I need a project. And it needs to occupy a significant...

Kurt_ · Post by **Kurt_** » Tue Mar 04, 2008 2:53 pm

I need some help with the circuit. The output on a 555 only outputs 200mA, right? So if V+ is 12V, how do I bump the 200mA up to 600mA? I was thinking of using a transistor setup, because it requires few parts, but I have no clue how it would work, or how much current I would get out of it.

Can someone help?

Electric Rain · Post by **Electric Rain** » Tue Mar 04, 2008 3:17 pm

The amount of current a 555 can sink is depended on the manufacture. Like I said, you should use a relay. Relays are really pretty simple... They're like electronic switches, and do pretty much exactly what you want. They only require a small amount of current to "activate" the "switch", but the switch can handle MUCH more current.

Better said:

Wikipedia wrote:A relay is an electrical switch that opens and closes under the control of another electrical circuit. In the original form, the switch is operated by an electromagnet to open or close one or many sets of contacts. It was invented by Joseph Henry in 1835. Because a relay is able to control an output circuit of higher power than the input circuit, it can be considered to be, in a broad sense, a form of an electrical amplifier.

Kurt_ · Post by **Kurt_** » Tue Mar 04, 2008 3:29 pm

Okay. What parts do a relay require? Because I have all the transistor parts on-hand.

My timer outputs 150mA

Don't think I'll go with a relay, because they're mechanical. ("Relays cannot be switched on and off at high speeds because they have a slow response and the switch contacts will rapidly wear out due to the sparking.")

Electric Rain · Post by **Electric Rain** » Tue Mar 04, 2008 3:42 pm

None. They are stand-alone devices. You simply energize the coil, and the switch activates. That's it.

Transistors probably won't be rugged enough anyway. When operating larger electro-mechanical devices, you either need to use relays or MOSFETs (big f***ing transistors

) But MOSFETs are really only for if you still need to maintain analog properties and/or high speeds (like a few milliseconds). Relays are just switches that use an electromagnetic coil to pull the contacts together.

Kurt_ · Post by **Kurt_** » Tue Mar 04, 2008 3:55 pm

Some digging in the magical drawers of parts and I found one or two relays (They're Tim's though, and I doubt I can use them) and some mosfets (Also Tim's, but there's a bunch and I'm sure I could take one. A problem is they're all SMT).

A relay does seem nice and simple, but I'm worried that it would be the most likely point of failure in the future.

Putting transistors in parallel would work to boost the current, right?

(Some more digging and I found a transistor that has a 600mA collector current.) With the 150mA from the 555, would the emitter current be 750mA?

Kurt_ · Post by **Kurt_** » Tue Mar 04, 2008 6:28 pm

I know it seems early for a bump, but I'm just so damn pumped for this!

http://www.onsemi.com/pub_link/Collateral/2N4401-D.PDF

That is the transistor I will be using. If the collector receives 12V from a pack of NiMH (providing current significantly over the 600mA rating of the transistor), will the transistor overheat from the excess current, or only allow 600 mA through and everything will be fine and dandy (I'm hoping for scenario #2, however something tells me it isn't that simple).

What voltage and current will I need (applied to the base) to allow the 12V 600-700mA through to the emitter?

Here's my diagram, I need some help on this too (I'm not sure if any of it will work). I'm hoping this setup will instantaneously (As soon as voltage is applied to the circuit) fire a paintball, instead of a delay first. (Firing a paintball = output voltage to transistor assembly).

Note that both are attached to switches. It will be one 3-way 1 on/2 on/off switch, and a tact or something for a trigger will be there as well. I didn't want to make any more mess than I had to, so I focused on the main guts and not little details I can easily do on my own.

(For the values I found this snippet of information, but don't have enough information about the speed of the paintball, how long it will stay in the barrel, or how long the wait in between shots should be to eliminate jamming. Can someone give me rough estimates? A high-speed camera should would be handy for all this...):

These are the formulas we use for the 555 to control the length of the pulses.

t1 = charge time (how long the LED is on) = 0.693 * (RA + RB) * C
t2 = discharge time (how long the LED is off) = 0.693 * RB * C
T = period = t1 + t2 = 0.693 * (RA + 2*RB) * C
Frequency = 1 / T = 1.44 / ((RA + 2 * RB) * C)

t1 and t2 are the time in seconds. C is the capacitor value in Farads. 220uF = 0.000220 F.

typamc95 · Post by **typamc95** » Tue Mar 04, 2008 6:37 pm

audiosurf board
a input device that would change lanes in audiosurf and other pc games when you lean to different edges, and power ups when you lean forward or back. Possibly using a surfboard as a body

vskid · Post by **vskid** » Tue Mar 04, 2008 6:43 pm

Kurt_ wrote:A relay does seem nice and simple, but I'm worried that it would be the most likely point of failure in the future.

You'll probably be able to go through several boxes of paintballs before the relay dies (unless its defective, of course). Theres something messed up with the brake light switch on my Explorer's brake pedal, so it flashes the lights pretty fast if you only push the brake a little (I know, the relays in back aren't insulated for some reason, so I hear them clicking). My brake lights still work, and they've probably gone off and on many thousands of times. Unless you have a money tree to buy paintballs with, you'll probably never shoot enough to kill the relay.

Kurt_ · Post by **Kurt_** » Tue Mar 04, 2008 7:04 pm

But why go through the money and trouble of buying a relay if I have all the parts for a transistor thingie for free right now? Or do all of y'all not know how to use one?

TypamC95: ...what?

Electric Rain · Post by **Electric Rain** » Tue Mar 04, 2008 9:10 pm

Kurt_ wrote:But why go through the money and trouble of buying a relay if I have all the parts for a transistor thingie for free right now?

I already told you why.

See if I ever try to help you again.

Kurt_ · Post by **Kurt_** » Tue Mar 04, 2008 9:29 pm

Fine. Does TI have a sample?

Electric Rain · Post by **Electric Rain** » Tue Mar 04, 2008 9:45 pm

No probably not... freeloader.

Seriously, they're like... less than a dollar if you know where to look. Here, this one should work fine. You'll probably need to buy a few other parts anyway, so it's not like the shipping is going to be a big deal; you'll have to pay it anyway.

Edit: 1337th post! W00t!

Kurt_ · Post by **Kurt_** » Tue Mar 04, 2008 10:28 pm

Well, I did some research I should have done a long time ago. Paintball guns use 800 PSI, which is a tad above what any part is rated for. The absolute lowest I can find is 250 PSI.

So I guess that's out of the question. How disappointing.

Any other cool projects I can do?

Electric Rain · Post by **Electric Rain** » Tue Mar 04, 2008 10:40 pm

Well, there's always the Wiimote arm canon thing I mentioned earlier.

I think you've dismissed this original idea too quickly, though. There are still cheap solenoids out there that can handle that kind of high pressure...

Kurt_ · Post by **Kurt_** » Wed Mar 05, 2008 11:03 am

Maybe it can be done, but not for the price I'm willing or with the tools I'm willing to use.

For something this cool, I'll chip in a good $100-$150 to get it built. But I challenge you to find either ABS pipe that can withstand 850 PSI (It only withstand around 200 PSI), a way to re-enforce ABS pipe to withstand 850 PSI, or a steel lathe/boring tool I can use.

Steel is costly, I'd need to know how to weld (for the ends), and if I mess up I have to start all over again.

And there's plenty of other cool things I can do (Metroid Arm Cannon is not one of them, I don't want to sacrifice a WiiMote)