View Full Version : Somebody Help!!!!

11-22-2005, 01:04 AM
hi everyone !
I m doing my Final project , my project is to build a robot which
will follow a stick , whenever the stick is moved forward the robot has to move forward and when the stick is moved left so do the robot should and when the stick is moved towards the robot , the robot is to go backwards

for that i m using IR sensors (TSOP1738) to detect the presense of the stick and hence i m converting the digital output of the Receiver to DC voltage by using a capacitor and a resistor .

i am using 2 555 timers to generate the 38KHz pulse and the receiver is receiving the reflected pulse .

I m using L293D to drive the motors . The Logic Circuit is implemented which gives the inputs to the L293D.

I m giving seperate powersupplies to the Logic and the Driver Circuit .
I m Supplying Voltage of 12Volts through the batteries which can supply at the max of 1 A current and hence the two circuits are running seperately.
I m giving 5 Volts to the Logic Circuit . For this i m using a regulator 7805 to regulate the 12 Volt supply to 5 Volts and hence the Logic Circuit is Giving the Output .
My Overall Circuit needs 340mA current in normal Conditions and 650mA while Switching but the Problem i m facing is that the Logic works fine when i lift the Robot in the air but when i place the robot on the floor the Logic eventually dies and the robot Gives some crap outputs, sometimes it doesnt senses and rotates in the Circle and sometimes it keeps on moving backwards and even while switching (means when some different action it has to perform according to the output of the sensors (i m using 3)) the regulator gives output of 3.46 Volts instead of 5 Volts

can somebosy help me in this project !
Is L293D not sensitive enough to detect the changes and work accordingly ?

can somebody tell me what should i do ? how to get rid of the problems !

My Logic truth table is :
S1 S2 S3 M1 M2
0 0 0 0 1
0 0 1 1 0
0 1 0 1 1
0 1 1 0 1
1 0 0 0 1
1 0 1 1 1
1 1 0 1 0
1 1 1 0 0

S1, S2, S3 are the three sensors and M1 and M2 are the motors
for Sensors 1 means it is sensing and 0 means it is not sensing
for Motors 1 means in the forward direction and 0 means it is moving backwards .The 3 sensors are at an angle of 45 degrees to the centre one
i m covering the sensors with black papers to absorb the radiations i.e. making a parabolic curve and placing the sensor inside it

SomeBody Please help me !!!!!


11-22-2005, 11:11 AM
Hi ashu,

the regulator gives output of 3.46 Volts instead of 5 Volts

The voltage drop across the regulator 7805 is around 2v. So make sure that you give atleast 7 volts to the regulator input. But in your case it seems that u r already giving 12v to it. Try using seperate batteries for driver circuit and logic circuit if u have not already done it.


11-22-2005, 07:42 PM
see the datasheet of 7805 u can see that

Vin-(7.5-20V) as i remember

Check for the ratings of adapter, most adapters have 12V,500mA ratings.

If you have power problems buy a second hand SMPS

then no power supply problems occurs later, it have 40A capability. Take from old PC like 486,P1

Bibin John

11-22-2005, 07:45 PM
but when i place the robot on the floor

This means that there is no problem in your logic circuit but it needs more currnet beacuse the regulator voltage drops down when motors consume more power.

If your power supply is capable of supplying 1 amp doesnt mean that your circuit will consume 1a, it will consume less but if you use higer rating supply it will consume more amps. Try using high amp supply or separate supply for both circuits. Also try placing a capacitor of high value at input of 7805.

11-23-2005, 10:10 AM
hi ashu,
i take it for grantdtat u must have made all connections right and have a common ground.....
check out how much current ur motor draws. wat is the max. current rating..... because l293dcan drive only .5amps of current thro the motors...
and u ve restricted things by putting 1amp supply. it wont allow more current to be drawn which may be those ir sensors and motors taken together want on loading....
try 74244 or 74245 buffers while driving l293d.
may be on loading the motors ur circuit is getting loaded and hence the voltages are falling below and tat might trigger similar probs.
these buffers will give u distinct output levels and are fully compatible with l293d......
post msg if u stil cant get it working