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Topic: 10 3mm LED Knight Rider light Pro Mini? (Read 543 times) previous topic - next topic

lifeofbrian

I need to build 2x 5 LED knight rider sets for the same RC car, as it has 5x 3mm holes on either side, it doesn't have to be super bright. Is that doable with a Pro Mini? Layman terms please, I'm a total noob.

 :smiley-mr-green:

ieee488


PaulRB

Yes. You can even have the LEDs fade from one to the next as they scan back and forth, instead of flashing on and off. You will just need 2 series resistors, 5 digital pins and 1 pwm pin. I can draw you a schematic if you need one.

lifeofbrian

#3
May 17, 2018, 03:29 am Last Edit: May 17, 2018, 03:33 am by lifeofbrian
That'd be amazing, thanks.

If you're using something like Fritzing, could you post the pic with the physical board if it's no extra trouble. A normal schematic would take me time to work out. I told you I was a noob lol.

Cheers.

EDIT: I just remembered I ordered 10 3mm LED's, not sure if there right or not?:

30° viewing angle, 20mA
5 - 12VDC
15-20mA

Yes. You can even have the LEDs fade from one to the next as they scan back and forth, instead of flashing on and off. You will just need 2 series resistors, 5 digital pins and 1 pwm pin. I can draw you a schematic if you need one.

Grumpy_Mike

#4
May 17, 2018, 07:16 am Last Edit: May 17, 2018, 07:17 am by Grumpy_Mike
Quote
30° viewing angle, 20mA
5 - 12VDC
15-20mA
That is not the way LEDs are normally characterised, you normally have a forward voltage drop at a specific current, like 3.2V @ 20mA. This is normally between 1.2V to 3.8V no higher.

What you posted implies it already has a resistor built in. Can you post a link to where you got them from please?

PaulRB

Lesson #1: post a link and ask here before you buy.

I don't use Fritzing, so I can only give you a proper schematic. It will be a very simple schematic, you won't have a problem figuring out how to wire it up physically.

PaulRB

You will just need 2 series resistors, 5 digital pins and 1 pwm pin.
No, after further thought, that won't work. It would need 4 resistors, 2 pwm pins and 5 digital pins. That's overly complicated and not much of a saving, so let's forget that idea. Just use 5 pwm pins and 10 resistors. Is so simple, there's no point even drawing a schematic!

lifeofbrian

#7
May 17, 2018, 10:58 am Last Edit: May 17, 2018, 10:34 pm by lifeofbrian
Yes, they're already pre wired.

LEDs

That is not the way LEDs are normally characterised, you normally have a forward voltage drop at a specific current, like 3.2V @ 20mA. This is normally between 1.2V to 3.8V no higher.

What you posted implies it already has a resistor built in. Can you post a link to where you got them from please?

PaulRB

#8
May 17, 2018, 12:22 pm Last Edit: May 17, 2018, 12:42 pm by PaulRB
This is how you post a link on the forum.

And did you notice that I have not quoted your entire last post in my post? Please only quote relevant sections of other posts when you need to. Otherwise use Reply.

The picture clearly shows a resistor inside the shrink tubing. Not something cleverer like a constant-current circuit.

The eBay page says voltage between 5V and 12V and current between 15mA and 20mA. This is impossible.

At 12V, to achieve 20mA current, the resistor would need to be around (12-2)/0.02 = 500R

But at 5V, the current would be (5-2)/500 = 0.006A = 6mA, not 15mA

So on the basis that the supplier is promising something impossible, I would not purchase. Fortunately for the supplier, I guess lots of his customers don't know Ohm's Law.

The supplier also says these leds are suitable for use with Raspberry Pi, which is a 3.3V device, so not in range 5V to 12V...

Grumpy_Mike

Quote
Fortunately for the supplier, I guess lots of his customers don't know Ohm's Law.
After seeing that their is no way to report an inaccurate description on eBay I have informed the supplier of his error. So it will be interesting to see if I get a response.

If nothing happens I might be tempted to report him to his local trading standards officer.

PaulRB

#10
May 18, 2018, 12:23 am Last Edit: May 18, 2018, 12:27 am by PaulRB
One of many many suppliers on eBay who don't understand what they sell on a technical level. Most of them don't have local trading standards officers in their countries. Where there are local trading officers, perhaps we should prefer if they focus their time on real criminals & fraudsters, and those who put life or health at risk through ignorance, before going after the relatively harmless, ignorant or lazy sellers.

Grumpy_Mike

Well this seller is in Scotland and surprisingly I got a reply. Unsurprisingly it was less than satisfactory.

The email I sent:-
Quote
To: dtsupplies@hotmail.co.uk
Subject: Incorrect description of eBay Item
 
Sir,
Your eBay item
Pre Wired LEDs 3mm Clear 5V-12V Various Colours/Packs Prewired UK Seller

Has a false description , it says:-
5 - 12VDC
15-20mA

This is a technical impossibility for an LED fitted with a series resistor. This has been causing confusion over on the Arduino forum.

It also says:-
Perfect for Arduino, ATMEL, PIC, PICAXE & Raspberry PI electronic projects
If the minimum voltage is 5V then it can not be perfect for a Raspberry Pi which only provides 3.3V at its output pins.

My suggestion is that it would be better if you just stated the forward voltage of the LED and the size of the series resistor, but if you do want to specify a voltage range then the current range must be correct to comply with the trades description act.

I would be obliged if you were to change the description of this product to a truthful one.

Mike Cook
The answer I received in full:-
Quote
Miss and not Sir thank you.
 
Sent from Mail for Windows 10
Recommendations to avoid this seller.

PaulRB


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