Does anyone know of a transistor that can detect metal coins? I have been trying to use a photo transistor, but that is really inaccurate. Whenever I put in a coin the vibration disturbs the photo transistor. I also tried to use the parallax motion sensor but that is only responds to human motion. Is there any other device that I can plug into the Arduino on the Digital Pins that will detect metal as it passes by?
Can't really tell in the photo, do you have anything pointing at the photoresistor? I think you may have better results with a light directly pointing at it, and possibly also shielding the photoresistor from excess light. (just a piece of black plastic around it should work fine)
Then you'd just have to calculate the time of each type of coin you're going to use.
This is all in theory, so I'm sure it won't be as simple as it sounds, but in THEORY it should work!
There are ... I don't know the name of them... they're used often in Robots, to read the wheel speed using the same idea.. I believe it's what you're using, but the other side has the LED pointing directly at the resistor, so there aren't any issues with excess lighting.
I have tried to put some white printer paper around the transistor to shield it from excess light. Do you think that a black shield works better?
Also I will be using 4 phototransistors, sorry the photo only shows 1. So, I can determine if a coin passes either 1, 2, 3, or all 4 transistors. However, if I have 4 phototransistors over each opening then they all trigger when any coin is sensed. So I am trying to find a transistor that will give me a digital 0 or 1 so that I can definitely know if a coin passes by the transistor.
I think the thing used in Robots is a Hall effect sensor, but I wasn't sure if that was going to work.
Best guess based on your photo is that you need a light source to detect and a shield around the detector to block out ambient light.
You could either do beam-break detection where your light sensor is on one side of the slot and your light source is on the other, or you could do a reflectance sensor where the light source and detector are on the same side. A beam-break sensor detects when the coin blocks the light, and a reflectance sensor detects when the light bounces off the coin.
The shield just limits the light that the detector can see. It's just like looking through a paper towel tube, the longer the tube is, the fewer light sources you can see. It helps if the inside of the tube is not reflective. A rolled up bit of paper works pretty well for this.
I'm not sure if a hall sensor would work for this. I know it will detect iron, but I'm not so sure about the non-ferrous metals in coins. I think you'll be better off with the optical sensors.
Well, real coin slots use a lever, atleast the ones I have opened... So when I designed one myself a few months ago, I decided why bother with a lever when you can just use a button that gets hit by the coin.
Hey jezuz, do you know of any button that would work in my setup, all the switches that i have found make the coins stop moving down the ramp. If I could use a button then the detector would be much more effective.
To be honest, it depends on your design... I would try to find some some tack-buttons ( really small) that are easily pressed, cause larger ones are usually quite hard to engage, esspecially if your expecting to have a coin fall on them. Like u said, it depends on design, do you have one in mind already? I can post one on here 2morrow (on iphone, can't post images) that would register all coins (penny, dime, nickel and quarter) if you wish.
Hmmm, I dont have an idea for any type of tack button, but I was thinking of putting some sort of toggle switch. The toggle would have to require a light touch, like a "paper thin" toggle, so that when a coin hits the toggle the switch would record a "1". I was thinking of placing 4 of these switches above the coin holes so that when coins are sliding down the ramp I could tell if how many switches were activated.
How would the toggle button go back into the "ready to read a coin hitting me" position? Do you need to count multiple coins, or are you waiting for just one? Anyway, if you are doing the conventional multiple coins slot that can judge which type of coin was placed into it, heres a design... shitty pictures I know, but hopefully you get the idea. All you need is 3 layers of plexiglass about 1/4 inch thick, so that the coins always fall in on their rims... anyway, here is the doodle I made last night if your interested (let me remind you it would cost you almost nothing, and if properly made would work quite nicely)
(Dunno how to scale pics on here... sorry for the huge size)
Hey jezuz, Im not really sure about your drawing, I included a picture with what I think you may be drawing but I'm not sure. Could you take a look at this and tell me if I am drawing this correctly? Also I just need to determine if one coin enters the appropriate tube.
So you want to detect different types of coins, but only one of each kind?if so, the reason I'm against the toggle is that once it flips, how will you set it back to the ready position? The reason the button works better is that it will always be ready to read a falling coin.
Also, the image you gave has the button vertically placed. It should be on an angle (like in my img) to more effectively detect falling coins.
Well, I guess its not clear in the picture but the coins are already falling into the correct slots because the red track has different grooves the indicate when a coin has enough room to fall. Therefore, I just need to detect when a coin falls into a container (so a sensor needs to be placed either above each cylinder or on the side. Also, the toggle I was thing of would not really be a toggle but some sort of switch that would move down when a coin falls into the cylinder, report a "1" and then move back to its original position (in an automatic, spring-like action). Therefore, I was thinking that the switch or toggle must be very light so when the lightest coin (dime) falls it can at least trigger the switch. If the dime can trigger the switch then every coin will work. I'm just trying to see if any switch could work because using light detectors over each cylinder may be inaccurate at times due to vibration.
Also, the toggle I was thing of would not really be a toggle but some sort of switch that would move down when a coin falls into the cylinder, report a "1" and then move back to its original position (in an automatic, spring-like action).
You're describing a "whisker switch" like this one from SparkFun. Lots of other suppliers out there, but you get the idea.
Cut a vertical slot in the side of the cylinder and let the spring finger protrude into it. Keep the hinge of the switch at the top of the vertical slot. The coin wouldn't fall onto the switch but it would trigger it as it passed on its way down. Even an American dime should be able to trigger it.
Yea, my drawing blows, but it also showed the coins being devised by size like you described. But TBAr's whisker switch is better for your design, as your coins will fall flat, rather than on their rims. If they fell on their rims, you would be able to use a button on an angle as I described.
Oh and the toggle that goes back into ready position is a button if you think about it.
