BLASTER / RECORDING INTERFACE UNIT
⚠ (:toc:)
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!BACKGROUND
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By "Blaster System" we mean the device that fires the cap, which in turns ignites the detonating cord used as seismic source.
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The Blaster must trigger two recording systems:
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* The GEODE, which records 96 channels from snow streamer
* The Vertical Seismic Profiling (VSP) recording, which digitize signals from a three-component geophone sensor that is lowered in borehole.
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Trigger from Blaster is a Contact Closure output. This means that an electronic component will make a short-circuit (a nearly so) between two wires in the Contact Closure connector.
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If we connect trigger inputs on the two recording systems to the same source (the Blaster), we risk problems when ground of these systems are possibly connected through the Contact Closure cable. So we decided to build an interface that inputs the Contact Closure from the Blaster, and outputs two Contact Closures - each isolated from the other - to the two recording units.
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!CIRCUIT DIAGRAM
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Attach:blaster-interface.png
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Component designations in circuit diagram are not correct in all cases (drawn in demo version of %newwin%[[http://www.cadsoftusa.com/ | Eagle Cadsoft]], not familiar with all details yet). Here is the correct list:
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(:table border=1 cellpadding=3 cellspacing=0:)
(:cell align=center bgcolor=#dddddd:) '''Name'''
(:cell align=center bgcolor=#dddddd:) '''Type/Value'''
(:cell align=center bgcolor=#dddddd:) '''Supplier'''
(:cell align=center bgcolor=#dddddd:) '''Supplier P/N'''
(:cell align=center bgcolor=#dddddd:) '''Datasheet'''
(:cellnr align=center :) D1, D2
(:cell align=center :) 1N4007
(:cell align=center :) -
(:cell align=center :) -
(:cell align=center :) -
(:cellnr align=center :) R1
(:cell align=center :) 560
(:cell align=center :) -
(:cell align=center :) -
(:cell align=center :) -
(:cellnr align=center :) R2
(:cell align=center :) 100k
(:cell align=center :) -
(:cell align=center :) -
(:cell align=center :) -
(:cellnr align=center :) R3
(:cell align=center :) 390
(:cell align=center :) -
(:cell align=center :) -
(:cell align=center :) -
(:cellnr align=center :) Q1
(:cell align=center :) BC557C
(:cell align=center :) %newwin% [[http://www.elfa.se | Elfa]]
(:cell align=center :) 71-072-95
(:cell align=center :) %newwin% [[https://www1.elfa.se/data1/wwwroot/webroot/Z_DATA/07105539.pdf | Link]]
(:cellnr align=center :) LED1
(:cell align=center :) RED
(:cell align=center :) -
(:cell align=center :) -
(:cell align=center :) -
(:cellnr align=center :) OC1, OC2
(:cell align=center :) PC815
(:cell align=center :) %newwin% [[http://www.elfa.se | Elfa]]
(:cell align=center :) 75-369-07
(:cell align=center :) %newwin% [[https://www1.elfa.se/data1/wwwroot/webroot/Z_DATA/07536907.pdf | Link]]
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!DESIGN NOTES
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!! Trigger inputs of Recording systems
The CLOSURE OUTPUTS of the Blaster Interface Unit should be connected to TRIGGER INPUT of our two recording system. The characteristics of these trigger inputs is summarized in table below.
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(:table border=1 cellpadding=3 cellspacing=0:)
(:cell align=center bgcolor=#dddddd:) '''Recording system'''
(:cell align=center bgcolor=#dddddd:) '''Open-circuit voltage'''
(:cell align=center bgcolor=#dddddd:) '''Short-circuit current'''
(:cell align=center bgcolor=#dddddd:) '''Equivalent output resistance'''
(:cellnr align=center :) GEODE
(:cell align=center :) 5.0 V
(:cell align=center :) 1.5 mA
(:cell align=center :) 3333 ohm
(:cellnr align=center :) VSP (Read-Well: AVALON)
(:cell align=center :) 4.2 V
(:cell align=center :) 13.9 mA
(:cell align=center :) 302 ohm
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!!Base current of Q1
* When CLOSURE INPUT is short-circuited, base current of Q1 is approx 14 mA. BC557C absolute max base current is 200 mA.
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!!Drive current of Opto-couplers
* When Q1 is ON, collector current (and hence drive current of Opto-couplers OC1 and OC2) is approx 10 mA.
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!PICTURES
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Image shows Blaster Interface Unit. Click image to enlarge.
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[[Attach:complete.jpg | Attach:blaster-interface-complete.png]]
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Details. Click image to enlarge.
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[[Attach:box-large.jpg | Attach:blaster-interface-box.png]]
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