FIRST LED signs for purchase!

[O'Sancheski]

Originally Posted by the man

I feel flashing lights wouldn't be to bad, as long as they are some what slow, as most of you might have noticed the robots have a large flashing light on them.

Yes, the robots do have a flashing light on them. But they are nowhere near as bright as an LED sign. Slow flashes still might cause headaches and even seizures.

Awesome idea. Would you be able to make team logos or team numbers?

[matt99199]

yes, any design is possible.

[DonRotolo]

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

Seriously: Thanks for the photos, that looks really nice. Although you probably won't get wealthy making these, for some teams they'll be a nice addition to their pit.

[matt99199]

the goal with these signs isn't as much to make money, its to provide a nice service with minimal cost as possible to make first look good and the customer happy.

[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.

[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.

[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.