a very simple sensor system for a newbie

Hi all
I will apologise now as I have very little electronics experience and have what for so will seam like a very simple question. I need a sensor system which I can run off small batteries AAA or AA’S, it has to be able to detect an object travelling at high speed (200 – 400 FPS) then trigger a switch for a second or less and the turn the switch off again ready for the next object.

I was wondering if I could use a beam set up, what I mean is when the object passes through the beam it is detected and the circuit is closed thus making the motor turn on, I don’t know how to time it or how to turn it off, or indeed any of the above!! lol

As I am sure you have all worked out by now I don’t really have a clue about electronics and would need some very kind person to let me know if what I want to do is possible and how I go about making it, a circuit diagram with components list and a “stupid blokes guide to putting together” would be fantastic.

I know it’s a lot to ask but I thought id ask and see what comes back, I have and am still looking over this and many other forums for diagrams already provided so again apologies if this is out there but haven’t found it yet.

Cheers

I spose you could try a laser and CDS sensor. Hook it up with a simple 555 'light detector' and it should work fine. has the circuit. I have built it myself and works well for high speeds. With the switch, I would think a realay is too slow. Im not exactly sure what you want, but these Maxim Analog switch IC could help (**broken link removed**,
datasheet: https://www.electro-tech-online.com/custompdfs/2007/04/MAX4620-MAX4640.pdf)
Be sure to choose the right one, that is, most likely a N.O. in a DIP package.

It is unlikely that you will find these in your local store, but, Maxim do offer free samples, anywhere in the world, two weeks.

Hope this helps.

hi

>it has to be able to detect an object travelling at high speed (200 – 400 FPS) then trigger a switch for a second or less and the turn the switch off again ready for the next object.

>I was wondering if I could use a beam set up, what I mean is when the object passes through the beam it is detected and the circuit is closed thus making the motor turn on.

Yes its possible to detect an object breaking a detector beam and do the things you ask.

You will have to tell us more about the 'object'
example:
How big/small, its dimensions would help, whats it made of.?
How far apart do you want the transmitter and detector to be.?
How often do the objects pass thru the detector beam.?

hi ericgibbs,

cool it can be done, well to answer your questions:

1) 6mm diameter, plastic
2) only 10mm apart
3) anything from 1 a min to 15 per second

would there be away to change the settings so if i wanted to trigger at 15 per second i could then change down to say 5 per second?

thanks for the help

hi,
Thats better.

Search this forum for 'beam detectors', there have been many threads regarding detector beams, that will give you some ideas.

When you have looked thru them, come back with specific questions and we will help you.

Edit: beam detectors

Cheers Eric,

I have had a good look at the beam detectors and am now even more confused, I think I need a dark alarm as I want it to trigger when the beam is broken, it will be placed in a tube so there will not be any other light source apart from the transmitter. So extra light noise shouldn’t be a problem.

I read that photodiodes work better with blue light so I could use a blue led as the light source (transmitter), a pin photodiode as the receiver and from what I gather a 555 to control the timing issues.

How that all goes together is out of my league. How do you set up a 555 to open and close a circuit?

Basically I want a circuit to do the following, I’m not a electrical person, I can follow clear simple instructions, but I don’t have the time to learn electronics 101 on this one, but hear is what I’m trying to do:

A 6mm plastic ball is fired at about 200 – 450 feet per second, when the ball passes a beam sensor it triggers some sort of system which will run a dc motor for half a second then turn it off ready for the next ball to pass through the beam. This all needs to run off AA or AAA or smaller batteries and it needs to be as small as possible. The rate of fire can be anything from 1 ball per minuet to 15 per second.

If anyone can help I would be grateful, and if you have any other questions please ask but like I said im not into electronics so asking me to give specifics is no good as I don’t know, sorry it’s not my thing. Again thanks Eric for trying to help me on this one.

If nobody can help then I’ll just have to contact an electrical engineer to design it for me, but here’s hoping somebody smart enough out there wants to help a thick dad with no time trying to impress his son.

ok i found this diagram, which i kind of understand, i just need to know where and how to connect the dc motor. that is if this is indeed the circuit i actually want to be using.

**broken link removed**

Well I think the most demanding specification you have to meet is the response time of the light sensor. At max velocity the beam will be interrupted for only around 5 microseconds if my calc is correct. This kind of speed is no problem for the rest of the electronic parts needed, schmidt trigger gate clocking a retriggerable one-shot multivibrator then driving a motor. So you need to research light sensors that can work this fast, I think pin diode type light sensors are the fastest but I'm really not sure.

Good luck

hi,
The 400f/sec is around 270 mph+

How do you plan to guide the 6mm balls thru a 10mm gap, can it be an enclosed tube.?

The electronics beam detection over a 10mm gap isn't a problem, Lefty's sums suggest a 5uSec blanking time, which isnt a problem.

Do you have some experience of electronics and assembly ?, need to ask, so that we can explain how to do it.

Your motor and mechanical subsystem will not be able to keep up with a rate of 15 balls per second.

newbie73 said:

some sort of system which will run a dc motor for half a second then turn it off ready for the next ball to pass through the beam.

The rate of fire can be anything from 1 ball per minuet to 15 per second.

Click to expand...

these numbers suggest your maximum rate of fire to be no more frequent than one object per 1/2 second plus some small reset time.

hi yes it will be travelling down a tube, i have looked into pin diodes and they can cope with these speeds. i have a little experiance with electronics like helping my son make up small lab kits ect,

cheers for all your help

hi,

Can you decribe the project in a little more detail, whats the motor do and
what fires the balls.

Do have any bits already for the project?

Regards

hi i can answer a few questions now.the balls are made of low grade plastic they are 5.96mm in diameter and are yellow or white. my son has a airsoft gun which he would like to make a piece of kit for that when he fires the gun it detects the ball and starts the small dc motor. the motors (four in total) will then spin small rubber wheels at the end of the barrel to give the ball extra spin, thus increasing its accuracy but not it fps.

i surrgested having the motors start then the system detects the first ball then if no other ball was detected within half a second it shuts down ready for the next. if it dose detect a ball within half a second then it keeps the system open and lets the motors run until the last ball is detected. this is now what i think we will have to design, or rather some kind person here, to sort out the subsystem not being able to keep up.

we have tried a mock up of the spinning motors and they do increase the accuracy by quite a fair amount. so all we need now is a system that can do the on off bit as described above.

Eric, we have the airsoft gun the extra barrel and my extensive workshop, i havent got any components as yet as i dont really know what to buy, didnt want to rush in and buy the wrong stuff. i can get almost any component required online so shouldnt be a problem.

again thanks all for your help and if we get this working ill have one happy little boy. and a lot of gratatude to you guys.

oh and to put your minds at ease, his airsoft gun is locked away with my real ones so he can only use it when im around.

cheers

hi newbie,

I saw a demo on TV sometime ago, showing the effect of 'spinning' a tennis ball.
It used a piece of plastic water pipe, the dia was chosen to suit a lawn tennis ball, it had electric motors which
imparted spin to the ball as it was shot out of the pipe, using a compressed spring as the launcher.

The difference in accuracy of a spinning ball was superior to a non spin.
If you give it a back spin, like a golf ball, it would be interesting to see what effect it had on the range??

I think a problem will arise in your project because of the response time of the motors to get up to speed
after detecting the 200/400fps ball.

Have you considered using a small switch, located on the left of the gun barrel extension, at some point where
your left hand would be,when holding the gun?

The idea would be to operate the switch with a left finger/thumb, just before the main trigger is pulled.
This should give the motor/rollers time to reach their terminal velocity before they grab the ball.
It would also eliminate the electronics requirement.

A microswitch should have a sufficient current rating to operate the motors directly.

Regards

hi eric,

yep i thought of that set up too, but my son has got it into his head that this will work, we have done some testing and the motors dont need to be running at TV, well not if you use four. i think that they will be up to about 1/4 speed (ish) by the time the ball gets to them.

in terms of accuracy with the motors running at about 1/4 speed and giving spin back its quite amazing the difference, although range is slightly decreased. Each motor can be set to run at a different speed thus creating different spin patterens and making the ball curve, so firing around slight corners is possible, again at a loss of range.

I would still like to build the detection system with him, even if it dosen't work at least both my som and i will have learnt a bit about electronics together.

again thanks for the ideas and for your help so far.

happy easter

hi,

Sorry a few more questions, as an engineer Im sure you know its difficult and risky to assume to much.

What power source do you want to use for the motors and electronics.?

Whats the voltage/current rating of the motors.?

Will the detector be located near the end of the existing barrel.?

Are you OK to machine Aluminium or Nylon to house the IR source/detector.?

Finally do you have a rough sketch you could post.?

hi Eric,

i would like to use AAA or AA batteries for all motors and electronics, the AAA's are better as they are quite light compared to the AA's but what ever you think is better i can use.

the motor's are rated at 1.5v to 4.5v DC, i have tested them on 3v DC and they work good at this setup.

the detector will be as close to the original barrel as possible i am hoping to get them mounted about 1mm from existing barrel.

i can turn and mill both aluminium and nylon so that no problem.

i have added a rough sketch of what we are trying to do, (so i'm no de vinci) the section behind the batteries is all yours for the circuit, i dont know what lengh yet so it depend on what size the circuit is.

again thanks for you help

sorry can seem to add any pics yet still trying