Arduino Triggered Fast Pulse generator to simulate gamma ray detectors

I’m looking for a circuit or Gizmo that will generate a 10-100 nanosecond 1-2volt pulse into a standard 50 ohm coax connector and load. These pulses should be rounded, not square. The pulses would be individually triggered by an Arduino pin on the rising edge. The timing of the Arduino pulses will be pseudo-random. The width of the Arduino pulses should be irrelevant to the output pulse.

We have pulse & signal generators but they do to much. We need a minimalist circuit as described. I searched ebay but every generator does too much and gets in the way.

I am writing software for high-energy neutron physics experiments. The software gathers data from gamma ray detectors and high speed A/D equipment. I have no control over availability of the neutron beam (very, VERY expensive!). A few random hours twice a month is inadequate for software development. The A/D system has coax input and expects fast 1-2 volt pulses. Generating simulated neutron/gamma ray events from an Arduino would greatly speed software development and debugging.

You might think people around here would know how to do this. But everybody buys fancy expensive gear and knowledge of basic logic/electronics has atrophied. Three cheers for the Maker revolution!

Any help would be greatly appreciated.

Joey Neutron :slight_smile:

Maybe something like the attached schematic? The propagation delay in the second inverter together with the associated R-C network define the pulse width. The pulse is generated when the input goes from high to low.

Thank you for your quick response. I get the general idea but my analog knowledge is minimal. Any recommended trial values for the resistor, 3 caps and coil?

For the R-C network feeding the inverter, I suggest 330 ohms for the resistor and then chose the capacitor according to the extra pulse length you want (about 3pF per extra ns). For the output network, it depends on the rise and fall time you want. Having thought it over some more, I think the final 100 ohm resistor should go in parallel with the first capacitor, not the second, and the two capacitors should have equal values. Decide on the corner frequency you want (say 25MHz for about 10ns rise and fall times) and calculate the inductor and capacitor values according to section "Pi type RF filter" at http://www.ti.com/lit/an/swra064/swra064.pdf.

Thanks again for the help. I have the parts already except perhaps the proper inductor. If it works OK your
$5 circuit (with an Arduino) will replace a $2000 box. I love it when smart simplicity triumphs.

Joey Neutron :slight_smile: