This assignment describes the electronic components to be used and their
integration with mechanical parts for the working of the autonomous
Block Diagram of electronic control:
Sensor Signal Condn. Microcontroller H-bridge Motor
The sensor is used to get inputs from the surroundings, specifically in our
case, to: 1. Follow a predefined path by differentiating between blue
background and white lines, and 2. To correctly pick up and place the
For line tracing, a circuit employing light dependent electronic devices
(photodiode, phototransistor or IR Tx-Rx) has to be used.
For block pick-up and placement, proximity sensors or contact switches may
Signal Conditioning Circuit:
The output of the sensors is in the form of analog voltage or current, and this
has to be converted into logic voltage levels compatible with the
microcontroller. A simple rail-to-rail operating comparator may be used. Use
of a Schmitt trigger circuit provides some immunity to noise and is
recommended. The following circuit is a single power supply Schmitt trigger
circuit operating at +5V and it gives output compatible to TTL levels.
In this circuit, the analog output of the sensor is given to the input terminal
of the comparator (1/4 IC LM339). Depending on crossing of threshold
levels of the Schmitt trigger, the output is practically obtained as +4.98V
(high) and +0.34V (low). This is compatible with the logic levels for TTL.
The threshold values for this circuit are +1.1V and +2.9V. These can be
adjusted by changing the values of R1, R2 and R3 according to given
The function of the microcontroller is to control the overall working of the
machine. It is meant to receive and process input signals and take suitable
controlling action based on the desired sequence of operations.
We have decided to use the AVR family of microcontrollers for autonomous
machines in Robocon. Required programmer and flash programming
software as well as programming hardware are already available. Previous
year’s controller (ATmega8518) and PCBs are also useful. If required we
might have to select another controller IC in place of ATmega8515. The
basic parameters and facilities are nearly the same in all AVR controller
versions. Only their number varies.
Selection criteria for the controller are:
1. No. of PWM generators for motor speed control.
2. No. of dedicated IO lines.
3. No. of external interrupts.
4. No. of 8-bit and 16-bit timers for delay generation
5. Availability of on-chip ADC and analog comparator
A complete list of available versions as listed on the manufacturer’s
(Atmel Corp.) is included along with their specifications.
The H-Bridge IC is the link between the electronics and the mechanical
domains in the autonomous machine. It is the actual device that regulates the
running of the motors. The H-Bridge controls the running of the motor on
the following parameters: run/brake, direction of rotation, speed of rotation.
The inputs to the H-Bridge are logic signals for run/brake and direction
control, as well as a PWM signal to operate the motor at fractions of rated
speed. PWM signal can theoretically run the motor at speeds from zero to
For ease of operation, it is desirable that each of the three parameters are
controlled independent of each other. In locally available H-Bridge ICs like
L298, all three controlling parameters are operating in the same two pins of
the IC. This causes difficulty in writing the programs as well as designing of
the PCB. The H-Bridge IC LMD18200 (first purchased during Robocon
2005) offers brake, direction, and PWM control on three separate pins, and
so it is easiest to use. Its electrical ratings are also suitable for the motors
that we will be using on our machines.
Max. operating voltage: +55V
Operating current: upto 3A continuous
Internal clamp diodes
Thermal shutdown and shorted load protection
Available in TO-220 as well as 24-pin DIP
The allowed power supply is upto 24V dc. Hence it will be better if we make
use of the maximum allowed power supply. It is recommended to use 24V
DC motors of required speed (and available torque)
Use of nickel – metal hydride (NiMH) batteries is preferred as they are easy
to charge and available with good current capacities. 12V or 24V battery
packs can be connected by soldering the cells together. Battery packs having
current capacities in excess of 2000 mAh can be made. To operate the
microcontroller at +5V supply, a voltage regulator has to be used.
It is not possible to use lithium ion (Li-ion) cells as they cannot be charged if
permanently soldered in the form of battery packs.
List of Electronic components:
1. Sensors (based on independent testing)
2. Signal conditioning circuit suitable for selected sensors
4. H-Bridge (specifically the LMD18200 H-Bridge IC)
4. NiMH batteries
Intention of this assignment was to:
1. List out the various electronic components required
2. Provide general information in electronics to everyone working on the
3. Seek suggestions from experts in order to improve the electronics design.
TE E&Tc (2007)