My project looks like it's perfect for the combination of Sainsmart Arduino UNO and the 8-channel 5v Solid State Relay Module. It's a kinetic artwork with eight, AC-powered light circuits. Three questions:

  1. Are these two boards compatible? That is, can the UNO's digital outputs interface directly to the Relay Module's inputs?
  2. It looks like the UNO needs a 9v supply and the Relay Module needs a 5V supply. Can these two boards operate correctly with a single DC supply?
  3. By some chance, does the UNO board offer a 5V DC output that could power the Relay Module?
  • 1
    \$\begingroup\$ Do you have links to these items? \$\endgroup\$ – Oli Glaser Jul 9 '12 at 3:49
  • \$\begingroup\$ If LEDs 5 through 8 don't light that's because they're reversed mounted :-). \$\endgroup\$ – stevenvh Jul 9 '12 at 18:46

OK, now at least we know what you're talking about.

They are compatible in the way that you can directly connect the Arduino output to the relay module's input. Arduino's logic is 5 V, and the module needs 2.5 to 20 V input to drive the relay. So that's OK.

The Arduino needs at least 6 V input (7 V recommended), but the circuit works at 5 V, and that 5 V is also available on the power connector, at the bottom of the picture.

enter image description here

Connect this 5V and the ground next to it to the relay module's power connector, and up to 8 of the digital I/O's shown at the top to the relay module's logic inputs and you're in business.

vicatcu explains that the Arduino can also be powered from the USB input, and that's true. But the relay module will draw up to 160 mA, and that may be more than your USB port will supply. The Arduino itself also needs around 50 mA.

edit 2012-07-09, re jippie's comment
The Arduino Uno's LDO voltage regulator can supply 800 mA, which should be sufficient for Arduino + relay module, together about 200 mA. At 6 V in the LDO will dissipate 200 mW, and that's no problem, but at 15 V in that becomes 2 W, and that may be too much for the NCP1117's thermal protection. After all this is an SMT device. So it's advisable to use an as low as possible input voltage, or use a separate 5 V wall wart to power the relay module.

  • \$\begingroup\$ Sure if the total current can be drawn from the on board ? \$\endgroup\$ – jippie Jul 9 '12 at 18:48
  • \$\begingroup\$ @jippie - Should be possible if you don't use the 5 V to heat your bathroom :-). The Uno's LDO can supply 800 mA. But current will be limited to a lower value if the regulator's thermal protection would set in sooner at 20 V in, for instance. \$\endgroup\$ – stevenvh Jul 9 '12 at 18:55
  • \$\begingroup\$ Was especially concerned about the cooling capacity on the uno. I have no feeling about how well these soldered on regulators can dissipate enough power onto the copper of the print. \$\endgroup\$ – jippie Jul 9 '12 at 19:01
  • \$\begingroup\$ @jippie - you're right. Added to my answer. Thanks for pointing it out. \$\endgroup\$ – stevenvh Jul 9 '12 at 19:03
  • \$\begingroup\$ Thank you so much for the detailed information. You guys are so helpful. Thank Stevenvh to have edited the link. \$\endgroup\$ – Thong Eric Jul 10 '12 at 2:08

I'm not exactly sure what you mean by compatible... The SSR module is not an Arduino Shield form factor so you won't be able to just stack it onto the Arduino Uno. But you should be able to connect the two boards with some hookup wire. From what limited information is available on the project page the SSR Module implements eight of these circuits: enter image description here

An Arduino digital output can drive the node labeled CH1 high to activate the relay.

The relay being referenced by the product page is discontinued by the manufacturer. That being said, looking at its datasheet, the operating current for the SSR is 7 to 20 mA, so it seems like a safe bet to operate the board from the 5V regulated output of the Arduino, which is derived from the 7 to 15VDC input provided to its 2.1mm barrel jack connector. You can also provide it 5V directly to the Arduino through the USB connector.

Finally, I know you didn't ask this, but if you are switching lights, you might be in some trouble with these relays. Incandescent lights, in particular, have a rather large inrush current when powered on cold. The relays on this board are only rated to handle 2A max, so keep that in mind. You might need to throw in some beefy current limiting resistors for example to counteract the initial inrush current.

  • \$\begingroup\$ Thank you for your attention and the information you provided for me. It saves me a lot of time in searching around. Thank you very much. \$\endgroup\$ – Thong Eric Jul 10 '12 at 2:05

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