January 16, 2009


Filed under: Gadgets,Projects — Rohith @ 11:44 pm
Tags: ,

At last we made a robot!

Here is our effort.

Theme :

Basically, you can think of this as a remote controlled toy car, on three wheels. You can control the two backwheels using your remote. The front wheel is free-rotation type. To move our robo forward, the two backwheels rotate forward, to move it left our left wheel rotates backward and our rightwheel rotates forward( imagine!) and similarly other two movements can be achieved.


Components :

To drive the two rear-wheels, we use two motors, which can be independently controlled. When we supply HIGH to a motor’s red and LOW to black wire, it rotates in clockwise direction. And in anti-clockwise direction vice-versa. So in this way we control the motors.(Here HIGH is +12V of battery. LOW is zero or negative of DC battery.)

We have to control these motors using a remote control. Thats our mission. The circuitry we are going to discuss about just enables us to do that. First, transmission of data( in bits, HIGH- 1, LOW -0). This transmission is done using RF(Radio Frequency) modules- RX+TX kit. We have a transmitter and a receiver in this kit. On our remote control, we can generate a signal 10,10 or 10,01 or so on with switches( HIGH- LOW /ON-OFF thingy!). Then we have to transmit this signal to the robot’s motors. The way it is done is that, its first encoded (using an encoder IC)and then fed into the transmitter of our remote, which transmits the signal. This encoded signal is received by a receiver(on the robot), which is fed into a decoder IC and the output is at its four o/p pins. So, say if we give a 1001(HIGH LOW LOW HIGH ) using the remote-control, we should get 1001 at the o/p pins of the decoder IC of the robot. This information is then used to drive its motors accordingly. The table below gives what signals we have to give to both the motors (Left- L, Right- R) simultaneously to control the direction.



10 10


10 01


01 10


01 01


But these motors need 9-12V supply, whereas our decoder only provides 5V at its o/p. So to drive the motors,instead of providing the decoder output directly to the motors, we use another IC( L293NE) . The working is discussed below.

List :

1. Chasis for the bot (Try to make one !)2. Wheels(2) 3. One Free wheel in front( Castor wheel) 4. Breadboard 5. RF modules( RX + TX kit) 6. Encoder +Decoder ICs (HT12D, HT12E ) 7. L293NE 8. 7805 Voltage Regulator (for +5V Vcc) 9. Resistors 10.Geared Motors (60 RPM) 11. Switches 12. PCB (or Option 4 or Both) 13. Single stranded Wires

Circuit + Working :


The above diagram is a simplified flowchart of our transmitter receiver setup. Now we’ll explain the circuit diagram.



So,in simple words, if we are to supply a 1001 to S1,S2, S3,S4 in the transmitter , we should get it at D1,D2, D3,D4 at the receiver.

Note : The Input and output pins of the transmitter and receiver ICs are Active Low type

Next step is driving the motors. We could connect D1 D2 to the first motor (10) and D3 D4 to the second motor(01). But we can get only a maximum of 5V from the o/p pins(D1-D4), whilst the motors require atleast 9V-12V for optimum performance. So to negotiate this, we use a motor driving IC L293NE.

l293pinoutIt works like this. When we supply a HIGH at Input1, we get the voltage Vc ( pin8 ) supplied by the battery, at the Output1(and zero for LOW i/p). And similarly at the other three inputs as well. For this, we have to keep the ‘Chip Inhibit’ (or Enable) labelled pins 1 & 9 HIGH.

Now, we connect D1 to Input1 and D2 to Input2. (1,0 here). When we make Pin 1 HIGH, we get the voltage Vc(9V or 12V, as supplied) at Output1 and zero at Output 2. These two signals can drive one motor. Thus we can drive two motors using one L293.

So, if all goes well, we should be able to drive our robot using our remote control.



Under Rs 1300/- or $30( Robokits)

PS : 1. BRAINs stands for Back Row Association Inc.

2. Any(if) reader who wishes to implement this circuit is expected to have atleast basic knowledge in electronics and ICs.

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