Rolling my own NIM module

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
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Rolling my own NIM module

Post by guest » Wed Jul 25, 2001 2:55 pm

I have spent the last few days working on a single width NIM module design which will effectively be an audio and visual ouput device for a number of detector systems.

I had to design the electronics around commonly conditioned NIM type signals. The signals are usually fast rise time, short duration, positive pulses of a few volts. I decided I would also want the system to respond to signals as small as 50mv or so. I designed an input stage around a simple single transistor design (2N2222) which includes a sort of sensitivity adjust pot.

The signal is then shaped up by a CMOS 4049 buffer and presented to a variable delay monostable (555). This then puts out a time stretched positive 12 volt pulse which is ground referenced.

I use one of those totally annoying sonalerts controlled by the pulse width control in the 555 circut. (~2ms to 1 second in three ranges.) This then just chirps based on the on-time pulse width. The reason for the long widths is for extremely infrequent pulses as in neutron background counting. I found that my BF3 units short audio out pulses could be missed coming so infrequently. A 0.5 second blast from a sonalert will signal a detection event that will not be missed in the next room, even! As a blessed, saving grace, I am putting a toggle switch on the sonalert to mute the device and preserve sanity over the long haul.

I added a 10,000 mcd green led as a visual indicator. The light is diffused by mounting the LED in a short legth of hot melt LDPE which mounts to the front panel.

I bread boarded the circuit last nite, debugged it and will assemble the device later this week or next.

I have a couple of more personalized NIM modules planned in the future. I have several older, blown up modules which I gutted to use as shells for this effort.

Richard Hull

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