I recently modded my home servers casing, and put two white cold cathodes in it. The cathodes take power from the 4-pin molex. An inverter converts the 12V DC into 600 - 800V for the cathodes. There is a simple on - off switch in the wire between the inverter and the molex.
I am going to include a Arduino board in the casemod to control some leds and fans. What I would also like to do is control the cathodes via the Arduino. Can I somehow have my Arduino board to control those cathodes? I just want to be able to turn them on/off via the Arduino board.
What kind of budget do you have and how much electronics experience do you have?
Easiest is probably a solid-state relay:
You can probably find cheaper if you look around.
Very simple installation: connect pin 1 to 12V pin 2 to the inverter, then connect pin 3 to a microcontroller output and pin 4 to microcontroller ground.
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The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, light sensor, potentiometers, pushbuttons
An SSR is a combination of an optocoupler and a triac - nothing else (well sometimes it also contains a diode and a resistor.)
This is mainly made for AC applications, and cannot easily be used for switching 12 V DC, as it will not switch off! There are also - very few - SSR for DC that come with a MOSFET rather than a TRIAC.
If you do not need absolute decoupling of your circuits then I should use a 60 cents MOSFET rather than a $6 SSR (though I think the SSR you pointed to is more around $12...)
(1) You need a "logic level" N-type, there have been many mentioned here in the forum, or just choose from whatever catalog...
(2) Connect gate with your Arduino output, source with with your Arduino ground and the12 V ground.
(3) Drain is connected to the (-) of the inverter, the (+) of which is connected to 12V.
(4) If you feel so, you can also use a 4.7k to 10k resistor between gate and Arduino pin; this is not strictly necessary.
(5) It might also be useful to connect a 100k resistor between gate and ground (a "pull-down") to avoid random switching in case the Arduino is powered off or a different program is running there..
One more question: would this SSR fit my needs? I'm talking about the Crydom D2W203F Solid St Relay.
No. As deSilva pointed out most SSR's are based on triacs and are only designed for switching AC currents. The SSR I selected for you (Crydom DO061A) is designed for switching DC currents since it uses a transistor. A more efficient cousin of it is the DMO061A which uses a MOSFET but I don't think it's as easy to find.
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The Quick Shield: breakout all 28 pins to quick-connect terminals
Click on the link at the center-top of the page you found that says "datasheet" The datasheet (always more trustworthy than what the distributor says) says it's electromechanical.
Diodes are cheap, buy some anyways. You can use them for Christmas decorations if nothing else.
from page 3 of data sheet - see also p.2 (graphics broken, naturally )
Ordering information
Electromechanical relay (EMR)
Example: 34 series slim electromechanical relay, 1 CO (SPDT) 6 A contacts, 24 V sensitive DC coil.
A B C D
0 1 0
3 4 . 5 1 . 7 . 0 2 4 . 0
A: Contact material D: Special versions
Series
0 = Standard AgNi 0 = Flux proof (RT II)
Type
4 = AgSnO2 9 = Flat version
5 = Electromechanical type
5 = AgNi + Au (5 [ch956]m) C: Options
No. of poles
1 = None
B: Contact circuit
1 = 1 pole, 6 A
0 = CO (SPDT)
Coil version 3 = NO (SPST)
7 = Sensitive DC
Coil voltage
See coil specifications
Selecting features and options: only combinations in the same row are possible.
Preferred selections for best avaliability are shown in bold.
Type Coil version A B C D
34.51 sens. DC 0-4-5 0-3 1 0
34.51 sens. DC 0-4-5 0 1 9
Solid state relay (SSR)
Example: 34 series SSR relay, 2 A output, 24 V DC supply.
3 4 . 8 1 . 7 . 0 2 4 . 9 0 2 4
Output circuit
Series
9024 = 2 A - 24 V DC
Type
7048 = 0.1 A - 48 V DC
8 = SSR type
8240 = 2 A - 240 V AC
Output
1 = 1 NO (SPST-NO)
Input circuit
See input specifications
