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OpenSprinkler’s 1-year anniversary! Yes, on Oct 9 last year, the OpenSprinkler project got posted on Hackaday and became known to the world for the first time. A lot of updates have happened during this past year. The hardware has gone through four cycles of changes, and the latest version is 1.4. From August 2011 we have started producing the surface mount version of 1.4, making it easier to manufacture and assemble the kit. The software has also been substantially improved. Many user-requested features have been included. I am proud to say that at this moment OpenSprinkler is probably the best Internet-based sprinkler timer with its price and the functionality it provides. I am hoping that in the upcoming years it will start making a positive impact on the technology innovation in consumer-level sprinkler products.

To honor the 1-year anniversary, all orders placed on Oct 9 (today) and 10 will receive a 10% discount. If you have ever considered buying OpenSprinkler but hasn’t made up your mind, there is no better deal than this!

Statistics wise, most OpenSprinkler orders came from the United States, which is not a surprise since we are based in the US. But OpenSprinkler has also reached places outside of the US. So far it has reached close to 30 countries. Here is an un-ordered list: Germany, Netherlands, Australia, South Africa, France, Bulgaria, Spain, Slovakia, Canada, UK, Finland, Portugal, Hungary, Singapore, Belgium, New Zealand, Italy, Turkey, Greece, Peru, Switzerland, Cyprus, Ukraine, Denmark, Estonia, Poland, Austria. I have also marked them on a world map, to give you a better visual:

I want to take a moment to thank the open-source movement. I am a strong supporter for open-source hardware and software. I believe open-source is important for pushing technology innovation and for promoting and implementing new ideas as quickly as possible. Unlike large-scale closed source products, open-source products are often started with a low budget and produced in small batches. We typically assemble kits on the level of a couple hundred per batch. This is how we can quickly update the design, fix bugs, introduce new features, and shorten the overall design cycle. If a particular design didn’t work out, we can simply abandon it and move on. There is little risk of losing big investment money. Also, having a project open-sourced makes it possible for the public to scrutinize the design, identify issues, contribute to the project, and build new projects. As a college educator, I am keen at understanding the underpinnings of how electronic products work, but more than that, I am keen at giving out the knowledge that I know.

Update: OpenSprinkler 2.0 or above uses a different switching regulator and does not require additional resistor any more. The information below is only relevant to OpenSprinkler 1.x.

As you know, OpenSprinkler uses a single 24VAc sprinkler transformer to power both the circuit and the sprinkler solenoids. Frequently people are using a WiFi adapter together with OpenSprinkler to provide wireless Ethernet connection. So how about using the same transformer to also power the WiFi adapter? Ah ha, good question. This turns out to be possible and quite easy to do!

The basic idea is that many of these WiFi adapters (such as the popular NetGear WNCE2001) can be powered using an attached USB cable. One end of the cable is a USB Male A connector, and the other end is typically a 2.5mm power jack that goes into the adapter. Since OpenSprinkler has a built-in USB port (which is connected to the +5V output of the 34063 switching regulator), it can be used to directly power the WiFi adapter. However, OpenSprinkler’s USB connector is a Female B type, so the trick to make this work is to throw in a USB Female A to Male B converter, as shown in the picture below:

You can get this converter from Rayshobby Shop or at online retail stores.

Hold on one second, this is not the only thing you need to do. You also have to solder an additional 1 ohm resistor to the circuit board. The reason is that these WiFi adapters are quite power hungry: I measured that the NetGear WNCE2001 draws about 300-400mA current during operation. On the other hand, OpenSprinkler (by default design) outputs about 330mA current on its +5V output, of which 180mA will have to power the mcu and Ethernet controller. So we need to increase the current output. Fortunately this is not too difficult to do. The trick is to reduce the resistance of Rsc — current limiting resistor for the 34063 switching regulator. According to 34063’s datasheet, the maximum output current is 0.33/Rsc. So if we put two 1 ohm resistors in parallel, Rsc is effectively 0.5 ohm, and hence the maximum output current increases to 660mA, enough to power both the circuit board and the WiFi adapter. Also, OpenSprinkler v1.3u and v1.4 have already designed a spare slot for the parallel Rsc, so it’s pretty easy to make the modification.

You can reduce Rsc even further to provide better safety margin. 34063 supports maximum output current of 1.5A. To do so, you can keep putting more 1 ohm resistors in parallel until you reach the desired resistance. The reason to use multiple 1 ohm resistors is because it’s lowest value common resistor. Anything below 1 ohm will have a big price jump.

Again, if you are interested in trying this, you can get the USB converter from Rayshobby Shop. We will also throw in a couple of 1 ohm resistor free of charge!