Feb 28th, 2012 by ray
The AASaver kit is now out of stock. In one day I’ve received about 92 orders, pretty crazy 🙂 I’ve placed another order of PCBs, and expect to have the kit back in stock in about three weeks. You can sign up to receive email notifications here: http://eepurl.com/jBK15, or alternatively, subscribe to my blog RSS Feed.
Feb 28th, 2012 by ray
What is AASaver? Well, simply speaking, it’s a small voltage booster that can bump the voltages on your AA batteries to 5V or 3.3V, which you can use to power flashlight LEDs or breadboard circuits. It has some nice features, including on-board flashlight LEDs, voltage selection switch, power switch, and breadboard pin headers. I like it and I find it really useful. It is available for purchase in my online shop. Check out the full product details and a video demo on the product page:
AASaver just got posted on Hack A Day yesterday afternoon. Thanks for the publicity (Hack A Day is awesome!), orders are pouring in! The version without LEDs is already out of stock. I have placed a batch of orders and it should be back in stock in about 3 weeks. If you want to get notified when it’s back in stock, sign up for the AASaver stock notification list, or simply sign up for my blog RSS feed.
Feb 6th, 2012 by ray
Rain/freeze sensors are useful for detecting rain or freeze conditions, and delays or stops watering accordingly. There are many types of rain sensors on the market. Recently I tried out this Orbit 57069 rain/freeze sensor. It’s very easy to connect to OpenSprinkler, and works quite well. The rain delay time can be easily adjusted by setting the water evaporation speed.
So how does this rain sensor work? It’s pretty simple. The sensor has two wires, which are normally connected to each other inside through a switch. The top of the sensor has a small chamber, which contains a string of sponge pads (see below). When it rains, the water will drip into the chamber and gets absorbed by the sponge pads. The pads will then expand and press against each other as well as the top of the chamber. When it expands to a certain point, the switch inside the sensor will be pressed down, disconnecting the two wires. The height of the chamber can be adjusted to control when the sensor is activated – in other words, the amount of rain that will activate the sensor. There are five options: 1/8, 1/4, 1/2, 3/4, and 1 inch.
Down below the chamber is an evaporation window. The size of the window controls how fast the absorbed water evaporates, thereby controlling the rain delay time. After the rain stops, the sponge pads will gradually shrink, and at some point the switch is released, thus the two wires are connected again. This is a very clever design because it’s purely mechanical, requires no power itself, and is easy to adjust. The downside is that you cannot set the delay time precisely – obviously the local humidity and temperature will affect the evaporation speed.
Once you figure out how it works, it’s very easy to connect it to OpenSprinkler. The diagram above shows the connection (Not sure where the ‘common wire’ is? Check out this diagram). Simply put, the sensor acts as a normally-closed switch placed on the common wire. When the sensor detects rain or freezing condition, it disconnects the common wire from the sprinkler valves. As is, it can work with almost any kind of sprinkler timer, without modifying the timer itself.
The sensor should be installed on the roof or next to the gutter. You need to run a wire from the sensor to your sprinkler timer. The sensor itself comes with a relatively long wire, so that shouldn’t be a problem. If you want, you can even get a wireless version at a slightly higher cost.
That’s it – if you need automatic rain delay control, this is an easy, inexpensive option you may consider.
Jan 2nd, 2012 by ray
Recently I was fortunate to receive a Microchip PICkit 2 from Newark.com to write a review on. I was very excited to get it because I have always wanted to learn about PIC microcontrollers. Why? Well, so far I have been quite experienced with Atmel’s AVR family chips, thanks to the Arduino that first got me into electronics. But it’s time to try something new in a new year 🙂 PICs offer several nice appeals including their product variety and functionality (e.g. support for USB, Ethernet, touch sensing etc.) and they have very competitive pricing. I know there are tons of debates about AVRs vs. PICs online. For now I am going to put them aside and make my own comparisons later after I get a good grip of both.
PICkit 2 is a very popular tool for programming and debugging Microchip’s PIC microcontrollers. If you want to learn PIC programming, you almost certainly should get one. With the latest device file, it can support most PICs available on the market (although for some of the newer ones it only supports programming and not debugging). Microchip has an updated version — PICkit 3 which supports everything, but I prefer PICkit 2 because it’s cheaper ($34.99) and provides everything I need.
The package (product no. PG164120) contains the programmer itself, two CDs, and a USB cable. The programmer looks very compact. It has a USB port (as well as a key ring) on the top, a red button and three LEDs (power, target, and busy) on the front, and the 6-pin ICSP (In-Circuit Serial Programming) port on the bottom.
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Since I am new to the ICSP pins and can easily get myself confused with the AVR’s ISP pins, I made a small label with all the pin names and attached it to the programmer. This way I will never forget the pins when prototyping circuits! The 6 pins are: Vpp, Vdd, Vss, ICSP-Data, ICSP-Clock, and the last pin is unused. Among them, Vpp can provide +12v for high-voltage programming, and Vdd/Vss can supply 5V or 3.3V to power your circuit, which is very convenient. The picture on the right below shows the circuit inside the programmer. It is based on a PIC18F2550 MCU.
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At this point I have to say that I like this programmer much better than AVR’s comparable programmer at the same price. Why?
So overall, I am really glad to find out that this small and inexpensive programmer packs a lot of nice features in it.
Next I will try to write my first PIC program. There are basically two pieces of software to install: the MPLAB (version 8.6) which is the programming IDE, and the PICkit 2 standalone program (version 2.61). They are in the attached CDs, but you can also download them online at Microchip’s product website.
The MPLAB integrates everything you need: programming environment, compiler, uploader, and debugger. However, it turns out that it won’t support some of the newer chips (such as the one I got) if you are using PICkit 2. That means you can compile the program but won’t be able to upload it to the chip. The upgraded version PICkit 3 can handle all chips, but I don’t have it! Fortunately, PICkit 2 has a standalone program to work with the newer chips. Be sure to download the latest Device File from that website.
To write a program, you can either use assembly language or use C. I am going with C since I don’t know how to accomplish even a relatively simple program in assembly language. It makes my head blow… Anyway, MPLAB comes with a free HI-TECH C compiler (PICC light version). You can follow the ‘Quick Start’ tutorial, available in the compiler’s installation folder to easily write your first ‘Hello World’ (i.e. flashing LED) program. Here is a snapshot of mine:
The ‘Config’ bits are a bit confusing to me at first. But a read of the microcontroller’s datasheet will make everything clear. These are similar to the fuse settings in the AVRs. The main difference is that here you write the bit settings directly in the program, whereas AVRs separate the program with the fuse settings.
For my first experiment, I picked the PIC16F1825 microcontroller. It has 14KB program flash, 1KB RAM, 256B EEPROM, USART, 12 I/O pins, and it costs only $1.50. I thought I made a good choice. Unfortunately soon I found a small issue, which is MPLAB does not fully support this microcontroller if you are using PICkit 2. You can still write and compile a program, but you can’t upload or debug the program (these are only available with PICkit 3). Fortunately, the PICkit 2 standalone program can still work with it. So the solution is to write and compile the program in MPLAB, and use the standalone program to upload:
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I made a simple testing circuit, consisting of the microcontroller, a 1×6 ICSP pin header, an LED bar graph and a resistor network. The goal is to, as we always do, flash some LEDs 🙂 The circuit is very easy to implement on a breadboard (see photo above). I basically started by connecting the 6 relevant pins to the ICSP pin header, then all port C pins (C0 through C5) to the LED bar graph, and finally the resistor network. Note that I also attached pin name labels to the microcontroller. In addition to the standard pin names (like A0, A1, C0, C1…), I especially marked the ICSP pins (VPP, ICSP-DAT, and ICSP-CLK). This makes it really easy to connect wires without having to look back again and again at the datasheet.
Upload a program: This is straightforward. First compile the program in MPLAB, then switch to the standalone program, import the compiled HEX file, and click on ‘Write’. The LEDs on the programmer will flash and after a few seconds it’s done.
Power the circuit: As I said earlier, the programmer can supply VDD anywhere between +2.5V to +5V. Note the checkbox for VDD ‘On’ and the voltage input box in the GUI above. Once you enable VDD, the Target LED on the programmer will light up, and the circuit will immediately start running. Voila, my ‘Hello World’ experiment is now complete!
I’ve also tried using the programmer in Linux (Ubuntu 11.04). First, MPLAB software installs and works just fine with Wine. Other than the GUI being a bit ugly, the software seems to be fully functional. Second, there is a tool called PK2CMD from Microchip website that works with PICkit2. You can use it to upload a compiled program to your microcontroller. Probably the only missing feature is debugging — there doesn’t seem to be a way to enable debugging in Linux. Well, you can always using MPLAB’s simulator to do software-based debugging. But if you definitely need hardware-based debugging, you can install Windows as a virtual OS in Linux. This way, all features of PICkit2 will be enabled.
So far my first experience with the PICkit 2 programmer has been very positive. It’s small, inexpensive, feature-rich, and relatively easy to use. I highly recommend it. In fact, if you are planning to learn PIC programming, I suggest getting this kit soon. Why? I’ve read from online websites that Microchip is discontinuing this product in favor of the newer PICkit 3, which is pricier and has actually received some negative comments (search for David Jones EEVblog PICkit 3 and you will find out). So before PICkit 2 runs out, go and grab one for yourself!
Resource Links
Finally, there are a few things I am yet to try, and I have put them on my todo list:
Dec 27th, 2011 by ray
At times you may want a simple web-based interface to directly control each sprinkler valve, without having to set up a complex schedule. I’ve written the svc_simple_web program exactly for this purpose. To start, take a look at the web interface of this program:
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Quite simple, isn’t it. The top line shows the current time; underneath it is the list of eight sprinkler stations. Clicking a button will turn on the corresponding station, and clicking the same button again will turn it off. To make it a bit more useful, you can set a timer (i.e. duration) for each station. The duration is specified by the number of hours following by minutes (hh:mm). Once a station is turned on, the program will keep track of the running time and stop that station when the duration time is reached. Meanwhile, the webpage will display the remaining watering time. You can set an individual time for each station, say 30 minutes for station 3, and 15 minutes for station 5. Setting the duration to 0:0 means there is no time limit: once on, the station will only be turned off when you manually click on ‘Turn it Off’. This way, you can either manually control the stations, or set a timer for it.
If you are interested, feel free to try this program and let me know your comments. The program can be downloaded on the following page:
Note that the software is now released in GitHub for the purpose of better version control. The code will be regularly updated. You can sign up for the RSS feed on the GitHub update history page, in order to track the updates.
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