Ideas for sensor

indy

I am working on a target system for various weapons from airsoft to real bullets. My ultimate goal is to mount a reactive target on a robot that will record hits in the target area. I have experimented with shock sensors, but have not found one that will ingore the shocks and vibrations of moving on the robot and also be sensitive enough to record a hit from a bullet. The shock sensors work great as long as they are on a stationary target, but I cannot find a suitable adjustment range when the target is mobile. Ideas ans comments appreciated.

Is there a accelerometer that will ignore movement, but sense impact?

Thanks

Duane Degn

What about having two accelerometers. One mounted on the target section and the other mounted securely to the robot's base. You could use the one attached to the base of the robot to detect vibrations from moving and use the data to filter the data coming from the accelerometer on the target.

The base accelerometer would probably also pick up the vibrations from "hits" but there might be enough of a difference between the two sensors to figure out what sort of acceleration is being detected.

There's also the possibility of using some sort of target that can sense impact. I don't now if films used for touch displays would work or not but that's one option that comes to mind. I also wonder if you could use some sort of capacitive touch sensor.

If you gave more details about the target and robot, someone might come up with better suggestions for sensing target hits.

indy

Thanks Duane, the dual accelerometer might be the ticket. Films might also be an option, but I fear the damage would drive the costs up. The robot has yet to be built, have experimented with a robo vac and it works great for smaller targets (airsoft only) but I want to construct a robo that will carry heavier weight. Have a plan in mind, but we will see if it works or not. The targets I hope to use would be a self healing target manufactured by some of the larger target companies.

Thanks again I will look at your ideas.

prof_braino

indy wrote: »

Is there a accelerometer that will ignore movement, but sense impact?

ADXL345 can detect impact and motion at the same time. It has a function "tap" and "double-tap". The tap threshold can be set from 62.5 mg/lsb up to 16 g. You can also specify the duration window for double tap. The taps can set interupt outputs while the device spit motion over I2C.

This parts should be pretty cheap, I got mine on a GY-80 inertial meansurement unit (10DOF IMU), I think they are going for $12 on ebay.

4 wires, 3.3 volts I2C, can sit on the prop's EEPROM pins.

indy

I will round some up and give it a go. Sounds like that might be the ticket. Do you have a circuit handy for these? I am as raw and green as can be in the electronics arena. Thanks so much.

davejames

How about one of these:
http://www.parallax.com/product/29132

You could close-couple the microphone to the target (out of the way so it doesn't get all shot up), and then tweak the level control to desensitize the sensor from any noise but a hit to the target.

Peter KG6LSE

I have been working as a contract job a airsoft target timer . We used a peizo element bonded to the metal target and a OpAmp .

not exactly what you are doing but I hope it helps .


Peter


EDIT I got the idea from a rock star drum set . ..

erco

+1 Peter. Remember the KISS principle.

Piezo disks are cheap, come in many sizes and excel at picking up impacts. They send out a voltage spike proportional to the impact, simple to detect.

https://www.youtube.com/watch?v=FFLfb1kFPow

indy

Thanks to all. I will attempt to craft a piezo circuit. It looks like the cheapest way out and should ignore the bumps and vibrations of the robot.

erco

Be sure to filter the piezo output, it can spike up to a hundred volts or more (at very low current), which could damage a micro if directly coupled. You can see in my video that I put an LED in parallel with the piezo. It's a crude filter which starts conducting at ~1.8V and dissipates excess energy as red light. The LED flashes dimly with each good impact, and that reduced voltage is high enough above the TTL low/high transistion voltage (~1.3V on the BS1 I used) to read as a high signal.