Rolling my own NIM module

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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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