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I follow Ray on Twitter, and saw this link posted yesterday:
http://rayshobby.net/announcing-the-first-dc-powered-opensprinkler-v2-3-dc/
Questions:
1) When will it be available to buy?2) As a US customer is it worth waiting for this version? So I know I save $12 on the transformer, but otherwise I see that the 9VDC has advantage of running DC solenoids, but the 24VAC can run weather sensors. I don’t have either of those things, so besides the $12, it doesn’t seem to really matter to me.
Unless there is some other advantage of the 9VDC that I am not aware of. Is there?
Thanks,
David
1) It’s already available:
http://rayshobby.net/cart/osdc
We will make it available on opensprinkler.com as well (still finishing up the product page, but should be done within a few days).2) The main benefit of the DC version is that the power adapter (9VDC) is easy to source and the same adapter works universally everywhere. If you’ve seen 24VAC transformers — they are heavy, bulky, expensive, and do not work universally (e.g. output voltage is proportional to the mains voltage). This is the main reason for the design of the DC version. For US customers, this is probably not a big deal, but if you ever need to replace the transformer, it might still be an advantage.
I consider 9VDC to be safer than 24VAC — the peak voltage of a typical 24VAC transformer can reach as high as 40V, which is somewhat dangerous. If you accidentally shorted the wire to something it can result in big damage. In contrast, 9V is a lot safer.
Also, in the past we’ve received several requests to make OpenSprinkler compatible with DC solenoids, and we ended up having to customize the controller for these customers by replacing triacs with MOSFETs. With the DC version the same controller can now work with both AC solenoids as well as DC solenoids. That’s a another advantage.
Going a little more technical: the MOSFETs used on the DC version can sink as much as 3 amp continuous and 30 amp impulse current. So it’s a lot more capable in terms of handling shorted solenoids and so on.
I have been wondering about this as well and I have a couple more questions.
I don’t currently have the rain sensors or other weather sensors but I would eventually like to get them and add them to my system.
Are there DC versions of the AC sensors available? Can they be used with OpenSprinkler(DC)?
Am I giving up anything (other than the 24 volt AC sensors mentioned above) by going with the DC version?
In other words, other than the AC Sensors, is there any advantage to the OpenSprinkler(AC) that seems relevant?
But, it should be possible to power the 24V ac Version with 9V DC.
The powersupply for the ICs works with 9V too and the Mosfets work in one direction. That should be possible, or?
To Power 9V DC valves and so.
If the Mosfet not big enough for the dc power. take some bigger one for ne next board generation and you can run on 24V AC and 9V DC with one board. 🙂 Wuhuu
one board, more possibilits, less cost.
by the way, half europe works with the 9V dc valves.
@BillyDaDad: if you need to use wireless sensors, you can power them separately with a 24VAC transformer. This is not ideal (i.e. having two transformers), but should work just fine. In fact, I am fairly confident these wireless sensors would work fine with 9VDC too. I’ve personally taken apart some of these sensors and it looks like the internal power circuit just consists of a rectification part followed by zener diode for voltage regulation. If so, there is no reason why they can’t be powered by 9VDC instead. Of course this isn’t ideal either, because the 9VDC power supply uses a plug type connector instead of the 24VAC adapter that exposes bare wires. In any case, the separate power supply option is always available.
@David: you are right that the AC controller will work fine with 9VDC (and since it has internal diode protection it won’t be damaged even if the polarity is reversed). In fact, in the past we’ve been customizing the AC controller for a few users who needed a DC version, but basically replacing the triacs with NPN transistors (or MOSFETs).
The MOSFETs are actually typically quite small, because MOSFETs have very low on resistance so as long as it’s fully on the power consumption is usually very low, even if it’s running a large amount of current.
I’m thinking about placing Arduino Trinkets to measure soil temperature out near the control valves. How hard would it be to get a (slow is OK) serial comm link back to the controller? I presume that doing this over DC makes it a lot simpler, but I don’t know what would be involved.
Both the AC and DC OpenSprinklers internally run on 3.3V DC, it’s just that one is powered by 24V AC, the other is powered by 9V DC. It’s pretty easy to modify the code to process serial communication. You may also consider I2C. But before that, what kind of sensor do you have? OpenSprinkler has several spare digital and analog pins, you can likely hook up your sensor directly to one of the spare pins.
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