Transcript Olin Student Projects 2008

Olin Student Projects 2008
Keith Gendreau
Code 662 NASA/GSFC
301-286-6188
A PIC Microcontroller Based
Pulse Detection and
Measurement System
Take an input analog signal, look for pulses above a
threshold, detect the peak voltage of each pulse, digitize
the peak voltage, write to a file the pulse time and peak
pulse height, continue….
Build on last year’s “Flux Meter”, if possible.
X-ray Detection and Pulses
X-ray photons
Vsignal
X-ray Detector
Amplifier
X-rays pack a lot of energy. X-ray detectors see
individual X-ray photons. If the detectors and
electronics are good enough, they can determine
the energy of the photon.
Science is to be gained by the energy of the
photons.
Pulses on an analog signal
(from an X-ray detector)
V
vpulse
Vpulse is proportional
to Energy of photon
Pulse widths: ~25 ns- 2µsec
t
tpulse
V
Noise pulses?
vthresh
t
Pulse#1
Pulse#2
Pulse#3
Desired Layout: Top view
Analog signal
From X-ray
Detector
On a BNC
Connector
Olin Pulse
Height Box
USB Output
Computer
With Olin
Software
To display/save
Events
Any type of computer, PC or Mac
(I prefer Mac, but whatever is doable)
Knob for
Additional
gain
Knob for
Lower Voltage
Threshold
Requirements
• Must handle pulses ranging from ~<
100 nsec to ~ 100 microsec wide
• Goal of achieving ~106 counts per
second (typically, it is much less than
this, I’d be happy with ~104 cps)
• Should be able to handle pulseheights
ranging from ~0 to 10 volts (positive).
Output Desires
• ASCII file with time and pulseheight for each event
above threshold
• Plot with histogram of pulseheights
• Flux vs time (like on the flux meter)
• Be creative.
• TCP/IP port?
• eg, The computer reading the instrument can
make the data available as a server to others as
client computers via a TCP/IP Sockets protocol
• Would be an extremely useful feature for beamline
work.
From http://www.edn.com/article/CA216167.html
QuickTime™ and a
decompressor
are needed to see this picture.
This is a circuit design I found
that can detect a pulse peak
And hold the pulse long
enough for a slow ADC to
measure the peak voltage. It
can then be reset to detect the
next pulse after the
measurement has been made.
** just a suggestion, maybe
other things exist…
This one should be fast,
though…
Other parts
• A threshold comparator
• A gain circuit to provide additional signal
amplification if necessary
• A PIC microcontroller to digitize the voltage,
control the peak detector circuit, and
communicate the results to computer via USB.
(Maybe build on last year’s “Flux meter”
Project?)
How to proceed?
• Use a signal generator to produce simulated
X-ray pulses that would come out of a
detector…
– Easy to control pulse width, rate, and pulse height
• Easier than using a detector..
• Toward last weeks of project, I will send you a
detector to try instead of the signal generator