Getting multiple outputs

[Murugesh_89]

Hi,

I am using a 3.3V operating pic microcontroller and the port output pins of uc is connected with 74HC245 ( 3.3v to 5v buffer ). The output of 74HC245 is connected as inputs to the attached circuit.

The attached circuit has 8 outputs and each is connecting with a 24V DC contactor. The contactor then connects with some ac motor. Totally six 3 phase induction motor and two single phase motor are controlled by this circuit.

The issue here is,
1. Some times, When i enable any one output say J1 the corresponding LD1 glows brightly but other led's are glowing blur. Hence all other outputs are also activated partially.
2. Some other time, When i enable any one output say J1 for long time the corresponding LD1(Brightly) and other led's(blur) switching On and Off periodically(like continuous pulses). Hence the other motors are also on/off periodically. But i dont change the output of microcontroller pin.
3. On power on itself with all the uc pins are low, the output led's in the circuit glowing blur and then it switched off.

Can anybody please help me on how to overcome this issue.....


Thanks...

 

[chuckey]

D21 isolates the relays from the +24V decoupling, put a big decoupling capacitor on the other side of it (1000 MF?) to earth. The 100 ohm in series with the back emf diodes should be removed (R20,37....) . I would put a .1 MF cap across each coil.
As for switch on, are you sure that your micro is not firing up its outputs as it moves into its proper program?

 

[Murugesh_89]

Thanks for your reply...

I want to know one more detail. Is it good to hit the Mosfet directly from the input connector in the board. That is, directly from the output of 74HC245 ( 5V supply given to 74hc245) to mosfet. Will it switch mosfet?