Electronic Targets. Matt Waterman Donato Salazar Dr. Abul Azad (Advisor) Tech 478 Senior Design II

Transcription

1 Electronic Targets Matt Waterman Donato Salazar Dr. Abul Azad (Advisor) Tech 478 Senior Design II Scroll down to page 48 to view the presentation without notes

2 The Project An electronic target system that can be shot with a variety of projectiles, reporting the location of each impact to a computer next to the shooter

3 Introduction to Target Shooting Target shooting is a popular sport in the US Paper targets, stapled to cardboard or plastic signboard, are typically used Impacts observed through: Direct observation (close range or shot spotter downrange) Optics (scope, binoculars, etc) Target reaction (steel plates, clays)

4 Project Overview Projectiles impact the target and a wave propagates outward from the impact point toward sensors mounted on the periphery of the target The wave arrives at each sensor at a different time depending on the impact location

5 Project Overview Continued Electronics monitor the sensors and precisely measure the arrival times (TOA) The arrival times are transmitted to a PC where the differences between the arrival times (TDOA) are used to calculate the impact location

6 Objectives Technical Design and build an electronic target system Target itself Electronics on target to detect impacts Software on laptop displays impacts Accurate to within 5 mm Portable

7 Objectives Additional Components are cheap and easy to find Design can be replicated by non-experts Publish the research, designs, schematics, software, etc online We plan to publish everything on our web site under the GNU (guh-new) general public license. The GNU GPL license is the most widely used free software license.

8 Research wikipedia.org Triangulation Multilateration Wave propagation Sonic boom Buffer amplifier Piezoelectric sensor and many more Wikipedia covers all of the topics used in this project. This is a list of some of the key articles which are very detailed and were very helpful. Nearly all of the information needed for this project can be found on wikipedia, usually written in a fairly easy-to-understand manner.

9 Research Other sources General internet (via google) Academic websites Dr. Bill Rison, New Mexico Tech EE 389 Forums, blogs, tutorials Journals and academic publications (via NIU library and google scholar) Patents Datasheets and manufacturer documents Textbooks and class notes Dr. Rison's Mathematical Engineering course materials proved instrumental to us understanding some of the math behind multilateration. Forums, blogs, and online tutorials proved very helpful when developing for the Atmel AVR microcontroller we used. There are dozens, maybe hundreds of patents covering systems like this. Some provided some interesting hints, though most were not very useful. Atmel produces great documentation for the AVR and its features. We drew extensively from what we learned in class.

10 Research Live-fire testing Measure and record supersonic shockwaves Test: Sensors Target designs Material durability Acoustic isolation methods Timing circuits Live-fire testing was critical for developing the project, but was a big hindrance. We could not get to the range as often as we would have liked, mostly due to distance and timing. It was hard to deal with problems that would come up at the range, like malfunctioning circuits or targets not behaving as expected.

11 Theory Wave Propagation May use supersonic ( soft target) or impact shockwaves ( hard target) Both methods work the same way, but require slightly different target designs, sensors, and amplification/buffering Target must provide uniform wave propagation Soft target: air Hard target: steel, plastic Targets may use supersonic shockwaves in what we call soft, or hollow, targets, or impact shockwaves on hard targets. Wood is not usually a suitable material for a hard target because waves do not propagate at the same rate in every direction.

12 Theory Wave Propagation Supersonic Shockwave Shockwave generated continuously at the front of the projectile Propagates outward at the speed of sound Arrives as an NWave Called an N-Wave because of the sharp rise and then decrease in pressure over the first period. The initial period of the wave is affected by the speed and shape of the projectile. A projectile traveling twice as fast as a projectile of the same size and shape will produce an N-Wave period half the length. This isn't useful for impact location detection, but may be useful to a shooter.

13 Theory Wave Propagation Impact Shockwave Impact shockwave generated by the projectile hitting the target (it may or may not go through the target) Shockwave generated is very similar to a supersonic shockwave Target surface will propagate the energy much faster than air Harder target surfaces will transmit farther, make larger targets Targets may be designed for the projectile to hit and bounce off, like steel. Other targets may be designed for the projectile to travel through the target, like plastic signboard. Steel can be used to make much larger targets than something like plastic signboard, but do you want a target that weighs hundreds of pounds? 1/2 steel plate weighs about 20 pounds per square foot. A 6 by 6 foot target a common size would weigh over 700 pounds.

14 Theory Multilateration D A= ( x x A ) +( y y A ) P Triangulation is easy Unknown point can be calculated using distance, angles, or both, to two known points The red dot represents the impact location on the target. The green lines extend from the impact location to the sensors. D sub A gives the distance from the impact to a point on the target. P is the propagation speed. Unfortunately, we do not know the distance from the impact to each sensor.

15 Theory Multilateration d AB =t A t B = [ ( x x A) +( y y A ) ( x x B ) +( y y B ) ] P Multilateration is more difficult because only TDOA are known Instead, since we only know the arrival times, we only know the difference between each distance. The blue lines are all the same length and are not known. In this situation, all we know is that the wave arrived at the bottom-right corner first, then arrived at the bottom-left a short time after, and so on. D sub AB is the difference in distance between the arrival times at points A and B.

16 Theory Multilateration TDOA between topleft and bottom-left Take the arrival time at the bottom-left corner and subtract it from the arrival time at the top-left corner, and you get...

17 Theory Multilateration Bottom radius is arbitrary (within a range) Top is TDOA plus same arbitrary distance...the orange line. Take an arbitrary length, out of a possible range, and use that as a radius from the bottom-left point. The arbitrary length, purple, is basically a guess at the length of the blue lines. Add the same length to the TDOA length and use them to form the hypotenuses of two triangles. If you do this over and over again while changing the arbitrary length, you will get something like...

18 Theory Multilateration Calculate repeatedly and you get a curve that intersects the impact point...this curve, which goes right through the impact point. With triangulation, all you need is two reference points to find a third unknown point. With multilateration, two reference points will give you an indication of where the third point is, but there are an infinite number of possibilities. But we have four points, so let's repeat this process.

19 Theory Multilateration Curves generated for each pair of sensors intersect at impact location Here we have done it for 4 of the pairs the edges of the target. You could also do it between diagonal pairs, but this is not shown. Notice that all of these curves intersect at the impact location. But how do you define these curves mathematically?

20 Theory Multilateration Hyperbolas Each TDOA produces a hyperbola 1= ( x x 0 )2 a 2 ( y y 0 )2 b 2 It turns out that these curves are actually hyperbolas. Here we've zoomed out on the same hyperbolas from before. The blue and orange hyperbolas are generated from the vertical pairs of sensors, while the green and mustard ones are from the horizontal pairs. They have many intersections, but since we know the order in which the signals arrived, some parts of the hyperbolas can be ignored. Also, the actual target face is limited in size. This is the equation for the general form of the hyperbola. In order to use it, we need to figure out a and b and adjust the offsets x naught and y naught.

21 Theory Multilateration Hyperbolas x CD 2 ( x ) ( y± y AD )2 2 1= PD BC x CD PD BC ( ) ( ) ( ) y AD 2 (± y ) ( x x AB )2 2 1= PD AB PD AB y AD ( ) ( ) ( ) Once you've adjusted these things, you get the two forms you see here. The top equation is for hyperbolas made using horizontal pairs of points and the bottom equation is for vertical pairs.

22 Theory Multilateration - So how do we use TDOA? Every two hyperbolas generate one possible impact location Due to TOA and propagation speed error, the intersections are unlikely to coincide Intersections averaged to produce the impact location Standard deviation indicates the certainty Propagation speed can be adjusted to minimize the deviation

23 Theory Multilateration How do we calculate intersections? Two equations with two unknowns Use triangulation equations and iterate through extra values added to three radii until a valid point is found Iterate through x or y values in the hyperbolas until the intersection is found Substitute hyperbolic equations to obtain quartic equation and apply the quartic formula We will explain how we did it later. In case you're not familiar with the quartic formula, we'll give you a glimpse. It looks something like...

24 Theory Multilateration Quartic what?...this. Actually, that's just part of it. Here's the whole thing...

25 Theory Multilateration Quartic Formula? If you can't read it, don't worry about it. We didn't. Actually, the quartic formula is very repetetive, so using it to solve quartic equations in software isn't hard at all. The hard part is putting our hyperbola equations, with all their possible variations, together to get the quartic equations in the first place.

26 Implementation Target Design - Hard Target Shockwave from impact propagates directly Piezoelectric discs mounted in the corners Plastic signboard, foam board, cardboard Plastic/acrylic suitable for Airsoft (plastic BBs) Steel Shockwave from impact propagates directly to the piezoelectric discs mounted in the corners If the design is meant to be consumable, it can be made of plastic signboard, foamboard, cardboard, or similar materials If it's intended to resist impacts, acrylic will work for something like plastic Bbs Steel can work for bullets, depending on what you're shooting at it, from how far, and the hardness of the steel. And how much you're willing to spend or carry.

27 Implementation Target Design - Soft (Hollow) Target Supersonic shockwave from bullet propagates through air Microphones in the corners, isolated from target frame Wood frame with rubber face and rear Design must provide noise isolation

28 Implementation Target Design - Soft Target Microphone Isolation Waves propagate more quickly in the frame Microphone must be isolated from frame Isolated from external noise Isolated from external noise, like from wind, previous shots, or from shots on other targets

29 Implementation Target Design - Hard Target vs Soft Target Hard Target Soft Target Sensors mounted directly to target Sensors carefully isolated Very heavy if made of steel Relatively light, even if large Propagates quickly (less accuracy) Propagates slowly (greater accuracy) Buffers usually required Amplification usually required

30 Implementation Target Design Target Materials Usually consumable (i.e. the projectiles create holes that eat away at the target) Some hard targets may be designed to not be consumable (e.g. steel) Soft targets that must provide noise isolation should use a target face that minimizes the size of the holes We tested numerous materials for hole size At least some part of the target is usually going to be consumable and will have to be replaced. Although some may be built to resist impacts For soft targets that are supposed to suppress external noise, you want to use a material that can expand around the bullets as they go through, leaving smaller holes We tested a number of materials, ranging greatly in price, trying to find something that works

31 Implementation Target Design Target Materials Hole Size These are four of the materials we tested, and we'll pass around some samples. The top-left sample is rubber roofing liner and is the cheapest material here. The holes are about half the diameter of the.22 caliber bullets we shot through them. Each target was shot 30 times. The bottom-right sample is silicon and is fairly pricey, but you can see the holes close up to almost nothing.

32 Implementation Target Design Target Materials Foam Board Foam Board is a great choice for a hard target design Polystyrene sandwiched between paper Propagation isn't perfect We have used Elmer's foam board and found it works very well. It's essentially cardboard but with styrofoam in between the panels. Since it's paper, wave propagation isn't perfect so accuracy will suffer. If you're building a target for a competition, you would probably use something else. Obviously, it is destructable. The holes in this aren't much smaller than the bullets making them, so you can't hit the same spot many times in a row. But it's very cheap, so you don't have to feel bad about replacing it. 8 dollars at Walmart gets you two 24x36 panels.

33 Implementation TOA Detection How do you detect wave arrival? Threshold is the simplest: Wave reached a certain value, triggers an arrival Implemented in: Software with ADCs Hardware with comparators Now we're going to switch gears into the electronics side. Time of arrival detection is the heart of the system, and we use some interesting techniques to time the shockwave arrivals. The most obvious, but not necessarily best, way to figure out when a wave has arrived, is to use threshold detection. Basically, when the wave reaches a certain level normally associated with its arrival, you trigger the timing system This can be done with a software routine if you're sampling the sensors with an ADC, but usually you'll want to just use comparators.

34 Implementation TOA Detection Why is threshold detection bad? If waves have different intensities, they will trigger at different times Propagation follows inverse square law, so widely-varying intensities a given But why is threshold detection not so good? As the shockwave propagates outward, the intensity drops off fairly quickly, following the inverse square wave. Depending on the impact location and several aspects of the hardware design, the waves may arrive at very different intensities and will trigger at different times. In this illustration, the thickness of the red bars indicate the time between a zero-crossing and a trigger level being eached. The black lines are the trigger levels. The difference in the thickness represents error.

35 Implementation TOA Detection Threshold with Zero-Detection Zero-detection compares the signal to 0 v Produces binary 1 when positive, 0 when negative Combine with threshold-detection for accurate timing It turns out we found a pretty elegant solution. Zero-detection can be done in hardware with comparators to generate a high signal when the wave is positive, and a low signal when its negative. When the signal goes from high to low or vice-versa, it has crossed zero. Zero-crossing on its own isn't useful, though, because it's constantly bouncing back and forth because of noise. But you can use threshold detection to figure out that a wave has arrived and then start looking at the zero detector.

36 Implementation TOA Detection Target Simulator Hmmm

37 Implementation Timer Circuit This is what we've done on our circuit. We use two LM339 quad comparators to provide the eight comparators needed to run threshold-detection and zero-crossing detection on four channels. LM339s are very cheap and easy to find. You can get them at Radio Shack. Performance is more than adequate for most needs. In our system, we send the threshold trigger outputs directly to our Attiny But we connect all of the zero-crossing detectors together with an OR gate and wire them up to a pin on the attiny capable of doing hardware timing. The zero-detectors are sequentially enabled by the attiny when zero-crossings are pending.

38 Implementation Timer Circuit

39 Implementation Timer Circuit - Specifications Olimex AVR board Atmel ATtiny MHz clock max 4 channels 2N5459 J-FET LM339 comparators RS232 output AC/DC powered

40 Implementation Timer Circuit Embedded Software AVRs are very fast (1 instruction per clock cycle) Software written in C, compiles efficiently Channel data (pins, TOA times) stored in a circular linked-list Channels scanned for threshold triggering and removed from the list when triggered Zero-detectors connected to ICP and enabled as needed AVRs are RISC processors with instructions specifically designed for C. C compiles very efficiently with AVRs, though AVRs don't have hardware floating point capability so floating point numbers are usually avoided. Our routine is built around a circular linked-list that holds data for each channel. A linked-list is a concept where you have data nodes and each node has a pointer connecting it to the next node. When we're looking for an impact, the routine will loop through the list, removing channels from the list as they are triggered. Zero detectors are enabled as needed and are connected to the input capture pin. The ICP can be set up to start and stop the timer in hardware or through interrupt routines.

41 Implementation Client Software Currently very basic Written in C Cross-platform compatible libraries used Interfaces with the timer system through serial connection Calculates several hyperbolic intersections, averages them, and computes standard deviation

42 Implementation Computing Hyperbolic Intersections Curves generated for each pair of sensors intersect at impact location

43 Results It works Current working model: Foam board target (.45 x.45 m) Piezo sensors Using only threshold triggering (zero detection not yet programmed) Accurate to 2 cm We have not been able to build a successful soft target

44 Results Demonstration

45 Cost Our Specific Implementation Part Price Olimex AVR Development Board $17 ATtiny2313 $2 2x LM339 (quad comparator) $ (quad OR gate) MCP4131 (digital potentiometer) $2 2x Foam Board $8 Various resistors, capacitors $5 Total: $40

46 Future Lots of shooting Work on website: Continue to improve hardware and software Get others involved

47 Conclusion We have shown that: The design principles are sound It can be built on a tight budget But we have lots left to improve

48 Electronic Targets Matt Waterman Donato Salazar Dr. Abul Azad (Advisor) Tech 478 Senior Design II

49 The Project An electronic target system that can be shot with a variety of projectiles, reporting the location of each impact to a computer next to the shooter

50 Introduction to Target Shooting Target shooting is a popular sport in the US Paper targets, stapled to cardboard or plastic signboard, are typically used Impacts observed through: Direct observation (close range or shot spotter downrange) Optics (scope, binoculars, etc) Target reaction (steel plates, clays)

51 Project Overview Projectiles impact the target and a wave propagates outward from the impact point toward sensors mounted on the periphery of the target The wave arrives at each sensor at a different time depending on the impact location

52 Project Overview Continued Electronics monitor the sensors and precisely measure the arrival times (TOA) The arrival times are transmitted to a PC where the differences between the arrival times (TDOA) are used to calculate the impact location

53 Objectives Technical Design and build an electronic target system Target itself Electronics on target to detect impacts Software on laptop displays impacts Accurate to within 5 mm Portable

54 Objectives Additional Components are cheap and easy to find Design can be replicated by non-experts Publish the research, designs, schematics, software, etc online

55 Research wikipedia.org Triangulation Multilateration Wave propagation Sonic boom Buffer amplifier Piezoelectric sensor and many more

56 Research Other sources General internet (via google) Academic websites Dr. Bill Rison, New Mexico Tech EE 389 Forums, blogs, tutorials Journals and academic publications (via NIU library and google scholar) Patents Datasheets and manufacturer documents Textbooks and class notes

57 Research Live-fire testing Measure and record supersonic shockwaves Test: Sensors Target designs Material durability Acoustic isolation methods Timing circuits

58 Theory Wave Propagation May use supersonic ( soft target) or impact shockwaves ( hard target) Both methods work the same way, but require slightly different target designs, sensors, and amplification/buffering Target must provide uniform wave propagation Soft target: air Hard target: steel, plastic

59 Theory Wave Propagation Supersonic Shockwave Shockwave generated continuously at the front of the projectile Propagates outward at the speed of sound Arrives as an NWave

60 Theory Wave Propagation Impact Shockwave Impact shockwave generated by the projectile hitting the target (it may or may not go through the target) Shockwave generated is very similar to a supersonic shockwave Target surface will propagate the energy much faster than air Harder target surfaces will transmit farther, make larger targets

61 Theory Multilateration D A= ( x x ) +( y y ) A A P Triangulation is easy Unknown point can be calculated using distance, angles, or both, to two known points

62 Theory Multilateration d AB =t A t B = [ ( x x A) +( y y A ) ( x x B ) +( y y B ) ] P Multilateration is more difficult because only TDOA are known

63 Theory Multilateration TDOA between topleft and bottom-left

64 Theory Multilateration Bottom radius is arbitrary (within a range) Top is TDOA plus same arbitrary distance

65 Theory Multilateration Calculate repeatedly and you get a curve that intersects the impact point

66 Theory Multilateration Curves generated for each pair of sensors intersect at impact location

67 Theory Multilateration Hyperbolas Each TDOA produces a hyperbola 1= ( x x 0 )2 a 2 ( y y 0 )2 b2

68 Theory Multilateration Hyperbolas x CD 2 ( x ) ( y± y AD )2 2 1= PD BC x CD PD BC 2 ( ) ( ) ( ) y AD 2 (± y ) 2 ( x x ) 2 AB 1= + PD AB 2 PD AB 2 y AD 2 ( ) ( ) ( ) 2 2 2

69 Theory Multilateration - So how do we use TDOA? Every two hyperbolas generate one possible impact location Due to TOA and propagation speed error, the intersections are unlikely to coincide Intersections averaged to produce the impact location Standard deviation indicates the certainty Propagation speed can be adjusted to minimize the deviation

70 Theory Multilateration How do we calculate intersections? Two equations with two unknowns Use triangulation equations and iterate through extra values added to three radii until a valid point is found Iterate through x or y values in the hyperbolas until the intersection is found Substitute hyperbolic equations to obtain quartic equation and apply the quartic formula

71 Theory Multilateration Quartic what?

72 Theory Multilateration Quartic Formula?

73 Implementation Target Design - Hard Target Shockwave from impact propagates directly Piezoelectric discs mounted in the corners Plastic signboard, foam board, cardboard Plastic/acrylic suitable for Airsoft (plastic BBs) Steel

74 Implementation Target Design - Soft (Hollow) Target Supersonic shockwave from bullet propagates through air Microphones in the corners, isolated from target frame Wood frame with rubber face and rear Design must provide noise isolation

75 Implementation Target Design - Soft Target Microphone Isolation Waves propagate more quickly in the frame Microphone must be isolated from frame Isolated from external noise

76 Implementation Target Design - Hard Target vs Soft Target Hard Target Soft Target Sensors mounted directly to target Sensors carefully isolated Very heavy if made of steel Relatively light, even if large Propagates quickly (less accuracy) Propagates slowly (greater accuracy) Buffers usually required Amplification usually required

77 Implementation Target Design Target Materials Usually consumable (i.e. the projectiles create holes that eat away at the target) Some hard targets may be designed to not be consumable (e.g. steel) Soft targets that must provide noise isolation should use a target face that minimizes the size of the holes We tested numerous materials for hole size

78 Implementation Target Design Target Materials Hole Size

79 Implementation Target Design Target Materials Foam Board Foam Board is a great choice for a hard target design Polystyrene sandwiched between paper Propagation isn't perfect

80 Implementation TOA Detection How do you detect wave arrival? Threshold is the simplest: Wave reached a certain value, triggers an arrival Implemented in: Software with ADCs Hardware with comparators

81 Implementation TOA Detection Why is threshold detection bad? If waves have different intensities, they will trigger at different times Propagation follows inverse square law, so widely-varying intensities a given

82 Implementation TOA Detection Threshold with Zero-Detection Zero-detection compares the signal to 0 v Produces binary 1 when positive, 0 when negative Combine with threshold-detection for accurate timing

83 Implementation TOA Detection Target Simulator

84 Implementation Timer Circuit

85 Implementation Timer Circuit

86 Implementation Timer Circuit - Specifications Olimex AVR board Atmel ATtiny MHz clock max 4 channels 2N5459 J-FET LM339 comparators RS232 output AC/DC powered

87 Implementation Timer Circuit Embedded Software AVRs are very fast (1 instruction per clock cycle) Software written in C, compiles efficiently Channel data (pins, TOA times) stored in a circular linked-list Channels scanned for threshold triggering and removed from the list when triggered Zero-detectors connected to ICP and enabled as needed

88 Implementation Client Software Currently very basic Written in C Cross-platform compatible libraries used Interfaces with the timer system through serial connection Calculates several hyperbolic intersections, averages them, and computes standard deviation

89 Implementation Computing Hyperbolic Intersections Curves generated for each pair of sensors intersect at impact location

90 Results It works Current working model: Foam board target (.45 x.45 m) Piezo sensors Using only threshold triggering (zero detection not yet programmed) Accurate to 2 cm We have not been able to build a successful soft target

91 Results Demonstration

92 Cost Our Specific Implementation Part Price Olimex AVR Development Board $17 ATtiny2313 $2 2x LM339 (quad comparator) $ (quad OR gate) MCP4131 (digital potentiometer) $2 2x Foam Board $8 Various resistors, capacitors $5 Total: $40

93 Future Lots of shooting Work on website: Continue to improve hardware and software Get others involved

94 Conclusion We have shown that: The design principles are sound It can be built on a tight budget But we have lots left to improve