Filter By

Availability

Availability

Selections

Selections

Price

Price

  • BDT 0.00 - BDT 230,000.00

Categories

Categories

Brand

Brand

Condition

Condition

Weight

Weight

  • 0 kg - 4,000 kg

Resistor Pack of 5

Resistor Pack of 5

  • Banner

Active filters
  • Categories: 3D Printed
  • Categories: Communication Module
  • Categories: Components
  • Categories: Instruments
  • Categories: Learning Kit
  • Categories: PLC
  • Categories: Programmer

Reference: RBD-0459

S7-300 CPU313C-2DP 6ES7 313-6CE01-0AB0

(0)
Model: S7-300 CPU313C-2DP Part No: 6ES7 313-6CE01-0AB0 Made in Germany SIMATIC S7-300, CPU 313C-2DP COMPACT CPU WITH MPI, 16 DI/16 DO, 3 FAST COUNTERS (30 KHZ), INTEGRATED DP INTERFACE, INTEGRATED 24V DC POWER SUPPLY, 32 KBYTE WORKING MEMORY, FRONT CONNECTOR (1 X 40PIN) AND MICRO MEMORY CARD REQUIRED
BDT 155,000.00
BDT 155,000.00 tax incl.
BDT 155,000.00 tax excl.
BDT 155,000.00 tax excl.
BDT 155,000.00 tax incl.
BDT 155,000.00 tax incl.
BDT 0.00 Tax
BDT 155,000.00 tax excl.
BDT 155,000.00 tax excl.
BDT 0.00 Tax
BDT 155,000.00 tax incl.
More
Last items in stock
In stock: 2

Reference: RBD-0264

Brand: SparkFun Electronics

Lockitron Mechanical Assembly

(0)
Lockitron Mechanical Assembly The Lockitron Mechanical Assembly from SparkFun is a perfect solution for the DIY home automation or Internet of Things (IoT) enthusiast, whether you want to make your life easier by not awkwardly fumbling with keys or add some extra security in your home with three-factor authentication.
BDT 6,000.00
BDT 6,000.00 tax incl.
BDT 6,000.00 tax excl.
BDT 6,000.00 tax excl.
BDT 6,000.00 tax incl.
BDT 6,000.00 tax incl.
BDT 0.00 Tax
BDT 6,000.00 tax excl.
BDT 6,000.00 tax excl.
BDT 0.00 Tax
BDT 6,000.00 tax incl.
More
Last items in stock
In stock: 1

Reference: RBD-2534

4 DOF High Precision 3D-Printed Stepper Motor Robotic Arm

(0)
3D-printed robotic arm with 4 stepper motors and 1 servo motor for precise control Robot arm size: approximately 25 x 13 x 29 cm Features claws for easy gripping Includes all necessary 3D-printed parts and motors The color and claw mechanism of the Robotic arm  may vary as our stock rotates. Current stock comes as assembled. 
BDT 13,499.00
BDT 13,499.00 tax incl.
BDT 13,499.00 tax excl.
BDT 13,499.00 tax excl.
BDT 13,499.00 tax incl.
BDT 13,499.00 tax incl.
BDT 0.00 Tax
BDT 13,499.00 tax excl.
BDT 13,499.00 tax excl.
BDT 0.00 Tax
BDT 13,499.00 tax incl.
More
Last items in stock
In stock: 1

Reference: RBD-2195

50 cm Micro USB Cable for Arduino Leonardo and Node MCU

(0)
Fully compatible with the PC. Moulded strain relief and PVC over moulding to ensure a lifetime of error-free data transmissions. Aluminium under mould shield helps meet FCC requirements on KMI/RFI interference. Foil and braid shield complies with fully rated cable specifications reducing EMI/FRI interference.
BDT 180.00
BDT 180.00 tax incl.
BDT 180.00 tax excl.
BDT 180.00 tax excl.
BDT 180.00 tax incl.
BDT 180.00 tax incl.
BDT 0.00 Tax
BDT 180.00 tax excl.
BDT 180.00 tax excl.
BDT 0.00 Tax
BDT 180.00 tax incl.
More
In-Stock
In stock: 185

Reference: RBD-1550

MaKey MaKey - An Invention Kit for Everyone

(0)
INVENTION KIT FOR THE 21ST CENTURY Connect the world to your computer Invent Everywhere
BDT 1,990.00
BDT 1,990.00 tax incl.
BDT 1,990.00 tax excl.
BDT 1,990.00 tax excl.
BDT 1,990.00 tax incl.
BDT 1,990.00 tax incl.
BDT 0.00 Tax
BDT 1,990.00 tax excl.
BDT 1,990.00 tax excl.
BDT 0.00 Tax
BDT 1,990.00 tax incl.
More
In stock
In stock: 19

Reference: RBD-0712

UNI-T Scope Digital Multimeter UT81B

(0)
Signal input data processing auto measure  waveform storage and transfer AC/DC voltage and current resistance diode continuity frequency duty ratio capacitance
BDT 17,999.00
BDT 17,999.00 tax incl.
BDT 17,999.00 tax excl.
BDT 17,999.00 tax excl.
BDT 17,999.00 tax incl.
BDT 17,999.00 tax incl.
BDT 0.00 Tax
BDT 17,999.00 tax excl.
BDT 17,999.00 tax excl.
BDT 0.00 Tax
BDT 17,999.00 tax incl.
More
Last items in stock
In stock: 1

Reference: RBD-0460

S7-300 SM322 6ES7 322-1BH01-0AA0

(0)
Model: S7-300 SM322 Part No: 6ES7 322-1BH01-0AA0 Made in Germany SIMATIC S7-300, DIGITAL OUTPUT SM 322, OPTICALLY ISOLATED, 16 DO, 24V DC, 0.5A, 1 X 20 PIN SUM OF OUTPUT CURRENTS 4A/GROUP (8A/MODULE)
BDT 25,000.00
BDT 25,000.00 tax incl.
BDT 25,000.00 tax excl.
BDT 25,000.00 tax excl.
BDT 25,000.00 tax incl.
BDT 25,000.00 tax incl.
BDT 0.00 Tax
BDT 25,000.00 tax excl.
BDT 25,000.00 tax excl.
BDT 0.00 Tax
BDT 25,000.00 tax incl.
More
In stock
In stock: 7

Reference: RBD-0443

GPRS GSM SIM900 Arduino Shield

(0)
Based on SIMCom‘s SIM900 Module Quad-Band 850 / 900/ 1800 / 1900 MHz - would work on GSM networks in all countries across the world. Control by AT commands - Standard Commands: GSM 07.07 & 07.05 | Enhanced Commands: SIMCOM AT Commands. Short Message Service - so that you can send small amounts of data over the network (ASCII or raw hexadecimal).
BDT 2,400.00
BDT 2,400.00 tax incl.
BDT 2,400.00 tax excl.
BDT 2,400.00 tax excl.
BDT 2,400.00 tax incl.
BDT 2,400.00 tax incl.
BDT 0.00 Tax
BDT 2,400.00 tax excl.
BDT 2,400.00 tax excl.
BDT 0.00 Tax
BDT 2,400.00 tax incl.
More
In-Stock
In stock: 22

Reference: RBD-0265

QR701 58mm Embedded Receipt MIni Thermal Printer

(0)
Printing method: Thermal dot printing Printing speed: 50 - 80mm/s Resolution: 8 points/mm, 384 points/line Effective print width: 48mm Character set: ASCII, GB2312-80 (Chinese)
BDT 3,790.00
BDT 3,790.00 tax incl.
BDT 3,790.00 tax excl.
BDT 3,790.00 tax excl.
BDT 3,790.00 tax incl.
BDT 3,790.00 tax incl.
BDT 0.00 Tax
BDT 3,790.00 tax excl.
BDT 3,790.00 tax excl.
BDT 0.00 Tax
BDT 3,790.00 tax incl.
More
In-Stock
In stock: 5

Reference: RBD-2695

US-015 Ultrasonic Module Housing

(0)
Custom 3D-printed enclosure designed specifically for the US-015 ultrasonic sensor module. Protects the sensor from dust, moisture, and impacts for enhanced durability and performance. Features two screw holes for convenient and secure mounting in various projects. Note: Filament Color may change as our stock rotates. 
BDT 80.00
BDT 80.00 tax incl.
BDT 80.00 tax excl.
BDT 80.00 tax excl.
BDT 80.00 tax incl.
BDT 80.00 tax incl.
BDT 0.00 Tax
BDT 80.00 tax excl.
BDT 80.00 tax excl.
BDT 0.00 Tax
BDT 80.00 tax incl.
More
In-Stock
In stock: 4

Reference: RBD-2196

50 cm Cable For Arduino UNO/MEGA (USB A to B)

(0)
USB Type: Type-A to Type-B Weight: 26 gm. Length: 50 cm Long cable for easy work Fully compatible with the PC. Molded strain relief and PVC over-molding to ensure a lifetime of error-free data transmissions.
BDT 130.00
BDT 130.00 tax incl.
BDT 130.00 tax excl.
BDT 130.00 tax excl.
BDT 130.00 tax incl.
BDT 130.00 tax incl.
BDT 0.00 Tax
BDT 130.00 tax excl.
BDT 130.00 tax excl.
BDT 0.00 Tax
BDT 130.00 tax incl.
More
In-Stock
In stock: 135

Reference: RBD-1129

Brand: RoboticsBD

Otto Bot Complete

(0)
Complete Assembled  Plug and Play Open Source Design Compatible With Arduino IDE DIY Kit
BDT 7,890.00 BDT 8,890.00
BDT 8,890.00 BDT 7,890.00 tax incl.
BDT 8,890.00 BDT 7,890.00 tax excl.
BDT 8,890.00 BDT 7,890.00 tax excl.
BDT 8,890.00 BDT 7,890.00 tax incl.
BDT 8,890.00 BDT 7,890.00 tax incl.
BDT 0.00 BDT 0.00 Tax
BDT 8,890.00 BDT 7,890.00 tax excl.
BDT 8,890.00 BDT 7,890.00 tax excl.
BDT 0.00 BDT 0.00 Tax
BDT 8,890.00 BDT 7,890.00 tax incl.
More
Out-of-Stock
In stock: 0

Reference: RBD-0833

Soldering Kit

(0)
Soldering Iron KOOCU V501 25W Constant Temperature Electric Soldering Iron Soldering Stand Soldering Lead Solder Resin Wire Cutter Sucker
BDT 1,035.00
BDT 1,035.00 tax incl.
BDT 1,035.00 tax excl.
BDT 1,035.00 tax excl.
BDT 1,035.00 tax incl.
BDT 1,035.00 tax incl.
BDT 0.00 Tax
BDT 1,035.00 tax excl.
BDT 1,035.00 tax excl.
BDT 0.00 Tax
BDT 1,035.00 tax incl.
More
In-Stock
In stock: 15

Reference: RBD-0552

A6 Pro Serial GPRS GSM Module Core Development Board

(0)
Working frequency: quad-band network, 850 / 900 / 1800 / 1900MHz Working voltage: 4.8-9VDC(On-board voltage regulator circuit supply power for A6 module) Working Current: maximum of 2A. RoboticsBD
BDT 1,100.00
BDT 1,100.00 tax incl.
BDT 1,100.00 tax excl.
BDT 1,100.00 tax excl.
BDT 1,100.00 tax incl.
BDT 1,100.00 tax incl.
BDT 0.00 Tax
BDT 1,100.00 tax excl.
BDT 1,100.00 tax excl.
BDT 0.00 Tax
BDT 1,100.00 tax incl.
More
Out-of-Stock
In stock: 0

Reference: RBD-0461

S7-300 IM 361 6ES7361-3CA01-0AA0

(0)
(PRICE NEGOTIABLE) Model: S7-300 IM 361 Part No: 6ES7361-3CA01-0AA0 Made in Germany SIMATIC S7-300,INTERFACE MODULE IM 361 IN EXPANSION RACK FOR CONNECTING TO CENTRAL RACK (IM360),24 V DC SUPPLY VOLTAGE, WITH K-BUS
BDT 0.00
BDT 0.00 tax incl.
BDT 0.00 tax excl.
BDT 0.00 tax excl.
BDT 0.00 tax incl.
BDT 0.00 tax incl.
BDT 0.00 Tax
BDT 0.00 tax excl.
BDT 0.00 tax excl.
BDT 0.00 Tax
BDT 0.00 tax incl.
Last items in stock
In stock: 2

Reference: RBD-0272

Brand: Waveshare

Logic Level Converter

(0)
Voltage level: 1.8V-6V Dimension: 38mm x 31.6mm Conversion  level  range:  1.8 V-6 V Instructions for use:  (3.3 V,  5 V  to  each other) 4 pairs of power supply interfaces, supports more situation Use tantalum capacitors for power filter, provides more stability VCCB 5V  power supply  (can  be an external  5V power supply)
BDT 550.00
BDT 550.00 tax incl.
BDT 550.00 tax excl.
BDT 550.00 tax excl.
BDT 550.00 tax incl.
BDT 550.00 tax incl.
BDT 0.00 Tax
BDT 550.00 tax excl.
BDT 550.00 tax excl.
BDT 0.00 Tax
BDT 550.00 tax incl.
More
Out-of-Stock
In stock: -1

Reference: RBD-2696

HC-SR04 Ultrasonic Sensor Housing

(0)
Custom 3D-printed enclosure designed specifically for the HC-SR04 ultrasonic sensor module. Protects the sensor from dust, moisture, and impacts for enhanced durability and performance. For convenient and secure mounting in various projects. Note: Filament Color may change as our stock rotates. 
BDT 85.00
BDT 85.00 tax incl.
BDT 85.00 tax excl.
BDT 85.00 tax excl.
BDT 85.00 tax incl.
BDT 85.00 tax incl.
BDT 0.00 Tax
BDT 85.00 tax excl.
BDT 85.00 tax excl.
BDT 0.00 Tax
BDT 85.00 tax incl.
More
Last items in stock
In stock: 3

Reference: RBD-2198

CH341 USB Programmer

(0)
Model: CH341 Series Main Chip: CH341B Dimensions in mm (LxWxH): 85 x 28 x 12 Weight (gm): 20 8-bit parallel in EPP or MEM mode
BDT 445.00
BDT 445.00 tax incl.
BDT 445.00 tax excl.
BDT 445.00 tax excl.
BDT 445.00 tax incl.
BDT 445.00 tax incl.
BDT 0.00 Tax
BDT 445.00 tax excl.
BDT 445.00 tax excl.
BDT 0.00 Tax
BDT 445.00 tax incl.
More
In-Stock
In stock: 26

Reference: RBD-1216

TI MSP430 LaunchPad

(0)
14-/20-pin DIP (N) Socket 20 pin LaunchPad standard leveraging the BoosterPack ecosystem On-Board EZ-FET emulator featuring EnergyTrace™ technology Supports MSP430G2xx2, MSP430G2xx3, and MSP430F20xx devices in PDIP14 or PDIP20 packages 1 user buttons and 3 LEDs for user interaction
BDT 2,500.00
BDT 2,500.00 tax incl.
BDT 2,500.00 tax excl.
BDT 2,500.00 tax excl.
BDT 2,500.00 tax incl.
BDT 2,500.00 tax incl.
BDT 0.00 Tax
BDT 2,500.00 tax excl.
BDT 2,500.00 tax excl.
BDT 0.00 Tax
BDT 2,500.00 tax incl.
More
Last items in stock
In stock: 3

Reference: RBD-0907

UNI-T UT603 LCR meter

(0)
Resistance (Ω) 200Ω/2kΩ/20kΩ/200kΩ/2MΩ/20MΩ Capacitance (F) 2nF/20nF/200nF/2uF/20uF/200uF/600uF Inductance (H) 2mH/20mH/200mH/2H/20H
BDT 5,950.00
BDT 5,950.00 tax incl.
BDT 5,950.00 tax excl.
BDT 5,950.00 tax excl.
BDT 5,950.00 tax incl.
BDT 5,950.00 tax incl.
BDT 0.00 Tax
BDT 5,950.00 tax excl.
BDT 5,950.00 tax excl.
BDT 0.00 Tax
BDT 5,950.00 tax incl.
More
In-Stock
In stock: 9

Reference: RBD-0462

S7-300 SM321 6ES7 321-1BH02-0AA0

(0)
Model: SIMATIC S7-300 SM321 Part No: 6ES7 321-1BH02-0AA0 Made in Germany SIMATIC S7-300, DIGITAL INPUT SM 321, OPTICALLY ISOLATED, 16DI, 24 V DC, 1 X 20 PIN
BDT 25,000.00
BDT 25,000.00 tax incl.
BDT 25,000.00 tax excl.
BDT 25,000.00 tax excl.
BDT 25,000.00 tax incl.
BDT 25,000.00 tax incl.
BDT 0.00 Tax
BDT 25,000.00 tax excl.
BDT 25,000.00 tax excl.
BDT 0.00 Tax
BDT 25,000.00 tax incl.
More
In-Stock
In stock: 6

Reference: RBD-0318

SIM900A Mini Module 5V

(0)
This module is intended for advanced users who require moderate knowledge of GSM systems and microcontrollers. It needs wiring and firmware updates to unlock the country lock.  Dual-Band 900/ 1800 MHz GPRS multi-slot class 10/8GPRS mobile station class B Compliant to GSM phase 2/2+ Dimensions: 24*24*3 mm Weight: 3.4g Control via AT commands (GSM 07.07...
BDT 1,050.00
BDT 1,050.00 tax incl.
BDT 1,050.00 tax excl.
BDT 1,050.00 tax excl.
BDT 1,050.00 tax incl.
BDT 1,050.00 tax incl.
BDT 0.00 Tax
BDT 1,050.00 tax excl.
BDT 1,050.00 tax excl.
BDT 0.00 Tax
BDT 1,050.00 tax incl.
More
In-Stock
In stock: 9

Reference: RBD-0280

Mini Breadboard

(0)
Tie-points: 170 (10×17) Size: 48 x 35 x 10 mm(LxWxH). Use: experimental, testing, robot Matching jumper, diameter 0.8mm Phosphor bronze nickel plated spring clips Accepts a variety of wire sizes (29-20 the AWG) **1 pcs Random Color
BDT 45.00
BDT 45.00 tax incl.
BDT 45.00 tax excl.
BDT 45.00 tax excl.
BDT 45.00 tax incl.
BDT 45.00 tax incl.
BDT 0.00 Tax
BDT 45.00 tax excl.
BDT 45.00 tax excl.
BDT 0.00 Tax
BDT 45.00 tax incl.
More
In-Stock
In stock: 633

Reference: RBD-2311

USB To Serial Cable TTL 4 Pin Rs 232 UART Converter Adapter Programming Module

(0)
USB 4 Pin TTL RS 232 UART Serial Converter Adapter Programming Module Cable. The PL-2303HX USB to TTL RS232 Serial converter is a low-cost USB to Serial Adapter.
BDT 220.00
BDT 220.00 tax incl.
BDT 220.00 tax excl.
BDT 220.00 tax excl.
BDT 220.00 tax incl.
BDT 220.00 tax incl.
BDT 0.00 Tax
BDT 220.00 tax excl.
BDT 220.00 tax excl.
BDT 0.00 Tax
BDT 220.00 tax incl.
More
In stock
In stock: 51

Reference: RBD-0908

Digital Tachometer DT2234C+

(0)
DT2234C+ digital laser RPM photo tachometer, non contact measurement tool  Professional tachometer measures the RPM of any rotational part with wide measuring range and high resolution Durable in using, large LCD display gives exact RPM data. RoboticsBD
BDT 1,550.00
BDT 1,550.00 tax incl.
BDT 1,550.00 tax excl.
BDT 1,550.00 tax excl.
BDT 1,550.00 tax incl.
BDT 1,550.00 tax incl.
BDT 0.00 Tax
BDT 1,550.00 tax excl.
BDT 1,550.00 tax excl.
BDT 0.00 Tax
BDT 1,550.00 tax incl.
More
In-Stock
In stock: 6

Reference: RBD-0670

Brand: RoboticsBD

Electric Mini Drill

(0)
Color: Grey Speed: 8500 RPM Collet Size: 0.5-3.0mm Full Accessories Set (14 pcs) 
BDT 1,060.00
BDT 1,060.00 tax incl.
BDT 1,060.00 tax excl.
BDT 1,060.00 tax excl.
BDT 1,060.00 tax incl.
BDT 1,060.00 tax incl.
BDT 0.00 Tax
BDT 1,060.00 tax excl.
BDT 1,060.00 tax excl.
BDT 0.00 Tax
BDT 1,060.00 tax incl.
More
In-Stock
In stock: 11

Reference: RBD-0465

S7-300 SM321 6ES7 321-1BL00-0AA0

(0)
Model: S7-300 SM321 Part No: 6ES7 321-1BL00-0AA0 Made in Germany SIMATIC S7-300, DIGITAL INPUT SM 321, OPTICALLY ISOLATED 32DI, 24 V DC, 1 X 40 PIN
BDT 25,000.00
BDT 25,000.00 tax incl.
BDT 25,000.00 tax excl.
BDT 25,000.00 tax excl.
BDT 25,000.00 tax incl.
BDT 25,000.00 tax incl.
BDT 0.00 Tax
BDT 25,000.00 tax excl.
BDT 25,000.00 tax excl.
BDT 0.00 Tax
BDT 25,000.00 tax incl.
More
In stock
In stock: 6

Reference: RBD-0314

Double-ended 50cm Cable Crocodile Clips

(0)
Colour: Red, Green, Yellow, White, and Black, etc. Cable length: 40 cm. RoboticsBD Net weight: 50 gm. They are very useful for connecting components to wires. It is insulation covered clips connected to the wire from both ends. RoboticsBD *You will receive 1 pcs cable of random color.
BDT 20.00
BDT 20.00 tax incl.
BDT 20.00 tax excl.
BDT 20.00 tax excl.
BDT 20.00 tax incl.
BDT 20.00 tax incl.
BDT 0.00 Tax
BDT 20.00 tax excl.
BDT 20.00 tax excl.
BDT 0.00 Tax
BDT 20.00 tax incl.
More
Out-of-Stock
In stock: 0

Reference: RBD-2315

Pogo Pin Probe Clip - 6 Pins with 2.54mm

(0)
Pin Pitch: 2.54mm Probe model: P75-E2 (pointed tip) Needle diameter: 1.3mm Needle sleeve model R75-3W Row pin number: 6Pin Row Number: Single row space between: 2.54mm
BDT 990.00
BDT 990.00 tax incl.
BDT 990.00 tax excl.
BDT 990.00 tax excl.
BDT 990.00 tax incl.
BDT 990.00 tax incl.
BDT 0.00 Tax
BDT 990.00 tax excl.
BDT 990.00 tax excl.
BDT 0.00 Tax
BDT 990.00 tax incl.
More
In stock
In stock: 19

Reference: RBD-1701

Brand: SparkFun Electronics

Capacitance Meter DIY Kit

(0)
Capacitance Meter DIY Kit Sparkfun Electronics
BDT 1,300.00
BDT 1,300.00 tax incl.
BDT 1,300.00 tax excl.
BDT 1,300.00 tax excl.
BDT 1,300.00 tax incl.
BDT 1,300.00 tax incl.
BDT 0.00 Tax
BDT 1,300.00 tax excl.
BDT 1,300.00 tax excl.
BDT 0.00 Tax
BDT 1,300.00 tax incl.
More
Last items in stock
In stock: 1

Reference: RBD-0911

Uni-T UT33A+ Digital Multimeter

(0)
Entry-level digital multimeters Palm Size 2mF capacitance test (UT33A+) Work safely in CAT II 600V environment
BDT 1,990.00
BDT 1,990.00 tax incl.
BDT 1,990.00 tax excl.
BDT 1,990.00 tax excl.
BDT 1,990.00 tax incl.
BDT 1,990.00 tax incl.
BDT 0.00 Tax
BDT 1,990.00 tax excl.
BDT 1,990.00 tax excl.
BDT 0.00 Tax
BDT 1,990.00 tax incl.
More
In-Stock
In stock: 8

Reference: RBD-0466

S7-300 SM332 6ES7 332-5HD01-0AB0

(0)
Model: Simatic S7-300 SM332 Part No: 6ES7 332-5HD01-0AB0 Made in Germany SIMATIC S7-300, ANALOG OUTPUT SM 332, OPTICALLY ISOLATED, 4 AO, U/I; DIAGNOSTICS; RESOLUTION 11/12 BITS, 20 PIN, REMOVE/INSERT W. ACTIVE, BACKPLANE BUS
BDT 75,000.00
BDT 75,000.00 tax incl.
BDT 75,000.00 tax excl.
BDT 75,000.00 tax excl.
BDT 75,000.00 tax incl.
BDT 75,000.00 tax incl.
BDT 0.00 Tax
BDT 75,000.00 tax excl.
BDT 75,000.00 tax excl.
BDT 0.00 Tax
BDT 75,000.00 tax incl.
More
In-Stock
In stock: 5

Follow us on Facebook