Author Archives: Robert

PCB etching with HCl and H2O2

As my electronics designs are getting more complex and my patience for soldering air-wires for all connections on a perfboard is decreasing, I started looking into making my own PCBs. Although there are professional PCB fabrication companies that are not very expensive, I am not so confident yet with my Eagle PCB design skills. Hence I decided to start fabricating some simple PCB boards myself to get a better insight in all aspects relevant for PCB boards.

Reading about the different options for etching PCBs, and following a instruction evening organized at the Hackerspace Nijmegen on using a small CNC mill for PCB fabrication, I opted for toner transfer using a laser printer and using HCl and H2O2 as described here.

My first attempt was with 10% HCl from the local hardware store (dat zeg ik, Gamma!) and 3% peroxide from the drugstore. Directly following mixing, etching went OK-ish, but rather slow. It took some 10 minutes for the 1-sided PCB board to be clean. The etchant turned into a nice green color. The second time (a month later) the etchant would not really work any more, and th ePCB only got dark. Rejuvenating the solution with some additional H2O2 as per instruction did not change anything. I guess the concentrations were too low, and after a few hours I abandoned the attempt and took the board out.

For the second attempt I ordered 30% Hcl and 10% peroxide in an online store. Using my old etchant solution, I diluted the H2O2 to approximately 3% and mixed that with the HCl in a 2:1 ratio (adding the acid to the HO2O, to prevent a strong exothermic reaction). I popped in my board (from the previous attempt, which had gotten quite dark). The result was a very nice etching process. The process was clearly visible and there were no bubbles.

You can see that half of the copper of the PCB board has been etched away

The result of the etching is quite nice.

Resulting PCB board. It is about 2×3 cm large and will contain a 6 pin DIP optocoupler with some resistors and a diode to implement a MIDI filter.

I am happy with the result of the etching. The ill-defined traces on the board are due to poor toner transfer; I had to make some corrections with a permanent marker (fine liner) on the board. Measuring the connection between all pads revealed that there was one short-circuit (on the left side of the board). I was able to remove that with an x-acto knife.

The next time I will design the traces in Eagle to be slightly wider and to have more space between them. In the Eagle design rules I used a 6 mil minimum trace width (the default), and a 12 mil clearance. And I have to practice more with the toner transfer… to be continued.

Restoring the AT firmware on the ESP8266

Most of the time I am using Wemos D1 mini development boards in combination with the Arduino IDE to make my own firmware to run directly on the ESP8266 chip. But I also have some bare ESP-01 and ESP-12 modules lying around, and recently I came up with the plan to use one of them.

The specific project requires very well controlled timing of an ADC, for which I will use a regular ATmega328P-based Arduino board. In this project the ESP8266 will only be used to transmit the data over WiFi. Neither my ESP-01, not my ESP-12 still have the original AT firmware, since I have been experimenting with various other firmwares.

This is where the challenge starts, since my plan required restoring my ESP-12 to the AT firmware and use a library like ESP8266wifi or WiFiEsp. I realize that I have been struggling with different firmwares before, hence this post to give a short review and to keep some notes for my own future reference.

Module form factor

The ESP8266 microchip comes on various development boards that include an USB interface, such as the Wemos D1 Mini and the NodeMCU board, but also as bare modules such as the ESP-01, 02, etc. This page on the ESP8266 wiki has an overview of all modules and this page has comparison of some of the raw modules with some of the development boards.

ESP-01 module:

ESP-12 module:

Flash memory capacity

Besides the number of GPIO pins that is exposed by each of the modules, another important feature is their flash memory capacity. The AI-Thinker website has a module list table that includes this. The ESP-01 module comes with 4Mbit, i.e. 1MB of flash. The ESP-12 module comes with 4MB. Note that there are development boards such as the Wemos D1 mini pro that even have more.

Firmware

As the ESP8266 is nowadays fully supported in the Arduino IDE, I prefer to develop my own custom firmware for the ESP8266 using C/C++ and the Arduino IDE and libraries. So the most confusing aspect of the ESP8266 for me is that there are multiple “standard” firmwares available for it, which I often accidentally confuse. These include

  • The AT firmware, comparable to the Hayes command set on old modems.
  • The NodeMCU firmware, which includes a LUA interpreter.
  • The MicroPython firmware, which includes a Python interpreter.
  • The Espruino firmware, which includes a JavaScript interpreter.

For the firmware options that include a Python or a JavaScript interpreter it should be mentioned that there are other versions from other companies/projects.

The NodeMCU project is more centrally managed/organized and includes a website where you can compile customized firmwares with support for specific hardware add-ons.

Restoring the AT firmware

To flash the firmware to an ESP8266, you will need to wire it up and get it in the right boot loader mode. There are many online tutorials for this and I won’t elaborate here. You will also need software to write the new firmware, I am exclusively using esptool.py.

I tried various options to flash my ESP-12 with the original firmware, most of which failed. The challenge is to figure out which firmware is compatible with my specific module, and to which flash memory locations to write the different pieces of the firmware. In the next section I will describe three things that worked, going from the oldest to most recent firmware versions.

Following the instructions here and using a rather obscure version of the firmware contained in a single binary file from here, I had success with:

esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x00000 v0.9.2.2\ AT\ Firmware.bin

Subsequently I was able to connect in a terminal program with 9600 bps and got

[System Ready, Vendor:www.ai-thinker.com]
AT+GMR

0018000902

OK

Using the old AT firmware from Espressif itself with the “Offical ESP8266 AT+ Commands” from their old GitHub repository I was also able to get it to work with:

esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x00000 boot_v1.1.bin
esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x01000 newest/user1.bin
esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x7C000 esp_init_data_default.bin
esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x7E000 blank.bin

Subsequently I was able to connect in a terminal program with 115200 bps and got

ready
AT+GMR

00200.9.4

OK

The Espressif ESP8266 SDK Getting Started Guide contains the most recent information about the layout of the flash memory. Using the 2.2.1 release from the Espressif NONOS_SDK repository and

esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x00000 boot_v1.2.bin
esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x01000 at/512+512/user1.1024.new.2.bin
esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x7C000 esp_init_data_default_v05.bin
esptool.py --port /dev/tty.usbserial-FTG54BPS --baud 115200 write_flash --flash_mode dio 0x7E000 blank.bin

I also had success and was able to connect in a terminal program with 115200 bps. This resulted in the following response

ready
AT+GMR
AT version:1.6.2.0(Apr 13 2018 11:10:59)
SDK version:2.2.1(6ab97e9)
compile time:Jun 7 2018 19:34:26
Bin version(Wroom 02):1.6.2

I did not have success with the 3.0 release from the Espressif NONOS_SDK repository. That one does not have the “512+512” directory, only the “1024+1024” directory, which I could not get to work on my ESP-12. Suggestions to make this work are welcome.

Motion capture system

For the EEGsynth project I have developed a full-body 8-channel motion capture system. It is based on the MPU9250 9-DOF inertial motion unit, which contains a three-axis accelerometer, gyroscope and magnetometer. I have combined this with the Madgwick AHRS algorithm, which takes the raw sensor data and computes the yaw, pitch and roll.

The design is based on one battery operated main unit that is worn for example in a Fanny pack around the waist, and up to 8 sensors that are attached to the arms, legs, etc.

The main unit contains a Wemos D1 mini, which is based on the ESP8266 module. It uses the TCA9548 I2C multiplexer to connect a maximum of 8 MPU9250 sensors.

The data from the IMU sensors is streamed using the Open Sound Control (OSC) format. The sampling rate that can be achieved with one sensor is around 200 Hz, the sampling rate for 8 sensors is around 60 Hz.

For initial configuration of the WiFi network it uses WiFiManager. After connecting to my local WiFi network, it has a web-server through which the configuration can be set, which includes the number of sensors and the destination host and port for the OSC UDP packets.

For the IMUs I am using MPU9250 modules that I purchased on Ebay for about 3 USD each.The MPU9250 units fit very nicely in a Hammond 1551MINI enclosure.

I designed the enclosure for the main unit in Fusion360 and printed it on my Prusa I3 MK3 3-D printer. I made two motion capture systems so far, one with black and one with white PLA filament.

The Arduino sketch and more technical documentation can be found here on GitHub.

First steps with a €20 single-channel EEG system

My friend Vladimir recently demonstrated a single-channel EEG system that he got at a hackathon in London. When he mentioned that it only costs €20 (or actually 20 GBP to be more precisely) I immediately decided to order one myself. The ICI-BCI system is a low cost open source brain computer interface.

The bag clearly and rightfully indicates that it is a totally experimental system, and that it should be used with caution.

The basic idea of the amplifier is that it takes an 1000 Hz analog audio signal from the computer or mobile phone, which is amplitude modulated by the ExG signal and subsequently fed back as microphone signal. So the system is fully analog and requires the DAC to be done by the audio input of the computer or phone.

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Configuring Multitech MDOT for TTN

I have a Multitech MDOT-BOX for testing. Configuring it for TTN requires the following connection to a computer, after which AT commands can be used to probe and set parameters. The following resets the MDOT to factory defaults and shows the configuration overview.

AT&F
AT&V

Firmware: 		2.0.0
Library : 		0.0.9-14-g4845711
Device ID:		00:80:00:00:00:00:b3:76
Frequency Band:		FB_868
Public Network:		off
Network Address:	00000000
Network ID:		6c:4e:ef:66:f4:79:86:a6
Network ID Passphrase:	MultiTech
Network Key:		1f.33.a1.70.a5.f1.fd.a0.ab.69.7a.ae.2b.95.91.6b
Network Key Passphrase:	MultiTech
Network Session Key:	00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00
Data Session Key:	00.00.00.00.00.00.00.00.00.00.00.00.00.00.00.00
Network Join Mode:	OTA
Tx Data Rate:		SF_7
Tx Power:		11
Log Level:		6
Maximum Size:		242
Minimum Size:		11
Maximum Power:		20
Minimum Power:		2
Data:			0

After adding a device to application page on the TTN console with OTA activation, the following identifiers/keys are listed on the TTN console page for the device

Device EUI
Application EUI
App Key
Device Address
Network Session Key
App Session Key

From the Multitech documentation: In OTA mode, the device only needs to be configured with a network name (+NI=1,name) and network passphrase (+NK=1,passphrase). The network session key, data session key, and network address are all automatically configured.

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EEG combined with VR

We recently had a meeting at the Astron radio telescope for the COGITO project with Daniela de Paulis, Stephen Whitmarsh, Guillaume Dumas and others. One of the goals of that meeting was to try out the combination of the EEG system with the Oculus Rift VR system.

For the COGITO project we are using the GTec Nautilus EEG system. Our specific system comprises of a 32-channel wireless amplifier that mounts on the back of the EEG cap, in combination with EEG caps in three different sizes. The caps have 64 holes at a subset of the  locations of the 5% electrode placement standard. We are not using the “Sahara” dry electrode option, but rather the regular wet electrodes.

We started by removing all electrodes and cups from the cap, to get a clear view on which electrode sites are accessible. The central electrode locations (i.e. the z-line), temporal electrode locations and occipital electrode locations are occluded by the VR head mount. But there are still plenty of electrode locations accessible.

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Art-Net to DMX512 with ESP8266

Update 26 May 2017 – added photo’s of second exemplar and screen shots of web interface for OTA.

Professional stage and theatre lighting fixtures are mainly controlled over DMX512. To allow a convenient interface between the EEGsynth and this type of professional lighting systems, I built an Artnet-to-DMX512 converter. It quite closely follows the design of my Artnet-to-Neopixel LED strip module.

Let me first show the finished product. It has a 5 pin XLR connector, a 2.1 mm power connector, and a multi-color status LED:

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GPS-enabled LoRaWAN temperature sensor

Together with the TTN Nijmegen community we are discussing possible applications of remote sensing nodes in Nijmegen. To get a better view on the TTN coverage in Nijmegen and to get a feel for what works (and what not), we are working on the implementation of some nodes.

The PoC2 TTN gateway will soon be installed by Michiel Nijssen at Maptools in Molenhoek. To help Michiel get started, we agreed that I would give him a fully functional node to play with. Michiel came up with a very concrete idea: it consists of a GPS-enabled temperature sensor that sends the data over LoRaWAN/TTN. Below you can find some details of a very fist implementation.

The node consists of

  • Teensy 3.2 MCU board
  • Dorji LoRa module
  • DS18b20 temperature sensor
  • Ublox NEO-M8N GPS module
  • 4k7 ohm resistor
  • small LED and 200 ohm resistor (not on photo)

I estimate that the material costs amount to 50 euro. It still needs to be soldered in a more sturdy form-factor and a battery and enclosure need to be added.

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Getting started with Pine64

UPDATE: see at the end for some problems that I encountered after the initial install.

The Pine64 is a single board computer that resembles the Raspberry Pi, but with a 64-bit CPU, up to 2GB of RAM and available for $15-$29. It was introduced with a Kickstarter campaign which I supported. My 2GB Pine64 has been lying on a shelf for quite some time, as I was waiting for the kernel, distribution and documentation to mature.

My first installation yesterday went fine (some slight troubles to get WiFi connected), but while updating the kernel, the root disk partition completely filled up and borked the installation. Hence I have to start again. Let me now document it, as I might need to repeat the installation more than a second time.

I primarily followed the instructions from https://www.pine64.pro/getting-started-linux/ with some additional information from http://forum.pine64.org/showthread.php?tid=982. I am working off an Apple MacBook Pro computer.

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ESP-8266 Art-Net NeoPixel module

As explained in a previous post, for the EEGsynth we want to use a neopixel array that can be controlled wirelessly using the DMX512 protocol. I purchased a number of Adafruit neopixel rings with 12, 16 and 24 elements respectively. Each RGBW pixel contains a red, green, blue and white LED. For the 24-pixel ring that means that there are in total 4*24=96 LEDs of which the intensity can be set.

The ESP-8266 module is a versatile WiFi module that comes in many versions. During development I especially like the NodeMCU version, which mounts the ESP-12 module on a development board with USB connection, and the even smaller Wemos D1 mini board. The Wemos D1 mini is hardly more expensive on Ebay than the simpler bare-bone ESP-8266 modules.

The hardware connection is simple: I connected Vcc and GND directly to the Wemos D1 mini board, and connected pin D2 to the data-in of the first pixel. Although the Neopixels are specified for 5V, in my experience the Adafruit rings also work fine at 3.3V, both for power and for the serial control signal. Each LED can take up to 20 mA when fully bright, which means that all LEDs of the 24-pixel RGBW ring can take up to 24*4*20 = 1920 mA, or close to 2 A. However, not all LEDs will be at full intensity at the same time, and driving them with 3.3V rather than 5V further reduces the current. I encountered no issues powering them over the USB port of my MacBook.

For the EEGsynth we want to map a small number of control signals to aesthetically pleasing light effects. E.g. it can control the hue, the frequency with which the array flashes, or the speed with which a bright bar rotates along the ring.

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