HI
Using this relay hfd2/012-s-l2-d at 12 volt dc note this is a dual coil relay.
Looking for a Arduino basic code to test, to reverse output dc voltage say with 2 leds to show both positions.
Could someone help this oldie with a example sketch. Thanks have several already on hand to use. Will once this is working try and H bridge.
Thanks
Chuck
Please post a link to the datasheet of that relay.
Relays normaly can't be operated by controller 20 mA outputs. Drivers are needed.
Definately NOT! One coil is used to close the contacts until the second coil is energized to release the contacts. You will need to use a MOSFET between your Arduino and EACH of the coils.
Surely you can write a pin to turn a digital pin high and low and a second pin high and low.
I drew a sketch and when I went to google to check my work I found this
Base Resistor for 2N3904 help - Electrical Engineering Stack Exchange
which was exact except I had 2K2 at the base, so. Forget my sketch, it was drawn with my finger anyway.
I just happen to have a lifetime supply of 2N3904 and 1N4001 parts... ppl like MOSFETs, too.
You need one copy for each coil obviously, and a moment HIGH lasting 5 ms will set (or reset) the relay. One output pin for each relay driver.
A simple test program with that and say 1000 ms between set and reset is trivial extrapolation from the basic blink, plain blink with delay which I think is among the very first examples in the IDE.
You could run the LEDs from the relay contacts. LED, series current limiting resistor like 1K, switching power to that combo wired to ground.
HTH
a7
Looking at the data sheet, it states in one of the footnotes that in order to maintain the "set" or "reset" status that the coil needs to be energized for at least 5 times the "set" or "reset" time, which would be about 25mS.
DO NOT energize both coils at the same time. Also do not energize a coil for an extended amount of time, since the relay is latching it may not be able to withstand the heat from a continuously energized coil.
Yes, THX. 4.5 ms to get there and 5x that to stay good and switched.
I use some similar "snick-snack" relays that latch in 5 ms and misst the fine print.
Another thing to know and appreciate rather than to learn the hard way cough! is that the coils are marked +/- to indicate the direction of current.
a7
So in actual fact, an H-bridge could be used to operate the relay, being disabled after the operate time; and putting the two coils in series ("+" to "+" and the two "-" to the bridge) would make it functionally equivalent to the single coil version while halving the current drain of using the coils separately. 
How exactly is that suppose to work? You are making an assumption about the actual mechanics of how the relay operates, and the data sheet specifically states to only power a single coil at a time, and with the correct polarity.
Which you will be doing, the other coil will be reverse polarity and not conducting.
That is why they are polarized.
Tom.... 
I was responding to Paul_B's comment about wiring with an H-bridge
I do not see anything in the data sheet that states a reverse-polarity coil will be non-conducting, and if it were non-conducting then wiring the coils in series would seemingly also prevent the other coil from conducting at that point.
If you absolutely have to use an H-bridge, then wiring the coils in parallel, with reversed polarity, and diodes in series with each coil to only allow current flow in the correct direction, might work, but between the diodes and H-bridge the voltage drops are starting to add up.
Hi,
Believe me, they do not conduct with reverse polarity, so parallel without the steering diodes will suffice. (The relays have the diodes built in.)
Tom.....
Whatever gives you that idea?
Do you imagine that the single and dual coil relays are somehow constructed differently?
It seems you do not understand how this device works at all! 
I have used them and come across them many times.
Tom...
This particular relay?
So why would the dual coil version have diodes incorporated when the single coil version does not - simply can not?
I've used similar single coil relays with internal diode.
Caught me first time as I thought the batch of relays was defective.
I thought the OP’s intent was to reverse the direction of current flow in the circuit the relay controls, viz:
For which a solid state solution might or might not be a desired choice.
a7
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