reed relays for DOUT module

[Dimitree]

hi everyone

I've seen that the example on the website about how to connect a reed relay to the DOUT module doesn't use any transistor and connect the pin directly to the transistor (adding just the protection diode). I've always read that it is recommended to use a circuit like this attached to the post

is it true for reed relays too, or it will work too if connected directly, with no problems?

many thanks to all

Dimitri

[nILS]

The reason for adding the transistor driver is simply that regular relais need quite a bit of current to switch and that may be too much for the shift registers to handle. Reed relays seem to need less current which allows them to be driven directly from the shift regiter pin - whichever you decide to use make sure the current draw is small enough or add the transistor driver.

[technobreath]

I have a question nils. I have never fully understood the transistor. I used to design cuircuts in simulators just to learn, but the simulator I felt wasn't too picky :) It accepted about anything - even stuff I knew to be wrong, so I don'trust the simulator at all. With that said, I am planning a LC build when finished with my gm5x5x5s and the mbsid, and I would like to control some stuff from the DOUTs that aint part of the console to begin with - i.e. record sign outside the studio on /off when record button is pressed etc... I want the option to switch AC 230v stuff from the console. This I could easily do with a relay solution, but this would be audible and annoying.

Is there some way to do this using descrete components? Can a regular transistor switch AC? What descrete components do if its not the regular transistor?

I have seen some high power descrete contactors used to switch on panel heaters in a big audiotorium - I understood it was used to prevent sparks and stuff cause of the high current. I can't remember the amp rating on the thing, but it was insane. I assume this is expensive components used (I don't know exactly the name). If someone knows anything about this, and can point me in the direction of what switching component to use, I should be able to figure out the rest myself.

[Dimitree]

thanks Nils, since I don't have much knowledge about electronics, is there a way to understand if there's enough current to drive my relay, with datasheets in the hand?

[TK.]

You should find the current consumption in the datasheet, it should be less than 10 mA.

Best Regards, Thorsten.

[Dimitree]

yes it's (+/-10%) 10mA, so I guess at limit?

[nILS]

technobreath: Yes it's possible, no I will not go into details of switching 230VAC in here. There be dragons, 230V is ouchy, especially if you don't already know how to do it :)

dimitree: 10mA +-10% is within spec, you could/should use a resistor in series with the DOUT output (like for LEDs) to limit he current (330R seems about right and will give you 15mA).

[technobreath]

technobreath: Yes it's possible, no I will not go into details of switching 230VAC in here. There be dragons, 230V is ouchy, especially if you don't already know how to do it :)

Hehe, you're quite right. It's ouchy I know. On second thought, I will not think of having external 230vac equipment connected and switched through my console anyway. I'll probably either make some box with relays and place them where I can't hear them. I know at least three electricians who would wire it up for me legally :P, or I will use 12 volt for the entire thing...

Edited January 10, 2011 by technobreath

[Dimitree]

many thanks again, I guess I'll add on my pcb the space to stuff transistor too, so in case the pic won't be able to drive the relays I won't need to threw away the pcb :D

next time I will search for <10mA relays