# Robotics/Computer Control/The Interface/Remote Control

Remote control is about controlling a robot (or any other electronic device) from a distance, either with or without a wire. Remote control methods can be split into two categories: wireless and wired.

### Wired Remote Control

Wired remote control or tethered control can be the right way to interface a computer with a stationary robot. For mobile robots the cable can become a burden for the robot.

#### Issues With Wired Remote Control
##### Limited Range

* Electric signals transferred over a wire lose energy because of the wires resistance. The result is that the amplitude of the signal decreases as distance increases.
* Reflections can be a problem when the data rate is high. This means a previous signal doesn't disappear before the next is transmitted. This is why transmission lines are "terminated" with a resistor to ground.
* Interference is caused by the magnetic fields of other conductors or capacitive coupling of high speed signals in other conductors. Shielding cables reduces interference, as does using differential signals (instead of using amplitude relative to ground to transmit '1's and '0's, using amplitude between 2 signal wires) through a twisted pair of conductors.

##### Mechanical Issues With Cables

* Cables have fixed number of wires in them, if you need more, you'll have to replace the whole cable, which can be very time consuming.
* Cables have a certain stiffness. The thicker the cable the more force you need to apply to bend the cable.
* Cables have a weight. This can make it hard for smaller robots to drag it around.
* They can get in the way of the robot.

#### Methods

Many of the mechanical issues of cables can be reduced by using thin cables with as few conductors as possible. Ideally such a cable would have only 3 or 4 conductors: Ground, power and one or 2 signal wires. See Networks for sending multiple signals through as few wires as possible.

#### Advantages

By using a cable you get around the problem of heavy batteries. The robot can be powered by an AC-outlet. Another benefit of a tether is the ability to easily use a PC to control the robot.

### Wireless Remote Control
#### IR

IR remote control is the best known form of wireless remote control. It's cheap and reliable, but limited to line-of-sight communication. Complete IR-receiver modules, like the TSOP1736, are available cheaply and can be interfaced with most controllers without much extra components. TV remote controls using RC5 (Phillips) can be used with such modules. If you want a faster data link, IRDA components could boost it significantly. Bluetooth and Wifi have replaced it on modern laptops, but IRDA components are still available.

#### RF

RF is widely known in model race cars, Wifi, and various other applications. These days complete RF transmitter/receiver modules are available at reasonable low prices. These modules are very easy to use and have ranges of around 100m depending on their environment. RF remote controls for high end model race cars have larger range but are much more expensive and limited in their use. While it is definitely possible to build RF transmitters from scratch, this is not advisable. Radio frequencies are strictly governed and building a transmitter that uses the wrong frequency quickly leads to a fine or worse. Know what you're allowed to do, before building one of these. It is possible to use a wireless telephone to provide an RF connection to your robot. The major restriction being data rates limited to 9.6kbaud or so.

#### Speech Recognition

In essence speech recognition is a form of remote control. Probably one of the hardest forms of remote control, but also one of the most impressive ones. Although today there are modules that contain a full speech recognition system capable of learning a dozen commands, those systems are still very limited as they can't handle sentences (just commands), need to be trained before they are useful and usually can only be used by one person.

#### Sound

Sound can also be used as remote control, generating a tone of a particular frequency isn't hard, building a receiver to detect this tone isn't too difficult either. Sounds like whistling and clapping hands have been used for remote control before (e.g. the keyring which makes a sound when you whistle).

### Network control

A further step would be to do the control over a network, from another device. This could be a wired network, like RS-232, RS-485 or Ethernet, or a wireless one, as WLAN, Bluetooth or ZigBee.