Feed on
Posts
Comments

We are getting ready to release the next minor revision of OpenSprinkler DIY kit, numbered 2.2u. This revision is largely the same with the current 2.1u, with three main differences:

  1. MCU clock speed is increased to 16MHz (from 12MHz previous), by using a 16MHz crystal.
  2. Built-in USB-Serial chip is added, by using CH340eG, which is a common chip in low-cost USB-serial converters.
  3. With the hardware serial chip, the bootloader is also changed to use Arduino Optiboot, at 115200 bps baud rate and a bootloader size of only 512 bytes.

IMG_0249IMG_0248

The first change above is to increase the processing speed and hopefully make the controller faster at handling complex algorithms and transferring data with the Ethernet controller. The second change above is mainly to solve the issue that it has been increasingly painful to install USBasp driver on Windows 8+. To understand the background, all of these have to do with firmware upgrade — how to reflash the microcontroller with new firmwares. Back in OpenSprinkler 2.0, I used to have a separate ATtiny45 chip on board to function as a USBtinyISP programmer, which can reflash the main MCU (ATmega644). This is not an ideal design because it involves an extra chip that we have to program; also USBtinyISP is not particularly fast. So when I designed OpenSprinkler 2.1, I made the conscious decision to get rid of ATtiny45. Instead, I decided to implement a USBasp bootloader for ATmega644, which can present the MCU itself as a USBasp programmer when a button is pressed on start-up. This is quite appealing because no extra chip is required, and the programming speed is considerably faster. The only caveat is that to use USBasp in Windows, you need to install the open-source USBasp driver. This was not the most pleasant thing to do, but wasn’t a big deal as the driver was fairly easy to install.

That is until when Windows 8 came out, with this feature called driver signature enforcement. It basically means the driver needs to be digitally signed with Microsoft, otherwise it won’t allow you to install the driver. Let’s be honest, for open-source developers, who wants to pay the big bucks to get the driver signed? So suddenly this has created an even bigger barrier for average users. The only way around the issue is to boot Windows 8 into a mode that disables driver signature enforcement. This step turns out to be unnecessarily complicated. I’ve often received comments about how it’s painful to install USBasp driver for Windows 8. I recently made a video to demonstrate how to update OpenSprinkler firmware — in this 11-minute video, 6 minutes were spent purely on explaining how to install USBasp driver for Windows 8. That’s an evidence of how unnecessarily complicated it is!

Anyways, I set out to find a better solution, and was glad that I discovered the CH340 chip. It’s basically a USB-serial chip that is often found in low-cost USB-serial cables / converters. It’s really inexpensive (less than 30 cents) and requires very few peripheral elements (just a crystal and filter caps). With this chip, you can now use the standard serial monitor to debug your program, and the bootloader can also now use the standard Arduino bootloader.

ch340g_closeup

What I like the most about this chip though, is that it does not require driver for Windows 7, 8 and above. What? Is that even possible? Yup, I’ve verified it — Windows 7, 8 and 8.1 all recognized it right away. The fact that it doesn’t require driver just makes it a whole lot easier to upgrade firmware. Windows XP and Mac OS still require driver for it, though, but that’s light years better than installing driver for Windows 8.

You may be wondering: wait a minute, what about the FT232 chip, which has been available on the standard Arduino since the beginning? Isn’t what I am trying to do here already done? Sure, CH340 is basically a replacement for FT232 — both are USB-serial converters. But there is an economic reason to go for it: even at volume quantity like 1000, FT232 costs about $3 to $4 per chip. That compared to 30 cents for CH340? You tell me. Another nice thing about CH340 is that it comes with SOIC-16 packaging, which is very easy to solder even by hand. This makes it more appealing than other low-cost alternatives like PL2303 and CP2102.

OK, I’ve done enough advertisement. I am not in any ways associated with the company that makes this chip, I am just excited, and regret that I didn’t know about it earlier :)

Continuing from my previous blog post about Hi-Link HLK-RM04 module, I have finally received the ESP8266 Serial-to-WiFi module that I’ve been waiting for. As I said previously, with the popularity of IoT devices, there is an increasing demand for low-cost and easy-to-use WiFi modules. ESP8266 is a new player in this field: it’s tiny (25mm x 15mm), with simple pin connections (standard 2×4 pin headers), and best of all, it’s extremely cheap, less than US$3 from Taobao.com!

IMG_3188IMG_3189IMG_3190

What is Serial-to-WiFi? Simply put, it means using serial TX/RX to send and receive Ethernet buffers, and similarly, using serial commands to query and change configurations of the WiFi module. This is quite convenient as it only requires two wires (TX/RX) to communicate between a microcontroller and WiFi, but more importantly, it offloads WiFi-related tasks to the module, allowing the microcontroller code to be very light-weighted.

There are already a lot of excitements and resources you can find online about ESP8266. I’ve included a few links below:

These are great resources to reference if you need help working with ESP8266. Below I document my own experience. I’ve also bought a few extra and put them available on the Rayshobby Shop for anyone who is interested in buying the module and don’t want to wait for the long shipping time from China :)

Pin Connections. ESP8266 is sold in several different versions. The one I received is the version with 2×4 male pin headers, and PCB antenna. In terms of the form factor, it looks a lot like the nRF24L01 2.4G RF transceiver. Here is a diagram of the pins:
ESP8266_pinout
Connect the top two pins (UTXD, GND) and bottom two pins (VCC, URXD) to the RXD, GND, VCC, TXD pins of a microcontroller. Note that VCC must be no more than 3.6V. The middle four pins are should be pulled up to VCC for normal operation. However, if you need to upgrade the firmware of the module, you need to pull the GPIO0 pin to ground — that way upon booting ESP8266 will wait for a new firmware to be uploaded through serial. This is how you can upgrade the firmware in the future.

A few quick notes for connection:

  • The typical operating voltage is 3.3V (acceptable range is 1.7V to 3.6V). As the module can draw up to 200 to 300mA peak power, make sure the power supply can deliver at least 300mA. For example, the 3.3V line from a USB-serial cable would be barely sufficient, in that case it’s better to use a LDO to derive 3.3V from the 5V line.
  • When using the module with a 5V microcontroller, such as a standard Arduino, make sure to use a level shifter on the URXD pin — a simple resistor-zener level shifter is sufficient. Again, this is to prevent over-voltage.

A schematic will make it clear. See below. In my case, I soldered the components and a matching female 2×4 pin header to a perf-board. This way I can easily plug in and unplug ESP8266. Again, if you are using a 3.3V microcontroller, you can do away with the LDO and zener diode.

esp8266_connIMG_3194

Experiments using a USB-Serial Cable. Before connecting to a microcontroller, it’s a good idea to use a USB-Serial cable (such as the inexpensive PL2303 USB-serial converter) to check out the basic functions of the module. Connect the PL2303 cable with ESP8266 according to the schematic above. Then open a serial monitor (such as gtkterms in Linux and putty in Windows) with 11520 baud rate (my ESP8266 seems to be set to 115200 bard rate; earlier versions use 57600). Then you can use a list of AT commands to talk to ESP8266. The AT commands are pretty well documented on this page. Below are some example input (shown in bold font) and output that show how to reset the module, list available WiFi networks, check the WiFi network it’s connected to, list IP address, and firmware version etc.


AT
OK
AT+RST
OK
ets Jan 8 2013,rst cause:4, boot mode:(3,6)
wdt reset
... ...
chksum 0x46
csum 0x46
ready
AT+CWLAP
+CWLAP:(0,"",0)
+CWLAP:(3,"freefly",-49)
OK
AT+CWJAP?
+CWJAP:"freefly"
OK
AT+CIFSR
192.168.1.130
AT+GMR
00150900
OK

A Simple Demo using Arduino.
Next, I connected ESP8266 to an Arduino. Because Arduino is already using the TX/RX pins for bootloader, make sure to unplug ESP8266 while flashing the Arduino, otherwise you may not be able to upload a sketch successfully. Also, you can’t use TX/RX for printing debugging information, since ESP8266 will be using them to communicate with Arduino. Instead, you can use another pair of pins (e.g. D7 and D8) as software serial pins, and use a PL2303 serial cable to monitor the output. This will help print debugging information.

I’ve also experimented with using software serial to communicate with ESP8266, but that has failed — ESP8266 requires 115200 baud rate, and that’s a little beyond the capability of software serial. So you have to stick with the hardware TX/RX pins.

The demo program first configures ESP8266 to log on to your WiFi network (SSID and password are given as macro defines at the beginning), then it sets ESP8266 as HTTP server with port number 8080, and it listens to incoming request. If you open a browser and type in http://x.x.x.x:8080 where x.x.x.x is the module’s IP address (printed to soft serial pins), you will see the output which is a list of analog pin values, and the page refreshes every 5 seconds. So this is a basic Hello World example that shows how ESP8266 can be configured as an IoT server, responding to incoming requests.

IMG_3193

Challenges. While my initial experiments with ESP8266 have been quite successful, I’ve also encountered minor issues that took me a while to figure out. For example, while the AT commands are well documented, they don’t seem extremely consistent — some commands allow question marks at the end, some don’t. I also see variations of the returned values from running the AT commands: sometimes there is an extra end of line character, sometimes there is none. These basically require a robust software library to handle all possible cases.

Overall I would say ESP8266 is a very promising WiFi module for IoT, particularly open-source IoT gadgets, because of its low cost, compact size, and the community development. It seems the manufacturer has also open source the firmware code, and thus the minor issues can probably be easily fixed through a firmware upgrade.

We have a small number of ESP8266 modules available in stock, and will continue to offer them if there are sufficient interests. Thanks!

We’ve just released a new OpenSprinkler Firmware Update program, with a video tutorial to walk you through the steps of how to upgrade your firmware. Hopefully this will make it easy for users to transition to the upcoming Firmware 2.1.0, which has a number of significant new features and improvements.

The new update program is written in Qt, and does not rely on Java any more. It’s cross-platform just like before. It also supports downloading the latest firmwares from the OpenSprinkler Github repository, and auto-detect of your OpenSprinkler hardware version. If you are a Windows user (especially Windows 8 and 8.1), you will still have to go through the hassle of installing driver. The video tutorial shows you a step-by-step guide of how to install driver.

For those who are interested in modifying the OpenSprinkler firmware code, I am experimenting with CodeBender.cc, which is a cloud-based Arduino platform. It’s really convenient in that it’s essentially a web-based Arduino IDE that runs in a browser; it also make it easy for people to share their code and modifications. I think its convenience will likely lower the barrier of programming, and motivate more users to modify OpenSprinkler firmware code to add custom functionality. I’ve made requests to add OpenSprinkler to their list of supported boards. Hopefully I will hear back from them soon!

We went to Boston for a concert last night and I swung by the Micro Center store at Cambridge, MA to check out the Rayshobby products that they carry in store.

IMG_0226IMG_0228

They have a pretty large ‘DIY Electronics’ section with all sorts of electronic goodies. This is what I pictured RadioShack should be.

After searching around a few times, I found the AASaver, SquareWear, and OpenSprinkler on one shelf. Very exciting! I do wish they were better organized, because as is, there are hundreds of kits and gadgets spread everywhere like baby toys at a daycare center. Seeing them in store does give me a good idea how to package the products more properly in the future.

IMG_0229IMG_0230

IMG_0232IMG_0233

So if you are interested in OpenSprinkler (DIY kit), AASaver, and SquareWear, and if you have a nearby Micro Center store, go and check them out. They also take online orders. I wonder if RadioShack could have been saved if they had taken the lead in offering a wider variety of DIY electronics products. Alas, it may be too late.

As the Internet-of-Things (IoT) are becoming more and more popular, there is an increasing demand for low-cost and easy-to-use WiFi modules. For Raspberry Pi and BeagleBone, you can plug in a cheap USB WiFi dongle (like the popular Edimax 7811). These dongles are generally less than $10. But for microcontroller-based devices, the options are much fewer and generally more costly. For example, an Arduino WiFi shield can easily cost $40 to $50; even the more recent CC3000 module costs about $35. If you are puzzled by the big price difference: those cheap WiFi dongles require a USB host system, which is beyond the capability of Arduino. Still, it’s unsettling to realize that a WiFi module or shield would cost more than an off-the-shelf WiFi router, even though the router is significantly more powerful.

Recently I saw a post on Hack A Day alerting us about a new Serial-to-WiFi chip. I immediately ordered two of those. I honestly don’t know what I should expect from these $3 parts, but perhaps it’s a good push towards a new wave competitions on low-cost WiFi solutions. Anyways, while waiting for the shipment to arrive, it reminded me that a while back I actually bought something similar: a Hi-Link HLK-RM04 Serial-to-WiFi module. It’s about $10, so still pretty low-cost. I am glad I didn’t lose it, so I took it out of a pile of electronics and started experimenting with it.

IMG_0222IMG_0221

As you can see, the module is pretty small (about 40mm x 30mm). The picture on the right above shows the components underneath the metal shield. The chip (RT5350F) is a 360MHz MIPS core with built-in WiFi support. The module is quite powerful — at factory default settings it functions as a normal WiFi router. Now, in order to get it to talk to a microcontroller like Arduino, I need to use its Serial-to-WiFi capability. What is that? Well it means using the serial (TX/RX) interface to send and receive Ethernet buffers, and similarly using serial to send commands to the module and query or change its current status. This is quite convenient because first, it only takes two wires (TX/RX) of the microcontroller to talk to the module, second, it moves WiFI-related tasks to the module allowing the Arduino code to be very much light-weighted.

Power-Up. To start the module you just need to provide +5V power. At the first use, the module boots up into a WiFi AP (access point) named Hi-Link-xxxx so you can actually log on to the WiFi network and change settings there. Here is what the homepage looks like (default IP: 192.168.16.254, default log-in: admin/admin):

hlk_rm04_1

Change Settings. For my purpose I need to set the module as a WiFi client so that it can log on to my home network, and allow the Arduino to communicate wirelessly through the module. So I changed the NetMode to WiFi Client – Serial, and put in my home network’s SSID and password. I also changed the Serial baud rate to 57600 (the default is 115200): the lower baud rate can help Arduino to communicate with it more reliably especially if I am going to use software serial. Make sure that the Local/Remote port number is set to 8080 or anything other than 80 (because 80 is reserved for the module’s homepage).

hlk_rm04_2

Receiving Data. Now after the module boots up, it appears as a device on my home network (for example, 192.168.1.147). If I type in 192.168.1.147 in a browser, I will still see the same homepage as above. However, now I can communicate with the module’s serial interface through port 8080. To see what’s going on, I used a PL2303 USB-serial converter: connect the serial converter’s +5V, GND, TXD, RXD to the WiFi module’s +5V, GND, RX, TX (note TXD->RX and RXD->TX), then I opened a serial monitor at 57600 baud rate (putty in Windows or gtkterms in Linux). Now type in http://192.168.1.147:8080 in a browser, I get the following output on the serial monitor:

GET / HTTP/1.1
Host: 192.168.1.147:8080
Connection: keep-alive
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
User-Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/37.0.2062.94 Safari/537.36
Accept-Encoding: gzip,deflate,sdch
Accept-Language: en-US,en;q=0.8,zh-CN;q=0.6,zh;q=0.4

Cool, this means the Ethernet buffer has been received through the serial RX pin. If I can then send something back through the serial TX pin, like acknowledgement plus HTML text, the data will be transferred back to the browser. This is basically how HTTP GET command works.

A Simple Arduino Example. To send data back through the serial TX pin, I used an Arduino to set up a simple example. To get reliable communication, I used Arduino’s hardware RX/TX (0/1) pins. The drawback of this is that when you program the Arduino you need to temporarily disconnect the WiFi module from these two pins, otherwise they will interfere with the uploading process. Here is a picture of the setup:
hlk_rm04_3

Next, I wrote an Arduino program to print out the analog values of A0 to A5. This is actually modified from the WebServer example in the Arduino Ethernet Shield library:

Basically receiving/sending Ethernet buffers is done through reading/writing into serial. Now open a browser and type in http://192.168.1.147:8080, I see the following:

analog input 0 is 521
analog input 1 is 503
analog input 2 is 498
analog input 3 is 510
analog input 4 is 525
analog input 5 is 548

Pretty cool, isn’t it! :) If I have a SD card connected to Arduino, I can also serve files, such as Javascripts or logging data, from the SD card.

Blinking LEDs. By analyzing the received buffer, I can also implement various HTTP GET commands. For example, the program below sets the LED blinking speed by using http://192.168.1.147:8080/blink?f=5 where f sets the frequency.

More on Changing Settings. Instead of using the WiFi module’s homepage to configure settings, you can also change settings by sending serial commands to the module directly. This can be done by pulling the RST pin on the module low for a couple of seconds, which switches the chip in AT command mode. Then you can send (through serial) any of the listed AT commands to change parameters such as SSID and password. This is a nice way to add some automation to the configuration process. Details can be found in the module’s datasheet.

Drawbacks. The main drawback of a Serial-to-WiFi module is that the data transfer speed is quite low. I tested transferring a file stored on SD card and am only getting 5 to 7 KB/s. This means to transfer a 1MB file it will take 3 minutes. Clearly not a good solution for bulk data. Another drawback is that if you need to restart the WiFi module it generally takes 35 to 50 seconds to boot up, that can be an issue for the impatient. Fortunately you likely don’t need to reboot the WiFi module frequently.

Overall the HLK-RM04 Serial-to-WiFi module is a reasonable and low-cost solution for adding WiFi to Arduino and similar microcontroller boards. At the price of $10, there is no much more you can ask for :)

Older Posts »