Brian Petrowicz

Motor Control

 

 

            My first challenge was to design a circuit that would allow both motors to be controlled via the HandyBoard.  I knew that I needed relays and transistors.  A relay is an electrical device such that current flowing through it in one circuit can switch on and off a current in a second circuit.  I used a DPDT, double pole double throw, relay that can be seen below (Fig. 1).  Pads 5 and 6 are the + and – of the main power source.  These get “thrown” to either 3 and 4 or 7 and 8.  Pads 1 and 2 control 5 and 6.  3, 4, 7, and 8 are the pads that are connected to the device you want to control.

           

                                                                                                       7                        8

                                                                                                       5                        6

               Fig. 2                                                                                                         

                                                                                    Fig. 1          3                         4

 

                           G     D    S

                                                                                                      1                          2

 

A transistor is a semiconductor device capable of amplification.  It has three prongs, a base, a collector, and an emitter.  If I had just used a relay, then the motors would just be on or off.  By introducing a power transistor, I was able to adjust the power level of the motors, allowing anything from full power (100) to zero power (0).  Using alligator clips, a small 5V motor, and a power supply, and with the help of a fellow classmate, David, we constructed a working circuit(Fig 3).

 

 

 

Below is a schematic of the circuit for one motor:

 

     12V

 

   +          -
 
                                                                                           Transistor

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


The next step was to incorporate it into the MCP.  Soldering everything together, and creating plugs for the HandyBoard I wired it up.  Writing a simple program to test the circuit, I downloaded it to the HandyBoard and ran it.  It worked!  Then, due to some extenuating circumstances, one of the transistors blew.  Inserting a diode into the circuit across the transistor fixed the problem.  Then one of the transistors was blown again.  Since everything was hardwired, it was a nuisance to replace parts.  Using sockets solved this problem.  If something caused a transistor to blow, we could just pull it out and plug a new one in.  With the circuit still not working all the time, fellow classmates got involved to help solve the problem.  Throughout the next few days, the circuit worked sometimes.  At one point, we had the HandyBoard that controlled the motors wired up as a slave to another HandyBoard.  We were able to have one tell the other what to do and in turn, control the motors.  It was definitely an enjoyable moment.  But now it is the end of the semester and we have run out of time.  As of now, the motor control circuit still does not completely work.  Now it is only a matter of time.