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OpenSprinkler Pi (OSPi) v1.0 is back in stock and available for shipping now. The kit includes one assembled and tested OSPi board, separation pillars, terminal blocks, 8-pin and 3-pin connection cables, and optional enclosure. You need to provide your own Raspberry Pi, and 24VAC sprinkler transformer. The board controls 8 zones, and can connect to standard OpenSprinkler zone expansion board to enable additional zones. Grab it now before it goes out of stock again!

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I would really like to give a big thumb-up to smart-prototyping.com. This is the first time I ordered PCBs from them (I got the link from dangerousprototypes.com), and I wasn’t sure what to expect. The order was placed on Feb 26 right after the initial batch of OSPi sold out. I selected DHL shipping (about $30) since I need it to be quick. On Feb 28 I decided to place a smaller order for the new zone expansion board prototype PCB, and I selected economy air shipping (about $4) since I don’t care how fast it comes. Then on March 5, exactly one week after placing first order, I noticed it got shipped out. I happily received the package on March 7. This is a total turn around time (from ordering to delivery) of only 9 days! What’s more surprising is that when I opened the package, I found my second order is also included. They must have figured out that since both orders are going to the same address, and both were ready upon shipping of the first order, why not put them together and use the fastest shipping. Clever! I am really impressed by their processing speed and the super-fast shipping time. Also, the PCB quality is very good, and their price is even cheaper than SeeedStudios. Highly recommended, and will definitely order from them again!

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Hi, I am glad to announce the arrival of OpenSprinkler Pi (OSPi) 1.0 — a sprinkler or irrigation extension board for Raspberry Pi that provides direct access and control of sprinkler valves. This post serves as a quick introduction to the hardware and software setups. A more dedicated webpage will be available soon. First off, a picture of the board:

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and a video introduction:



Background

Since the beginning of Raspi, there have been many published DIY projects on how to use Raspi for home automation need. I bought a Raspi a few months ago, and have been quite happy with it since then, but I at that point I had not thought about designing an OpenSprinkler extension board for it. The idea of OSPi first came when I noticed that several OpenSprinkler users were setting up Raspi to work with OpenSprinkler. There are many good reasons to do so, for example, to enable logging, to customize the default Javascript files, and to allow more advanced features such as weather-based and learning-based control. At one point I started thinking: wouldn’t it be nice to design an extension board for Raspi, so that it can directly talk to sprinkler valves through the GPIO pins, without an additional layer of microcontorller and Ethernet controller? This has been on my todo list for quite a while, until one day I was playing with Raspi, and I suddenly that the I can actually fit a Raspi inside the existing OpenSprinkler enclosure. As soon as I figured this out, I couldn’t resist ordering a small batch of prototype PCBs right away.






The content below has been updated and moved to a dedicated product page for OSPi at http://pi.opensprinkler.com.


Amid all the fun and exercise of snow shoveling following the heavy snowstorm Nemo, I was able to finish and check in a new firmware update for OpenSprinkler. This new firmware, numbered 1.8.3, is a relatively minor update. You don’t have to update if you don’t need the new features explained below. There are two main changes:

The first is adding back the Sequential option that was available in firmware 1.7 but disabled in 1.8 due to a bug that was tricky to fix. This option allows you to set the controller to run in either sequential mode (where station runs are serialized) or concurrent mode (where stations are allowed to run simultaneously). The support for this option is now added back (with the bug fixed), and the Program Preview Javascripts have also been updated so you can easily check and verify the controller schedules in concurrent running mode. For most people this is probably not that useful, because sprinklers are typically set to run sequentially to maintain water pressure (similar to how people in the same house usually take showers in turn!) But there are times when you may need to run stations in parallel, say, if you want to speed up the overall watering time, or if you want to run master stations in a non-conventional manner, or if you want to use OpenSprinkler to control not only sprinkler valves but also home lighting and other devices. These are all cases where station runs have to overlap with each other. If this feature is useful to you, go ahead and upgrade to 1.8.3.

The second change is a new Device ID option which assigns the last byte of the controller’s MAC address. This new option allows you to run multiple controllers on the same network by giving each controller a different MAC address. Note that OpenSprinkler uses a software MAC, and is programmed with exactly the same MAC on every unit. I know, this sounds lame, but it’s just because I haven’t spent any time to figure out how to flash a random MAC address. Since most users won’t have more than one controller on the same network, it is not a serious issue. With the Device ID, you can easily customize the MAC address, albeit only the last byte. So again, if you find this feature useful, go ahead and upgrade to 1.8.3.

There are a couple of other minor changes. For example, the network status icon has been removed, instead, the LCD now displays no status icon if the network is on, and a question mark if the network is lost. Also, the Run-Once Program data is not stored in EEPROM any more; instead, you have to type in the water duration each time you start the Run-Once program. I know, this sounds a bit inconvenient, but I had to do it to make space for the new features. If you want to upgrade to 1.8.3, please follow the Firmware Update Instructions.

A slight annoyance I found recently is that I couldn’t compile the OpenSprinkler source code any more on my upgraded OS — Linux Mint 14. It turns out that Mint 14, based on Ubuntu 12.10, installs avr-gcc 4.7.2 by default, which apparently broke some of the Ethernet library code. This is quite annoying. My temporary workaround is to install Linux Mint 13 (based on Ubuntu 12.04 and installs avr-gcc 4.5.3 by default) on a VirtualBox in the host system, and then I can compile the code again in the virtual OS. I haven’t found an easy way to downgrade avr-gcc 4.7.2 to 4.5.3, so I will just stick to this option for now. Apparently next time I should really transition to use Arduino 1.x, which comes with its own avr-gcc compiler so I don’t have to worry about the OS installed avr-gcc breaking old code.

OK, that’s all. Back to snow shoveling tomorrow!

Dan K. from California wrote an excellent blog post about how to set up a Raspberry Pi to work with OpenSprinkler. The link to the blog post can be found here:
http://xperimentia.com/2012/12/14/setting-up-a-raspberry-pi-to-work-with-opensprinkler/

and you can download his scripts from the OpenSprinkler GitHub repository (link given in his post). The scripts basically consist of two parts: 1) storing and serving Javascripts required by OpenSprinkler on a Pi server (recall that currently these Javascripts are served on the rayshobby.net server); 2) using Pi to log OpenSprinkler status (this part is based on Dave Gustavson’s PHP scripts). As Raspi is compact, low-cost, and low-power, it is becoming an increasingly popular embedded Linux platform. The combination of Pi with OpenSprinkler also makes it possible to develop sophisticated features in the future like weather-based irrigation control, or leaning-based control like the Nest thermostat. Perhaps it’s time for me to think about an OpenSprinkler Pi Edition 🙂

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The Making of the AASaver

A few weeks ago I received a new batch of the AASaver PCBs at home. I thought, now that I am fairly experienced, it would be interesting to document the process of how I assembled the circuit boards. As you will see below, my assembly setup is manual and is nowhere near the capability of making more than a hundred boards at a time (for that I would outsource the assembly to a professional company). Still, it’s reasonably efficient such that I can enjoy the process of making without losing my mind or temper :).

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Step 1. Stenciling

AASaver is designed with all surface mount components. So the first step is to apply solder paste by using a stencil. I used my recently purchased laser cutter to make a stencil out of a Kapton film sheet ordered from Amazon. There are plenty of online tutorials on how to use a laser cutter to make solder paste stencils, so I won’t repeat them here. If you don’t own a laser cutter, you can easily make a stencil using copper sheet with the standard toner transfer and etching method. The tutorial can be found in my previous blog post here. Before I had the laser cutter, I have always used home-made copper stencils, and they work just as good.

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(Left: stencil made from Kapton sheet; Right: stencil made from copper sheet with home PCB method).

Next, I used old PCBs to make a 3-sided frame that fits the PCB tightly. Then align the stencil with the PCB such that the holes and solder pads match together. I then taped the stencil to the frame for easy lifting up. This allows me to quickly insert and remove a PCB. Since the AASaver board uses fairly big components (0805 and SOT23-6), the alignment does not have to be extremely accurate. Now, before proceeding, you need some tools, including some gloves for hand protection and stencil wipes for cleaning (both are available from from Amazon),

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as well as solder paste (which I got from dealextreme.com) and a credit or membership card as applicator. Now, put a sizable amount of solder paste onto the applicator, and then start pressing it down onto the stencil. I usually do two passes: the first swipe leaves a thick layer of solder paste; then the immediate second pass scrapes the excessive paste off the stencil sheet. Use only medium pressure — you don’t need to press very hard. After stenciling, lift up the stencil and remove the PCB from the frame. Check the solder paste on each pad and make sure everything looks ok. If something is wrong, use stencil wipe to clean the solder paste off the PCB and start over.

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The stenciling step doesn’t take much time. Once you are experienced, you can do it quite quickly: finishing 100 AASaver PCBs took me less than 20 minutes.


Step 2. Populating Components

The second step is populating components onto the PCB. This is the most time consuming step and you will probably want to take short breaks in between :). I used to do it with tweezers, which required a lot of patience. Recently I discovered a couple of tools that can help increase productivity quite a bit. The first tool is a vacuum pen. It comes with a portable vacuum pump, two plastic tubes, and a pen with several different needle sizes. This is available on eBay if you search ‘pick and place vacuum pen‘. Be careful that the unit only works with 220V (designed for Chinese market). So in order to use it with 110V, you need a step-up transformer, which I got from Amazon for about 7 bucks. Well, if you plug it directly into 110V power line, there shouldn’t be any damage, the pump probably just won’t start.

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The second tool I discovered is the SMT feeder. Again, this is available from eBay by searching ‘SMT feeder‘. These are similar to feeders found on automatic pick and place machines, except they are static and do not automatically advance the tapes. I made some labels to help me remember the components on each line.

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With these tools, placing components is much easier than using tweezers: I no longer have to dump components out of the tape, or flip components to face up, or spend a lot of time adjusting the orientation of the components. Such a time saver :).

So how do you use the vacuum pen? Notice that on the side of the pen there is a small hole. When you cover the hole with a finger, it creates vacuum suction pressure through the needle of the pen, which allows picking up components. Then when you remove your finger, the air flows through the hole, and releases the component from the needle. I typically use my index finger for this.

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To demonstrate: first, get the needle close to a component and cover the hole; then pick up the component (as long as your finger covers the hole, the component won’t fall off); finally, carefully approach the PCB, press down the component to where it should be placed, and release the finger. The placing step definitely requires some practice. You can use your other hand to help stabilize the movement and the ‘touch-down’.

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The first few times I used the pen, I was shocked at how poorly the components were placed. I felt it’s a complete piece of junk. But then as I used it more, I realized that I do get more experienced with practising (feels kind of like playing a video game :). Anyways, now I can place components at pretty good speed and accuracy. Practice maker perfect. Note that sometimes you need to change the orientation of a component, and that can be done by simply rotating the PCB around with your other hand. Here is another example of picking and placing an SOT23-6 component, and lastly a picture of the fully-populated board:

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These are 25 boards that have components placed and ready to be toasted:

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Step 3. Reflow Soldering

The next step is the fun step, which is the ‘cook’ the PCBs so that the components will be reflow soldered onto the boards. I used to do this step with a toaster oven and a digital thermometer to monitor the temperature. Because I was lazy, I didn’t implement any sort of feedback control. As a result, there were a couple of times that I ‘over-cooked’ the PCBs till they burned and smelled terribly. So I decided to buy a real reflow oven. The one I purchased is model T-962A from eBay (which used to sell at ~$400 but is now more expensive). Note that its sister model T-962 is cheaper but also has a much smaller soldering area.

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This reflow oven does the basic stuff: it lets you select a pre-programmed reflow temperature profile, or program a custom profile if you want; it follows the selected profile quite accurately, by using an internal infared heating element, a cooling fan, and microcontroller-based feedback control; it also has a glass slit window on the front to allow you to monitor what’s happening inside the drawer. The user manual even describes how to use it to solder double-sided PCBs, which I haven’t tried yet.

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The oven also has its drawbacks: the standard profile takes 7~8 minutes to finish one cycle of reflowing, which is not very fast but perhaps can be accelerated using a custom profile; also, the heating is not entirely uniform — the area close to the boundary is cooler than the center, causing PCBs placed nearby the boundary to be poorly soldered. But once I am aware of these limitations, I can cope with them.

One important thing to keep in mind is that you should place the reflow oven outdoors. Even with lead-free solder paste, the exhaust from the reflow process is unpleasant at least, and probably harmful to your health. So keep it out of your living area.

Once the reflow is done, I get back a tray of freshly baked ‘cookies’. Satisfied 🙂 Take a close look at the PCBs and see if everything looks ok. Especially check if there are any un-soldered paste. If so, put them back and bake again.

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Step 4. Testing

We are not done yet, so don’t bite. The last step is testing, to make sure the circuit board functions as expected. First, perform a quick visual examination. Occasionally components may drift off its position, probably due to insufficient solder paste. These are easy to fix with a hot air gun or even a standard soldering iron. To facilitate testing, I built a simple rig using an existing AASaver PCB and some pogo pins I got from eBay. Here is my setup:

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Because AASaver is a regulated voltage booster, the main things I need to test are whether its output voltages are within spec (5V and 3.3V), and whether it maintains the voltage levels (within 5-10% tolerance) under a given current load (320mA). So my test setup includes a multimeter, AA battery holder, and a power resistor to produce the required current load. If the board passes the test (i.e. outputs and maintains the designed voltage levels with load), it will be put into the ‘success’ bin; otherwise, it will be put into the ‘to-be-fixed’ bin for further checking. For a simple board like AASaver, the success rate (yield) is close to 100%.

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This is a picture of a fully-assembled AASaver in action. It takes two AA batteries, new or used, and can function as an LED flashlight as well as breadboard power supply with switch-selectable 5V and 3.3V output.

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That’s all. Feel free to leave your comments, questions, and suggestions. Thanks!


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