Fullscreen HTML5Med Res (??MB)HTML4

ESP8266 Features WiFi – 802.11b/g/n 32-bit RISC CPU 512KB-16MB flash memory HTTP & FTP IPv4 TCP/UDP 17 GPIO pins SPI I2S and Software I2C 10-bit ADC Fig.1: block diagram of the ESP8266 IC. The left-hand side of the diagram contains the RF sections while the right-hand side is the baseband and CPU section. team led by radio astronomer Dr John O’Sullivan. The IEEE 802.11 protocol was first released in 1997 and has since been revised and updated numerous times. 802.11 is a set of MAC (media access control) and PHY (physical layer) specifications for implementing WLAN (wireless local area network) data communication in the 2.4GHz, 3.6GHz, 5GHz, 5.9GHz and 60GHz frequency bands. There are many different versions of the 802.11 protocol. Those that are most popular for WiFi are 802.11a, 802.11b/g/n and 802.11ac. These mainly differ in terms of their PHY specifications, as shown in Table 1. The ESP8266 chip The ESP8266 is a self-contained WiFi networking transceiver and microprocessor, packaged in a single 32-pin QFN SMD chip measuring only 5 x 5mm. It operates in the internationally unlicensed 2.4-2.5GHz ISM (Industrial, Scientific and Medical) band and is compatible with the 802.11b/g/n protocols. The downside to the 2.4-2.5GHz band is that it is also used by Bluetooth devices, microwave data transceivers using the Nordic nRF24L01+ chip and also plagued with various sources of noise like microwave ovens. So this is a somewhat noisy band, and becoming noisier all the time. The block diagram of Fig.1 shows what’s inside the ESP8266. On the left are the RF sections, including the transmitting and receiving sections, the T/R switch, an LNA (low noise amplifier) and an RF balun for connecting to one or two antennas. On the right is the baseband section which includes an integrated 32-bit siliconchip.com.au RISC CPU, a memory controller with both ROM and SRAM, all of the registers and sequencers for implementing a full TCP/IP stack and interfaces for SDIO (SD cards), SPI (serial peripheral interface), GPIO and I2C communication with external MCUs and/or external flash memory. Incidentally, the RF output power in 802.11b mode is +19.5dBm, or just under 100mW. When this output is being provided in transmit mode the chip’s current drain from the 3.3V supply is 215mA, corresponding to around 710mW. In receive mode with 1024-byte packets, the current drops to around 60mA (<200mW). The chip also has two power saving modes: standby mode, where only the RTC and watchdog remain active (current <1mA) and deep sleep mode where only the RTC remains active and the current falls to below 12µA. The chip can be woken up to transmit packets in less than 2ms. The ESP-01 module The ESP-01 module is quite small, measuring only 25 x 14.5mm, including the PCB track antenna and the 8-pin interface connector. Fig.2 shows the complete circuit for the latest version (V2) of the ESP01 module and there’s very little in it apart from the ESP8266EX chip itself, a tiny 26MHz crystal and a 25Q80 1MB flash memory chip. There are two LEDs, one to indicate when the module is powered up (LED1) and the other to indicate when serial data is being transmitted (LED2). All of the connections to and from the external micro are made via CON1 at upper left. The module is designed to operate from 3.3V and should not be connected Celebrating 30 Years The ESP8266 is a low-power, selfcontained WiFi chip. The main use of the ESP8266 is to provide a WiFi interface for other microcontroller devices. However, the ESP8266 IC is powerful enough to be used as a low-power computer, combined with being able to flash the firmware with your own program code using a bootloader. It has an extensive API provided on ROM which implements various timer, hash (MD5 & SHA1), WiFi and TCP/ UDP functions etc. A list of API functions can be found at: siliconchip.com.au/link/aaj4 siliconchip.com.au/link/aaj5 Some potential uses include: Remote file manager Web server Ad-hoc network Data logger Baby monitor What is it? April 2018  77 Fig.2: complete circuit diagram for version 2 of the ESP-01 module. The PCB track antenna has a range of approximately 300m under good conditions with line of sight and possibly 10m at best indoors. to a 5V supply. The logic inputs of the ESP8266EX are not tolerant of 5V, so if your external micro operates from 5V the interconnections need to be made via logic level translation circuitry. We have read that applying 5V to its input pins does no harm but this is an undocumented feature and we don’t suggest you rely on it. Another point to note is that the ESP8266EX chips used in the latest versions of the ESP-01 module (V2) are programmed to communicate with an external PC or micro at a default rate of 115,200 bps (baud), while earlier versions were set up for 9600 bps. This can cause complications when you try to use the newer ESP-01 modules with an Arduino Uno or equivalent. in most versions of Windows, Linux and macOS. Note that although the popular USB/ UART bridge modules also provide a 3.3V output, this is generally only capable of supplying 100mA or so. That’s why you need to use an additional LDO regulator, like the LM1117T shown, to provide for the higher current levels needed by the ESP8266 when it’s transmitting data packets. Your PC will be able to communicate with the ESP8266 and hook up to a local WiFi router and network, using a standard communications terminal program like Tera Term. Note that this won’t give your PC direct access to the wireless network, since it won’t have a network driver that understands how to communicate with the ESP8266. Programming it directly While you can use the ESP-01 module purely as a wireless “bridge”, it’s also possible to program the ESP8266 directly, ie, to run some code without a separate micro. That’s because the ESP8266 does have a built-in CPU of its own, together with RAM and EEPROM. In fact, ESP8266/Arduino enthusiasts have come up with a nifty Connecting to a PC Interfacing the ESP-01 module with a computer is quite easy. All that’s needed is a USB-UART bridge module to provide a communications link with the computer (via a USB port) and also to derive power from the computer via a 5V-3.3V LDO (low-dropout) regulator to reduce the supply voltage to 3.3V. The basic circuit needed is shown in Fig.3, although we’ve shown two versions of the USB-UART bridge module – one with a micro USB socket and the other with a type A socket. Both use the popular CP2102 chip, for which there’s a VCP (virtual COM port) driver 78 Silicon Chip Fig.3: if you want to connect the ESP-01 module to a computer, all that’s needed is a USB-UART bridge like the CP2102 and LDO regulator to reduce the USB port’s 5V supply voltage to 3.3V. Celebrating 30 Years siliconchip.com.au Arduino board package which allows the ESP8266 to be programmed via sketches written in the Arduino IDE, using standard Arduino functions and libraries. Information about this Arduino “core” is available at https:// github.com/esp8266/Arduino Using it with an Arduino Connecting the ESP-01 module to an Arduino is a little more complex than you might expect, mainly because of the need to power the module with its own 5V-3.3V LDO regulator and also because logic level translation circuitry is needed to interface between the module and an Arduino’s I/O pins. The easiest way to do this is to use a WiFi module interface shield like the Freetronics ESP1SH, as shown in Fig.4. The shield mounts on the top of an Arduino and provides an 8-pin header socket for plugging in an ESP01 module and an LD1117 3.3V LDO to power the module plus logic level translation circuitry for the TX and RX data lines. There’s also a pushbutton switch (S2) for reprogramming the ESP-01’s flash memory, another pushbutton switch (S1) to reset both the ESP-01 and the Arduino together and most importantly, an 8-way-by-3 header strip which allows you to link the level shifted ESP-01 TX and RX lines to one of eight possible pins on the Arduino. An enlarged view of the latest ESP-01 module. It features a few SMD components including a 26MHz crystal and 1MB of flash memory. The GND pin is at the top-right of the PCB, while Vcc is at the bottom-left. Link header That link header on the ESP1SH shield is important because of the point mentioned earlier, about the latest ESP-01 modules being programmed to communicate at 115,200 bps. This a problem with the Arduino Uno and its clones because the ATmega328 CPU used in these modules has only one hardware UART, which is normally used for communication with the PC via the onboard serial/ USB bridge. To communicate with another serial device like the ESP-01, you need to use a software-driven serial port with a different pair of pins for the TX and RX lines. But these software-driven serial ports can only operate at a maximum speed of 38,400 bps. But there is a workaround. First, you download a do-nothing sketch to the Arduino and set it running, so that it ignores the hardware UART temporarily. Then connect your ESP-01 module siliconchip.com.au An enlarged photo of the silicon die and metal layers of an ESP8266 (a variant of the ESP8089). The RF section is at upper left and takes up a larger portion of the chip. The area below and right is memory while the I/O pads are along the edges. https://zeptobars.com/en/read/Espressif-ESP8266-wifi-serial-rs232-ESP8089-IoT Celebrating 30 Years April 2018  79 Fig.4: connecting the ESP01 module to an Arduino via the Freetronics ESP1SH shield. The benefit of using this shield is that it provides a 8-pin header to plug the module into, handles the level shifting from 5V to 3.3V, and logic level translation circuitry for the transmit and receive pins. However, this of course is not the only way to connect the ESP8266 to an Arduino. to the same hardware UART RX and TX pins (D0 and D1). You can then reprogram the ESP-01 directly from the PC so that it defaults to a data rate of 38,400bps or less, making it compatible with the software serial port. Then reconnect the ESP-01 TX and RX lines to a different pair of pins on the Arduino and set those up as a software serial port. Alternatively, you could simply use the hardware TX and RX pins to communicate with the ESP-01 with the limitation that you must disconnect it when re-programming the Arduino board. This will limit your use of the Serial Monitor for debugging, though. Things are a lot easier if you use an Arduino Mega, Mega 2560R, Freetronics EtherMega or the Duinotech Mega, because these all use either the ATmega1280 or 2560 processors, both 80 Silicon Chip of which have a larger flash memory plus an additional three UARTs. Each of these can provide a serial port which operates at 115,200 bps or more. The ESP1SH shield’s header strip allows you to link up the ESP-01’s TX and RX lines to any serial port you wish, without the need for reprogramming. In the case of the Mega2560R, all you need to do is connect the ESP01 TX line to pin 19 (RX1) and the RX line to pin 18 (TX1) using a pair of short male-to-female jumper leads. This is shown in both Fig.4 and the photo at right. We’ll look at what’s involved in programming an Arduino Mega to use the ESP-01 module for WiFi communication shortly. In the meantime, let’s look at how the ESP-01 can be linked to a Micromite. Connecting a Micromite? How to connect an ESP-01 module Celebrating 30 Years to a Micromite is shown in Fig.5. Note that we still need to use an LM1117T LDO regulator to provide 3.3V to the ESP-01, since its current drain is somewhat higher than that available from the Micromite’s own 3.3V regulator. But the TX and RX lines from the ESP01 can be directly connected to the RX and TX pins of the Micromite, since no level translation is needed. There’s no problem with data rates either, providing you use the connections shown, which use the Micromite’s hardware UART port (COM1). This can operate at 115,200 bps without any problems, provided you are running the Micromite at a clock frequency of 40MHz (the default), 50MHz, 30MHz or even 20MHz. WiFi via the ESP-01 Because the ESP8266 chip in the ESP-01 module is designed to communicate via standard Hayes AT modem siliconchip.com.au Fig.5: when connecting the ESP-01 to a Micromite you still need a 5V-3.3V LDO regulator. However, no level translation is needed so the data pins can be connected directly. text commands, using it to add WiFi capabilities to your microcontroller project is relatively easy. All your Arduino sketch or MMBasic program needs to do is set up the ESP8266 chip using the appropriate AT commands, and then respond to the data it gets back from the ESP8266. If this sounds a bit daunting, you can find a list of all the commands here: siliconchip.com.au/link/aaj7 If you want to use the ESP-01 module with a Micromite, you’ll get a lot of help and guidance by studying a program that Micromite guru Geoff Graham wrote to accompany his article published in the December 2014 issue of Silicon Chip. The program is called “WEBServer.bas” and can be downloaded for free from siliconchip. com.au/Shop/6/2890 You’ll also find that Geoff Graham’s article in the December 2014 issue has a listing of the main AT commands needed to communicate with the ESP-01/ESP8266 (page 33, www. siliconchip.com.au/Article/8194). The ESP1SH shield makes most of the connections between the ESP01 and the Arduino Mega, when you plug it in. The only additional connections you need to make are between the level translated TX and RX lines of the ESP-01 (the uppermost and lowermost rows of pins on the shield’s 8x3 programming header) and the IO19/ RX1 and IO18/TX1 pins of the Ar- duino Mega. As shown in the photo below and in Fig.4, these added connections are made by short male-tofemale jumper leads. Just remember to remove the jumper shunts which come with the ESP1SH shield, because these can only be used to connect the ESP-01’s TX and RX lines to the Mega’s IO0/ RX0 and IO1/TX0 hardware UART (or to pins IO2-IO7 for using a software serial port). The jumper lead from one of the uppermost TX pins of the shield’s 8x3 header needs to be connected to the Mega’s IO19/RX1 socket (blue lead in Fig.4), while the lowermost RX pins on the header should be connected to the Mega’s IO18/TX1 socket (red lead in Fig.4). If you get these two connections swapped, your Mega won’t be able to communicate with the ESP01 module. Programming the Mega for WiFi communication via the ESP-01 is fairly easy. You’ll find quite a few Arduino sketches on the web which illustrate how you can use the ESP8266, and there’s also a WiFi Library available on the main Arduino website (see www. arduino.cc/en/Reference/Libraries). To get you started, I’ve adapted a simple pass-through sketch that I found on one of the websites so that it’s capable of running straight away on the Mega/ESP1SH/ESP-01 setup. The sketch makes the Mega behave as a relay station or mirror between All that’s needed extra when using the Freetronics ESP1SH is two jumper leads to connect the transmit and receive lines. www.freetronics.com.au/products/ esp-01-wifi-module-shield With an Arduino Mega As mentioned earlier, the easiest Arduino to connect with the ESP-01 module is the Mega. It’s especially easy if you use a WiFi shield like the Freetronics ESP1SH to interface between the two, as shown in the adjacent photo. siliconchip.com.au Celebrating 30 Years April 2018  81 ing with the Mega and ESP8266 at 115,200 baud (bps). Why not try programming the ESP01 WiFi module yourself? // Sample program from Fig.6. void setup() { Serial.begin(115200); Serial1.begin(115200); } void loop() { if (Serial.available()) Serial1.write(Serial.read()); if (Serial1.available()) Serial.write(Serial1.read()); } Loading your own code onto the ESP8266 Fig.6: the sample serial passthrough program running on an Arduino Mega. This program merely repeats data to and from the ESP-01 module. your computer and the ESP-01 and its ESP8266. So any AT commands sent from your computer via the Arduino IDE’s Serial Monitor utility are relayed to the ESP8266, and any responses from the ESP8266 are relayed back to the IDE’s Serial Monitor. This makes it easy to try sending various AT commands to the ESP-01 and to see its responses. The sketch is listed at the end of this section and you can also download it from the Silicon Chip website. The screen grab shown in Fig.6 shows how this works. The lines underlined in red are those with the AT commands sent to the ESP-01/ ESP8266, while those without any underlining show the responses coming back from it. The first AT command is basically just an enquiry to see if the ESP8266 is awake, with it returning OK if it is. Similarly, the command AT+GMR resets the ESP8266 and also gets it to respond with information concerning its firmware. Then the command AT+CWMODE=1 directs the ESP8266 to assume WiFi client mode, as opposed to access point mode (mode 2) or client/access point mode (mode 3). The additional command shown in Fig.6 is AT+CWLAP which asks the ESP8266 to list any WiFi access points currently available within its range. Of the three lines you can see in Fig.6, the last line corresponds to my office network router, while the other two are routers or peripherals in nearby homes. The other point to note from Fig.6 is that the Arduino Mega I was using at the time had been allocated to virtual COM port 20 (top left), while the IDE Serial Monitor was communicat- The WeMos D1 R2, which is based around the ESP8266, was used in the Water Tank Level Meter project (Feb 18). 82 Silicon Chip If you do this, you will lose the AT command set capabilities, since these are provided by the default code loaded into the ESP8266 processor. But it does allow the ESP-01 to become an independent module without the need for many external components. The best demonstration of this is in our NTP Clock project article on page 58, where we turned an ESP-01 into a device which pretends to be a GPS module, supplying NMEA data from its serial port and a 1pps signal but it actually gets the time, date and location data from NTP and location servers on the internet. This allows you to use a GPS-synchronised clock in a location where a GPS signal is not available. So we won’t go into great detail about how to program the ESP8266 yourself here, as you can refer to that article on page 60 and examine its source code (which can be downloaded from the Silicon Chip website) to see how it works. SC Links for using the ESP-01/ESP8266: https://espressif.com www.siliconchip.com.au/link/aaj6 https://forum.arduino.cc/index.php?board=11.0 http://bbs.espressif.com www.electrodragon.com/w/Wi07c www.siliconchip.com.au/link/aaj7 www.sparkfun.com/products/13678 https://en.wikipedia.org/wiki/ESP8266 www. siliconchip.com.au/link/aaj8 https://github.com/espressif https://github.com/esp8266/Arduino https://github.com/tttapa/ESP8266 https://github.com/acrobotic/Ai_Docs https://github.com/espressif/esp8266_mp3_decoder/ Celebrating 30 Years siliconchip.com.au