AVR-Chat

--- In AVR-Chat@yahoogroups.com, "Daniel Boyer" <dpboyer@d...> wrote:
> 
> > There isn't one. They are just IRleds, so as long as you have 
> > 2-3 volts across them, you'll be fine.  
> 
> Will 5V across them be okay, or do I need to do something to bring 
my 5v
> down to around 3 just for the relay?

http://www.dpicts.com/Laa110.pdf 


Now that you have defined the part, it is easy to layout a schematic.

As you guys noticed, there are almost 50 responses to this, with one 
common subject line.   This makes it hard to search the archives for 
the best answers.

To review, a mechanical relay with coil will spike back when the coil 
collapses and that spike will fry the driving circuit.  A ULN2803 (8 
channle) darlington or TIP120 (single channel) darlington will have 
an internal doide to protect themselves.  you can use other 
transistors or mosfets, but either add the protection diode or make 
sure the chip has it internally.

the diode shorts the reverse voltae that the coil releases when the 
magnetic field collapses.

Often, one uses a resistor from the pin of the uC to a transistor to 
drive the transistor.  that transistor would then control the relay 
coil.   A pull-down resistor would be needed to make sure the 
transistor were off hard and not potentially floating.

As for the SSR in question, If it is driving an external relay, you 
need a diode on THAT relay to protect the SSR !

Hope this addes some clarity and offers some help.

Dave