• Banner

Active filters
  • Availability: In stock
  • Categories: Display
  • Categories: HMI
  • Categories: Motor
  • Categories: PLC
  • Categories: PLC Cable
  • Categories: Thermal Printer

Reference: RBD-0951

N20 DC 6V 200RPM Mini Metal Gear Motor

(0)
This is a DC Mini Metal Gear Motor, ideal for making robots Lightweight, high torque and low RPM. Fine craftsmanship, durable, not easy to wear. With excellent stall characteristics, can climb hills easily. You can also easily mount a wheel on the motor’s output shaft.
BDT 350.00
BDT 350.00 tax incl.
BDT 350.00 tax excl.
BDT 350.00 tax excl.
BDT 350.00 tax incl.
BDT 350.00 tax incl.
BDT 0.00 Tax
BDT 350.00 tax excl.
BDT 350.00 tax excl.
BDT 0.00 Tax
BDT 350.00 tax incl.
More
In-Stock
In stock: 200

Reference: RBD-0469

S7-300 SM322 6ES7 322-1BL00-0AA0

(0)
Model: S7-300, SM322 Part No: 6ES7 322-1BL00-0AA0 Made in Germany SIMATIC S7-300, DIGITAL OUTPUT SM 322, OPTICALLY ISOLATED, 32DO, 24V DC, 0.5A, 1 X 40 PIN, SUM OF OUTPUT CURRENTS 4A/GROUP (16A/MODULE)   6ES7 322-1BL00-0AA0  
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
Last items in stock
In stock: 2

Reference: RBD-1251

7 Inch TFT IPS Monitor for Raspberry Pi

(0)
Input Voltage: DC 7.4~35V. Input Current: DC 0.5A-1.5A. Power Consumption: ≤8W Watts. Resolution: 1024 x 600. Aspect Ratio: 16:9 & 4:3. Contrast Ratio: 500:1. Monitor Mount is not Available.
BDT 6,390.00
BDT 6,390.00 tax incl.
BDT 6,390.00 tax excl.
BDT 6,390.00 tax excl.
BDT 6,390.00 tax incl.
BDT 6,390.00 tax incl.
BDT 0.00 Tax
BDT 6,390.00 tax excl.
BDT 6,390.00 tax excl.
BDT 0.00 Tax
BDT 6,390.00 tax incl.
More
In-Stock
In stock: 10

Reference: RBD-0470

S7-300 SM331 6ES7 331-7PF01-0AB0

(0)
Model No: S7-300, SM331 Part No: 6ES7 331-7PF01-0AB0 Made in Germany SIMATIC S7-300, ANALOG INPUT SM 331, OPT. ISOL.,2/3/4 WIRE, 8AI, RESISTANCE, PT100/200/1000 NI100/120/200/500/1000, CU10, PLUS CHARACTERISTICS ACCORDING TO GOST STANDARD 16 (INTERN 24) BIT, 50MS, 1 X 40 PIN
BDT 76,000.00
BDT 76,000.00 tax incl.
BDT 76,000.00 tax excl.
BDT 76,000.00 tax excl.
BDT 76,000.00 tax incl.
BDT 76,000.00 tax incl.
BDT 0.00 Tax
BDT 76,000.00 tax excl.
BDT 76,000.00 tax excl.
BDT 0.00 Tax
BDT 76,000.00 tax incl.
More
In stock
In stock: 5

Reference: RBD-1108

0.56 Inch 3 Digit 7 Segment Red Common Cathode Display

(0)
Bright Red LED chip, which is made from AlGaAs on GaAs substrate Blackface and RED LED segments Type: Common cathode No. of Pins: 12 Low Current Consumption High Brightness
BDT 50.00
BDT 50.00 tax incl.
BDT 50.00 tax excl.
BDT 50.00 tax excl.
BDT 50.00 tax incl.
BDT 50.00 tax incl.
BDT 0.00 Tax
BDT 50.00 tax excl.
BDT 50.00 tax excl.
BDT 0.00 Tax
BDT 50.00 tax incl.
More
In-Stock
In stock: 93

Reference: RBD-1061

6V TT DC Gear BO Motor Dual Shaft

(0)
Low density: lightweight, low inertia. Capability to absorb shock and vibration as a result of elastic compliance. Ability to operate with minimum or no lubrication, due to inherent lubricity. The relatively low coefficient of friction. Operating Voltage(VDC): 3~12 Shaft Length (mm): 8.5 Shaft Diameter (mm): 5.5 (Double D-type) No Load Current: 40-180mA....
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
In-Stock
In stock: 185

Reference: RBD-0471

S7-300 SM331 6ES7 331-1KF01-0AB0

(0)
Model: S7-300, SM331 Part No: 6ES7 331-1KF01-0AB0 Made in Germany SIMATIC S7-300, ANALOG INPUT SM 331, OPTICALLY ISOLATED, 8 AI, 13 BIT RESOLUTION, U/I/RESISTANCE/PT100, NI100, NI1000, LG-NI1000, 66 MS MODULE UPDATE, 1 X 40 PIN 6ES7 331-1KF01-0AB0  
BDT 45,000.00
BDT 45,000.00 tax incl.
BDT 45,000.00 tax excl.
BDT 45,000.00 tax excl.
BDT 45,000.00 tax incl.
BDT 45,000.00 tax incl.
BDT 0.00 Tax
BDT 45,000.00 tax excl.
BDT 45,000.00 tax excl.
BDT 0.00 Tax
BDT 45,000.00 tax incl.
More
In-Stock
In stock: 4

Reference: RBD-1068

N20 12V 100 RPM Micro Metal DC Gear Motor

(0)
This is a DC Mini Metal Gear Motor, ideal for making robots Lightweight, high torque and low RPM. Fine craftsmanship, durable, not easy to wear. With excellent stall characteristics, can climb hills easily. You can also easily mount a wheel on the motor’s output shaft.
BDT 295.00
BDT 295.00 tax incl.
BDT 295.00 tax excl.
BDT 295.00 tax excl.
BDT 295.00 tax incl.
BDT 295.00 tax incl.
BDT 0.00 Tax
BDT 295.00 tax excl.
BDT 295.00 tax excl.
BDT 0.00 Tax
BDT 295.00 tax incl.
More
In-Stock
In stock: 13

Reference: RBD-0914

MAX7219 4 Channel Dot Matrix Display Panel

(0)
Driver Chip: MAX7219 Input Voltage: 3.7 to 5.3 V Input Current: 320 mA Display Dimensions: 32x32x6 (LxWxH) mm PCB Dimensions: 128×32 (LxW) mm
BDT 650.00
BDT 650.00 tax incl.
BDT 650.00 tax excl.
BDT 650.00 tax excl.
BDT 650.00 tax incl.
BDT 650.00 tax incl.
BDT 0.00 Tax
BDT 650.00 tax excl.
BDT 650.00 tax excl.
BDT 0.00 Tax
BDT 650.00 tax incl.
More
In-Stock
In stock: 27

Reference: RBD-0472

S7-300 SM 323 6ES7 323-1BL00-0AA0

(0)
Model: S7-300,SM 323 Part No: 6ES7 323-1BL00-0AA0  Made in Germany SIMATIC S7-300, DIGITAL MODULE SM 323, OPTICALLY ISOLATED, 8 DI AND 8 DO, 24V DC, 0.5A AGGREGATE CURRENT 2A, 1X20 PIN
BDT 35,000.00
BDT 35,000.00 tax incl.
BDT 35,000.00 tax excl.
BDT 35,000.00 tax excl.
BDT 35,000.00 tax incl.
BDT 35,000.00 tax incl.
BDT 0.00 Tax
BDT 35,000.00 tax excl.
BDT 35,000.00 tax excl.
BDT 0.00 Tax
BDT 35,000.00 tax incl.
More
Last items in stock
In stock: 3

Reference: RBD-1305

0.56 Inch 1 Digit 7 Segment Red Common Cathode Display

(0)
Bright Red LED chip, which is made from AlGaAs on GaAs substrate Blackface and RED LED segments Type: Common anode No. of Pins: 10 Low Current Consumption High Brightness
BDT 17.00 BDT 20.00
BDT 20.00 BDT 17.00 tax incl.
BDT 20.00 BDT 17.00 tax excl.
BDT 20.00 BDT 17.00 tax excl.
BDT 20.00 BDT 17.00 tax incl.
BDT 20.00 BDT 17.00 tax incl.
BDT 0.00 BDT 0.00 Tax
BDT 20.00 BDT 17.00 tax excl.
BDT 20.00 BDT 17.00 tax excl.
BDT 0.00 BDT 0.00 Tax
BDT 20.00 BDT 17.00 tax incl.
More
In-Stock
In stock: 99

Reference: RBD-1114

DC3-12V N20 Gear Motor & Mount Bracket & 43mm Wheel

(0)
N20 Micro Gear 12V 100RPM DC Motor (High Torque) Mounting Bracket for N20 Micro Gear motors 3PI miniQ Car wheel Tyre 44mm N20 DC Gear Motor Wheel
BDT 480.00
BDT 480.00 tax incl.
BDT 480.00 tax excl.
BDT 480.00 tax excl.
BDT 480.00 tax incl.
BDT 480.00 tax incl.
BDT 0.00 Tax
BDT 480.00 tax excl.
BDT 480.00 tax excl.
BDT 0.00 Tax
BDT 480.00 tax incl.
More
In-Stock
In stock: 10

Reference: RBD-0473

S7-300 SM323 6ES7 323-1BH01-0AA0

(0)
Model: S7-300,SM323   Part No: 6ES7 323-1BH01-0AA0     Made in Germany     SIMATIC S7-300, DIGITAL MODULE SM 323, OPTICALLY ISOLATED, 16 DI AND 16 DO, 24V DC, 0.5A, AGGREGATE CURRENT 4A, 1X40 PIN
BDT 35,000.00
BDT 35,000.00 tax incl.
BDT 35,000.00 tax excl.
BDT 35,000.00 tax excl.
BDT 35,000.00 tax incl.
BDT 35,000.00 tax incl.
BDT 0.00 Tax
BDT 35,000.00 tax excl.
BDT 35,000.00 tax excl.
BDT 0.00 Tax
BDT 35,000.00 tax incl.
More
Last items in stock
In stock: 2

Reference: RBD-1306

8*8 LED matrix module common anode of LED matrix

(0)
Easy to Install on Breadboard. Bright LED lights. Compact Design. LED Size: 3mm. Configuration: Common Anode.
BDT 95.00
BDT 95.00 tax incl.
BDT 95.00 tax excl.
BDT 95.00 tax excl.
BDT 95.00 tax incl.
BDT 95.00 tax incl.
BDT 0.00 Tax
BDT 95.00 tax excl.
BDT 95.00 tax excl.
BDT 0.00 Tax
BDT 95.00 tax incl.
More
In-Stock
In stock: 78

Reference: RBD-1248

Miniature Vibrating Motor

(0)
Speed(RPM):19000 Motor diameter: 6mm Shaft diameter: 0.8mm Shaft length: 4mm Rated voltage: 1.5V-3.1V
BDT 150.00
BDT 150.00 tax incl.
BDT 150.00 tax excl.
BDT 150.00 tax excl.
BDT 150.00 tax incl.
BDT 150.00 tax incl.
BDT 0.00 Tax
BDT 150.00 tax excl.
BDT 150.00 tax excl.
BDT 0.00 Tax
BDT 150.00 tax incl.
More
In-Stock
In stock: 50

Reference: RBD-0474

S7-300 SM322 6ES7 322-1HH01-0AA0

(0)
Model: S7-300, SM322 Part No: 6ES7 322-1HH01-0AA0 Made in Germany SIMATIC S7-300, DIGITAL OUTPUT SM 322, OPTICALLY ISOLATED 16DO, RELAY CONTACTS, 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: 4

Reference: RBD-1249

Shaftless Vibration Motor

(0)
Voltage Range: DC 2.5-4V. Motor Diameter: 10 mm. Motor Thickness: 3.4 mm. Min. Rated Speed: 9000RPM Max. Rated Current: 90mA
BDT 150.00
BDT 150.00 tax incl.
BDT 150.00 tax excl.
BDT 150.00 tax excl.
BDT 150.00 tax incl.
BDT 150.00 tax incl.
BDT 0.00 Tax
BDT 150.00 tax excl.
BDT 150.00 tax excl.
BDT 0.00 Tax
BDT 150.00 tax incl.
More
In-Stock
In stock: 73

Reference: RBD-1332

I2C Graphic 128x64 LCD Adapter

(0)
Adapter: Graphic 128x64 Communication: i2c 
BDT 499.00
BDT 499.00 tax incl.
BDT 499.00 tax excl.
BDT 499.00 tax excl.
BDT 499.00 tax incl.
BDT 499.00 tax incl.
BDT 0.00 Tax
BDT 499.00 tax excl.
BDT 499.00 tax excl.
BDT 0.00 Tax
BDT 499.00 tax incl.
More
In-Stock
In stock: 8

Reference: RBD-1250

37GB 12V High Torque Gear Motor - 195 RPM

(0)
DC 12V 195 RPM 37GB-545 Gear Reducer Motor Consumes less current  Higher durability 
BDT 1,500.00
BDT 1,500.00 tax incl.
BDT 1,500.00 tax excl.
BDT 1,500.00 tax excl.
BDT 1,500.00 tax incl.
BDT 1,500.00 tax incl.
BDT 0.00 Tax
BDT 1,500.00 tax excl.
BDT 1,500.00 tax excl.
BDT 0.00 Tax
BDT 1,500.00 tax incl.
More
In-Stock
In stock: 20

Reference: RBD-0476

S7-300 SM331 6ES7 331-7PF11-0AB0

(0)
Model: S7-300,SM331 Part No: 6ES7 331-7PF11-0AB0   Made in Germany SIMATIC S7-300, ANALOG INPUT SM 331, OPTICALLY ISOLATATED, 8 AI THERMOCOUPLE, TYPE B, E, J, K, L, N, R, S, T TXK/TXK(L) ACCORDING GOST 16 BIT, 50 MS, 1 X 40 PIN
BDT 70,000.00
BDT 70,000.00 tax incl.
BDT 70,000.00 tax excl.
BDT 70,000.00 tax excl.
BDT 70,000.00 tax incl.
BDT 70,000.00 tax incl.
BDT 0.00 Tax
BDT 70,000.00 tax excl.
BDT 70,000.00 tax excl.
BDT 0.00 Tax
BDT 70,000.00 tax incl.
More
Last items in stock
In stock: 2

Reference: RBD-1335

LCD Graphic 128x64 Display ST7920 12864B

(0)
Based on ST7920 Resolution: 128 X 64 pixels Operating voltage: 5V Viewing Area: 72mm x 40mm Display mode TN/STN
BDT 995.00
BDT 995.00 tax incl.
BDT 995.00 tax excl.
BDT 995.00 tax excl.
BDT 995.00 tax incl.
BDT 995.00 tax incl.
BDT 0.00 Tax
BDT 995.00 tax excl.
BDT 995.00 tax excl.
BDT 0.00 Tax
BDT 995.00 tax incl.
More
In-Stock
In stock: 15

Reference: RBD-1257

Mini Air Pump Motor USB Power Cable

(0)
Simple Plug and Play operation. USB input Plug It Can operate on any 5V DC power supply like Power bank 1 Meter cable with DC jack provides the convenience to connect and disconnect project easily
BDT 590.00
BDT 590.00 tax incl.
BDT 590.00 tax excl.
BDT 590.00 tax excl.
BDT 590.00 tax incl.
BDT 590.00 tax incl.
BDT 0.00 Tax
BDT 590.00 tax excl.
BDT 590.00 tax excl.
BDT 0.00 Tax
BDT 590.00 tax incl.
More
In-Stock
In stock: 20

Reference: RBD-0477

IM 153-1 200M 6ES7 153-1AA03-0XB0

(0)
Model: IM 153-1,200M Part No: 6ES7 153-1AA03-0XB0  Made in Germany SIMATIC DP, INTERFACE IM 153-1, FOR ET 200M, FOR MAX. 8 S7-300 MODULES
BDT 40,000.00
BDT 40,000.00 tax incl.
BDT 40,000.00 tax excl.
BDT 40,000.00 tax excl.
BDT 40,000.00 tax incl.
BDT 40,000.00 tax incl.
BDT 0.00 Tax
BDT 40,000.00 tax excl.
BDT 40,000.00 tax excl.
BDT 0.00 Tax
BDT 40,000.00 tax incl.
More
Last items in stock
In stock: 2

Reference: RBD-1342

LCD Display 16x2 with Female Header

(0)
For Standard LCD 16x2 with Male Header. Press here For Standard LCD 16x2 with Female Header. Press here For Standard LCD 16x2 with I2C adapter board soldered. Press here. For Standard LCD 16x2 with White Background. Press here. For Standard LCD 16x2 with Blue Background. Press here.
BDT 255.00
BDT 255.00 tax incl.
BDT 255.00 tax excl.
BDT 255.00 tax excl.
BDT 255.00 tax incl.
BDT 255.00 tax incl.
BDT 0.00 Tax
BDT 255.00 tax excl.
BDT 255.00 tax excl.
BDT 0.00 Tax
BDT 255.00 tax incl.
More
In-Stock
In stock: 16

Reference: RBD-1340

N20 12V 200 RPM Micro Metal DC Gear Motor

(0)
This is a DC Mini Metal Gear Motor, ideal for making robots Lightweight, high torque and low RPM. Fine craftsmanship, durable, not easy to wear. With excellent stall characteristics, can climb hills easily. You can also easily mount a wheel on the motor’s output shaft.
BDT 295.00
BDT 295.00 tax incl.
BDT 295.00 tax excl.
BDT 295.00 tax excl.
BDT 295.00 tax incl.
BDT 295.00 tax incl.
BDT 0.00 Tax
BDT 295.00 tax excl.
BDT 295.00 tax excl.
BDT 0.00 Tax
BDT 295.00 tax incl.
More
In-Stock
In stock: 58

Reference: RBD-0478

ET200M IM 153-4 6ES7 153-2BA00-0XB0

(0)
Model: ET200M IM 153-4 Part No: 6ES7 153-2BA00-0XB0  Made in Germany SIPLUS ET200M IM 153-4 PN IO HF -40 ... +70 GRAD C START UP TEMP -25 DGR C WITH CONFORMAL COATING BASED ON 6ES7153-4BA00-0XB0 . DP, ET 200M INTERFACE FOR MAX. 12 S7-300 MODULES, SUPPORTS FAIL SAFE MODULES, HART MODULES SHARED DEVICE, MEDIUM REDUNDANCY PROTOCOL
BDT 70,000.00
BDT 70,000.00 tax incl.
BDT 70,000.00 tax excl.
BDT 70,000.00 tax excl.
BDT 70,000.00 tax incl.
BDT 70,000.00 tax incl.
BDT 0.00 Tax
BDT 70,000.00 tax excl.
BDT 70,000.00 tax excl.
BDT 0.00 Tax
BDT 70,000.00 tax incl.
More
Last items in stock
In stock: 3

Reference: RBD-1349

16x2 Serial LCD Module Display for Arduino Assembled

(0)
For Standard LCD 16x2. Press here.For Standard LCD 16x2 with Male Header. Press hereFor Standard LCD 16x2 with Female Header. Press hereFor Standard LCD 16x2 with I2C adapter board soldered. Press here.For Standard LCD 16x2 with White Background. Press here.For Standard LCD 16x2 with Blue Background. Press here. Model: LCD1602 Interface: I2C Interface...
BDT 340.00
BDT 340.00 tax incl.
BDT 340.00 tax excl.
BDT 340.00 tax excl.
BDT 340.00 tax incl.
BDT 340.00 tax incl.
BDT 0.00 Tax
BDT 340.00 tax excl.
BDT 340.00 tax excl.
BDT 0.00 Tax
BDT 340.00 tax incl.
More
In-Stock
In stock: 4

Reference: RBD-1341

N20 12V 300 RPM Micro Metal DC Gear Motor

(0)
This is a DC Mini Metal Gear Motor, ideal for making robots Lightweight, high torque and low RPM. Fine craftsmanship, durable, not easy to wear. With excellent stall characteristics, can climb hills easily. You can also easily mount a wheel on the motor’s output shaft.
BDT 295.00
BDT 295.00 tax incl.
BDT 295.00 tax excl.
BDT 295.00 tax excl.
BDT 295.00 tax incl.
BDT 295.00 tax incl.
BDT 0.00 Tax
BDT 295.00 tax excl.
BDT 295.00 tax excl.
BDT 0.00 Tax
BDT 295.00 tax incl.
More
In-Stock
In stock: 58

Reference: RBD-0479

S7-300 FM353 6ES7 353-1AH01-0AE0

(0)
Model: S7-300,FM353 Part No: 6ES7 353-1AH01-0AE0   Made in Germany SIMATIC S7-300, FUNCTION MODULE FM 353, FOR POSITIONING WITH STEPPER MOTOR, MODULE EXCHANGE W/O PG, PREQUISITE STEP7 V3.1 INCL. CONFIG. PACKAGE ON CD
BDT 30,000.00
BDT 30,000.00 tax incl.
BDT 30,000.00 tax excl.
BDT 30,000.00 tax excl.
BDT 30,000.00 tax incl.
BDT 30,000.00 tax incl.
BDT 0.00 Tax
BDT 30,000.00 tax excl.
BDT 30,000.00 tax excl.
BDT 0.00 Tax
BDT 30,000.00 tax incl.
More
In stock
In stock: 4

Reference: RBD-1346

Mini Servo SG92R

(0)
Model: SG92R Weight: 9 gm Operating voltage: 3.0V~ 7.2V Servo Plug: JR Stall torque @4.8V : 2.5kg-cm
BDT 295.00
BDT 295.00 tax incl.
BDT 295.00 tax excl.
BDT 295.00 tax excl.
BDT 295.00 tax incl.
BDT 295.00 tax incl.
BDT 0.00 Tax
BDT 295.00 tax excl.
BDT 295.00 tax excl.
BDT 0.00 Tax
BDT 295.00 tax incl.
More
In-Stock
In stock: 63

Reference: RBD-1167

Brand: Waveshare

Raspberry Pi 7inch HDMI Touchscreen LCD with Case

(0)
Resolution:1024 x 600 Display Port: HDMI Touch Type: Capacitive Touch Points:5 points 7-inch IPS screen with a hardware resolution of 1024×600. 5-points capacitive touch control. Using Raspberry Pi, it supports Raspbian / Ubuntu / Kali / Retropie and WIN10 IoT, no need to install any drivers.
BDT 7,990.00
BDT 7,990.00 tax incl.
BDT 7,990.00 tax excl.
BDT 7,990.00 tax excl.
BDT 7,990.00 tax incl.
BDT 7,990.00 tax incl.
BDT 0.00 Tax
BDT 7,990.00 tax excl.
BDT 7,990.00 tax excl.
BDT 0.00 Tax
BDT 7,990.00 tax incl.
More
In-Stock
In stock: 13

Reference: RBD-0480

S7-300 CP 340 6ES7 340-1AH01-0AE0

(0)
Model:  S7-300,CP 340  Part No: 6ES7 340-1AH01-0AE0   Made in Germany SIMATIC S7-300, CP 340 COMMUNICATION PROCESSOR WITH RS232C INTERFACE (V.24) INCL. CONFIG. PACKAGE ON CD  
BDT 50,000.00
BDT 50,000.00 tax incl.
BDT 50,000.00 tax excl.
BDT 50,000.00 tax excl.
BDT 50,000.00 tax incl.
BDT 50,000.00 tax incl.
BDT 0.00 Tax
BDT 50,000.00 tax excl.
BDT 50,000.00 tax excl.
BDT 0.00 Tax
BDT 50,000.00 tax incl.
More
Last items in stock
In stock: 2

Follow us on Facebook