Objectives

 

1. To understand the working of bicore circuits.
2. To understand the interaction study of neuronal circuits.

 

Theory

 

Nv Neurons or Nervous Neurons

 

The Nv neuron is a very simple circuit building block mainly consist of three different elements such as, one resistor, one inverter and one capacitor (Fig.1). The original concept of Nv neurons was patented by Mark W Tilden. He and his colleagues realized the use of these simple Nv building that produce complex patterns useful for the autonomous robot control. This Nv networks are the core of the most BEAM designs. Non-branched Nv networks are often known as core with a numeric prefix denoting the number of neurons in their loop-bicore, tricore, quadcore, quincore, hexcore etc. The “Bicore” and “Microcore” are the simplest and most common Nv neuron network system. 

 

 

Fig.1. Nv Neuron

 

A basic Nv neuron consists of a R/C differentiator followed by a voltage gain block to square up the differentiator output. When two or more Nv neurons are connected in a network, it is able  create a self-sustaining pattern generator that is simple to interface to sensor inputs, which react to the environment, and to simple connect to small motors, which provides the action and mobility for an automaton. There are several variations of this network, all of which belong to a class of circuits better known as "relaxation" oscillators .Nv networks are hardwired and  non-linear nature of the circuit allows it to be "programmed" with new behaviors by adjusting or tuning the Nv network. 

 

BEAM Robotics

 

BEAM robotics is a new emerging field whose procurement provides new wings to human creativity and imagination. It was developed a robotic physicist, Mark W Tilden in 1991. BEAM robotic is an acronym for Biology, Electronics, Aesthetics and Mechanics. It is a form of robotic system which uses analogue circuits such as comparators instead of a microprocessor for their driving purposes.

 

The word Biology in BEAM refers to the idea that nature provides many elegant models that can be used to design robotic models. BEAM robots are typically made of solar cells that they can survive by using solar energy. Electronics refers to that the robot contain electronic sensors which detect the presence of light and directed the robot towards the light. The Aesthetics and Mechanical aspects of BEAM come into the play in design part. A well designed BEAM robot is very neat, tidy and attractive.ie a good Aesthetics means that “it’s nicer to look at”, so that it can draw attention and admiration of other robot builders. 

 

BEAM robots works on the principle of the neuron approach where the nervous networks are possible for the generation of the random patterns .The generated random patterns interact with the sensors and motors feedback circuitry to control their mechanisms. In other words, the mechanism of BEAM robotics involves the circuits (i.e. Nv net of nervous neurons) which stimulates the biological neuron behaviors. BEAM robotics can be robust and efficient in performing the task for which it was designed. It mimics biological neurons by using a set of analogue circuits and facilitates the robots response to its working environment. The robots that uses both analogue and microprocessor electronics are known as mutants.

 

Bicore Circuits

 

Bicore circuits are the basis of advanced BEAM Robots. Most of the intermediate to advanced BEAM robots are built of bicore circuits. The little circuits known as bicore or suspended bicore which developed by Mark W Tilden. The bicore is an oscillating circuit. Nv neurons are the building blocks of bicore circuits. The prefix “Bi” in bicore defines the two states or nodes or cores which makes the central part of the robots nervous net.

 

The basic bicore (Fig. 2) is obtained by adding two Nv neurons and connecting the output of the second to the input of the first.

 

Fig.2 . Bicore Circuit

 

Also, taking out one of the resistors results in the formation of different circuit with similar behavior and the circuit becomes undergrounded and is called the suspended bicore (Fig. 3).The suspended bicore works quite differently from the normal bicore circuits.

 

                                        

Fig.3. Suspended bicore

 

74AC240 CHIP

 

The bicore circuit that we uses is the 74AC240 integrated circuit. This chip is an octal inverting buffer which means it can take 8 lanes of data and flip them around while making the signal stronger. The chip is shown below (Fig. 4), where the chip pin is numbered in a counter clockwise manner. The inverter in the chip is little harder to access individually, but are much easier to group together to amplify a signal.

 

       

Fig.4. 74AC240 Chip    

Image courtesy: http://ho.psdr3.org/teachers/Holman_Robotics_Club/The_74AC240_IC.html)

 

How does it works?

 

The 74AC240 chip contain eight logic gates that inverts the signals going into them. Whatever goes in, each gates gets inverted, i.e. low signal becomes a high signal and a high signal becomes low one. By combining three gates on one side and three gates on the other, we can make two teams of inverting gates that buffer the signal and make it more powerful, Bicore (Fig.5). The signal passing back and forth between the two nodes send high and low (on or off) pulses to the servomotor.  Result is the back and forth movement of the motor shaft, is transferred to our gears to create a reciprocating walking motion.  Remaining two gates are used as sort of the controller for the two three-gate teams.

 

 

Fig. 5. Working mechanism of 74AC240 chip