View Full Version : need help for roborace

02-21-2010, 11:34 PM
hi guyz, i am using a remote which has 6 terminals...
(a) terminal 1 for power +5v
(b) terminal 2 for power 0v
(c) terminal 3 for output 1
(d) terminal 4 for output 2
(e) terminal 5 for output 3
(f) terminal 6 for output 4

button pressed:
output 1 output 2 output 3 output 4
1.up +5v 0v 0v +5v
2.down 0v +5v +5v 0v
3.left 0v +5v 0v +5v
4.right +5v 0v +5v 0v

i have connected these output terminals to l293d ic.....the pin8 was connected to +7.4v(Vin)..
the prob. is that when no button is pressed the pin 3(output pins) are giving me 1.3v....this destroys the difference between
1 logic and 0 logic...also i would like to tell you that i didnt used coupling capacitor(100nf and 10uf) as the source is li-ion battery and connected it directly to lm7805 ic as capacitor 100nf was not available near my home...what should i do...what is the fault going in it??

02-22-2010, 09:03 AM
From where you got the RC module. Give the link.

02-22-2010, 12:08 PM
Pin 3, 6 are outputs for motor drive. How does it matter what the voltage is on this pin??

These pins are 'floating ' Motor H-bridge outputs and does not indicate logic state. The residual voltage is due to the internal drive transistor junction drop - .7v per transistor in the bridge.

It is wrong to measure the O/p pin voltage with ref to -ve or VDD. You must measure between pin 3 & 6.

Just dont bother. Connect a motor to 3 & 6. It will run.

02-22-2010, 07:15 PM
sorry my question is wrong....
actually the pins 2,7,10,15 (the input pins of the ic) are on voltage level 1.3v to 1.8v when no switch was pressed instead of being 0v.....
at pressing the switch the voltage increases to approx. 5v....but since the low level is at 1.3v(or 1.8v here) the difference between 1.3v and 5v is not there...by this i mean that l293d is assuming both logic levels are high....therefore all the outputs are always high whether there is any input pressed........
what should i do?? shall i use transistors or any other thing like that

02-23-2010, 02:57 PM
Make sure your motor voltage (Vs) ground and Logic voltage(Vss) ground and your Wireless Receiver's grounds are common.


02-23-2010, 05:45 PM
Connect 10k resistor from input pin to ground.

02-23-2010, 07:59 PM
what do you mean?? why to connect input to ground if i am using logic 1 and 0 both.....

02-23-2010, 08:03 PM
if possible can u post the circuit of roborace project....

02-24-2010, 06:07 AM
Utkarsh, we are trying to help you out with what you have provided us. We have no clue about what roborace and/or any other specification about the RC module and the other components.

What we do here, is show you the path. You have to walk it yourself... Think of it as a learning process.


02-24-2010, 10:07 AM
what do you mean?? why to connect input to ground if i am using logic 1 and 0 both.....

1. First Brush up your Ohms Law from the high school text book.
2. Then, if you still dont get it- just connect the resistor like I said, and see.

__________________________________________________ _________________________________________
I can be a baby-sitter......but WHERE IS THE BABY????

02-24-2010, 09:20 PM
do u mean to say that connect resistor in parallel with input....

02-27-2010, 11:30 AM
hey did this thing...it worked ,i.e., the low is now at 0v...but another problem has creeped up which is that the high voltage is around 0.5v....what to do now???

02-27-2010, 03:28 PM
You could havew ' fried' the L293D.
1. Connect the motors first . You must not operate the L293D for long time without load.
2. Pin 1, 9, 16 = 4 volts atleast. It wont work if it is below 4v.
3. Pin 8 voltage ( should be the Motor voltage 4.5V to 30 V)
Now check if the Output changes when you press the key. You candirectly connect a wire to the input and use this to apply 0v 0r +5v.