FIRST LED signs for purchase!

[Micah Chetrit]

Originally Posted by DonRotolo

I wonder if he can make one with DEDs?
(Dark-Emitting Diodes. When power is applied they absorb the light from the room)

Do DEDs even exist? link please. That would be pretty sweet though.

[matt99199]

lol no DEDs do not exist but if there was a type of device it would be a LRD, light receiving diode

[PAR_WIG1350]

Originally Posted by matt99199

also i will fix the signs for free is something happens to them that is not the customers fault. such as some becoming burnt out for no reason or wires becoming undone. not saying anything will happen but i will fix anything for free.

A current limiting resistor should reduce the risk of the signs burning out, if youu don't already have one in the design.

[matt99199]

i actually figure out the exact amperage of each sign and fit a fuse accordingly

[Micah Chetrit]

Originally Posted by matt99199

i actually figure out the exact amperage of each sign and fit a fuse accordingly

I assume it's a resetting fuse, so we don't have to have extras laying around?

[matt99199]

it is a choice to have any kind of desired, the fuse never really blows so it can just be a slow blow. but if the customer wants a auto or manual reset, that can be arranged

[Alan Anderson]

Originally Posted by PAR_WIG1350

A current limiting resistor should reduce the risk of the signs burning out, if youu don't already have one in the design.

Originally Posted by matt99199

i actually figure out the exact amperage of each sign and fit a fuse accordingly

I infer from your response that you aren't using resistors. If that's true, what do you use to control the current through the LEDs?

[matt99199]

the voltage is balanced by the number of LED's for each color i use

[Alan Anderson]

Originally Posted by matt99199

the voltage is balanced by the number of LED's for each color i use

I asked about current, not voltage. Do you know what the I-V curve of a diode looks like?

If you don't have a way of controlling the current, you can easily end up overstressing the LEDs and burning them out. A simple series resistor is usually good enough, but a fancy constant-current source circuit will keep the brightness much more consistent.

[matt99199]

oh, i misunderstood your comment. i just use a master fuse and 12v voltage regulators.

[Libby K]

Originally Posted by Akash Rastogi

Is the use of the FIRST logo or name for profit legal?

Not unless the OP has asked FIRST already (and as a summer intern for marketing, I can pretty safely say that he has not.)

http://usfirst.org/roboticsprograms/...logo+standards

"FIRST graphics may not be incorporated into any item for commercial sale without written approval from FIRST Marketing. Please e-mail requests to marketing@usfirst.org and allow at least 2 business days for response."

That page also has the FIRST branding and design standards listed. matt99199, if you could adhere to those with your signs (after you contact FIRST, of course), that would be lovely...not to mention legal.

[J@GMFlint]

By just staying with team numbers or names & team logos you can streamline your mfg. and then easily avoid the whole "FIRST" issue, while still providing something cool for the pits.

Something light-weight that can fit safely on the typical pit sign ploes, or hang from curtains would be ideal.

What kind of power supply(s) do you have? Can the signs be battery operated easily? What kind of fonts are available? I think someone already asked, do you have any examples? Sorry we missed checking your sign out at MARC!!

Sounds like a cool idea, keep up your enthusiasm!

[Alan Anderson]

Originally Posted by matt99199

...i just use a master fuse and 12v voltage regulators.

Then you're not controlling the LED current. For a commercial product that ought to last indefinitely, this is not a good way to do things. Please forgive the continued threadjack, but I think the point is important.

LEDs work because of current through them. There is a specific current that is best. The typical way to set that current is to use a series resistor whose value is chosen based on the expected voltage across it. Let's say you have a 12 volt supply and your LEDs drop 2.2 volts. You can put four LEDs and a resistor in series, and the resistor will see 3.2 volts. If you want 40 milliamps to flow, you should use an 80 ohm resistor. It'll be dissipating just over 1/8 watt, so a quarter-watt resistor is appropriate.

If you use five LEDs in the series string, the resistor only sees 1 volt and should be 25 ohms, and only dissipates 40 milliwatts, but you're getting to the point where imperfect tolerances can cause a relatively large variance in LED current. If you try to use six LEDs, the total voltage drop across them is more than the supply voltage, and no current will flow.

If you use five LEDs and no resistor, you'll be putting as much current through the LEDs as the power supply can provide at 11 volts. This is not how you want to treat the LEDs. With a capable power supply, the LEDs will overheat and die.

Commercial LED lamps often use a circuit that supplies a constant current. That's technically the best solution, though it's probably more complicated and expensive than necessary for a simple decoration.

[matt99199]

battery operated can be done, robot batteries also, but i always used a 120v-12v transformer that could control power changes.

any type of font is possible, i use auto cad for most of it, so that is why it looks so good when it is done.

all pictures that i had of other signs where deleted when my system got trashed thanks to ubuntu linux. i only had those others because they where on fb.

as for the resistor stuff, it works fine and would cost way too much with that many of them. i have had these signs running for half a year continuous and nothing went wrong or shorted out. it might be beacuse of the choice of transformer i used. so unless something cateoustrophic happens, i'm not worried about the current flow. another reason they couldn't have a problem is because i undervoltage them. i use 12v but the outcome is 12.6, so if there was a problem with current then the extra LED or 2 would level it out.

[PAR_WIG1350]

Originally Posted by matt99199

battery operated can be done, robot batteries also, but i always used a 120v-12v transformer that could control power changes.

any type of font is possible, i use auto cad for most of it, so that is why it looks so good when it is done.

all pictures that i had of other signs where deleted when my system got trashed thanks to ubuntu linux. i only had those others because they where on fb.

as for the resistor stuff, it works fine and would cost way too much with that many of them. i have had these signs running for half a year continuous and nothing went wrong or shorted out. it might be beacuse of the choice of transformer i used. so unless something cateoustrophic happens, i'm not worried about the current flow. another reason they couldn't have a problem is because i undervoltage them. i use 12v but the outcome is 12.6, so if there was a problem with current then the extra LED or 2 would level it out.

With parallel wiring, one resistor could regulate the current for many LEDs arranged in groups of 4 or 5 in series. It might even be possible to get away with one resistor per color, although higher wattage resistors might be necessary (but I don't know this for sure). Additionally, resistors are probably the cheapest electronic devices in existence ranging from $0.30 each for ten watt resistors down to $0.004 each for a reel of 5000 1/8 watt SMD resistors. 1/4 watt resistors can be found for $0.10 for a package of 10 (not SMD). The LEDs will cost far more than the resistors do by far, so I wouldn't worry too much about the cost of resistors especially when you consider the alternative of having to buy a new set of relatively expensive LEDs.