerical arguments in the range -1 to 31, which are encoded using mostly characters in the range of uppercase letters.
www.veear.eu Command Details This section describes the format of all the command strings accepted by the module. Please note that numeric arguments of command requests are mapped to upper-case letters (see above section). Some commands share the same lower case letter, because there were no command identifiers available when the protocol has been expanded, but the first argument is used to discriminate.
www.veear.eu CMD_LEVEL 'v' (76h) [1] Set SD level Strictness control setting (1-5): 1 = easy 2 = default 5 = hard A higher setting will result in more recognition errors.
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www.veear.eu CMD_PLAY_RP 'p' (70h) Play a message recording [1] Fixed to (-1) [2] Message index (0-31) [3] Playback options (bit-mask): Bit 2 (4) = playback speed (0 = normal, 1 = fast) Bit 1-0 (0-3) = volume attenuation (0 = normal, 1 = -2.2dB, 2 = -4.5dB, 3 = -6.
www.veear.eu CMD_SERVICE + SVC_VERIFY_SD '~' (7Eh) Service protocol expansion 'V' (56h) Verify command raw data [1] Group index (0 = trigger, 1-15 = generic, 16 = password) [2] Command position (0-31) Expected replies: STS_SUCCESS, STS_RESULT, STS_SIMILAR, STS_ERROR Status Details Replies to commands follow this format. Please note that numeric arguments of status replies are mapped to upper-case letters (see the related section).
www.veear.eu STS_INVALID 'v' (76h) Invalid command or argument In reply to: Any invalid command or argument STS_TIMEOUT 't' (74h) Timeout expired In reply to: CMD_RECOG_SI, CMD_RECOG_SD, CMD_TRAIN_SD STS_LIPSYNC 'l' (6Ch) [1-N] Lip-sync streaming data Mouth position (0-31): 0 = fully closed 31 = fully open Note: New values are available at request around every 27ms until timeout occurs or command is interrupted. A new status is sent at the end (see STS_TIMEOUT, STS_INTERR).
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www.veear.eu Communication Examples These are some examples of actual command and status characters exchanged with the EasyVR module by host programs and the expected program flow with pseudo-code sequences. The pseudo-instruction SEND transmits the specified character to the module, while RECEIVE waits for a reply character (a timeout is not explicitly handled for simple commands, but should be always implemented if possible).
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www.veear.eu Read used command groups # request mask of groups in use SEND 'm' IF NOT RECEIVE = 'k' THEN ERROR # read mask to 32 bits variable # in 8 chunks of 4 bits each SEND ' ' mask = (RECEIVE – 'A') SEND ' ' mask = mask + (RECEIVE – 'A') * 24 SEND ' ' mask = mask + (RECEIVE – 'A') * 28 ...
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www.veear.eu Built-in Command Sets In the tables below a list of all built-in commands for each supported language, along with group index (trigger or word set), command index and language identifier to use with the communication protocol.
www.veear.eu Error codes Below the list of the most useful error codes that may be returned by training or recognizing commands.
www.veear.eu Protocol header file This file “protocol.h” can be used with applications written in the C language. You can download a recent copy from the VeeaR website.
www.veear.eu #define STS_TOKEN 'f' // received sonicnet token <1-2> #define STS_MESSAGE 'g' // message status <1> (0=empty, 4/8=bits format), length <2-7> // protocol arguments are in the range 0x40 (-1) to 0x60 (+31) inclusive #define ARG_MIN 0x40 #define ARG_MAX 0x60 #define ARG_ZERO 0x41 #define ARG_ACK 0x20 // to read more status arguments #endif //PROTOCOL_H A better source of information and a reference protocol implementation for the C/C++ language can be found in the Arduino Library source.
www.veear.eu EasyVR Arduino Library The EasyVR library implements the serial communication protocol to manage the EasyVR module and the EasyVR Shield from Arduino boards and controllers and it enables easy access to all the EasyVR features. Installation To install the EasyVR library on your Arduino IDE use the menu Sketch > Import Library ... > Add Library and open the released zip archive.
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www.veear.eu Enumerator EASY Lowest value, most results reported NORMAL Typical value (default) HARD Slightly higher value, fewer results reported HARDER Higher value, fewer results reported HARDEST Highest value, fewest results reported enum TrailingSilence Trailing silence settings used for recognition of built-in words or custom grammars (including the mixed trigger group), in a range from 100ms to 875ms in steps of 25ms.
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www.veear.eu ATTEN_NONE ATTEN_2DB2 ATTEN_4DB5 ATTEN_6DB7 No attenuation (normalized volume) Attenuation of -2.2dB Attenuation of -4.5dB Attenuation of -6.
www.veear.eu enum BridgeMode Type of Bridge mode requested Enumerator BRIDGE_NONE Bridge mode has not been requested BRIDGE_NORMAL Normal bridge mode (EasyVR baudrate 9600) BRIDGE_BOOT Bridge mode for EasyVR bootloader (baudrate 115200) Constructor & Destructor Documentation EasyVR (Stream & s) Creates an EasyVR object, using a communication object implementing the #Stream interface (such as #HardwareSerial, or the modified #SoftwareSerial and #NewSoftSerial).
www.veear.eu bool setMicDistance (int8_t dist) Sets the operating distance of the microphone. This setting represents the distance between the microphone and the user's mouth, in one of three possible configurations. Parameters: dist (1-3) is one of values in Distance Return values: true if the operation is successful bool setKnob (int8_t knob) Sets the confidence threshold to use for recognition of built-in words or custom grammars.
www.veear.eu Return values: true if the operation is successful bool changeBaudrate (int8_t baud) Sets the new communication speed. You need to modify the baudrate of the underlying Stream object accordingly, after the function returns successfully. Parameters: baud is one of values in Baudrate Return values: true if the operation is successful bool sleep (int8_t mode) Puts the module in sleep mode.
www.veear.eu Return values: true if the operation is successful bool eraseCommand (int8_t group, int8_t index) Erases the training data of a custom command. Parameters: group index (0-16) is the target group, or one of the values in #Groups (0-31) is the index of the command within the selected group Return values: true if the operation is successful bool getGroupMask (uint32_t & mask) Gets a bit mask of groups that contain at least one command.
www.veear.eu bool dumpGrammar (int8_t grammar, uint8_t & flags, uint8_t & count) Retrieves the contents of a built-in or a custom grammar. Command labels contained in the grammar can be obtained by calling getNextWordLabel() Parameters: grammar flags count (0-31) is the target grammar, or one of the values in Wordset is a variable that holds some grammar flags when the function returns. See GrammarFlag is a variable that holds the number of words in the grammar when the function returns.
www.veear.eu Note: The module is busy until recognition completes and it cannot accept other commands. You can interrupt recognition with stop(). bool hasFinished () Polls the status of on-going recognition, training or asynchronous playback tasks. Return values: true if the operation has completed int8_t getCommand () Gets the recognised command index if any.
www.veear.eu Return values: true is a conflict occurred during training. To know what caused the conflict, use getCommand() and getWord() (only valid for triggers) bool isMemoryFull () Retrieves the memory full indicator (only valid after addCommand() returned false). Return values: true if a command could not be added because of memory size constaints (up to 32 custom commands can be created) bool isInvalid () Retrieves the invalid protocol indicator.
www.veear.eu void sendTokenAsync (int8_t bits, uint8_t token) Starts immediate playback of a SonicNet token. Manually check for completion with hasFinished(). Parameters: bits token (4 or 8) specifies the length of trasmitted token is the index of the SonicNet token to play (0-255 for 8-bit tokens or 015 for 4-bit tokens) Note: The module is busy until playback completes and it cannot accept other commands. You can interrupt playback with stop().
www.veear.eu Parameters: index volume is the index of the target sound in the sound table (0-31) may be one of the values in SoundVolume Return values: true if the operation is successful Note: To alter the maximum time for the wait, define the EASYVR_PLAY_TIMEOUT macro before including the EasyVR library.
www.veear.eu Parameters: wait specifies whether to wait until the operation is complete (or times out) Return values: true if the operation is successful Note: It will take some time for the whole process to complete (EasyVR3 is faster) and it cannot be interrupted. During this time the module cannot accept any other command. The sound table and custom grammars data is not affected. bool resetMessages (bool wait = true) Empties internal memory used for messages only. Commands/groups are not affected.
www.veear.eu void recordMessageAsync (int8_t index, int8_t bits, int8_t timeout) Starts recording a message. Manually check for completion with hasFinished(). Parameters: index bits timeout (0-31) is the index of the target message slot (8) specifies the audio format (see MessageType) (0-31) is the maximum recording time (0=infinite) Note: The module is busy until recording times out or the end of memory is reached. You can interrupt an ongoing recording with stop().
www.veear.eu Parameters: threshold timeout (0-1023) is a measure of the strength of the input signal below which the mouth is considered to be closed (see LipsyncThreshold, adjust based on microphone settings, distance and background noise) (0-255) is the maximum duration of the function in seconds, 0 means infinite Return values: true if the operation is successfully started bool fetchMouthPosition (int8_t & value) Retrieves the current mouth position during lip-sync.
www.veear.eu Parameters: port is the target serial port (usually the PC serial port) Return values: non zero if bridge mode should be started Note: The EasyVR Commander software can request bridge mode when connected to the specified serial port, with a special handshake sequence. void bridgeLoop (Stream & port) Performs bridge mode between the EasyVR serial port and the specified port in a continuous loop. It can be aborted by sending a question mark ('?') on the target port.
www.veear.eu EasyVR Commander The EasyVR Commander software can be used to easily configure your EasyVR module connected to your PC through a QuickUSB cable, an adapter board, or by using the microcontroller host board with the provided “bridge” program (available for ROBONOVA controller board, Arduino 2009/UNO, Parallax Basic Stamp). You can define groups of commands or passwords and generate a basic code template to handle them.
www.veear.eu Wordset - built-in set of SI commands (for instance in Figure 3 above, the Wordset 1 is selected) Grammar – custom set of SI commands (created with Quick T2SI Lite software). Speech Recognition The recognition function of the EasyVR works on a single group at a time, so that users need to group together all the commands that they want to be able to use at the same time.
www.veear.eu Figure 5 – Alert dialog in case of training conflicts The software will also alert if a command is too similar to an existing one by specifying the index of the conflicting command in the "Conflict" column. For example, in the following Figure 6 the command "TEST_CMD_ONE" sounds too similar to "TEST_CMD_ZERO" (i.e. they have been trained with a similar pronunciation).
www.veear.eu Note: If you want to re-train a command you need to erase the previous training first. Note: "Vocal passwords" (Group 16) are much more sensitive to environment noise and distance from the microphone: be sure to train and to verify the password in similar conditions. Recognition Settings The module comes programmed with some default settings that can affect voice recognition. These parameters can be altered in those case where the default values do not offer the best performance.
www.veear.eu good, but then you may also lose a few correct results. So, in the end, you need to find the best compromise. Ticking “Use “Fast” SD/SV Recognition” will use a faster algorithm for SD and SV recognition. In a similar way, faster SI recognition can be obtained by lowering the Trailing Silence (default is 400 ms).
www.veear.eu Testing SonicNetTM Another feature available from the “Tools” menu is the “SonicNet”, a wireless communication protocol based on transmission and detection of special sequences of tones, called “tokens”. Two kinds of tokens can be selected: a short version, with up to 16 different tokens, and a long version that provides up to 256 tokens.
www.veear.eu A pop-up window will display the current state of token detection: Tokens may also be transmitted from the module with the “Send” button. An optional delay parameter can be used to indicate that the token will be mixed with the next sound played from the Soundtable, after the specified amount of time since the playback begins. In this case the SonicNet dialog will close to let you choose a sound to play back.
www.veear.eu Real-Time Lip-Sync Another feature available from the “Tools” menu is the “Real-Time Lip-Sync”. In fact, starting from Firmware revision 4, you can use this feature to let your “animatronic” characters “speak” moving their lips. Clicking on “Real-Time Lip-Sync” will open the following window: Figure 10 - Lip-Sync interface with animated mouth If you click on “Start” the virtual mouth on the window will start moving in sync with your voice.
www.veear.eu Using Custom Data Sound Table The EasyVR module can play one of the sounds or sentences saved on its internal flash memory. A predefined “beep” sound is also always available, even when no sounds have been downloaded to the module. The custom sounds are organized in a so-called “sound table” that users can prepare and build with the special QuickSynthesisTM tool. Please refer to this application’s own manual for details about the creation of a sound table.
www.veear.eu Figure 11 - External tool for creating a Soundtable Note: Only one Soundtable can be downloaded to the EasyVR module, so make sure you include all the sounds you want to use in a single project. Speaker Independent Custom Vocabularies The set of built-in Speaker Independent recognition vocabularies can be expanded with custom grammars, that you can create with the QuickT2SITM tool (a separate license is required to use the software).
www.veear.eu Figure 12 - External tool for custom vocabularies Several projects can also be combined together if they are using the same acoustic model (language data) using the Acoustic Model Combiner included with the tool. This is useful if you have many command vocabularies, in order to save space in the EasyVR memory. Updating Custom Data Once the sound table and/or custom recognition grammars have been created, they can be processed by the EasyVR Commander and downloaded to the module.
www.veear.eu Figure 13 - Interface to build and download custom data The download process will connect at a higher speed to the EasyVR module, so the “bridge” program running on your host device might not work (in particular Robonova and Basic Stamp cannot be used for this purpose) and you might need a true “serial adapter”. The full speed used is 230400 bps, but the option “Slow transfer” can be used to reduce it to 115200, for better compatibility with slower serial adapters 6.
www.veear.eu Message Recording Starting from firmware Revision 1 of the EasyVR 3 module, it's possible to record up to 32 messages. The communication protocol and Arduino library have been updated accordingly (see related chapters). The first time you update the module with a firmware with message recording capability, the serial flash memory of the module has to be formatted.
www.veear.eu Updating Firmware The EasyVR firmware can be updated in a similar way to custom data by using the command “Update Firmware...” from the “Help” menu. Note that you must first disconnect from the module and do the steps required to start it in “boot-mode” (see the section Flash Update). Firmware files can be found in the EasyVR Commander installation folder (default C:\Program Files (x86)\VeeaR\EasyVR Commander), for instance file “EasyVR3_FW_Rev0.EVRFW” is the EasyVR 3 firmware Revision 0.
www.veear.eu QuickUSB Adapter Cable Product Description The QuickUSB is an USB-to-UART adapter cable, easy to use and supported on all the major operating systems. It plugs into a standard USB port and brings all the UART signals to a convenient 6-pin 2mm pitch female connector (Hirose DF11 Series). QuickUSB Features USB 2.0 Full Speed interface Full UART (RX/TX and RTS/CTS) at 3.3V Data transfer rates from 300 bps to 3 Mbps Extended operating temperature range: -40°C to 85°C Cable Length: 1.
www.veear.eu Operating Conditions Symbol VCC Ta Parameter Min Typ Max Unit DC Power Output (VBUS) * 4.5 5.0 5.5 V Ambient Operating Temperature Range -40 25 85 °C Typ Max Unit (*) Output current might be limited by USB Host and internal adapter settings Electrical Characteristics These are applicable to pins RXD, CTS. Symbol Parameter Min VIH Input High Voltage 1.5 3.3 V VIL Input Low Voltage 0.0 1.0 V These are applicable to pin TXD, RTS.
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