Measuring the Water-Level of a Cistern

Written by Stefan on 10. Mai 2013 — Leave a Comment

To measure the water level of our cistern, I started to build a little cistern monitor based on a hacked TP-Link MR3020 router running OpenWrt and a SRF05 ultra sonic range finder. The software project mainly consists of a kernel module and a web service to access the
data through a simple web-ui or by CSV download. The sources for both (and some build instructions) could be found on github.

CisternMongoose web-ui

CisternMongoose web-ui

Since the TP-Link has some unused GPIOs, the SRF05 could be connected directly to the TP-Link by using a single line for triggering/data acquisition. The values from the sensor are exported to sysfs by the kernel module. Then, the web-service reads out the data from there and provides them as JSON. Also the web service provides a simple static HTML page using microAjex to retrive and display the JSON. The web service is written in plain C and uses the excellent mongoose as a foundation. Thus, the whole thing is only about 110k small. To create a long-term statistic, the measured data is written to a CSV file every hour.

MR3020 with Kyle supervising and SRF05 connected

MR3020 with Kyle supervising and SRF05 connected

MR3020 cracked open

MR3020 cracked open, wires for 3.3V, GND and data connected

(Unfinished) mounting of MR3020

(Unfinished) mounting of MR3020

Cistern cover, sensor (with enclosure) below

Cistern cover, sensor (with enclosure) below

Posted in C/C++, Linux, Programming | Tagged , , , , , , ,

Simulate Circuits Online

Written by Stefan on 20. Februar 2013 — 1 Comment

PartSim is a online circuits simulation. It allows one to draw and simulate schematics in your web-browser:

PartSim includes a full SPICE simulation engine, web-based schematic capture tool, and a graphical waveform viewer.

PartSim

PartSim

Posted in Electronics | Tagged , ,

Scratch Remote Sensor API

Written by Stefan on 1. Februar 2013 — Leave a Comment

Pynetsense is a Python library that provides a simple to use API for implementing Scratch networking sensor clients. For communicating with Scratch, the remote sensor protocol is used.

Beside providing a simple API to manage messages and variables, a wrapper framework is provided. The wrapper framework helps with implementing sensor clients that run in the background as daemons.

Currently there is a fully featured wrapper included for wrapping the GPIOs of an Raspberry Pi into an Scratch remote sensor client. This allows one to access the GPIOs of the Pi from Scratch by simply setting/getting some global variables.  The videos below show how the Pi wrapper is used from Scratch. For more details see the project page.

Raspberry Pi GPIOs as Remote Sensors Part 1

Raspberry Pi GPIOs as Remote Sensors Part 2

Posted in Linux, Microcontrollers, Programming, Python, Raspberry Pi | Tagged , , , ,

CadSoft Eagle Tutorial Videos

Written by Stefan on 2. Januar 2013 — Leave a Comment

Jeremy Blum is about to post a series of CadSoft Eagle Tutorial Videos. I think they are very well done and easy to follow. Thus, if you are about to learn Eagle, they might come in handy.

Posted in Electronics | Tagged , , ,

Record from Webcam to OGG with GStreamer

Written by Stefan on 19. November 2012 — 2 Comments

Using gstreamers gst-launch, one could easily record the live stream from a webcam directly to an OGG-container using theora-encoding. By splitting the input from the v4l source (through “tee”) into two parallel sub-pipes, it is possible to show the recorded stream on the screen, while saving it to the OGG-file on the other processing path.

For more details see the following shell-script:

Posted in Linux, Misc | Tagged , , , , , , ,

pyscmpd 0.1 released

Written by Stefan on 14. November 2012 — Leave a Comment

First public release of pyscmpd is available.

pyscmpd is a music player daemon I use to convert my Raspberry Pi into a “soundberry”. The daemon is talking a subset of the MPD protocol, but instead of serving local MP3 files, it connects to soundcloud.com and serves the streams found there. Because of the MPD protocol, a huge number of clients could be used as a front end to the daemon (e.g. ncmpcpp, sonata). It is user configurable, which parts of soundcloud.com are made available for browsing (by defining categories and adding groups or users to them).

Posted in pyscmpd | Tagged , , ,

Poor Mans Scratch Sensor Board

Written by Stefan on 7. November 2012 — Leave a Comment

“scratch-sherpa” implements the protocol of the Scratch Sensor Board (also known as Picoboard), as supported by the educational Scratch  programming environment. A MSP430 Launchpad with my uSherpa firmware as foundation is used.

The (unedited) video below shows some examples of how the board could be used with Scratch:

Posted in Microcontrollers, MSP430, uSherpa | Tagged , , , , ,

Carambola SoC Stand Alone with MSP430 Piggyback

Written by Stefan on 28. Oktober 2012 — Leave a Comment

Like I wrote in this article, it is pretty easy to run the Carambola SoC stand alone. Today I finished the Carambola-MSP430 (for MSP430 stand-alone see this article) Piggyback I intend to use as a replacement for the current jumper wired brains of my Carambot.

The Carambola comes with 2mm pin connectors, I used a 2mm perf board to host the Carambola, and then piggybacked the MSP430 on a 2,54mm stripe board. The MSP430 communicates with the Carambola through UART1 with the help of uSherpa-Firmware and the uSherpa-Python-Client-API.

Since the Carambola on the Robot is powered from a 7.4V LiPo battery, two DC step-down converters from Pololu are used: one for 5V which goes to USB, and one for 3.3V which powers the logic of the Carambola as well as of the MSP430. The Carambola seams kind of picky regarding the 3.3V supply. I was not able reliably powering the Carambola by using standard LM7805/TS2940 regulators. The step-down converters are mounted in diagonal to the perf board, since the have a 2,54mm pin-out, and by placing them like so, I barely was able to solder them to some of the whole of the 2mm perf board.

An other thing a noticed about the Pololu Step-Down Voltage Regulator D24V6ALV was, that they do not come up reliably when SHDN pin is left open. The manual says, it could be left open, or connected to VIN to enable the board. Well leafing it open was no success, connecting it to VIN works well.

Carambola and MSP

Carambola and MSP

Carambola with MSP piggyback

Carambola with MSP piggyback

The following table shows, how pins of the Carambola are connected:

From Carambola PIN Connected to PIN
5V power supply for USB (21) VOUT output of 5V D24V6ALV
3.3V power supply for Carambola (22) VOUT output of 3.3V D24V6ALV
UART 1 TX uSherpa-communication (31) RX of MSP430
UART 1 RX uSherpa-communication (32) TX of MSP430
UART 2 TX for serial debug console (35) RX of FTDI
UART 2 RX for serial debug console (36) TX of FTDI
GND ground (37) GND
UDP D+ for USB (38) USB D+
UDP D- for USB (39) USB D-
UPHY for USB (40) 3.3V to select USB master
Posted in Carambola, Misc, MSP430, uSherpa | Tagged , , , ,

Carambola SoC Stand Alone

Written by Stefan on 14. Oktober 2012 — 9 Comments

I just was playing around a little running the Carambola SoC stand alone (without dev-board). The picture blow shows what needs to be connected to boot the Carambola, access it through serial line (by using a TTL USB to serial converter), and optionally connect USB (I used a web cam):

Carambola Stand Alone (with USB)

Carambola Stand Alone (with USB)

Some notes about power consumption:

  • You need to supply at least 300mA, otherwise the Carambola is starving.

Some notes about the USB connection:

  • For using USB, 5V has to be provided to pin 21 (when not using USB, there is no need to provide 5V).
  • UPHY (pin 40) needs to be grounded to tell the USB controller to run in master mode.
  • No ESD protection when connecting as described! Thus, I recommend not to hot-plug devices when using this unprotected approach!
Posted in Carambola, Misc | Tagged ,

Propeller-Installer Project of the Week at Parallax

Written by Stefan on 9. Oktober 2012 — Leave a Comment

My little installer script for helping setting up a Propeller Tool-chain on Linux/ARM, also mentioned on hackaday last month, was chosen for “project of the week” from Parallax (the makers of the Propeller).

Parallax Project of the Week

Parallax Project of the Week

Posted in Linux, Programming, Propeller, Raspberry Pi | Tagged , , , ,
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