[TriEmbed] ESP8266 Serial Connection

Tue May 19 22:52:39 CDT 2015

Regarding RX/TX mismatches, Particle (formerly Spark) has a great datasheet for their older "Core" dev board: they have pictures with arrows on them showing the flow of data to/from the RX/TX pins.
Picture here: http://docs.particle.io/assets/images/core-pin-usart.jpgFull HW datasheet here: http://docs.particle.io/core/hardware/
Those simple arrows would have saved me at least a few hours of debug on similar designs... An even better idea would be to print the arrows on the silkscreen.
Scroll down that page and you'll see that the SPI and other signals are also marked with direction arrows - such a simple but brilliant idea! Clearly they have empathy for us users.
Unfortunately it looks like they ditched the arrows on their newer (recently Kickstarted) "Photon" product.
-svec

     On Tuesday, May 19, 2015 11:37 PM, Jon Wolfe via TriEmbed <triembed at triembed.org> wrote:

 I've been bit by the janky power supply problem more times than I can count. The worst ones are where your setup seems to work 75%-90% of the time, and you drive yourself crazy trying to track down the issue. I've hit the tx/rx match-up issue before too. Most of the time though, I've seen TX->RX and RX->TX as the working connection. I think some devices/adapters take the nomenclature approach where everything is labeled from the "point of view" of the "master" device, eg, "RX" on a peripheral is the line where the main device receives data, even though the peripheral is transmitting from it's point of view to the other device. confusing.You would think that mis-connecting those would cause dangerous line contention, but as often as I have messed it up, I've never fried a chip that way. YMMV.I have seen a few sources on the Internet stating that the RX and TX on the 8266 "seem" 5V tolerant. But the "official" datasheet says it's not. If you want a little bit nicer chip that has (mostly) 5V tolerant I/O and has additional I/O's, and can *probably* handle higher baud rates than the esp8266, check out the EMW3162 from MXChip. Seeed Studio has them, http://www.seeedstudio.com/depot/EMW3162-WiFi-Module-p-2122.html.  I have some, and if I don't need all of them, I may put them up on Anibit. The major downside to the EMB3162 is their decision to use 2mm spaced pins. 2mm female headers are a royal pain to find domestically. I made some breadboard/2.54mm adapters for them here https://oshpark.com/shared_projects/opehJKc7 The built-in stock firmware for the EMW3162 has a (not very similar to ESP8266's AT) command set to act as a Wifi peripheral, but the on-board CPU that does the heavy lifting is  an STM32F205 Cortex-M3 ARM chip with 1 MiB of flash. You can write more elaborate code for the device itself than the Arduino's most people connect to them.It's more expensive than the ESP8266, but it can do more. Another downside is that it's even less documented than the esp8266, but I've exchanged a number of emails with the MXChip engineers, and they've been pretty willing to answer my questions. On 2015-05-19 16:38, Nathan Yinger via TriEmbed wrote:
Success! It did indeed need more power, and the tx pin on the ESP had to be wired to the rx pin of the Sparkfun FTDI board, which is opposite of other serial adapters I've seen.

For those interested, I got the 'AT OK' response with 9600 baud and NL + CR line ending.

Thanks for the help,~Nathan
On Tue, May 19, 2015 at 1:19 PM, Pete Soper via TriEmbed <triembed at triembed.org> wrote:

This is nice information.

 I looked at it a bit and one thing that jumped out and swatted me on the nose is the fact that the radio board 3.3v power supply current draw can greatly exceed the current an FTDI chip can put out. The "usual" FTDI chips (and it appears Sparkfun is using a vanilla FT232RL) can only source about 50ma at 3.3 volts from their internal regulators. The ESP8266 board has typical (i.e. possibly far from "worst case") current requirements looking like this (from the table on the web site linked to below):

 802.11b, CCK 1Mbps, POUT=+19.5dBm 215mA
 802.11b, CCK 11Mbps, POUT=+18.5dBm197mA
 802.11g, OFDM 54Mbps, POUT=+16dBm145mA
 802.11n, MCS7, POUT =+14dBm135mA
 802.11b, packet size of 1024 bytes, -80dBm60mA
 802.11b, packet size of 1024 bytes, -70dBm60mA
 802.11b, packet size of 1024 bytes, -65dBm62mA
 Standby0.9uA
 Deep sleep10mA
 Saving mode DTIM 1 1.2mA
 Saving mode DTIM 3 0.86mA
 Shutdown0.5uA

 So a lot of the time you're basically trying to kill the FTDI chip. I personally let the smoke out of one of these by accidentally telling it to try to supply a motor controller (off by an inch with the wire in the breadboard and hit the wrong power rail). They will die if tortured enough.

 So plan on the FTDI's 5v line driving an outboard 3.3v regulator with proper capacitors on both sides. An oscilloscope could confirm the radio is getting a proper supply and that it's not being yanked down by sudden changes in current demand.

 -Pete

On 05/19/2015 11:00 AM, Christian Lilley via TriEmbed wrote:
All of the information on the ESP8266 can be found here. According to the wiki the baud rate should be 57600. Sparkfun does mention that a level shifter should be used and that it should not be connected directly to 5V sources. 
 Here is an example using the Arduino's software serial to communicate with the ESP and the normal serial lines to communicate with the FTDI board. This guy uses a 9600 baud rate but I don't know if that is a custom setting he uses.
Christian Lilley | Electrical Engineer
 919.794.8627 ext 129christian.lilley at gomohu.com
 www.gomohu.com

On Tue, May 19, 2015 at 10:44 AM, Nathan Yinger via TriEmbed <triembed at triembed.org> wrote:

So, I have an ESP8266, a new serial adapter (https://www.sparkfun.com/products/9873), and I'm trying to get them to communicate.
 When I power up the ESP8266, it creates a wifi network where I can join and ping it, but as far as I can tell, reprogramming it requires a serial connection.
 When the ESP8266 is powered on, the 'tx' light on the serial adapter flashes continuously, which I assume means the ESP8266 is transmitting something. Nothing appears in my serial monitor though, not even gibberish.

 I'm using the serial monitor that comes with the Arduino IDE, with various baud rates and line endings. I haven't found any documentation about the byte length, parity, or character encoding used by ESP8266. I get a TTYUSB device in /dev when I plug in the serial adapter, so it appears to be doing something.
 Does anyone know what's required to make the chips do something? Or have a working setup they could bring to the next meeting?
 Thanks,~Nathan
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 -- 
Jon Wolfe
Anibit Technology LLC.

https://anibit.com

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