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Portable Battery Powered NIM LogicPulse Generator
A thesis submitted in partial fulfillment of the requirementfor the degree of Bachelor of Science in
Physics from the College of William and Mary in Virginia,
by
Benjamin E. Kincaid
Advisor: Prof. Michael A. Kordosky
Prof. Gina L. Hoatson
Williamsburg, VirginiaMay 2017
Contents
Acknowledgments iii
List of Figures v
Abstract v
1 Introduction 1
1.1 Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.3 Logic Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.4 Multivibrators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.4.1 Monostable Multivibrators . . . . . . . . . . . . . . . . . . . . 2
1.4.2 Astable Multivibrators . . . . . . . . . . . . . . . . . . . . . . 4
1.5 Operational Amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.6 Integrated Circuit Packages . . . . . . . . . . . . . . . . . . . . . . . 4
2 Design 6
2.1 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 Subcircuit: Timer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3 Subcircuit: One-shot . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.4 Subcircuit: Inverting Follower . . . . . . . . . . . . . . . . . . . . . . 16
i
3 Prototyping 18
3.1 Pocket Pulser Rev 1.1 . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.1.1 PCB Design Software . . . . . . . . . . . . . . . . . . . . . . . 18
3.1.2 Designing the PCB . . . . . . . . . . . . . . . . . . . . . . . . 18
3.1.3 Completed PCB and Components . . . . . . . . . . . . . . . . 21
3.2 Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.3 Pocket Pulser Rev 1.2 . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.4 Pocket Pulser Rev 1.3 . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4 Outlook 34
5 Conclusions 36
ii
Acknowledgments
I would like to thank my adviser Prof. Kordosky, without his sage advice, I
wouldn’t have known how to begin. I would also like to thank William Laney for
showing me Eagle, teaching me how to solder surface mount devices and for assisting
me with learning how to design and order custom PCBs. Without his help I would
be stuck to this day.
iii
List of Figures
1.1 One-shot truth table . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Examples of the two IC packages used in this project. . . . . . . . . . 5
2.1 Schematic of the timing circuit. . . . . . . . . . . . . . . . . . . . . . 8
2.2 Overview of the 555 timer on breadboard . . . . . . . . . . . . . . . . 9
2.3 the oscilloscope’s trace of the output from the timer circuit. . . . . . 10
2.4 The schematic of the one-shot. . . . . . . . . . . . . . . . . . . . . . . 12
2.5 Picture of the two one-shots used throughout the project . . . . . . . 13
2.6 Overview of the SN74AHCT123 in the original test circuit. . . . . . . 14
2.7 Output from the one-shot in the test circuit. . . . . . . . . . . . . . . 15
2.8 Schematic of the inverter follower . . . . . . . . . . . . . . . . . . . . 16
2.9 Picture of LT1360 in test circuit. . . . . . . . . . . . . . . . . . . . . 17
3.1 Schematic used to design the PCBs. . . . . . . . . . . . . . . . . . . . 19
3.2 Pocket Pulser rev. 1.1 design layout. . . . . . . . . . . . . . . . . . . 20
3.3 Incorrectly populated Rev 1.1 board. . . . . . . . . . . . . . . . . . . 22
3.4 Schematic used for LTSPICE simulation. . . . . . . . . . . . . . . . 24
3.5 LTSPICE output transient. . . . . . . . . . . . . . . . . . . . . . . . 25
3.6 Schematic without grounded non-inverting input. . . . . . . . . . . . 26
3.7 LTSPICE transient with ground disconnected. . . . . . . . . . . . . . 27
3.8 Rev 1.1 with grounding wire. . . . . . . . . . . . . . . . . . . . . . . 28
iv
3.9 Output of Rev 1.1 with grounding wire. . . . . . . . . . . . . . . . . . 29
3.10 Board layout for Pocket Pulser Rev 1.2. . . . . . . . . . . . . . . . . . 31
3.11 Board layout for Pocket Pulser Rev 1.3. . . . . . . . . . . . . . . . . . 33
v
Abstract
I designed, built and tested a hand held, portable device designed to output
NIM logic, a system of logic based on negative current. The purpose of the pulse
generator is to determine whether NIM logic compatible devices are functioning nor-
mally. Specifically the tester is designed to verify the functionality of NIM crates.
The device has not been completed, but some of the main requirements determined
at the start of the project have been met; it is able to run with a 9 volt battery as its
power source, the frequency of the pulses and the pulse widths meet my predetermined
specifications.
Chapter 1
Introduction
1.1 Objective
The goal of my project is to create a portable pulse generator that tests de-
tector capable of accepting Nuclear Instrumentation Module (NIM) logic. The exact
detectors that it will be tested on are NIM crates which are NIM logic compatible,
meaning they accept specific negative current signals as triggers. The device must be
convenient and easy to use and since it will be used on NIM logic modules, it must
output NIM logic compatible pulses. The tester will output NIM pulses at a fixed
frequency, that can be used to verify whether the counts detected by the NIM crates
match those that were output by the pulser.
1.2 Motivation
NIM is an old but still widely used standard at national laboratories and in
some industries. In particular the high energy experimental research at William
and Mary uses NIM crates in their experimental apparatuses. Having a tester to
verify that the individual inputs of the crates are operating correctly would allow for
greater confidence in the the observed results from the detectors and the ability to
troubleshoot faulty NIM crates.
1
1.3 Logic Standards
There are a few different logic standards that are in widespread use. Two of the
most common that were used through out this project are transistor-transistor logic
(abbreviated to TTL) and nuclear instrumentation module (NIM)[2]. While TTL is
more commonly used overall, NIM is also used in many national laboratories.
The TTL standard is based on a voltage scale from 0 to 5V . There are ranges
in which signals are interpreted as true/High or false/Low. Generally Low is 0 to
0.8V and High is 2V to 5V . Signals that fall between the two ranges are considered
undefined. Many modern integrated circuits (ICs) are TTL compatible. Most of their
outputs and inputs are designed to handle TTL logic[6, see page 486].
By contrast, NIM logic uses a negative signal with true/High defined as a current in
the range −14mA to −16mA, with Low defined as 0mA. Because many coaxial cables
have a characteristic impedance of 50Ω, this corresponds to a HIGH of −0.8V [2].
1.4 Multivibrators
Multivibrators are a family of logic gates used extensively in pulse generation. Multi-
vibrators come in different varieties, but all multivibrators move between logic levels
i.e. High and Low. They can be programmed to have specific timing characteris-
tics and pulse widths. In the designs for this project monostable multivibrators and
astable multivibrators are used for their versatility.
1.4.1 Monostable Multivibrators
Monostable multivibrators are commonly referred to as “one-shots” and have a single
stable state for the output. When a one-shot is triggered, the output jumps High,
or to the positive rail, for a time that is determined by a network of resistors and
capacitors. One-shots can be used to created pulses that are tailored to various spec-
2
ifications depending on the pulse width and duty cycle of the output. One-shots have
three triggering inputs that are named differently depending on the manufacturer’s
preference, but all of these conventions follow a similar truth table as seen in Fig. 1.1.
Figure 1.1: One-shot truth table
The truth table pictured comes from the data sheet for the SN74AHCT123-EP monos-table multivibrator[3].“L” corresponds to a voltage Low, “H” corresponds to a voltageHigh. The upward and downward facing arrows represent rising and falling edges.The“X”s represent no input. On the list of outputs the ”Q” is the standard outputas discussed above, the output voltage is generally at ground, and the jumps to thepositive rail briefly. “Q” is the inverse of Q, the output is held High and then pulsesdown to ground simultaneous to when Q pulses High.
3
1.4.2 Astable Multivibrators
Astable multivibrators are generally referred to as “clocks”, “timers”, or “oscillators”.
Clocks produce pulses periodically with a frequency and duty cycle determined by a
network of resistors and capacitors. Clocks do not have a single stable state for their
outputs, rather they move between High and Low regularly. Clocks can be used to
set the frequency of triggered events in circuits.
1.5 Operational Amplifiers
Operational Amplifiers (op amps) are among the most commonly used IC types due to
its versatility. Op amps can be used in a number of configurations, but the one relevant
to the designs implemented in this project is the inverting follower/attenuator. The
inverting follower and attenuator, both “invert” their outputs compared to the input
signal. The attenuator differs from the follower because it also diminishes the signal
whereas the follower simply inverts the input signal[6, see pages 178-180].
Op amps can used as inverting attenuators become unstable if their gain drops
below 1 because not all op amps are stable at “unity gain” or high frequencies[7, see
page 652]. However, almost every op amp is stable at a non-inverting gain of 2, which
corresponds to an inverting gain of 1. To avoid stability concerns, it is often safest to
attenuate the input prior to it entering the op amp, so the op amp can be used as a
simple inverting follower.
1.6 Integrated Circuit Packages
The two main package types for ICs are “throughhole”, and “surface mount”. Through-
hole packages are more expensive, but are easily mounted to breadboards, as they
are explicitly designed to be used on them. Surface mount packages, on the other
4
hand, are specifically made to be used with printed circuit boards (PCBs). Surface
mounted device (SMD) packages tend to be less expensive and generally give better
performance assuming the PCB is laid out optimally. However, it difficult to use
SMDs on breadboards, requiring special sockets or adapters to affix them. I used
both types during this project. An example of what each looks like can be seen in
Fig. 1.2.
Figure 1.2: Examples of the two IC packages used in this project.
The chip to the left is a throughhole 555 timer, the one in the middle is aSN74AHCT123D one-shot, which has an SMD package. Lastly, on the right is anSMD to throughhole adapter that is compatible with the one-shot. There are morespecifications to each package. For example, the one-shot’s package type is a smalloutline integrated circuit with 16 legs (SOIC16). However, this can be found on thedata sheets for any of the devices discussed.
5
Chapter 2
Design
During the initial design phase, I ordered and installed parts on a breadboard
to verify that they would work in the capacity that I intended. The following is a
discussion of the initial construction of the circuit on a breadboard and the later
movement of the parts onto PCBs.
2.1 Requirements
The primary requirement of the test circuit is that it must be able to reliably test
NIM crates. For this to be a success the output from the circuit must trigger NIM
logic compatible detectors and the counts the detector sees must be the same as the
tester was designed to output. However, this is not the only requirement that it must
meet. To be useful the tester must also be portable, so that it can be battery powered
and easily used in a variety of experimental setups. The tester must have an on and
off to preserve battery life. The output pulses should be relatively square and they
must be fast, on the scale of 50ns. The output port must be a LEMO connector so
that it is compatible with NIM crate inputs.
6
2.2 Subcircuit: Timer
To fire the tester’s output pulse at a desired frequency, I first made a clock based
timing circuit. The specific IC that I employed throughout the designing and proto-
typing process is the 555 timer. The 555 timer is widely used in many applications
due to its flexibility, it can be used as a clock or one-shot. For my design, it was
used in its astable configuration as displayed in the schematic view in Fig. 2.1. All of
the component values (in Fig. 2.1) were determined using the formula for setting the
frequency as outlined in its data sheet[9].
f ≈ 1.44
(RA + 2RB)C(2.1)
In Fig. 2.1, R1 and R2 correspond to RA and RB respectively, and C1 is the C used
in Eq. 2.1. C2 is a simple shunt capacitor used to decouple any extraneous noise that
might be carried by VCC . Using R1 = 100kΩ, R2 = 22kΩ, and C = 1nF ,the expected
frequency of the output is approximately 10kHz. I decided to use 10kHz mainly for
convenience’s sake. There are a number of other frequencies that are possible, but
10kHz is a fairly low duty cycle and it was easy to find suitable components.
While the expected frequency is 10kHz, throughout testing the actual frequencies
most commonly observed were closer to 9kHz. This was caused by tolerances in the
components being used. Specifically, capacitors are more expensive as they become
closer to the specified value. The capacitors I used were off by anywhere from 5−10%.
However, as discussed above, 10kHz is purely arbitrary.
The standard output of the clock is TTL and the other ICs used in the construction
accept TTL inputs.
7
Figure 2.1: Schematic of the timing circuit.
The pins are numbered based on their physical arrangement. When counting on thechip itself the first pin is marked with a circle or divot along the narrow edge closestto the first pin. The pins are counted counter-clockwise from the first one. CLKOUTis the clock’s output signal which is in TTL.
8
Figure 2.2: Overview of the 555 timer on breadboard
This is the original breadboard test circuit. The three purple wires are the positivesupply, the black wire is ground, green and orange are part of the RC network, andyellow is the output.
9
Figure 2.3: the oscilloscope’s trace of the output from the timer circuit.This picture shows lower frequencies being used to diagnose a jitter discovered in
the one-shot’s output.
10
2.3 Subcircuit: One-shot
The clock is used to trigger a monostable multivibrator (one-shot) whose main pur-
pose is to refine the pulse width of the output. I used several different one-shot ICs
during the development of the design.
Originally, the one-shot I used was an SN74LS221. In the very first iteration of
the design, the IC’s limitations were immediately obvious; specifically, this one-shot
had trouble producing very small pulse widths. Its outputs were more Gaussian in
shape than square. To mitigate this problem, I used a different one-shot for the next
iteration.
The second one-shot I used was a SN74AHCT123. This one-shot was a SMD and
required the use of a special adapter to place it on a breadboard. With the one-shot
being the only change to the test circuit, the output was much closer to the square
wave I needed. While the output should ideally be “square”, my concern is mainly
focused on it being square enough to trigger NIM logic. As long as the outputs
reliably triggered NIM logic, then the tester will have met the requirements.
The output from the one-shot, prior to entering the next subcircuit, passes through
a simple voltage divider. I used the voltage divider to attenuate the output voltage
to around 0.8V . This was done to prevent any risk of instability on the part of the
op amp that was used to invert the signal.
11
Figure 2.4: The schematic of the one-shot.
This schematic shows the first gate of the SN74AHCT123’s two independent one-shotcircuits. My design only utilizes the first subcircuit. The falling edge of the Clock’ssignal is the trigger for the output pulse in this configuration. The other two triggerinputs are tied High. The values used for R1, and C1 are based on the equationgoverning pulse width from the data sheet[4]. C2 is a decoupling capacitor or shunt,used in the same capacity as the one observed on the clock’s schematic. The outputis attenuated by a simple voltage divider to the right of the IC. The equation relatingthe one-shot’s output and the attenuated output is derived from the Thevenin circuitprinciple [6, page 11].
VTh = VinR2
R1 +R2
(2.2)
12
Figure 2.5: Picture of the two one-shots used throughout the project
The IC on the left is the SN74LS221, and the one-shot to the right is theSN74AHCT123.
13
Figure 2.6: Overview of the SN74AHCT123 in the original test circuit.
The SN74AHCT123 is mounted to the adapter because the part is a SMD and wouldotherwise not work with a breadboard. All of the red wires are tied to VCC , the yellowwire is the triggering output coming from the clock, and black is ground. The orangeand white striped wire is part of the capacitor and resistor network used to set thepulse characteristics, and the white wire is the output from the one-shot.
14
Figure 2.7: Output from the one-shot in the test circuit.
The width of the pulse is fairly close to 80ns as determined using the full width athalf max. The peak of the signal is almost 5V.
15
2.4 Subcircuit: Inverting Follower
NIM logic is a negative current based logic. To convert the positive TTL to negative
NIM, I used a fast op amp as an inverting follower. An op amp is called “fast” based
on its characteristic slew rate, the rate at which its output can change depending on
the input signal. Because the pulses were only a few tens of nanoseconds in duration,
most op amps could not follow the input pulses. The LT1360 does have a fast slew
rate at800V
µs[1]. Because of its slew rate, an LT1360 op amp was first tested as a
proof of concept. By looking at the slew rate as a slope, it can change at0.8V
nsby
converting the microseconds to nanoseconds. However, this op amp proved too slow
to follow the input reliably.
I decided to use a faster op amp. The LT1818 has a slew rate of2500V
µs[8].
Unfortunately, because it was more specialized, it was only available in SMD packages.
This made testing with a breadboard difficult. Therefore, I moved the testing platform
to a PCB instead.
Figure 2.8: Schematic of the inverter follower
This is a schematic view of an LT1818 in an inverting follower configuration. Thecapacitors are for decoupling. The resistors need to be the same value for the |G| tobe 1.
16
Figure 2.9: Picture of LT1360 in test circuit.
The green wire is the signal coming from the one-shot to be inverted. The leftmostblue wire is the negative supply(-5V), black is ground, and red is the positive sup-ply(5V). The other two blue wires are the feedback loop with feedback capacitorsthat were used for testing stability. The orange and white striped wire is the outputfrom the op amp.
17
Chapter 3
Prototyping
3.1 Pocket Pulser Rev 1.1
The components for this prototype were only available in SMD packages, this necessi-
tated a change to PCBs from breadboards. I needed to learn how to use PCB design
software and how to order custom designed PCBs from a fabrication house.
3.1.1 PCB Design Software
For this project I used Eagle, a free lightweight, and relatively simple to use CAD
owned by Autodesk. Eagle has different phases for designing a board. They are
making the schematic, then laying the parts and routing the traces around the board.
There are many tutorials around the web that give in depth instructions for using
Eagle. The one I used was from Sparkfun.
3.1.2 Designing the PCB
Once the schematic was designed in Eagle, I laid out the board and routed the traces
between the components. I then sent the designs to OSHPark, a fabrication house,
to be constructed. The cost for making a small board is relatively low. In all the
versions made for this project, the cost of the boards was far less than the components
that went on them. For my designs it was typically 5− 7$ for sets of three.
18
Figure 3.1: Schematic used to design the PCBs.
The full schematic used in the PCB design process. The pair of small two wire ports at either end of the schematic areheader pins for the positive and negative supply, and the output pin and the ground pin.
19
Figure 3.2: Pocket Pulser rev. 1.1 design layout.
The red traces are on the top copper layer. The blue are on the bottom layer. Thegreen circles are vias that connect the top and bottom layers. This initial design inretrospect had too many right angles and too few shunts for decoupling supplies toisolate each IC from errant noise from the power supply.
20
3.1.3 Completed PCB and Components
After the PCBs arrived, I attached all the components to their locations around the
board. Doing this required learning how to solder surface mount components using
solder paste and a Reflow oven, owned by the Makerspace in Small Hall.
Once everything was soldered in place, I tested the circuit for functionality. Each
order from OSHPark included 3 identical PCBs. On my first attempt, the output
pulses were nonexistent. After tracing the signal through the components on the PCB,
I isolated the problem to the section for the inverting follower, which is the final stage
before the signal is output. I discovered I had attached the op amp backwards. It
was rotated 180 degrees when I soldered it down, so the signals were going to the
wrong legs of the IC Fig .3.3.
21
Figure 3.3: Incorrectly populated Rev 1.1 board.
This is the first completely populated board. The op amp in the left corner is reversedfrom the orientation it should be.
22
On the second attempt, I laid the op amp properly and I verified that the rest of
the components were correctly placed around the PCB. After everything was attached
properly, this board’s output was tested. However, the output for this board was also
unexpected. It was outputting approximately 3V DC. With the second board also
not functioning as intended I moved the op amp subcircuit to simulation software for
more testing.
3.2 Simulation
To simulate the LT1818 as accurately as possible, I used LTSPICE to analyze the
issues occurring with the first revision PCB. I chose LTSPICE because it is free, is
made by the manufacturer of the IC being used, and has inclusive SPICE libraries
for all of the company’s manufactured parts. Utilizing LTSPICE, it became apparent
that the inverting follower should have inverted and followed the signal from the one-
shot. Because it was not even operating as most op amps would if wired correctly,
I determined that it was likely wired incorrectly and moved on to investigating the
design for the PCB. I found that the non-inverting input had not been grounded
correctly.
Inputting similar conditions into LTSPICE yielded the same results observed in
the PCB. The output floated to almost 3V and looked like a constant DC voltage.
23
Figure 3.4: Schematic used for LTSPICE simulation.
This schematic is the view of the circuit that was simulated in LTSPICE. It depictsa correctly connected inverting follower. The SPICE directions for the simulator touse are at the bottom of the schematic.
24
Figure 3.5: LTSPICE output transient.
This is the simulation of the transient of the LT1818 when following an idealized square pulse. The gray is the squarepulse with a finite rise time. The turquoise is the inverted output from the op amp. The purple shows the virtual groundat the inverting input of the op amp.
25
Figure 3.6: Schematic without grounded non-inverting input.
The schematic is identical to Fig. 3.4 with the exception that the ground is discon-nected from the non-inverting input.
26
Figure 3.7: LTSPICE transient with ground disconnected.
In this figure, the output hovers around 3.5V instead of pulsing periodically.
27
Once the core issue was discovered,I soldered a wire between ground and the leg
into the non-inverting input to see if the signals started to behave more as expected.
This was done as a proof of concept to insure that solving the grounding issue would
yield the simulated results. After soldering the grounding wire, the board output
signals were close to what the simulation predicted, but the edges of the square waves
were rounded. This was likely due to the first PCB design having, too many right
angled traces and the shunts not being placed at each individual power pin for all the
ICs being used.
Figure 3.8: Rev 1.1 with grounding wire.
This is the second board with the grounding wire soldered to the non-inverting inputof the op amp.
28
Figure 3.9: Output of Rev 1.1 with grounding wire.
This is the output of the rev 1.1 board after having the grounding wire attached.The signal is negative as it needs to be for NIM logic, but the shape is not as squareas would be ideal and this is likely due to the many right angles used in the traces.However, there is no ringing in the signal.
29
3.3 Pocket Pulser Rev 1.2
Having uncovered the cause of the problems with the first iteration of the PCB design,
I did a second revision to correct them. I designed the second PCB to have short
traces for signal clarity.There were no right angles in the traces used for the outputs,
and I removed a feedback capacitor that when simulated had rounded the edges of
the square pulses when the capacitor was too large.
After initial testing, I discovered that the circuit output 0V DC. Returning to
the board design I discovered that the output of the one-shot is nonzero, but after
being attenuated the signal was grounded without ever passing through the op amp
subcircuit. With this issue discovered, I designed a new PCB layout to correct this
oversight and to move the project towards portability.
30
Figure 3.10: Board layout for Pocket Pulser Rev 1.2.
This is the design for the Pocket Pulser rev 1.2. It has no right angles in the signaltraces and minimal vias. It also has a shunt at every supply pin on each of the ICsto further try to reduce the effects of errant noise.
31
3.4 Pocket Pulser Rev 1.3
When I was designing the layout for Rev 1.3, I started experimenting with the Rev
1.1 board. I used a voltage divider and a nine volt battery to split the positive 9V
into 4.5V and −4.5. I did this to power the positive and negative rails of the pulse
generator to take it a step closer to being fully portable. For the voltage divider I
used 1MΩ resistors to isolate each terminal from ground to insure there was only a
small current draw. I then added these resistors into the board layout for Rev 1.3
so that it will be battery powered. in addition to this change, I shrank the footprint
of the PCB from Rev 1.2. I did this because OSHpark charges based on the area of
the PCB to be printed. I rerouted the traces from Rev 1.2 to have the fewest turns
possible, and placed all filtering capacitors as close to the pins they were for as I could.
I also grounded the second subcircuit in the one-shot, because if it is left floating it
can cause issues with performance. The most easily observed issue is that while the
one-shot will pulse at the same frequency as the clock, they are not synchronized.
When observed on an oscilloscope the two voltage signals pass one another which
should not happen if the clock is triggering the one-shot.
32
Figure 3.11: Board layout for Pocket Pulser Rev 1.3.
This is the design for the Pocket Pulser rev 1.3. It has no right angles in the signaltraces and minimized the distance between shunts and the pins they filter to preserveoutput clarity.
33
Chapter 4
Outlook
Most of the work designing the final device has been completed. Assuming revision 1.3
works as expected, the final issues that need to be considered are maximizing battery
life, attaching a LEMO connector to the output, and putting the pulse generator in
a housing.
A minor concern for power consumption issues when making the tester battery
powered, was that the standard 555 timer can draw relatively large supply currents
when the timer is active which could lead to sagging in the output, and having
poor performance. Other than the timer, most of the other components have supply
currents that are on the scale of µA which most batteries can easily supply. There
are newer versions of the same clock, 7555 timers, that have much smaller supply
currents 60µA[5]. For final development the timer could be switched, maximizing
the battery life of the pulse generator.
As far as constructing a case for the tester, it simply needs to be functional, and
most housings made of non-conductive materials would work because the PCB foot
print is around one square inch in total area. For prototyping purposes printing and
test fitting a design from one of the 3D printers in the Makerspace could be the next
step towards developing a case for the electronics. If I did use a 3D printed case, I
would make it out of the much less toxic, and easier to use PLA so that I would have
34
less fear of warping and could print the case at a lower temperature overall.
Ideally the output port would be a female LEMO connector for maximum ease
while using the device. This way a LEMO cable could be connected between the
tester’s port and the NIM crate being tested. This would leave the length of the
cable up to the discretion of the person utilizing the tester and could be altered to fit
the specific lab setup being tested. However, LEMO connectors are more expensive
than the rest of the parts for the tester combined. It is possible to use a male instead
of female connector, but it would be less convenient. Another solution could be to use
a BNC connector and then use and an adapter to female LEMO for testing purposes.
However, it would be preferable to have the LEMO over the BNC so that anyone using
the pulse generator would not need to have an adapter when testing NIM crates.
35
Chapter 5
Conclusions
The current tester is not able to output NIM logic reliably; however, it is nearly NIM
compatible and could be made so by tweaking the voltage divider’s component values.
At this time revision 1.3 has not been tested, and it is the newest attempt to output
recognizable NIM logic. Despite not having a fully finished and working tester, thus
far it can be concluded that the project’s initial design principles were reasonable,
that it is possible to build this device. With continued design and testing a finished
device is capable of being ready for extensive testing with only a few more iterations
of PCBs.
36
Bibliography
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[3] Dual Retriggerable Monostable Multivibrator. SN54AHC123A, SN74AHC123A.Texas Instruments. Oct. 2007.
[4] Dual retriggerable monostable multivibrator with reset. 74AHC123A, 74AHCT123A.Rev. 4. Nexperia. Nov. 2011.
[5] General Purpose Timers. ICM7555, ICM7556. Intersil. May 2016.
[6] Paul Horowitz and Winfield Hill. The Art of Electronics. Cambridge UniversityPress, 1989.
[7] Paul Scherz and Simon Monk. Practical Electronics For Inventors. McGraw-HillEducation, 2016.
[8] Single/Dual Operational Amplifiers. LT1818 and LT1819. Rev. B. Linear Tech-nology. May 2010.
[9] xx555 Precision Timers. NA555, NE555, SA555, SE555. Texas Instruments. Sept.2014.
37
