Schmitt Trigger Circuit

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Steven Sesselmann
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Joined: 27 Apr 2015, 11:40
Location: Sydney

Schmitt Trigger Circuit

Post by Steven Sesselmann » 05 Sep 2019, 13:54

Hi All,

Not sure if any of you do any neutron counting, but if so this might be of interest.

I have developed a new circuit for the Russian neutron counters. Lot's of people have bought these tubes on eBay and not been able to make them work, that's because they don't operate like other proportional tubes, they operate in constant discharge mode i.e. there is a constant albeit small current running through the tube all the time. For this reason they require a big 100 M Ohm load resistor, and consequently the baseline looks like a pond in a hurricane, however the short pulses from neutrons stand well above the noise and are detectable.

This circuit employs a schmitt-trigger which is a special feedback circuit that lifts the baseline when a pulse is encountered, and drops it again as the pulse falls below the trigger.

This board is designed to be used as a stand alone preamplifier or built into the GS-USB-PRO so a detector can just be connected straight to the SHV.

It looks simple enough, but a lot of R&D went into this one.

There are two adjustments, the blue trimpot adjusts the pulse volume, and the grey trimpot adjusts the trigger level. Getting these setting right is critical in order to make it work, and is best done with an oscilloscope. A small LED (D01) flashes when a pulse is detected and can help with the adjusting.

The board is available here; ... tt-trigger


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