thomashp

Recipes 

Anyone using an arduino digital pin to directly drive an SSR? Most of the input currents for the 40A SSRs I'm looking at is 10-20mA. I think the arduino should be able to handle that. I'm trying to build a very minimal system that basically controls 2 heating elements and has 2 thermometers. Should I stop being cheap and lazy and use some transistors or can the Arduino directly drive these babies?

http://cgi.ebay.com/NEW-Solid-State-Relay-40A-SSR-40DA-3-32VDC-24-380VAC-/270653345266?pt=LH_DefaultDomain_0&hash=item3f0432 4df2

DeNomad

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An arduino should be able to drive those things just fine. I would suggest looking at the hardware index page: http://arduino.cc/en/Main/Boards

http://arduino.cc/en/Main/ArduinoBoardDuemilanove This is the board I have. It says the I/O pins can handle up to 40 mA.

Also... how are buying SSRs cheaper than grabbing some transistors? Transistors are dirt cheap.

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utopeya

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Disclaimer: I'm no electrician, and I'm no Arduino expert. That said, my system's Arduino is directly connected to the SSRs, and it seems to be working fine. The control voltage of my SSRs (cheap Ebay ones that get shipped to you directly from Asia) is 3-32VDC, and the Arduino pins output at 5VDC.

Edit: and yes, like DeNomad said, 40 mA. Like I said, I'm not an expert...

thomashp

Recipes 

Sorry for the confusion. I didn't mean transitors or SSRs. I just wondered if I needed transistors and SSRs. I guess I'm just trying to minimize the amount of parts and wiring I had to do. I'm lazy. I think it's probably good practice to use transistors as it isolates the Arduino from the SSRs and the higher voltage, but I guess the SSR already does that...
I guess the only thing I have to worry about not using transitors is that the max draw from all the I/O pins can't be more than 200mA. I think I might just use a few transistors just so I don't have to worry about it.

shushikiary

Recipes 

Well it depends on which ATMEGA chipe you are using exactly, but the current need of the SSR exceeds the max current sink or supply of the pins on the ATMEGA chips. You can run it that way but you'll decrease the life of the chip.

Easiest way is to do what brewtroller does and get your self a darlington pair chip and drive it using the ATMEGA and have it sink the current for the SSR, sense each pin on the darlington pair can easily sink 200ma usually a pin so you'll be fine running multiple.

What you really need to do is double check your spec sheet for your specific part and make sure it can sink or supply the current you're asking of the pin.