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How can I trigger an LED sign to turn on when an object is tossed into a bucket? Answered

I am designing a bucket with a small LED sign on it, and I want the sign to light up when people successfully hit a target in the back of the bucket. Everything has to run on battery power, and the entire product has to be mounted on a pole (which will be held in hand).

I have considered motion sensors (Parallax PIR) and some sort of laser trip-wire (as one would find on a garage door system), but I am not sure how to implement either. 

I have also looked into shock sensors, the kind used on some window and door security devices, however, I am not sure that the objects being thrown would be able to provide the shock needed (think toy cars, beaded necklaces and other small novelty toys).

The sign will consist of up to 200 LEDS, and it would be nice to have it stay lit for a second or two before turning off again.


Try a "piezo disk". You'd be amazed how much signal you can scrape off them. They are really cheap too.


Thank you for your reply. A piezo disc sounds like something I should really consider. Would this be effective if they managed to hit the inside of the bucket without hitting the back of the bucket? Also, I understand the piezo disk generates electricity, but I imagine I would need a relay to switch on enough power to light the LEDs. What voltage does a small piezo disc produce?


worst case a tactile at the bottom of the bucket..

You won't get enough to trigger a relay, but you WILL get enough to drive a simple detector circuit.

You can even put muliple discs on your bucket and wire them to the same circuit.

If I post a circuit, can you follow it ?


I would really appreciate it if you posted a circuit.

The detection part is really pretty easy, certainly if you can whack the disk - try this and see if it does what you want. You SHOULD be able to put a single LED on the output of this circuit, and it should flash when you whack the disk.

The rest we can work on if this works....


piezo sensor.jpg

I found the part and built the circuit, but it didn't flash. The led stayed lit and only flickered a little when I tapped on the disk. What might I have done wrong?

Turn the disk round, or add another inverter - there's another 5 in that package.

Thank you, that worked for me. I managed to set up a 555 timer and used the output from the inverter to light an led for a second (which is about the length of time I am looking for). How can I take the signal coming from the 555 and use it to power the number of leds that I am planning to use? I have been running everything on 9 volts (with a voltage regulator for the inverter). Also, the piezo doesn't seem to be very sensitive to my tapping it. Is there a way to make it more reliable?

Play with the resistor - assuming you used one ??

Remove the resistor and see if that helps...BUT put another diode, from the input to the supply, with its cathode to the supply - this is a CLAMP to make sure the input volts can't exceed the supply.

Driving lots of LEDs is the least of your problems yet, but basically, we will add a fat transistor, switched on by the 555.


Removing the resistor did the trick. Now that the detector circuit is working for me, what should be my next move?

Get a power transistor - I suggest an IRL 540, connect it to the output of your 555 (put a 4k7 resistor from the output to the supply line.

200 LEDs is going to take a lot of wiring !!!!

The LEDs that I am using are rated at 3V .02I, .06W.

...so multiply the number of LEDs by the current, and see if the 510 can handle it.

Thank you for all of your help with this project. I am not by any means finished yet, but this is the schematic of what I have wired up. It seems to work consistently, but I am not sure if there is something I am overlooking or forgetting to consider. Also, I am sorry for the mess and confusion when it comes to the layout of this schematic.

I added the potentiometer to pin 7 on the 555 so as to be able to adjust the time that the lights stay lit. I added the push buttons to pins 2 and 4 so I can test the timer, but they shouldn't be needed when I actually solder it all together. The leds on the inverter were just there so I could see what the inverter was doing. I am sure you can tell that I still have no concrete idea of what the applications of that chip are.
Also, I am sure that I used more diodes than necessary.

Bucket Lights_schem.png

You shouldn't put diodes between the output and input to the inverters, though you might add a 5V zener across the input from the piezos, to protect the inverter.

I did that, tested it, and now the piezo aren't triggering the circuit. Is there something else that might not be right about this schematic?

Its really hard to read your circuit I'm afraid. There are rules to these things, like inputs come in on the left, outputs go out on the right.

Ground lines go horizontally across the bottom, positve supply lines are always horizontal and above the grounds.

Try redoing the diagram and I can see what you have.

Here is an edited copy, and a link to a larger image of it.
I hope that is clear enough for you to analyze.

The Zener shouldn't be in series with the piezo, it should be in parallel with it, so the marked end of the diode goes to the input pin, the other goes to ground. The piezo doesn't need to be tied with a resistor to the supply either.

I moved the Zener and removed the resistor, but now the circuit doesn't seem to be working. I can get the 555 to trigger with the pushbutton switch on pin 2 but not with the inverter.

Check you can "kick" it, by putting 5V on the input to the inverter, where the piezo goes.

I did that to no avail, then I replaced my inverter to rule that out. I am getting a half volt from the piezo when I strike it.

Hmm. Lose the diode again, It might be loading the circuit too much. Very surprising

That made the difference. I have only been driving an indicator LED up until now. Why is it that you told me to put a power transistor between the output of the 555 and the LED sign?

I've soldered everything together and it works brilliantly. Thank you for your help with this project. I will post pictures and a video of the bucket in action once I finish mounting it all on the bucket.

Please don't forget to Best answer this question - it was a darned good question !!!

I pulled what I think is a piezoelectric disc from a small toy beeper, but I cannot tell which part of the disc connection is positive and which part is negative. Also, I fried one of these discs earlier when I was soldering to it. What might I be doing wrong?

I am also looking for the inverter in that circuit you posted. Is there a common product from which I can harvest that component, or am I limited to what I can purchase online?

I think one has to be very clear about final version of product while designing any kind of a product. More so when electronics is involved.

You say bucket ( handheld ), what will be the size ? You say small LED sign ( of 200 LEds). It can not be called small if it is battery powered. If it is handheld, what kind of battery, are you going to use ?

Also we have to define the objects that will be thrown into the basket otherwise you will not be able to define the impact. This is very important while designing the electronic circuit.

Once everything is very clear, it will be very easy to get answers.

Defining a product, as if the final proto is in your hand is a must step for successfully developing any product .

I am using a 5-gallon painter's bucket. The items being thrown will vary in size, weight, density, and mass, but I think the smallest impact will come from the beaded necklaces (the kind found around Mardi Gras celebrations). However, there will be items of significantly larger impacts, weighing in at around three to four pounds dead weight.

The batteries being used will most likely be 2500 mAh NiMH batteries, as I have more than a few of them lying around and I can recharge them as needed.

When you say that it cannot be considered a small sign if it is to be run on batteries, what do you mean by that? Why is that so?

I am not sure just how much voltage the circuit will need as I do not yet have an understanding of all the components involved. I do know that the LEDs require up to 3 volts, so I imagine I will start with 2 batteries.

To light up any LED you will require proper voltage, supplying enough current.

This will be different for different color LED & for different size of LED. A normal red led will consume around 5 to 10 mA for 3 V.

Now consider upper limit- 10 mA. For 200 leds to light it will require 200 * 10 mA= 2 Amp. So your batteries should provide current to monitoring circuit as well as a sudden burst of this high amp when needed. Will you please tell me why 200 ?

Also please define " back of a bucket". Can you put it on a paper ?( This step is be very important !). How much area ? This will give you answer for choosing the right technique & right sensors.

I made a mock-up of the sign and mapped the leds to it. In order to make the sign as bright and consistently lit as I want it, 198 leds would need to be used. 200 is just an easier number to work with.
I am referring to the bottom of the bucket when I say "back of the bucket". If you look at the simplified target image I posted with this question, imagine that the target is in the bottom of the bucket, with the opening of the bucket facing you. This isn't the best image to represent what I am trying to do, as it shows the bucket pointing directly at you, but in reality, it will be angled up by about 20-30°. This will hopefully prevent items from falling back out of the bucket.
The diameter of the bottom of the bucket is 10 inches.

put a small button right where your "centre target" is...then connect it to a timer that counts like 5 seconds attached to an L.E.D.:this will make the L.E.D. light up for 5 seconds after the target is hit

Tactile switch *might* work. A toy car would probably set it off. But steve has a better solution, if you can manage to scrape up a piezo.