Trigger Lights.... Continued

[jman 31]

I thought we had hi jacked bencthemusicians thread enough, so I am cleaning this subject up by starting a new thread. You can see all of my previous blunders and some great input from others HERE. When this is a final product, I will do a write up on the final outcome. Keep in mind that this thread is just a progress report!!!!!!

I have two schematics to try now. One that I have compiled using bits of a Keith Raper switch


And one that JimFiore provided which I think has the most potential.


I will build both of these and report back as soon as I can. I think it's getting close.

[JimFiore]

FYI, if you don't get enough sensitivity out of the above, try a Sziklai pair in place of Q1: http://en.wikipedia.org/wiki/Sziklai_pair
You get super high current gain like a Darlington but with only one PN junction worth of turn-on voltage required.


Oh, and we had great weather for the 30k run this morning: mid 30's, a little overcast, relatively calm, and the streets were completely clear of snow and ice (and road sand, too). The target for this year's event is around $1.2 million raised for heart disease research/cures. (The 30k is just one of many runs and walks at the event.)

[jman 31]

Originally Posted by JimFiore

Oh, and we had great weather for the 30k run this morning: mid 30's, a little overcast, relatively calm, and the streets were completely clear of snow and ice (and road sand, too). The target for this year's event is around $1.2 million raised for heart disease research/cures. (The 30k is just one of many runs and walks at the event.)

Nice man. It's good to hear about people doing good things!

[kittmaster]

You should put the diode inline to rectify only the positive part of the waveform. As it stands, you'll allow the full postive wave but clamp a -.7 volts which will still effectively turn the led on as you expect, but some circuits will not like the negative voltage.

[JimFiore]

The purpose of the diode in the circuit above is to clip possibly damaging inverse voltage across the base-emitter junction (I only put it in because I'm not sure how large the negative peak will be). If you put a diode in series with the base you will simply lower the circuit's sensitivity. You want as much positive potential as you can get (the 3k3 will do the base current limiting).

[jman 31]

PROGRESS REPORT:

Both circuits performed about equally well as far as I can tell by eye. Great sensitivity and response! They would even register the light taps with the drum stick. I will try to get a scope and do some more intensive testing before I decide between the two. I tried a darlington transistor setup with JimFiore's schematic and it seemed to help (I would have done the Sziklai pair as Jim suggested, but I couldn't find any pnp transistors in my stash without a bunch of searching. I still may give that a try when I get some hunting time). I have really found out that I need a breadboard bad!!! This soldering and unsoldering is for the birds. (no offense if you are a bird!)

The weak point of the whole operation is the LED. It doesn't emit nearly enough light to do what we are after. I need some input on the best bang for the buck as far as lighting goes. It needs to flash very bright for just the strike of the drum, but not have any hesitation in lighting. I would prefer it to run on a 9v battery as that is what I would like to design each of the triggers around.

We are close! The trigger part is in the bag in my opinion. It can be set up easily to run in parallel with your drum trigger piezo. Now it's just a matter of getting the flash we want. Please give me some ideas for the lights.

Jman

[JimFiore]

What kind of lights are looking to trigger? Strobes? PARS?

[jman 31]

Originally Posted by JimFiore

What kind of lights are looking to trigger? Strobes? PARS?

These lights will be inside the drum shell. I will need different colors for the effect. I need something that will flash, just for the strike of the drum but put out enough light that it will show good on a reasonably dark stage. It will obviously only flash through the head and out the bottom unless you have clear shells, so it will not be a direct light that you will see. Check out this video.

[kittmaster]

Originally Posted by JimFiore

The purpose of the diode in the circuit above is to clip possibly damaging inverse voltage across the base-emitter junction (I only put it in because I'm not sure how large the negative peak will be). If you put a diode in series with the base you will simply lower the circuit's sensitivity. You want as much positive potential as you can get (the 3k3 will do the base current limiting).

Completely incorrect.....

[slyone]

Originally Posted by JimFiore

The purpose of the diode in the circuit above is to clip possibly damaging inverse voltage across the base-emitter junction

As drawn, it doesn't quite do that, at least not safely. The diode should be wired to the right of the base resistor, directly across the base-emitter junction. As originally drawn, if the input voltage goes negative, there is no current limit for the diode. The diode shorts the trigger (input power supply).

I'm not sure I see how the LED might turn on with a reverse voltage input tho' unless there's a collector-base breakdown involved.




Lyle

[steve_huck]

have any of you guys seen theese before???

http://www.xoxide.com/sounaccat.html

They are sound reactive cold cathodes for a pc. they sel boxes you plug them into which makes them sound reactive. idk, thought you guys might be interested

[jman 31]

Originally Posted by steve_huck

have any of you guys seen theese before???

http://www.xoxide.com/sounaccat.html

They are sound reactive cold cathodes for a pc. they sel boxes you plug them into which makes them sound reactive. idk, thought you guys might be interested

The problem with that is it would trigger to every sound. We are trying to get something that will only trigger when a particular drum is struck. Nice idea though.

[steve_huck]

ah i see. i think they would be kinda cool to setup on your desk or somethin though.


http://www.xoxide.com/cocasoackit.html

in that link it says that you can change the sensitivity, with the little box things they sell. but i think your right proolly wouldnt work to well

[jman 31]

Originally Posted by slyone

I'm not sure I see how the LED might turn on with a reverse voltage input tho' unless there's a collector-base breakdown involved.




Lyle

Lyle,

Can you expound upon that statement? I don't have any idea what that means as I only dabble in electronics and am not an electrical engineer. Any input that you guys can give in layman's terms would be a lot easier for the rest of us to follow. Diagrams really help a lot!

Thanks,
Jeremy

[slyone]

Originally Posted by jman 31

Lyle,

Can you expound upon that statement? I don't have any idea what that means as I only dabble in electronics and am not an electrical engineer. Any input that you guys can give in layman's terms would be a lot easier for the rest of us to follow. Diagrams really help a lot!

Thanks,
Jeremy

On the main reason for the post, as you have your diode drawn originally it has no resistor in series with it in the situation where the trigger voltage goes negative. The diode will become a short and clamp any trigger voltages exceeding -.7 volts. If there's enough energy in the trigger voltage, the diode will be destroyed rather quickly.

The second was in response to Kittmaster

"As it stands, you'll allow the full postive wave but clamp a -.7 volts which will still effectively turn the led on as you expect, but some circuits will not like the negative voltage."

I don't see the method in which a negative input voltage can turn on the LED unless the negative input voltage and the power supply voltage (9V in this case) add up to exceed the collector-base junction rating of the transistor. That's a large voltage (30V+) relative to the voltages you're working with. In a nutshell, if you exceed the voltage a transistor can withstand, current will start to flow. In your circuit, the only path that might be possible is from collector to base.

Let's say you have a 9V supply. There is then 9V at the collector of the transistor. If you have a trigger voltage go to -6V, then there's -6v at the base of the same transistor. A voltmeter from the collector to the base will show 15V (the difference between the two voltages). If the reverse voltage gets bigger, then the applied voltage at the transistor's collector to base gets bigger too. It has to get beyond the breakdown voltage from collector to base before any current will start flowing. Until current can flow, the LED will never light up. Make sense? The clamp diode makes sure this can never happen.

Lyle