AVR-Chat

Daniel Boyer wrote:
> 
> > All of the SSRs I've ever used have a resistor, internally,
> > in series with the LED and the input is rated by voltage or
> > voltage range, i.e. 3-28V. Daniel, what
> > is the input voltage and current requirements for the SSR you
> > are using?
> 
> First off the SSR that I am using is a true SSR in that is has an LED
> inside which activates a MOSFET... As to bruce's question about the
> input voltage range of my SSR: I don't know... I have looked over the
> datasheet ( http://www.dpicts.com/Laa110.pdf ) many times and can not
> find an input voltage anywhere.  This may be my problem, but I don't
> know; I would appreciate it if someone could look at the sheet and tell
> me where the input voltage is listed.  I'm about to rewire the
> transistor and see if it works, if not I do have a 5V relay from
> Radioshack that I can try in place (I really didn't want to use the RS
> Relay because of size, but I will if I have to and then look for an
> alternative later.)
> Thanks,
> Daniel
> KC9DAG

Looking at Pg 1 of the data sheet, we have just the LED for input. On Pg 2,
under Electrical Characteristics, we need 5 to 50 mA for input control. The
AVR will source 10 mA at an output voltage of 4.3 V when operated @ 5V. The 
LED will drop 1.2 V @ 5 mA. Let's assume 1.3 V @ 10 mA: 4.3V - 1.3V = 3.0V.
Since R = E/I (Ohm's Law), R = 3.0V / 0.01A = 300 Ohm. So put a 300 ohm
resistor in series with the input LED and it should work. 

Another issue is switching speed; the specs list 3 mS max for turn-on and 
turn-off with typ turn-on times around 1 mS. How fast are you trying to 
switch the relay? A 10 mS pulse should do it but 100 uS will never make it...

Bruce