what could be the posible reason

[tech_pro]

hi

I hav made a circuit that shifts between the output of tow relays to run the DC motor in CWand anti clock wise direction


wat i do is that i hav written a program in 89S51 that toggles its output 1-0 and 0-1 on port2 ( pin 21 and 22)

these pins are the connected to the latch that drives the relay with BJT in between

the circuit was running fine with very little problem( a wrong connection)

so wat happend wen i rectified the connection

the program of the controller runs fine if no latch attached

if i place the latch in between the pin 22 stops toggling and the pin is continusly at 0V

i m unable to pick the problem

please help wat cud be the probable cause

to mention i have checked the circuit by removin u-controller and gave latch direct input with either polarity the circuit rumnnig fine

please help

uzmeed

 

[vinoth8051]

Hi,
Kindly attach the circuit of latch section and indicate how you are interfacing with 89s51. It would be easy for people to help.

 

[BradtheRad]

Did you include diodes across the relay coils? The purpose is to absorb high voltage spikes created by coils when they're switched off.

If you leave off the diode, spikes can inflict damage on nearby devices.

 

[Senthilkumar_rjpm]

Check diode across relay coils as bradtheRad told... & Plz conform following things.. 103 disc capacitor between VCC & GND near to Microcontroller... check Power on reset pin dry soldering... jus add 2 or more 100Nanofarad box type cap betweein Vcc & Gnd as well as relay driver pins...