MolPad released to Windows App Store


MolPad is a chemical structure drawing app specifically designed for tablets. It allows you to draw chemical structures freehand with a finger, stylus or mouse, just as you would with pencil and paper. The raw ink is converted on the fly to an underlying connection table. Both chemical bonds and handwritten atomic symbols are recognised, cleaned and incorporated into the structure.


  • Intuitive to use
  • Designed specifically for tablets
  • Chemically intelligent
  • Recognises bonds and basic atomic symbols
  • Gesture support for drawing rings
  • Supports industry-standard Molfile format

Find MolPad here.

Feedback and suggestions for improvement welcome!

Arduino powered Vileda cleaning robot – Part 2 (software)

Part 1 described the hardware portion of this project. TL;DR: the existing microprocessor was replaced with an Arduino.

Part 2 covers the low level robot control and iRobot Create emulation software.

A couple of hardware modifications have been made since part 1 was written:

  1. The Arduino Uno was replaced by a Nano. This is not only a lot smaller but also has a couple of extra IO ports.
  2. A battery voltage sensor was added in the form of a simple 4:1 resistor divider.

Thearduino pin mapping is now:

μC Pin Function Arduino Pin/Dir Notes
1 Right Bumper D6 In HIGH on bump
2 Over current In Unused
4 Right wheel forward D10 Out PWM IN1
5 Right wheel backward D9 Out PWM IN2
7 Fan & Side brush motor Out Unused
8 Wheels up D11 In All 3 wheels OR’ed
9 L switch D12 In LOW when pressed
10 L switch LED D13 Out Active LOW
12 M switch A6 In LOW when pressed
13 S switch A7 In LOW when pressed
14 Green LED A2 Out Active LOW
15 Red LED A3 Out Active LOW
16 M switch LED A4 Out Active LOW
17 S switch LED A5 Out Active LOW
NC Battery Voltage A0 In Via 4:1 divider
21 Left wheel forward D3 Out PWM IN4
22 Left wheel backwards D5 Out PWM IN3
23 Left bumper D2 In HIGH on bump
24 Speaker D4 Out
26 Main brush motor A1 Out Unused
35 Left wheel encoder D7 In
39 Right wheel encoder D8 In
40 +5V regulated 5V


For the software it was decided to emulate an iRobot Create 2. This has a documented API (iRobot Create 2 Open Interface) so all design decisions have already been made. Also, because this is a popular platform, third party software exists to directly control the robot and a driver for ROS integration is available.

Not all of the Open Interface commands were implemented, just those required for motor control, odometry and common sensors. The source code can be extended as needed. Some constants may need changing.

The code is straight forward in operation:

  • The serial port is monitored for any incoming commands. The commands are parsed and executed which results in motors running, sensor data being returned or robot state being updated.
  • Wheel encoder pulses are accumulated via two interrupt handlers
  • Every 15ms the internal state is updated. Sensor data is streamed out if requested. If the robot is moving, the motor power is updated. In normal driving mode (velocity and radius specified) a PID controller for average velocity is cascaded with another PID controller to keep the wheel speeds in the required ratio for the specified turn radius. In “Direct” driving mode (velocity of each wheel specified), two PID controllers, one for each wheel, are used to keep the velocities at the requested values
  • The Arduino PID Library is used with some modifications including bias value support

Full code available on GitHub here.

To verify compatibility the code was tested with the following:

  • The Create. program from here. (If running on Windows 10 need to run as administrator)
  • The create_autonomy ROS driver