Electronic Design For Dummies

[Harterz]

Hi. I am what can only be described as a complete novice when it comes to electronic design. However, I am looking for guidance for an idea I have.
I want to have a series of LEDs come on when a metal object passes over them. There would be a series of rows of maybe 10 LEDs in each row. The LEDs must work independently of each other (I am trying to demonstrate the alignment of the metal object as it passes over electromagnets (?)), and they should remain on until a reset button is pressed.
Can anyone offer help as to where I might begin?
Thanks

[bwts]

Not sure what ur talking about! But maybe look for some metal detecting circuits or may be use infared beams and sensors (when a beam is broken the appropriate LED for that beam lights up) but this will not b metal specific. Also if u R putting the metal object over the LED how R U going to see he LED?<p>B

[Harterz]

Thanks for the reply. The metal will be about 1" x 4" and will pass over the sensors. The leds which were immediately below the metal and have lit up should then remain lit until the system is reset manually. The idea is to show the track of the object to identify how closely it followed a target line.
I like the idea of IR sensors, or I thought some magnetic system might work (inductors?). I do not need to differentiate between metal and non metal - all objects can be measured whatever the material, metal is simply the most prevalent and I was thinking of the magnetic angle.

[Donald S. Lambert]

I am also not too knowledgeable in the field of electronics but I think I see what you want to do. You want to know how the object passes a certain spot, that is if it is centered in the path and also if it is traveling parallel to the path or if the object is turned at an angle to the path. If you had a grid of LEDs bigger both in length and width than the object you could put a device in that will trip the sensors when the object is over the grid and that will take a snapshot of the tracking and the position of the object at that the moment.<p>I am trying to see the project through you eyes and I may have gotten far off base. HTH Greybie

[Harterz]

Greybie, you have it exactly!

[Donald S. Lambert]

Before I retired in 1987 I used to wok occasionally with EE engineers. I had to sort of read their minds.<p>I can visualize what you need, sort of. You will need an emiiter LED, probably infrared, and the sender will need to have the light sent down a tube to keep it from interacting with the other receivers of the beams. Since you will have the sender and receivers located at the target spot it will be too cluttered with them to see the LED indicators that will position the object unless they are located above the units immediately above the object being tested for position. From that I guess someone more knowledgeable in electronics will have to help you. HTH Greybie.

[Bernius1]

??? Indoors or out ? How far above the sensor grid will the object be passing? If indoors ,with
proximity of 3-9 inches, an array of photo-transistors (i-r or light),with the tubes for
discretion between sensors, with 2-4 lamps (IR LED's) at the corners,and in the middle, an iron-
core choke,set vertically,feeding a flip-flop to
latch high when ferric metal is sensed.
...LaForge out....

[MrAl]

Hello there,<p>Sounds interesting.<p>Can you have all the led's turned on at first,
then turn each one off as position data
indicates?
In this way, the led's themselves would provide
the light for each sensor positioned above
each led. The sensor would detect the lack of
light reaching it and trigger your control
logic.<p>Also, it would be good to know what the max
speed of the object to be detected would
travel, as you could use a multiplexed system
to reduce the amount of wiring, as well as
possibly the number of sensors needed if the
object doesnt travel that fast.<p>I did something somewhat similar, which only
used one light source and one detector to
measure the speed of a rotating fan blade
with three blades. I used a laser diode
and a regular photo diode. Every time
one blade interupts the beam, the frequency
counter would count one pulse. Dividing
by three gave the rotational speed for that
particular fan.<p>The advantage of using one sensor per LED is
of course speed; you could probably detect
a very fast moving object and even calculate
its' velocity using a modified form of a
frequency counter to measure pulse width
between sensor activity.<p>
Good luck with your circuits,
Al

[Dimbulb]

I like to think of the magnetic field like a balloon expanding and contracting very quickly. <p>The frequency remains constant until metal object is introduced . The metal object changes the balance of a simple RF tank circuit and the frequency is thrown off. Radio designers use the term "hand capacitance" which you can easily observe if you remove the metal shielding on a radio oscillator when you put your hand near the circuit the radio goes off frequency.<p>The detector in this case uses a narrow bandwidth
of the field strength variety that measures the carrier. It only detects this narrow bandwidth so is made selective with a preselector employing high and low filters followed by a germanium diode that changes the waves to current. <p>
A 9 volt battery with a 7805 regulator is applied to a low voltage single supply op-amp used as a adjustable gain mode. The op-amp outputs to the LM3914 which puts out a nice LED display.<p>This is simular to an S-meter detecting signal strength which became popular on radios and VU meters on stereos. Formerly displayed on 200 uA analog meter and now LCDs.<p>The idea of using bigger brighter LEDS would require small modification to boost the outputs of the 3914 with a transistor array.<p>Taking the project to a macro component hobby level would involve a redesign of the display stage of the circuit using SOT-23 and 1206 size surface mounts and encapsulating them in epoxy along with the LEDS.