LED's with drums help

I am trying to get some LED's to light up when I hit my drums. I can light up the LED's just fine with a battery, but when I hook a piezo transducer to my drums and strike them, the LED's barely light up... how can I get the LED's to light up all the way when I hit them? I am thinking it is the sensitivity of the piezo transducer? is there any practical way to get this to work? I am not really knowledgeable so please explain things thoroughly. thanks!

Helped someone else out with something similar awhile back:




The piezo is on the left.
D1 and D2 act to rectify the output of the piezo.
D3 limits the maximum output voltage of the piezo.
R1/R2 and C1 controls the time the LEDs stay on.
Q1 is a 2N7000 N-channel enhanced MOSFET. They don't pass a lot of current, but this is only a few LEDs we're talking about, right?
D3-D5 are typical red LEDs rated for 2v.
R3-R5 limit maximum current through the LEDs.
V1 is a 6v battery.

you will need some circuitry to amplify the signal from the piezo sensor, usually an opamp would do such as the LM324.... check out this site http://www.edrum.info/index.html, for some info on interfacing the piezo to an opamp, I myself just built the 16 Channel MIDI drum trigger for some Edrums I am building using piezo sensors, then I will interface it to the rockband controller so I can use my drums instead of the controllers drums....

wow this is confusing.... I didn't realize it took that much. Since the schematic was way out of my league, what items will I actually need?? and this is just experimenting for me, just to give me something to do... but yeah I just wanted to hook up three or four LED's. could you explain it in non-electrical engineering terms? haha

fbchurch2009 said:

wow this is confusing.... I didn't realize it took that much. Since the schematic was way out of my league, what items will I actually need?? and this is just experimenting for me, just to give me something to do... but yeah I just wanted to hook up three or four LED's. could you explain it in non-electrical engineering terms? haha

Click to expand...

I would go for Sarges circuit then, this is the simplest way to do it....

My .02

Easy isn't always so.
I will try to explain what is happening as best I can for you to understand.

When you strike the piezo, It is only producing a slight voltage for a very short time. The LEDs require more power, longer to reach full brightness. What Sarge was showing you basically took the piezo as a signal/switch to tell the LEDs to stay on longer, with more current than it would with just the piezo hit alone.

A trip to a local electronics shop with a printout of SgtWookies post and this parts list should get you what you need.

Parts list:
one - piezo (you already have) as XTAL1
two - 1N4148 diodes as noted on schematic as D1 and D2
one - 1N4744 diode as D3
one - 47k OHM resistor as R1
one - Variable resistor 1 MegaOHM as R2
three - 220 OHM resistors as R3 R4 and R5
one - 10 nanoFarad Capacitor as C1
one - 2N7000 MOSFET as Q1
three - LEDs as D2 D3 and D4
one - 6v battery as V1 -- A CR123 should give you decent life typically sold as camera batteries.

alright thanks for the help! this is just out of curiosity. What actually tells the LED how long to stay on? could I get the light to fade out instead of just turning off instantly... this is interesting stuff

Oh, boy. The answer is yes...how much are you willing to spend?

You could get yourself an Arduino type system for micro controllers. Around $30.
Then you could use you piezo to trigger it to run a PWM (pulse wave modulation) program to light and fade the LEDs untill triggered again. (write the code yourself or use pre-written ones - there are MANY)

You would then have the ability to add other drums to the mix much easier.

checkout http://www.arduino.cc

I would be interested in seeing a schematic using discrete components. Maybe slowly draining a capacitor?

I just realized something. What would sarge's schematic do for me? If I hooked a set up like that to my drums, would the LED's just stay on after one hit, or just flash quickly on and go off. I want it to just flash on and off after one hit.

I just realized something. What would sarge's schematic do for me? If I hooked a set up like that to my drums, would the LED's just stay on after one hit, or just flash quickly on and go off. I want it to just flash on and off after one hit.

Click to expand...

It would flash 1 time for each hit. You could adjust the time it stays lit with the variable resistor (Labeled R2 in his schematic).

Thanks BMorse and retched for trying to help him out with the circuit I posted; I've been on some necessarily long-winded replies to other threads.

fbchurch2009,
The idea of the circuit I posted is that the diodes D1 and D2 take the brief blast of AC voltage from the piezo, and rectify it to a DC voltage. C1 is a capacitor; it is where the DC voltage charge is stored (and on the gate of the 2N7000 MOSFET as well).

The Zener diode D3 has a breakdown voltage of 15v. If the voltage tries to go higher than 15v, the Zener shorts it out to prevent the voltage on the MOSFET gate from exceeding it's design limit (20v).

When the voltage on the MOSFET gate (the terminal on the left side of Q1) exceeds about 4v, it turns on, which allows current to flow from the battery + terminal through the resistors and LEDs, through the MOSFET's drain terminal (on top) through the source terminal (on the bottom) to the battery negative terminal.

R1, the 47k resistor, and R2, the 1MEG potentiometer, provide a discharge path for the DC voltage stored in C1 and the MOSFET gate. R1 provides a minimum time for the MOSFET to be turned on, and R2 allows adjustment of the maximum time for it to be turned on. So, you could just have a fairly quick "blip" from the LEDs, or a bright blip and fade to black, or anywhere in between.

how much do you think this little experiment will cost?

Sarge, I appreciate the ability to learn from your designs. If I can help take the load off you to help someone else its a given. thank you.

fbchurch2009, You can get all of the parts under $10. Probably enough to make a few of them.

The 2N7000 MOSFET will be the "sticky wicket" to obtain, as we have no clue where you are (hint, hint) - including your general location in your profile is a good thing.

If you are in the USA, Radio Shack should have the resistors, D1/D2 and the pot. You can also use a 12V Zener, which Radio Shack carries. They don't carry a 2N7000, but you might be able to substitute a IRF510 MOSFET for it, but the IRF510 MOSFET has a higher gate charge than a 2N7000. I have not tried this, as I don't have a piezo available.

Otherwise, you could order everything I specified in the original schematic from Digikey.com - and request that they ship the order via USPS 1st Class Mail to save on shipping costs.

hey, thanks for help guys! I will see what I can do with it!

Post a pic of the finished product. I'd love to see it done.

Hey everyone. First off I want to say thank you to SgtWookie, Bertus and all the other amazingly intelligent people on these forums. I followed the schematic that SgtWookie posted in this thread and managed to make a working circuit. You can see a video at the following address:
http://www.youtube.com/watch?v=mtmQJBf65h0

I made some modifications and ended up using 2 Luxeon Stars, a 9V battery and the IRF510 MOSFET instead of the n27000. One thing that I would like to fix before I get it all set up on a board is improving the sensitivity. The lights really only flash when the drum is struck moderately hard within a couple inches of the piezo. Is there any way to boost sensitivity? I was wondering if the use of a little mic like they sell in Radioshack would be better although I would want to keep it from triggering off guitars and other drum hits. Or what about possibly wiring in a second piezo? Or maybe the size of the piezo matters? Would the N27000 offer more sensitivity since you mentioned the gate requires less charge?

Another thing I noticed is I originally used a 500k resistor in place of the 1M pot. This worked fine but I wanted to see if I could change the on time as you suggested with the use of a pot. I wired a 1M 0.5 watt pot in and noticed no difference in light brightness or on time. I believe I ended up using a 100k resistor in place of the 47k you suggested for R1 could this be the reason the pot has no effect?

eduardonoso said:

I made some modifications and ended up using 2 Luxeon Stars, a 9V battery and the IRF510 MOSFET instead of the 2n7000.

Click to expand...

A 9v battery is a poor choice to power a Luxeon Star with, as much of the power will be dissipated inside the battery itself. Several AA cells (or larger) in series would be a better choice. At any rate, using a capacitor (say, 220uF to 1,000uF) across the battery terminals will help to reduce the power dissipation in the battery itself.

One thing that I would like to fix before I get it all set up on a board is improving the sensitivity. The lights really only flash when the drum is struck moderately hard within a couple inches of the piezo. Is there any way to boost sensitivity?

Click to expand...

Did you try decreasing the size of C1? C1 is there to compensate for the low gate charge of the 2N7000 MOSFET. The smaller C1 is, the more sensitive it will be. Of course, the gate capacitance is essentially in parallel with C1, so if the total gate charge is large, it'll never be very sensitive - it will just take too much current to bring the gate high enough over the threshold voltage to turn on.

I was wondering if the use of a little mic like they sell in Radioshack would be better although I would want to keep it from triggering off guitars and other drum hits. Or what about possibly wiring in a second piezo?

Click to expand...

I think the mics that Radio Shack sells are electret mics; which means they must be powered to provide an output.

Adding more piezos might do the trick; you would also need a D1 and D2 for each piezo.

Or maybe the size of the piezo matters? Would the N27000 offer more sensitivity since you mentioned the gate requires less charge?

Click to expand...

A larger piezo would respond to lower frequencies better.

The 2N7000 is a low current N-ch enhanced MOSFET. You'd fry it trying to drive Luxeon Stars.

Another thing I noticed is I originally used a 500k resistor in place of the 1M pot. This worked fine but I wanted to see if I could change the on time as you suggested with the use of a pot. I wired a 1M 0.5 watt pot in and noticed no difference in light brightness or on time. I believe I ended up using a 100k resistor in place of the 47k you suggested for R1 could this be the reason the pot has no effect?

Click to expand...

It's an experimental circuit. You'll need to experiment to see what works best. The idea with the 1MEG pot was to be able to slow the discharge time of C1 and the gate on a variable basis. The leakage current in the diodes is probably what's causing the decay times to be faster than expected. Changing to more modern diodes and a lower-power Zener may help to correct that.

Can somebody tell me what type of capacitor Sarges circuit needs

chongolio said:

Can somebody tell me what type of capacitor Sarges circuit needs

Click to expand...

Metalized poly is preferred. However, ceramic, "green cap", or just about any capacitor should work. Your mileage may vary.

It is just an experimental circuit, cut to the bare bones.