Question about SSROZ boards (5V common ground)

[kwebdesigns]

On the SSROZ boards the optocouplers use a 5V common system. Is there a special reason for that? (besides being supported by most controllers) I use an AVR micro controller to control my lights and use relays with a common ground system. I would like to use SSROZ boards because it would be cheaper than creating new ones. If I were to change my design to a common 5V would the micro output 5V to the relay whenever the lights are off and go to ground whenever they are on? Does this pose any wear on the optocoupler having 5V applied to 2 pins on the optocoupler?
Thanks in advance. :D

[P. Short]

The 595 chips that people have been using for a while can only sink or source 70 mA total due to power/ground pin limitations. This meant that they needed an external buffer chip for use with 10 mA or 15 mA opto-couplers. For various reasons people commonly chose the ULN2803 for this buffer chip, which is an open-collector output chip, hence the 'standardization' on common 5V.

As to your questions about what your micro would output in a common 5V system, the answer is yes (assuming that there is an even number of inversions between the output of the micro and the SSR input).

Is your AVR micro board some sort of commercial product, or is it something that you've designed and made yourself?

--

Phil

[kwebdesigns]

Thanks for your help. I saw a friend computerize his Christmas lights and decided to make a last minute attempt myself. I did not have time to order a controller so I made one out of spare parts that I already had. If you are not familiar with AVRs they are a micro similar to PICs.

[NogginBoink]

You should still be able to use the AVR... just write a '1' to the pin for off, and a '0' for on.

Going to a common +5V would require a new circuit board, since the low voltage side of the circuit is an LED, the 'D' standing for 'diode' which will not work if you reverse polarity.

[kwebdesigns]

Thanks to everybody that helped. I built a new relay with a common 5V and it worked.