to clarify I am a complete newbie to this sort of thing, but I am a very mechanically inclined machinist and have a lot of 12v electrical experience, so im not completely incompetent. I would like to do a project and i’m told that it should not be that difficult.
Project Overview: Build a device that will detect the impact of a projectile on a piece of steel and trip a relay that will in turn flash an LED array.
Complications: The projectile will be a 100-230 gr projectile traveling 1000-3000 FPS, so a lot of force and in varying amounts of force. Upon impact the projectile will disintegrate and splash the area surrounding the steel plate. Also there is the possibility that the projectile will miss the steel plate and could be a hazard to the device, this makes the environment the device is in quiet harsh.
What i’m Thinking: What I would like to have is a multi component system consisting of wireless sensors that could be placed on steel plates, sensors would be powered by batteries? and would have to have a 8-10 hr run time. Each sensor would wirelessly communicate with a receivers that would have the led array attached. The range of these sensors could be quiet short as the led array only needs to be far enough away to protect it, 300’ max. This alone would accomplish the goal, but to add icing to the cake it would be great if i could have a wireless controller that would cause the led to flash to help locate the steel plate. but the range of the remote would have to be a mile plus line of sight. also ideally the remote would let me choose what reciever i want to make flash but if it made them all flash that would be ok as well. if push came to shove i could use a wired connection from the sensor to the relay but i would have to protect the connection. The led’s i have in mind are 12v and already have selectable patterns so there will already be 12v power and the relay will just have to be held open for a certain amount of time, 5-10 seconds.
What im looking for is recomendations on components and how to make it work. there is already a commercially available version of this on the market that will do everything i have specified for approximately $500. so anything over this price is a no go.
The mile+ is the only hard part of your project. Seriously you guys are shooting on a 1 mile range !?!
If the target plates are on swingers then the non-RF link electronics are trivial (and not so bad if not). I did that 20 years ago for my bowling pin shooting. Do you need/want the LEDs to be downrange or would some indication at the shooting line be acceptable (or both). More details will help us help you.
yes we do shoot up to a mile :). the targets for for these plates will be mounted on t posts so the will not have a lot of movement. here is the link to the commercial version. http://www.rtacprecision.com/i.r.i.s…html this is exactly what we are wanting to do. they have a great system but for 500ea i just cant justify it.
the biggest thing we need is 100% confirmation of hits, its even hard to see splash at that range. the only advantage of having the led down range near the target is to help some shooters locate the target. some of out targets are located in small clearing on the side of a mountain, if you don’t know exactly where they are at they can be hard to locate.
I have been doing some more research today, it looks like if all i want is a hardwired system all i would need is a rasberry pi, vibration sensor and a relay to trip the 12v side? this may be a simple option but it seems like i should be able to do better.
I found this on amazon and it seems like it might work for the short range rf link
I have heard of guys using the rdf900 modems in UAV applications and that would definatly get me the range ( up to 40km) but that would be $200 right there. if it could run the entire system it might work.
the other thing that might work would be to have sensors on the targets that all communicate with a downrange box, that box then relays hits via a rdf 900 to a box at the shooter position and displays hits on a small led panel or even a screen. it would still be nice to have something down range to id target locations. if i can build a well enough refined system ill build it then put out a how to and plans to the shooting community. im sure there are lots of guys out there that would like to be able to build something like this.
a microphone or accelerometer on the back of the steel plates. Either could easily sense the impact.
Since you have line-of-sight to the target and both ends at fixed then a low power TX with directional antennas on both the TX and RX will easily get the range for the RF link. There for the low cost XBee Series 1 modules with the SMA connector would work.
I’m sure something as simple as a piezo sensor feeding a one-shot that triggers one of the XBee 900MHz radios will work. Cost will be about $100 for receiver & transmitter. I can get one of those sensors to detect me punching a desk without needing any kind of amplifier at all. Add a one-shot to stretch the pulse and you will be able to see it on an LED. Sensor + one shot circuit + LED + perf board + batteries, etc. is probably around $10 all in?
The major concern I’d have is shock. Assuming you mount the sensor/transmitter to the back of the target (the target won’t ever be penetrated, will it?), then you’re subjecting the electronics to quite a bit of shock on every impact.
Besides that, it seems like quite a simple design.
[edit]
I just had a minute so I tested one of those piezo sensors. If anything, it may be too sensitive. If I have a half hour later tonight I can prototype something with a Trinket (SF needs their own version of this!) that will blink an LED when triggered by an impact. Doing it in software is easier than wiring up a 555
[edit2]
Not surprisingly, it works. I have the sensor mounted to a piece of perf board that is in turn screwed to a piece of scrap aluminum plate and held in a drill press vise. The sensor feeds into a digital input on an Adafruit Trinket and a trigger causes it to flash the LED a few times. I think the cast iron of the vise is absorbing a lot of vibration because I have to hit it pretty hard to register an impact. I’ll post a video as soon as I can remember how to use my webcam
The only thing about a piezo is that it can generate really high voltages (> +/-100V), although with little current, and that’s a good recipe to fry a CMOS input pin. So I’d condition it, maybe even buffer it, to keep the MCU alive after multiple hits. Someone here has previously mentioned the use of some little shake detector “switches” (I’ll see if I have the link) that would also make good hit detectors. But this is the easy part.
My thinking was to place the electronics behind the target plate where they can’t get hit. But putting an antenna behind a metal plate is not a recipe for long range. Putting the antenna near the target, but offset, will mean it will get hit at somepoint and it’s a mile away ! I’m not sure if I read the IRIS description properly but it seemed to me that the detector was wireless, but only had a short range. So I assume the LEDs and downrange receiver are somehow far enough away from the target plate that a hit is unlikely or they’re armored/protected. The downrange receiver then does the communications with the radio at the shooting position.
BTW is the shooting location a single constant place or do you shoot from various, widely separated locations ? How separated, in angle when measured from the shooting location, might you expect the various targets to be ?
I’m wondering about the ability to use 2 high gain antennae, at the shooter’s location and downrange, or whether only 1 such antenna is possible. You don’t want to have to aim and re-aim the downrange antennae if the shooting position changes. You might be able to aim the high gain, at the shooter’s location, for each target (if needed).
Lastly I worry about multipath because both transmitter and receiver are expected to be at basically ground level.
EDIT : I don’t have the link to the switch mentioned above but Adafruit has a similar sort of item.
a microphone or accelerometer on the back of the steel plates. Either could easily sense the impact.
Since you have line-of-sight to the target and both ends at fixed then a low power TX with directional antennas on both the TX and RX will easily get the range for the RF link. There for the low cost XBee Series 1 modules with the SMA connector would work.
i thought about a microphone also but there are problems with that, like wind noise, the sound of the bullet hitting things besides the target (ground or rock) and there is the sonic crack of the bullet passing by. accelerometer was my first thought as well, but i also found "vibration sensors" I'm not certain but my guess would be that these are accelerometers as well.
lyndon:
The major concern I’d have is shock. Assuming you mount the sensor/transmitter to the back of the target (the target won’t ever be penetrated, will it?), then you’re subjecting the electronics to quite a bit of shock on every impact.
I'm not sure how shock will affect it either, it will most likely be mounted in a delrin box that i machine out, or a project box of some sort, then attached via velcro or double sided tape?
Mee_n_Mac:
My thinking was to place the electronics behind the target plate where they can’t get hit. But putting an antenna behind a metal plate is not a recipe for long range. Putting the antenna near the target, but offset, will mean it will get hit at somepoint and it’s a mile away ! I’m not sure if I read the IRIS description properly but it seemed to me that the detector was wireless, but only had a short range. So I assume the LEDs and downrange receiver are somehow far enough away from the target plate that a hit is unlikely or they’re armored/protected. The downrange receiver then does the communications with the radio at the shooting position.
BTW is the shooting location a single constant place or do you shoot from various, widely separated locations ? How separated, in angle when measured from the shooting location, might you expect the various targets to be ?
I’m wondering about the ability to use 2 high gain antennae, at the shooter’s location and downrange, or whether only 1 such antenna is possible. You don’t want to have to aim and re-aim the downrange antennae if the shooting position changes. You might be able to aim the high gain, at the shooter’s location, for each target (if needed).
Lastly I worry about multipath because both transmitter and receiver are expected to be at basically ground level.
EDIT : I don’t have the link to the switch mentioned above but Adafruit has a similar sort of item.
I would agree with putting the sensor on the back of the target, thats what i was planning. the wireless sensor sends its signal a short distance to the downrange receiver. that receiver is placed a short distance away from the target. i’m personally fine with it being within 10 yards (i would like the option to place it up to 100 yds) for the type of shooting we are doing, if you are missing by 10 feet then your doing something horribly wrong yet alone 10yd or 100yd.
for all intensive purposes the shooter will be in one position i think that having 2 high gain antennas should be possible. multipath could be an issue, do you think using somthing like the 900 xbees would work better that the 802s?
there are a few constants in this project, the led that will be used is a 12v led array and has built in Flash patterns.(i already have these) the led will be hooked up to a relay and 12v battery. whatever device i use will have to be able to trip the relay for a set time period then turn off. for example it receives the signal that a hit has been made it trips an output that triggers the relay. the output stays on for 10 seconds then shuts off.
I think either a piezo or mic will work. Both would need signal conditioning that includes a Voltage clamp (TVS + resistor). The mic would need other sound proofing so that other external noise is not picked up.
The electronics could be a package that is not mounted to the target plate but still behind the plate. Then short wires to the sensor on the plate. If the impact is too large a little foam or rubber tape could subdue the impact on the sensor.
To move the RF antenna away from the target an IR LED link might work.
The other is to use a smaller, cheap and easily replaced antenna at the target so when it does get hit just replace it.
lrmatt:
for all intensive purposes the shooter will be in one position i think that having 2 high gain antennas should be possible. multipath could be an issue, do you think using somthing like the 900 xbees would work better that the 802s?
I ran some quickie calculations and I think an XBee Pro 900 (50 mW) Tx'ing through a 9 dB antenna should have sufficient power to reach 1 mile w/a low error rate even when the receiving XBee uses only a simple dipole antenna. And I now see there are even more powerful XBees than that !
To me there’s a question of how to “wire” the target to the just-far-enough-away downrange XBee. You could copy the way the IRIS people did and have another wireless link between the target tower and the “remote” XBee tower. Or (if possible) just run buried/armored cables between the two. Battery (and solar ?) power would reside on the “remote” tower w/the LEDs and the XBee and some circuitry to run the XBee.
Probably the microcontroller “brain” would be there too. All in a weather-tight enclosure. Then you’d run wires to bring power and ground from the remote tower to the target tower and up to the hit detector. A hit sensing line would then run back to the “brain”. Meaning a cable w/2 connectors (DE-9) and a weatherproof cable w/3 (or more) conductors. And mating connector on the enclosures (remote and hit detector). This may be easier to do (if the cable can be protected) but it might not be less expensive given how cheap you can get the Nordic pair you linked to.
If I read you correctly, you’re talking about wiring the target sensor box to the remote display box?
OK, we’re talking a mile run of cable. That’s expensive all on its own. Then the installation costs will also be a bear. And add to that signal conditioning and protection over the 1 mile run or you’ll have damage from induced current from lightning strikes, it will pick up noise, will have to be underground rated or otherwise protected (water will penetrate insulation over time. Ask me how I know!!)
[edit: OK, it looks like you’re talking about just a wire from the target to its transmitter. I’m with waltr and suggest putting it all in one box with an antenna sticking up. If anyone hits the antenna, replace it]
It would be cheaper to buy two 900 MHz XBees that can cover the range and be done with it.
My suggestion:
Stage 1: A piezo sensor mounted to the target and wired to a mini/micro Arduino with back to back diodes to protect the input. Sample with an analog input for versatility and blink an LED when a threshold is reached. This will answer 90% of the questions and it’s easy and cheap (about $20 all in) to prototype. Shoot at it all you want and work out the mounting, shock & vibration and other issues.
Stage 2: Get two XBees communicating. They have a basic “wire replacement” mode built in so what one end reads will be reflected on the other.
Stage 3: Connect the Arduino circuit to the target XBee and the remote XBee to the relay/LED
Stage 3.5: ???
Stage 4: Profit
But in any case, build something. That’s when the real problems no one thought of show up.
lyndon:
If I read you correctly, you’re talking about wiring the target sensor box to the remote display box?
OK, we’re talking a mile run of cable. That’s expensive all on its own.
Not quite. The IRIS system has a remote control at the shooter's location. It talks to a downrange tower that has LEDs and a battery enclosure and dipole antenna and ??? This is located some 10's of yards from the target post w/the target and a hit detector module on the back of the target. It seems that the hit detector has it's own battery and conveys hit info to the downrange tower via some short range RF link. Every downrange target has this pair, a target post and a "semi-remote" tower.
I was thinking that the OP could replace the short range RF link w/a wired connection … so as to simplify things.
lyndon:
[edit: OK, it looks like you’re talking about just a wire from the target to its transmitter. I’m with waltr and suggest putting it all in one box with an antenna sticking up. If anyone hits the antenna, replace it]
I hope my edited post above shows w/better clarity what I was talking about.
I would disagree w/replacing the antenna just because when you have enough shooters shooting at it, it will get hit. Who want’s to trudge a mile to replace it ? But there’s also the LED indicator that has to be run off the XBee. And that’s a bigger, more $$ target when it get’s hit. So I think some semi-remote tower is needed.
