prevravanth

Hi,

I am using 89S51 and RS 232 for serial communication.

I drived relays using ULN2003 . I am using Embedded C

Now i want switch multiple relays and how to connect these multiple relays
using limited I/O pins.

Kindly help me ..

Thanks

kchriste

Use a shift register with a built in latch. Something like the 74HC595 will work and you can cascade as many as you want.

__________________
--- The days of the digital watch are numbered. ---

ljcox

This is a simple solution as you only need 2 i/o lines. One for the data and one for the clock signal.

The data should be clocked into the SR as quickly as possible so that the relays don't chatter. The time to clock in all the data should be less than say one tenth of the relay operate time - or faster.

__________________
Len

Sceadwian

The 74HC595 that kchriste mentioned is a latching shift register, it has a built in storage register that holds the contents of the shifted data until a third line is toggled then the output latch is updated. It requires one extra I/O line for operation but the latch updates all the lines at the same time. Perfect for driving relays such as this to avoid any possibility of triggering the relay accidentally. You could operate it as a standard shift register by tieing the update to the clock line if needed.

__________________

ljcox

Or he could use a non latching SR such as the 4014 or the 74HC164.

Another possibility would be to programme another PIC, such as a 16F84 or 16F628, etc. to receive data sent on one line and output it in parallel to drive the relays.

__________________
Len

ikalogic

to reduce cost, and use a minimum number of I/o lines, using a 89S51 at 24 Mhz and a 74164 SR will work perfectly, the relays wont notice anything until the voltages are seteled down..

In your case send the data as fast as you can do it, the 74164 response will allways be much higher than the maximum output frequency of the uC at 24 Mhz.

good luck

__________________
Ibrahim Kamal
check my electronics and robotics page: http://www.ikalogic.com/

justDIY

allegro makes a latching shift register (similar to the 74hc595) plus mosfet current sink combo chip... might help to cut down on the amount of IC's and/or soldering

http://www.allegromicro.com/sf/6821/

__________________
If you don't have a planet, what good are gold bars?

want to contact me directly? gmail gordonthree
check out my project website: http://projects.dimension-x.net
Favorite numbers:
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0