[Dan the audioman]

Ok, so I'm wiring this "trigger box" for my pneumatic potato gun...hehe. Anyway I have three 9 volt batteries in a series to provide the necessary power to activate the air release valve.

I want an LED to come on when I flip a certain "safety switch". However, whenever I wire it up, the LED works for about 5 minutes or so and then burns out. My guess is that 27 volts is way too much for the little LED.

So my question is: do i need to put a resistor in the circuit before the LED? and if so, how many ohms?

If there's anything else that you think that i need to know, please tell me.

Thanks,
Dan

 

[skyskraper]

yeah you need a resistor.

say your led has a drop of 2v and a draw of rougly 20ma at 2v, a 1.2k ohm resistor is about the lowest i'd go, and thats to get full power from the led, i'd probably scale the led brightness down if it was simply an indicator with say a 3.2k or so resistor.

resistor = (voltage source - voltage drop of led)/current draw of led

 

[nikongod]

many ohms.

tangent describes 9in excelent detail) how to select the resistor value for an led based on voltage.

you will probably want several to a "teen" miliamps in the led so it will be daylight visible. but deff not straight off of the battery.

 

[PachmanP]

YES!!!! put a resistor in there.

probably want as large a resistor as you can and still get the LED to light up. Might wanna start around one mega ohm and go down from there but that number is really just a stab in the dark.

 

[Dan the audioman]

Thanks i already fixed it. I put in a 3.3k resistor and it works great.

Thanks for the quick help!

Regards,
Dan

 

[jerb]

for any futer projects you have try an led calculator such as This but there are many others out there aswell

 

[morphie]

pneumatic potatoe gun huh... interesting...

 

[videocrew]

we made a pneumatic tennis ball gun ala american gladiators back in high school.

i'm not sure most of you know all that a bruise can be...

 

[sbelyo]

spud guns are cool.... personally I like the hair spray/striker combo. I like the sound it's kind of like " Pooomf "

 

[Firam]

Quote:

Originally Posted by sbelyo spud guns are cool.... personally I like the hair spray/striker combo. I like the sound it's kind of like " Pooomf "

Funny untill it explodes in your face.

 

[rodentmacbeastie]

I like what we used for water baloons on our house boat trip a few years ago. Took a swivel recliner, some surgical tubing, some fabric for the ballon holder and a couple of pieces of wood. extended the wood in front of the chair and tied the tubing to form a sling shot. We then put the chair on the top deck of the boat and voila! instant turret. One man laoding and firing, double baloon thickness ammo and about a 150 yard range. We had many groups of warring(sp?) boats and ours was the most feared. Could knock an unsuspecting person right off their boat. Way too much fun for childish adults.

 

[blip]

Quote:

Originally Posted by rodentmacbeastie I like what we used for water baloons on our house boat trip a few years ago. Took a swivel recliner, some surgical tubing, some fabric for the ballon holder and a couple of pieces of wood. extended the wood in front of the chair and tied the tubing to form a sling shot. We then put the chair on the top deck of the boat and voila! instant turret. One man laoding and firing, double baloon thickness ammo and about a 150 yard range. We had many groups of warring(sp?) boats and ours was the most feared. Could knock an unsuspecting person right off their boat. Way too much fun for childish adults.

That's awesome! My friends and I have built ballon slings before but nothing that sophisticated.




But we did build a flame thrower one time

 

[sbelyo]

Quote:

Originally Posted by Firam Funny untill it explodes in your face.

I haven't seen one blown up yet... That PVC Glue is super strong

 

[skyskraper]

i have a friend who is missing the top bit of his thumb and index finger from a spud gun, although it was powered by an aerosol can. like anything, its dangerous, but if you do it right it's safe.

about 6 yrs ago i had a water bomb sling similar to rodents, but we used school chairs, mounted on an equipment transport table, we pushed each other around shcool at max speed launching water bombs and fruit 250m + christ i miss high school