Electronic stuff

This page will hopefully undergo some major iprovements sometime in the future... As for now, you can find here some information about:

Lastem BabucABC and Campbell SR50: let'em talk to each other!

Here are some information on the digital interface I designed for the Forni Glacier AWS (Automatic Weather Station), the first permanent AWS operating on the surface of an Italian glacier. The AWS is operated by the Glaciology Group at University of Milan (Italy) and is based on a Lsi Lastem BABUC ABC 20 channels datalogger. A GSM modem link is planned to allow for remote data download, AWS management and early misfunctioning detection. The following map shows the microwave direct viewshed based on a DEM (Digital Elevation Model) of Forni Valley and the AWS location, assuming an exceptional snow cover thickness covering the whole AWS but the antenna.


During system integration of the AWS in the lab at the Earth Sciences Dept. of Milan University we got stuck on the issue of controlling a Campbell Scientific SR50 sonic ranger with BabucABC datalogger, in order to record snow height data. The (proprietary) serial data line built in BABUCs would not have worked natively with the SR50, and we were late on schedule for field setup of the AWS (the first snowfall could have arrived at any moment). Thus, a workaround was devised which is performing quite since autumn 2005, in spite of the air temperature reaching down below -25 °C around Christmas day.
SR50 datasheets detail the serial formats available from the sonic ranger, and the pulse train option was selected as the safest bet. The trigger pulse required to start the measurement was also specified, but no reliable way to generate it using Babuc's actuator outputs could be found, since they are designed for a different purpose (i.e., actuated power supplies). Trickily enough, on the bench a seemingly acceptable trigger pulse could be generated by simply shifting the available 12 V step output to the required TTL levels with a passive network. Similarly, the Babuc managed to count the pulse train in a somewhat crude but effective way by directly feeding a pulse count input with the SR50 output. Satisfied with this, we set up the AWS for a test run at the Mountain Rescue base in Santa Caterina Valfurva (thank you all for your help!!) just to find that nothing worked anymore. Measurment triggering was unreliable, and readouts were "null"... Likely, the reason was the lower temperature at the test site, but hey! the whole thing was expected to work even at very low temperatures...


So, just in case you need to use these nice pieces of hardware togehter: at the Babuc datalogger you need one spare actuator output and one spare anemometer/rain gauge input (yes, rain gauges... they output pulse trains too, right? No, but don't be picky for now). The Babuc is fast enough to count the pulses when the SR50 is set for the lowest bitrate. Then, you have to account for Babuc expecting "contact closures" trains, not positive pulse trains, at its rain gauge/wind speed input.
We got by using a few CMOS logic gates for building a monostable, the simple control logic, a capable output driver and some bonus fanciness (test led indicator, just to use up the unused gates), and a transistor for the pulse train readout by the Babuc ABC.


As for the "soft" side, you will have to customize an operative code with proper converison coefficients for converting the SR50 output to a distance, and to program the operation of the actuator. A quite nice Babuc ABC feature allows for only acquiring signals received within a customizable time window ending with the actual sampling instant, so you can cheaply add robustness to the system by setting a window long enough for full pulse train counting but short enough to reduce the probability of also counting possible interferences. This is useful irrespective than the Campbell being always powered (SR50's have a very low power standby mode) or not.
In case you are interested in buying a replica of the interface being used at the Forni AWS (complete with a detailed connection diagram and a floppy with the customized operative code to upload in the BabucABC) feel free to write me in due advance. You will receive the ready to operate assembled board housed in a protective but not watertight case (not shown in the picture). Gerber files ready for PCB fabrication by a third party manufacturer can be purchased too, just contact me. These files are for the rev. 1 board, which is a double layer printed circuit board: top and bottom copper layers, top and bottom solder masks, top silkscreen overlay, and drill files. Please note that a double layer PCB is not strictly necessary, but I wanted plated holes and this usually imply a double layer quotation anyway. I could easily supply you with Gerbers for a single layer version if you prefer to get cheaper PCB manufacturing quotations.


You may contact me about feasibility and fees for on-site assistance or consultancy on technical or scientific issues related to these two instruments and to the data they collect.



A remotely controlled fiberglass boat with a 5-thermistors thermocline profiler

This is a long-delayed project aimed at obtaining a detailed map of water temperatures at various depth below the surface of ice contact lakes, with particular emphasis on the hazardous area bordering calving cliffs. The main purpose is pinpointing and monitoring the submerged inputs feeding such lakes. The test site is Miage Lake, which is known to feature such submerged waterways, normally filled but occasionally also drained almost completely by this hidden water circulation.
A small, remotely controlled fiberglass boat has been equipped with a towed vertical array of thermistors at various depth. The boat will roam in the ice cliff area collecting temperatures from the array and positioning data from an on-board GPS unit. The remote control is capable of operating from lake shores but a rubberboat will be available at a safe stand-off position from the ice cliff, to provide support in case of any problem.



Unfortunatley the project has been delayed by almost two years due to the sudden emptying of Miage Lake just the week before the first skeduled test, which should now take place later this summer.
From the electronics viewpoint, the circuit is fairly easy. Five similar thermistors, each one with its precision resistors retwork, are wired singularly to five inputs of a Campbell CR200 datalogger onboard of the ship. Th CR200 is programmed with a CR-BASIC routine to acquire the input at short constant intervals syncronized with the GPS unit, which will record positioning data in its own internal memory. A planned later addition to the same vessel will be a thermal notch profiler device.



More information will be uploaded once the system will be fully operational and its details and the first field data will have been published.



Brand-new Crystal Semiconductors CS5396 24 bits delta-sigma A/D converter ICs for sale

This might be your chance to get 5 of these SMD devices in perfect conditions, still sealed in their ESD and moisture protecting bags! The CS5396 was the first commercial 24 bits delta-sigma A/D converter featuring a 120 dB dynamic range (A-weighted, beware!). And you get 2 channels (stereo) with each CS5396!
These devices are really cool to play with, especially due to the crazy analog world at sub-uV noise levels, but unfortunately I came to meet them a bit too late, so that after a short while (and when this 5 pcs order was already shipping) I decided to switch to devices from later product line. Nowadays Cirrus Logic is not anymore producing the CS5396, which was used in many high end equipment, especially in the professional digital audio segment.
They were rather expensive devices when in production, and I don't know what their price and availability is today. Their price as new spare parts will surely rise to the stars in a few years. My current rate (top quality packaging included) is 100.- € each, or a 450.- € bargain price (10% discount) if you buy all of them at once; shipping worldwide with your preferred carrier is at your charge. Write me if you are interested!

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http://www.citterio.net/electronics/electronics_en.html was last updated on 16 August 2006.