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I had the urge to send this out a week ago, but I was holding on to it because I had to hear some feedback, suggestions, and issue reports from the initial users. Now I am ready to spread the words:
As always, the first question I need to answer is: what’s new in this version? Here is a list of highlights:
• New features:
Custom station names: each station can have a custom name up to 12 letters long.
Per-station master operation control: each station can individually activate the master station.
Run-once program: similar to the manual override feature on some sprinkler timers.
Station delay time, and master on/off adjusted time: fine tune station turn-on and turn-off time.
Water level/percentage: globally scales water time up and down based on local weather conditions.
Automatically reconnect: improves reliability on unreliable networks.
Support for RTC and automatic RTC detection: keeps time running even when power or network is lost.
Full range of time zones: living in Nepal? No problem.
• Improved features:
Program now has an ‘enable’ flag which allows you to enable or disable each program individually.
Improved Graphical Preview feature, which shows each station’s name and scheduled on/off time.
So this is another major upgrade since Firmware 1.6. So what happened to Firmware 1.7? Well, that was a quick update for the preparation of OpenSprinkler 1.4 orders: except for added support of RTC, it didn’t have any major changes. So I had to number this one 1.8 to distinguish it from the previous version.
Also taking a suggestion from the Forum, I’ve starting using minor revision numbers (1.8.0, 1.8.1 etc.) to keep track of changes in between major releases. This way you can easily find out whether your version is up to date.
I’ve also made a video tutorial (above) for those who want a video guide on how to use this firmware. I ended up having to switch between different ways of recording, so the audio quality is not consistent. Sorry about that, and enjoy the video!
Look at what came in the mail today:
It’s my first Raspberry Pi (Raspi)! I know I should have got it much earlier, but I was not fond of being put on a waitlist. Apparently I should have kept better track of it: I was checking some stuff on Newark.com the other day and accidentally noticed that Raspi is in stock. Without any hesitation I immediately placed an order. Three days later, it’s here!
First impression:
Gosh, it’s small! It’s the size of a credit card, and the build quality is pretty sold. It’s powerful eough to run a Linux system with X server, and it even has HDMI output so I can directly use it with my high-resolution LCD. The setup was quite easy. The machine boots from an external SD card. All I did was to grab a 4GB SD card, follow the instructions here to flash the default raspbian image onto the card, and insert it to the SD card slot on board. Then I used a micro-USB cable to power it up. I also digged out an old 3.5 inch LCD screen from Dx.com and it works perfectly with Raspi (though the resolution is low, hence it’s not really good for reading, but good for showing 🙂
Standard keyboard and mouse should work well out of box. This version (model B) of Raspi has two built-in USB ports. Of course you can use an USB hub to extend the ports. It doesn’t have a WiFi chip on board but it does have a Ethernet jack. I plugged in a NetGear WNCE2001 WiFi adapter and instantly I have WiFi connection. It also works with a variety of USB WiFi dongles, so it’s really convenient.
One of the biggest selling points of Raspi is of course its price: this model B is just $35 before tax and shipping (keep in mind that even an Arduino board, which has a must simpler microcontroller, would cost almost $30). This is totally impressive, especially considering we have to factor in reseller margins on top of the manufacturing cost. I don’t what’s the profit margin, but perhaps it is consistent with a recent article that discusses how you can’t make money any more on hardware, instead, it’s the software and service that keep consumers to buy in.
Anyways, I am glad I finally got one. There is a lot of stuff I am excited to experiment with using Raspi, and I am sure I will come up with some itneresting project ideas along the way. A thumb up for Raspi!
About two weeks ago we started shipping out OpenSprinkler v1.4, and I figured it is now time to write a short post to announce it. What are the new updates in v1.4?
• DS1307 RTC
The main update is that the external EEPROM (24LC128) is replaced by a DS1307 Real-Time Clock (RTC). I am aware that RTC has been requested since the beginning of OpenSprinkler, and I apologize for taking so long to add it. There are multiple reasons: the limited PCB space, the cost of DS1307, and the fact that NTP sync is often good enough. The limited PCB space is probably the biggest reason. Fortunately since the latest interval program does not use external EEPROM any more (i.e. everything is stored in internal EEPROM), there is now space to add RTC. The software has also been updated to support DS1307. Specifically, if RTC is enabled in options, the controller will not rely on NTP to get time any more. In addition, there is an on-board button cell battery which will keep the time running even when power is lost.
If you own a previous version of OpenSprinkler which does not have built-in DS1307, you can easily add an external RTC module, available in Rayshobby shop. Our module comes with a built-in rechargeable battery, pin headers, and jumper wires for easy connection to your OpenSprinkler board. Follow this link for instructions on how to connect. These modules are also available on eBay, or Adafruit, or SparkFun, but they are usually pricier and without jumper wires.
• Screw Terminals
As you may have noticed from the pictures, the screw terminals have been upgraded to the two-piece (plug and socket) type, which makes it easier for installing and uninstalling wires. Now when you need to make changes to wires, you can simply take out the plug piece, insert and tighten wires, and plug it back in. There is no need to open the enclosure.
• Pin Changes
The second update is that a few pin assignments been changed to free up analog pins A2 and A3. These pins are precious for connecting to external sensors. Also, digital pin D3 is now wired internally to the rain sensor, so you no longer need to solder a separate wire. As in previous version, if you are not use the RFM12B transceiver, digital pins D2 and D10 are also free to use.
• Surface Mount Version
The last major change is that there is now a surface mount (SMT) variant 1.4s, which uses the same circuit as the through-hole version 1.4u but most components have been changed to surface mount package. This variant is created to improve our productivity of full assembled and tested kits. So from now on, all orders of fully assembled kits will receive the SMT version, while the DIY kits will continue to use the through-hole version.
The images below are close-up views of the SMT version (front and back):
As you can see from the front image, most components are surface mount, except the peripheral components like screw terminals, connectors, buttons, and big capacitors. Two crystals and the button cell battery for RTC are on the back side. The SMT version uses the same software as the through-hole version, but it does have a few differences:
It has two extra analog pnis A6 and A7, which are accessible in Arduino programs.
The Ethernet connector is changed from SparkFun RJ45 jack to Hanrun 911105A, which is less expensive and more widely available.
There is a slide switch on the top-left corner of the PCB. This is used internally by us to switch between programming ATtiny45 and ATmega328. You should keep it in the ‘INT’ position.
Future Plans
To give you a heads-up, version 1.4 is likely to be the last one in this hardware generation, and will also be the last through-hole version. The next version OpenSprinkler 2.0 will be SMT only, and will switch to a completely different microcontroller in order to accommodate new features like better user interface, on-board wifi, logging, and more sensor options. However, the development of 2.0 will likely take more than a year, so it won’t be available until after summer next year (2013). Meanwhile, feel free to send me comments and suggestions on how to improve the OpenSprinkler functionality, and I will consider them for version 2.0!
The past month has been a bit crazy. I just completed a series of traveling from mid-July to early August. It’s really hard to get work done while traveling. The good news is that I am back now, refreshed and energized to crank out some new projects.
AASaver v1.1 back in stock
The first bit of news is that AASaver v1.1 is now back in stock and available in my hobby shop. If you’ve noticed from my earlier post, version 1.1 improves upon the original version by adding a switch to control the LEDs, so the same board can be used simultaneously as breadboard power supply and LED flashlight. Another update is that both LEDs are moved to the same side so they point to the same direction. The separate LED switch was actually a suggestion made by Michael Castor from MakerShed. So I would like to thank Michael for making this suggestion. The original plan was to sell AASaver in MakerShed. However, due to some of their policy changes, that plan fell through. Nonetheless, AASaver has been quite successful and more than 370 have been sold to date. It got posted on Hack a Day, Adafruit blog, and also got reviewed by Dave Jones on his EEVblog. Anyways, if you have any suggestions for the AASaver, please let me know and I will consider them for the next update.
434MHz RF transmitter/receiver pair
A couple of new products have also become available in my hobby shop. The first is a 434MHz RF transmitter/receiver pair. These are compatible with similar products you can find at SparkFun or other retailers. It’s inexpensive, and is very handy for implementing wireless communication for your microcontroller projects. In addition, I have been using the receiver to reverse engineer wireless power sockets, remotes, and sensors, and using the transmitter to simulate or interface with these devices. Check my blog post here for an example of how to use them. If you are only interested in the RF transmitter, you can get it separately from my shop page.
DS1307 RTC module with built-in battery
This is a DS1307 Real-Time Clock (RTC) module that has built-in 3V rechargeable lithium battery and recharging circuit. Very handy for projects that need offline time keeping. To use this module, connect four pins: Vcc, Gnd, SDA and SCL. Note that Vcc must be connected to +5V: it won’t work with +3.3V. You can find DS1307 Arduino library from the Arduino Playground, and a variety of other websites. The module also comes with an on-board 4KB EEPROM that uses the same I2C interface, a 1×4 pin header, and female-female jumpers for easy connection to your existing projects, such as OpenSprinkler kits that do not have built-in DS1307. Highly recommended!
DHT11 Temperature/Humidity Sensor
This DHT11 Sensor is the first product in the Sensors category. It is a low-cost temperature and humidity sensor that requires only one digital I/O pin to read both temperature and humidity values. Very handy as an add-on sensor to OpenSprinkler. The operating voltage is 3-5V, and measurement range is 20%-80% humidity (5% accuracy), 0°-50°C temperature (±2°C accuracy). You can find the product datasheet, an Arduino tutorial by Adafruit, and an Arduino library from the product link above. Note that Adafruit’s library does not work with 8MHz Arduino, which is what OpenSprinkler is running at. So i recommend the library at the third link on the products page.
USB-to-Serial (TTL) Converter
This product has been mentioned in an earlier post, but I just want to bring it up again since it has been very popular. It is an integrated USB-to-Serial converter based on Prolific PL2303HX chip. ‘Integrated’ means the circuit is in the USB connector itself, so it’s quite compact. This inexpensive converter is very handy for debugging and creating serial communication. To use it you usually only need to connect three pins: Gnd (black wire), TX (green wire), and RX (white wire). Keep in mind that TX should be connected to the RXD pin of your microcontroller and vice versa for RX. No driver is necessary under Linux. For Windows and Mac, follow the product link to download driver. Once installed, The device will report as a Serial COM port. You can then use Arduino’s serial monitor, putty, gtkterm, or any of your favorite serial monitor to talk to it.
So much for the product update. There will be a few follow-up posts about the update of OpenSprinkler and SquareWear. These are more major updates that I have to talk about in separate posts 🙂
Update: check out the RFToy — an easy-to-use standalone gadget to control remote power sockets. Also, support for remote power sockets have been added to OpenSprinkler firmware 2.1.1.
In previous blog posts, I’ve described two ways to use an Arduino to interface with an off-the-shelf remote power sockets / switches. The first method uses transistors to simulate button presses. It involves some soldering and hacking the remote control unit. The second method uses an oscilloscope to sniff the signal sent by the remote control, and then simulates the same signal using an RF transmitter. But what if you don’t have an oscilloscope, or don’t know where to place the probe to take the measurement? In this post, I will describe a very simple method to sniff remote control signals. It only requires a 434 MHz RF receiver, a couple of resistors, an audio cable, a sound card (with line-in), and an free audio processing software. (Note: some RF remote sockets work at 315 MHz frequency range).
Update: check out the RFToy — an easy-to-use standalone gadget to control remote power sockets. Also, support for remote power sockets have been added to OpenSprinkler firmware 2.1.1.
To get started, I picked a set of indoor wireless power sockets from Amazon. This is different from the model I had before, and it’s not based on the PT2262 encoder, so I cannot predict the RF signal by just looking at the circuit board connections. The reason I picked this model is because it has separate On and Off buttons for each socket, instead of just a Toggle button. So if you want to make sure the socket is on, just repeatedly send the on signal. With only a toggle button, if there is a power reset or if the previous command was not successfully received, you will mess up the control and end up with completely flipped on/off status.
RF Sniffing Circuit
Ok, here is the fun part: how can we sniff the signals sent by the remote control to the sockets? It turns out that most of these remote controls work in the 434 MHz band (note: some work in 315 MHz), so we can use a cheap 434 MHz RF receiver to intercept the signal. To record the signal, a simple way is to use your sound card and an audio recording software. The sound card can digitally sample the signal at high speed (e.g. 48,000 Hz), and it can record a signal over a long time, so it is more convenient than using an oscilloscope.
This is by no means a new idea. I found it when reading this forum post. Scroll down and you will see the schematic to make the sniffing circuit. One important thing is that you should plug the audio cable to the Line-In jack on your sound card, not the Mic jack.
The picture on the left is my implementation of the circuit. I used my handy AASaver to provide the +5V needed by the RF receiver. This way, the whole circuit sits on a breadboard without any external power adapter. I can easily insert it to the sound card at the back of my desktop PC.
Record the Control Signals
I used the open-source Audacity software in Linux to record the signals. All I have to do is to start recording, and press each of the 6 buttons on the remote control. Then I will zoom in and analyze the signals. Below is a snapshot:
Basically when you press a button, the same sequence is sent multiple times. Each sequence consists of two types of square waves: a long on followed by a short off, which I call a ‘1’, and a short on followed by a long off, which I call a ‘0’.
How can we find out the timing (i.e. the width) of the signal? In Audacity, if you zoom in the signal to the extreme, you will see the actual signal sample points. Remember that we know the sampling rate, which is 48000 Hz by default. So if we count the number of sample points, and divide that by the sampling frequency, then we will get the timing. For example, below is a snapshot of a short on. I counted that there are about 21 sample points, so the width of it (i.e. a short on or short off) is
Similarly, I figured out that a long on or long off is about 1300 us, which is three times the width of a short on or off. Also, there is about 12.5 ms delay before re-sending the same sequence. These timings don’t have to be very accurate.
With the timings figured out, I can now write down the complete sequence corresponding to each button:
Each ‘1’ is a 433 us on followed by a 1300 us off, and each ‘0’ is a 1300 us on followed by a 433 us off. The first 4 bits indicate socket on/off, the next 8 bits are always the same, and the 4 bits following from that indicate the index of each socket.
With these patterns recorded, I can reproduce the signal using an Arduino and a 434 MHz RF transmitter. The RF transmitter has one data pin, which can be connected to any Arduino I/O pin. Since there is a little bit of overhead when using Arduino’s delayMicroseconds function, I reduced the short delay time to 410 us. This way, the signal generated by the code is almost identical to the that produced by the remote control.
Download
Download example Arduino code here. This example program assumes the RF transmitter data pin is connected to Arduino pin D3, which you can change at the beginning of the file.
Use OpenSprinkler to Control Power Sockets
Now that my Arduino can talk to the remote power sockets, how about adding Internet-based control? For example, sending control signals through a web interface, or even setting a time schedule to turn on or turn off sockets automatically during a day? Aha, my OpenSprinkler is perfect for this purpose. There are two reasons, first, the OpenSprinkler is an integrated circuit that includes ATmega328 + Ethernet + LCD + USB programmer; second, the latest OpenSprinkler software provides a nice web interface where you can set an interval schedule or switch to manual control mode. All that I have to do is to connect the RF transmitter using one of the available pins on board, and then add a few lines of code to send the RF signal wherever the corresponding sprinkler station is turned on or off. This way, I can easily use the same web interface to control power sockets. Internet of things instantly!
The image above shows my implementation. I used a half-built OpenSprinkler, with everything except the switching regulator section and the solenoid driver section. The RF transmitter is connected to the controller using three wires. Again, one of the nice things is that I can directly use the software already written for OpenSprinkler, to set a time schedule for automatically turning on or off power sockets. In addition, I can switch to manual control mode, which also has built-in timers.
What’s Next?
My next plan is to use the sniffing circuit to reverse engineer RF signals sent from wireless temperature, humidity, and rain sensors. This will allow me to use an Arduino and a RF receiver to decode the wireless data and get local temperature, humidity, and rain information. Of course the tricky part is to figure out how the data is encoded. So I will have a couple of posts in the next week or so about RF hacking. Stay tuned!
Ok, this post is a bit late, as 1.3u has already started selling since Tuesday this week. Anyways, 1.3u is a minor revision since 1.2u. There are only a few changes (see Release Notes for details), so I didn’t make a release video. This post explains why these changes were made and some of the technical details.
Added shift register OE (output enable) line
This is mainly to address an issue with 74HC595 shift register that on powering up the output values are undefined. This can potentially lead to valves being randomly turned on for a short period of time before the mcu takes over and clears output values. It is not a huge issue, but quite annoying. It turns out that one simple solution is to add a control line to the 74HC595 OE (output enable) pin. This pin is active low, which means when set to low it enables output, and when set to high, it forces the output to be in high-impedance state, therefore the triacs will not turn on and the valves will remain closed.
In 1.3u, Arduino digital pin 3 is assigned to control OE, and a pullup resistor is used to pull the pin high by default. On start-up, before the mcu takes over, OE is high, disabling output; then when the mcu completes initialization, it sets OE to low, enabling output. That’s it. Simple solution.
Because of the added line, the extension board connector has been changed to 2×4 format (previously it was 2×3). If you own a previous version of OpenSprinkler and would like to use 1.3u extension board, you just need to solder a wire between the OE pin and Gnd , in order to enable output by default.
TXD/RXD are now used as general I/O pins.
This change was made to free up the A2 and A3 analog pins, since there have been many requests to make more analog pins available in order to connect external sensors like temperature and humidity sensors. Because TXD and RXD are now used as general I/O pins, they can no longer be used for Serial communication. In fact, since they are not used to control the LCD, calling Serial.begin() or Serial.print will cause the LCD to display garbage. If you need Serial communication, you can use the SoftSerial library which can simulate Serial communication on any pins.
Added coin battery holder.
Warning: this is a feature under development. It requires software support which is not available yet. The goal is to have a backup battery which allows the mcu to continue time keeping even when power is lost. Actually the easiest solution would be to just add a DS1307 Real-Time Clock (RTC). But my main hesitation is that DS1307 is quite pricy. Well, it’s not hugely expensive, but at $2 a piece (volume pricing), it is actually more expensive than the ATmega328 mcu. Isn’t that a bit silly? Anyways, the time keeping business can be well handled by the mcu itself. First, the mcu can run at a voltage as low as 1.8V, so when power is lost, it can continue running on a low-voltage battery; second, during power loss, the mcu will mostly be in sleep mode, using an external 32.768 kHz clock source, and occasionally waking up to update the time counter. This way, it can basically do whatever the RTC chip can do.
The only tricky part is detecting power loss (which is already possible with the Power Sense pinout), and turning off peripheral components such as the Ethernet controller to minimize power consumption during sleep mode. These require some further experiments, which have been put on my todo list.
Another minor change is adding two resistors for the LEDs on the RJ45 Ethernet connector. In OpenSprinkler v1.1 and v1.0, the Ethernet connector did not have built-in LEDs. Then when I changed to use SparkFun’s RJ45 in v1.2, I forgot that it actually has built-in LEDs… So in this version the LEDs are wired in, which makes the circuit more complete 🙂
That’s all for OpenSprinkler v1.3u update. In case you are wondering about the frequent hardware changes, keep in mind that we are continually improving the design based on feedback and comments received from users. We run small batches (a couple hundred) for each version, that’s why we can have quick turn-around time in integrating new hardware features. At some point when the hardware becomes mature, we will make a surface mount version to improve the production throughput. Hopefully that point won’t be too far away!
I am glad to announce that the new interval program has been released and available for download at the OpenSprinkler GitHub page. This is a major software update since the initial release in October last year. Here is a list of new features in this version:
Program-based scheduling. Each program consists of a set of days (including weekdays, odd/even day restriction, and interval days), stations, start, ending, interval, and water time. The firmware supports up to 64 programs.
Choice of running stations either sequentially or concurrently.
Graphical Preview of each day’s program.
Integrated Manual Mode. When activated, the manual mode allows turning on or off stations using buttons on the homepage. An optional timer can be set to automatically shut stations off.
Support for rain sensor and location-based weather checking.
Details can be found in the video below, and the OpenSprinkler Instructions of Use page. This software version is compatible with all existing hardware versions, including v1.0, v1.1, and v1.2u. Feel free to give it a try. To find out how to re-program the MCU with new firmwares, please refer to the Re-programming Instructions. From now onw, the new interval program will replace the previous svc_full_schedule program, and become the default program shipped with all pre-flashed MCUs.
Technical Details
You will find that the new program has significantly improved the web user interface. This is made possible by using external Javascripts. As I described in a previous post, a major challenge in designing full-featured web interface is the limited program memory (flash) size of the ATmega328 MCU. The trick to get around with this limitation is by using external Javascripts stored on remote servers to ‘beautify’ the webpages. When you access the OpenSprinkler webpage in a browser, two pieces of information are combined in the browser: one is the essential data provided by the controller, the other is the set of Javascripts used to format webpages. The process to combine the two actually happens in your browser, which can interpret and execute complex Javascripts. This is called Client-Side processing. In addition to releasing the MCU from carrying the heavy ‘formattting’ code, another advantage of this separation is that you can easily replace the Javascripts to present data in a different format. This is in a sense similar to web Templates. Finally, debugging Javascripts is also a lot faster and easier than debugging microcontroller code, because it requires no re-flashing of the MCU, and most modern browsers support checking and error reporting of Javascript code.
One downside with this approach is that the Javascripts must be placed on a server that’s constantly available. Currently the scripts are stored on the Rayshobby web server, which is quite reliable. The path to the scripts is:
http://rayshobby.net/scripts/java/svc1.6/
There are 7 scripts involved: home.js, progmode.js viewoptions.js, viewprog.js, plotprog.js, modprog.js, manualmode.js. These are used to format various pages, including the homepage, program modification page, program preview page etc. However, if you ever want to customize the Javascripts yourself, you need to make a copy of these scripts and put them on your home server, a cloud server, or any file hosting server that can provide direct file access links. Note that the Javascript files are simply text files that store (human-readable) Javascript code. So any server that can host a text file is ok. If you decide to direct the scripts to your own server, simply modify JAVASCRIPT_PATH macro defined at the beginning of interval_program.pde, and point it to your new path.
You don’t have to worry about the security of using scripts stored on the Rayshobby server. Remember, in client-side processing, your controller data is never sent to the server; rather, it is sent to the browser that you are using to view the webpages. The browser will then retrieve the Javascripts and combine them with the data to present the webpages. Clearly there is no way we can ‘log’ your data or keep a record of your data, so it’s safe.
The Weather feature you saw in the demo video above is implemented using a Python script and Google Weather API installed on the Rayshobby server. This is an example of Server-Side processing, because the Python script runs on the server and not in your browser. The reason this requires server-side processing is because first, the Google Weather API returns fairly long XML data that cannot be directly parsed by the MCU, second, the MCU needs to periodically retrieve weather data, so it needs to initiate requests on its own and cannot rely on the existance of a web browser. Thus the Python script serves as a mechanism to convert complex XML data to microcontroller-readable format, and since it runs on the server, the microcontroller can send requests to it at any time.
OK, so much for the technical details. There is no way to cover all details in a single post. If you want to find out more about how the software works, please refer to the source code, or post a message on the forum.
A couple of new products have been just added to Rayshobby Shop page. These include a 434MHz RF transmitter and a USB-to-Serial (RS232) converter.
So what are they good for? The 434MHz RF transmitter is a general-purpose RF transmitter with on-board PCB antenna. It is compatible with SparkFun’s 434MHz RF transmitter. You can find a lot of example code online, including Arduino code. The module has three pins: Vcc, Gnd, Data. The operating voltage is 3~12V (5V standard), and the current draw is about 5-15mA. The higher the voltage, the longer the transmission range. Typical transmission range without external antenna (i.e. using on-board antenna) is 160 feet; and it extends to 500 feet with an external antenna. I’ve shown an example use of the transmitter in a recent article A New Way to Interface with Remote Power Switches. It provides a simple way for a microcontroller to switch wireless power sockets. Very handy and inexpensive for home automation projects.
The USB-to-Serial converter is an integrated cable based on Prolific PL2303HX chip. It is a convenient tool for microcontroller to host communication through USART. It is similar to an FTDI cable, but at a significantly lower price. It doesn’t have a Reset line though, so it cannot be used for re-programming Arduino or OpenSprinkler v1.1/v1.0. However, it is very handy to connect to your OpenSprinkler v1.2’s TXD/RXD pins in order to easily debug your code. The cable length is 3 feet (1 meter). The wires are colored as follows:
On Mac or Linux, you don’t need to install any driver: it is already supported by the operating system. On Windows, you can download the driver following the link here. Once installed, the device will report as a Serial COM port. You can then use any Serial Monitor to communicate with your microcontroller. Some standard serial monitors are Arduino’s built-in serial monitor, Putty, or gtkterm (on Linux). I’ve been using this converter a lot for printf debugging of OpenSprinkler code.
Again, both of them are now available for purchase on Rayshobby Shop page.
Over time I’ve received some questions regarding the hardware design of OpenSprinkler. Here are some common questions and my answers:
Why using a switching regulator?
Since OpenSprinkler uses a single power supply (i.e. 24VAC sprinkler transformer), it is necessary to step down 24VAC to 5VDC and 3.3VDC in order to provide power to the circuit. The simplest and most common way is to use a 7805 linear regulator. But here is a catch: due to the relatively high current consumption of the ENC28J60 Ethernet controller, the whole circuit draws about 150 to 180mA current during operation. Using a linear regulator in this case will cause a lot of power waste. Specifically, (24-5) * 0.18 = 3.42 Watt will be wasted on heat due to the voltage conversion. This is pretty bad. That’s why I made the conscious decision to use a switching regulator to achieve higher efficiency. The switching regulator in this case is estimated to have 75% efficiency, so the power waste is more like (5 * 0.18 / 75% – 5 * 0.18) = 0.3 Watt. Much better and green!
Why having both 5VDC and 3.3VDC supply voltages?
This is because the LCD requires 5V supply, and the rest of the circuit requires 3.3V. The microcontroller can work with both voltages, but the ENC28J60 Ethernet controller and the RFM12B transceiver require 3.3V. That’s why the circuit provides both 5VDC (VIN) and 3.3VDC (VCC).
Why using triacs to control solenoids? What about relays?
While a lot of other sprinkler control circuits found online use relays to switch solenoids, I made the conscious decision to adopt triacs. There are many reasons this is more preferable. First, triacs are semi-conductor components, so they are much smaller than relays, more durable and act much faster. Second, they are low-cost and significantly cheaper than relays. Third, they are also slightly more power efficient: each triac requires only 5 to 7 mA holding current to switch on solenoids, while relay coils often consume more current. In fact, a sophisticated design can use an AC triggering circuitry to trigger triacs only during zero crossings, further reducing the power consumption. All in all, triacs are great choices for switching low-voltage AC devices.
Why does OpenSprinkler v1.2 adopt a USBtiny programmer?
If you’ve noticed, the previous versions of OpenSprinkler relied on external FTDI programmer. That was designed to be compatible with standard Arduino and variants. The main advantage of FTDI is that it not only does re-programming, but also it is a USB-to-Serial converter, which allows the microcontroller to easily send and receive messages from your computer. However, it also has two main downsides. First, it is expensive: an FTDI programmer or cable can easily cost more than 15 bucks, and we don’t like to stock it due to the cost. Second, using FTDI requires a bootloader, which takes away some (512 bytes) program space from ATmega328. Therefore we have decided to go with an on-board USBtiny ISP programmer based on ATtiny45. We like this solution a lot better because this way every OpenSprinkler board has a built-in USB programmer, so you don’t need to worry about purchasing a programmer separately. It is low-cost and does not require a bootloader, so it’s a win-win choice.
I just finished a batch of ordering yesterday, and felt that it would be fun to document my favorite distributors, suppliers, and PCB manufacturers. This is basically a review of some websites and stores that I regularly buy electronic components, supplies, and PCBs from. It’s suitable for buying in small to medium quantity (i.e. a few to a few hundred). When rating them, I consider a combination of factors including price, easiness of choosing parts, and shipping time and cost. Keep in mind that I am located on the east coast, so shipping cost and time may be different for you. Also, there are some negative reviews, you have been warned 🙂 Hope my comments and recommendations will be useful for other hobby makers.
Components
First of all, Octopart is a great distributor search engine. If you know the part number, you should definitely check with Octopart to compare prices across many distributors.
Part selection: very easy, most components have high-quality pictures and datasheets. You can sort by price with a given quantity. Also, they have a comprehensive selection of components. Most parts I need can be found easily.
Shipping: inexpensive and extremely fast. They offer USPS first-class and priority shipping. If I order by 9pm EST, the order is shipped the same day, and arrives on the third day after shipping. Also, keep in mind that USPS delivers on Saturday as well. So if I missed something and need it in a hurry, I can order by 9pm EST on Thursday and still get the parts Saturday morning. For a small order (weighs 13 oz or below), I just choose USPS first-class, and that usually costs 3-4 dollars. I am basically getting the speed of Fedex 2-day service but with a fraction of the cost. Super! One of the main reasons I prefer Digi-Key.
Pricing: competitive for many categories: microcontrollers, capacitors, resistors, inductors, terminal blocks, just to name a few. The price can be higher than other distributors if you only buy in small quantity. However, considering the low shipping cost and fast shipping time, I would still definitely go with them for getting a few prototyping parts.
Customer service: excellent. I had to return an order once and it was processed quickly without hassle. Also, there were a few times that I needed to remove or add a few parts after ordering, and I was able to do these quickly through online chatting. Great customer support.
I use them for: getting a small quantity of prototyping parts, or buying a large quantity of microcontrollers, capacitors, resistors, inductors, terminal blocks etc.
Part selection: not that easy, many components have datasheets but are missing pictures and certain information. Trying to find a part without knowing the part number can be tricky. They don’t have a comprehensive selection of components like Digi-Key, but they seem to carry a wider variety of SMT parts. You can sort by price. My suggestion is to use Digi-Key to search and find the part you want, and then check with Future Electronics to see if they have it available.
Shipping: very inexpensive for buying relatively large quantity, and very fast. They offer flat-rate shipping ($9 for Fedex Ground, $15 for 2-Day, and $33 for Next-Day service). No matter how many components I put in the order, the rate is the same. The package is shipped the same day if I order by 10pm EST. Very convenient.
Pricing: extremely competitive. This is where I find the lowest price. Often their single-item price is lower than the volume price found elsewhere. Super! I usually go with them for buying various ICs, capacitors, crystals, diodes, transistors, LCDs, IC sockets, pin headers.
Customer service: pretty good. They assign a customer representative for you, although it could take time to get response from them. Select parts carefully before ordering, because return can be tricky.
I use them for: buying a batch of ICs, capacitors, crystals, diodes, transistors, LCDs, IC sockets, pin headers.
3. AVnet
I have only used them twice, so I don’t have much to comment on.
Pros: competitive price, flat-rate shipping.
Cons: not easy to select parts. Again, it helps if you have the part number ready.
Cons: shipping is expensive and unpredictable. Cut-off time for same-day shipping is much earlier compared to Digi-Key or Future, and the shipping cost always comes out higher than I expected. After a bad experience with the customer support (an email got no response in the end), I stopped using them. I know many people use Mouser for their competitive price. Frankly, if price matters, look for Future Electronics, AVnet, Arrow, or Verical. They are cheaper than Mouser and have flat-rate shipping, so you won’t get ripped off by unpredictable shipping cost.
PCB
For ordering PCBs, I highly recommend Seeed Studio Fusion PCB service. They are awesome: their service is low-cost, high-quality and fast. Yes, it’s a company located in China, so shipping can take longer time. But they process orders promptly. I usually order on Sunday evening (which is morning in Chinese time), and my order is in production the same day. Manufacturing takes 1 week, and shipping takes another week (I go with express mail options). If you don’t mind waiting for 2-3 weeks, you can get free International shipping with orders of $50 or above. If time matters, pay the extra $20-$30 to get DHL, which delivers in a week. That’s a total of two weeks to get PCBs delivered to your door. Plus, you get free DHL for orders of $500 or more. I generally use them for all PCB orders, whether prototyping quantity (i.e. 10), to batch quantity (a few hundred).
I’ve also used Advanced Circuits. They are US-based company, reliable, and extremely fast. Their price can be expensive, especially if order quantity is less than 200. I use them when I need a batch order of PCBs in a hurry and cannot wait for international shipping.
Supplies and Materials
Amazon: you will be amazed how many things you can get from Amazon. I get all sorts of things ranging from shipping tapes, labels, scales, to protective gloves, plastic organizers, to solder, copper board, electric wires, to cartridges, sprinkler solenoids etc. Get an Amazon Prime membership and you will receive most orders with 2-day shipping for free.
Techni-Tools: they have a wide range of soldering tools, solder bits, SMT soldering tools, wipes, conductive foam. Price can be expensive, but I am happy to invest on high-quality tools that I can use for a long time.
All-Spec: I get tweezers and all sorts of polybags, mylar bags from them. Very competitive price, and fast shipping.
ShippingSupply: I get most of my corrugated shipping boxes from them. Shipping cost can be a bit expensive. So buy in large quantity and stock them.
ULine: I get some corrugated boxes, and lots of labels from them. Good price, very fast and low-cost shipping.
eBay: eBay is a great place for getting things for cheap, and things that are hard to find elsewhere. Last year I bought Pogo pins, lead-free solder paste, RF transmitter modules, shipping label printer, and a bunch of home improvement store coupons on eBay.
