Fluctuation in appliances

Thread Starter

bhargav shankhalpara

Joined May 9, 2010
Hello everyone...

i need help in my project CELLPHONE BASED DEVICE CONTROL...

in this project i use DTMF decoder for decoding tones and based on that switching particular appliances using electromagnetic relay, i use P89V51RD2 microcontroller to get DTMF codes and ULN2003 relay driver for relay ON and OFF. this circuit has also manual control option.

My problem is that when i connect normal load such as resistive load it working fine, but when i connect inductive type load such as fan, old chock based tube-light etc...it will make all devices turn off, even in my home anywhere this kind of load turn on or off it will generate fluctuation in my circuit that will change relay state...

please suggest me that what is actually problem...

and also i thing that if i use uln2003 than i can neglate flyback diode...? is that diode create that kind of problem...??

please help me...!!



Joined Jul 18, 2013
The ULN2003 has built in BEMF diode so for relay coil output it should not be required for those small relays.
I would expect the supply to the board be completely isolated, unless there is a common connection somewhere between the DC supply and the controlled AC?
Do you have a schematic?