Brighter LED - Page 1
Forum section: electronics / beginners

author: machinehead
author_rank: Newbie
timestamp: May 11, 2021, 02:24:42 am
content: Hi All,I need to replace a Bivar MPR5YD panel mount indicator with something brighter.The supply voltage is 450mVdc and this measurement is limiting my choices as towhat devices I can use. On paper.According to the MPR5YD datasheet the Vf is 2 and the mcd is 4.Should I look for an LED with the same Vf and higher mcd or approach this fromanother slant?I would like to keep this simple and just make the swap, but if not I'm open tosuggestions. One method I'm considering is using an SS relay along with an external(solar) power source.Thanks for your time

author: Jwillis
author_rank: Super Contributor
timestamp: May 11, 2021, 03:38:42 am
content: millicandela (mcd) is the intensity . One thousand mcd =1 candela so the higher the number the brighter the intensity.The MPR5YD is 40 mcd not 4 . Probably a typo .You may be able yo just swap out but make sure the maximum current is equal to or greater. You may have to recalculate any series resistor .

author: JustMeHere
author_rank: Frequent Contributor
timestamp: May 11, 2021, 03:59:47 am
content: The answer is one line above on the datasheet:https://www.mouser.com/datasheet/2/50/MPR5XX-880393.pdfBivar MPR5YD In that part number the D stands for diffused. The one above it is clear. The diffused one is 25 mcd and the clear one is 40 mcd. Look at MPR5YC.

author: rdl
author_rank: Super Contributor
timestamp: May 11, 2021, 04:03:38 am
content: How are you getting this number?I don't think I've ever seen an LED that would actually light up at only 450 mVQuote from: machinehead on May 11, 2021, 02:24:42 am

author: james_s
author_rank: Super Contributor
timestamp: May 11, 2021, 04:04:02 am
content: The supply voltage is 450mV? That doesn't sound right, even the lowest voltage visible LEDs I'm aware of have a forward drop of something like 1.2V. How did you arrive at that value?

author: machinehead
author_rank: Newbie
timestamp: May 12, 2021, 02:08:22 am
content: Thanks for the replies.I measured the voltage at the LED while it was energized and double checked....yesit reads 450mV on my DMM.If it matters, I relocated a garage door sensor LED using the MPR5YD about 20 years agoand it still functions as it did day 1, but unfortunately our vision has not kept up.So yes, this voltage reading is what prompted me to register here looking for advice.Thanks again

author: james_s
author_rank: Super Contributor
timestamp: May 12, 2021, 02:34:13 am
content: I suspect it's being run on either AC or pulsed DC which is fooling your meter. An oscilloscope would tell the full story but it probably doesn't matter, just about any indicator LED ought to work.

author: machinehead
author_rank: Newbie
timestamp: May 12, 2021, 03:02:39 am
content: Thanks JamesNo scope here, but I did use the AC setting on the DMM and measured .75VAC which only confusesme further. I guess I'll try the clear lens for now.The color is not a factor. Would changing the color help at all?Thanks

author: rdl
author_rank: Super Contributor
timestamp: May 12, 2021, 04:40:44 am
content: The MPR5xx looks like just a holder with a standard 5mm LED. The base might be glued but maybe it will unscrew or you could possibly cut it off. That at least will enable you to use any available 5mm LED. Some modern LEDs are insanely bright. But if you do that I'd measure the voltage at the wires with the LED removed before shopping for a replacement. A better idea of how the LED is being powered is needed.

author: james_s
author_rank: Super Contributor
timestamp: May 12, 2021, 07:02:59 am
content: Do you have a true-RMS meter? It's also possible that the average voltage really is 450mV, but it is fed in pulses of greater magnitude.It's been a while since I reverse engineered the remote for my door opener but IIRC it uses AC, I don't recall whether it's 60Hz from the power line or something else, but by clever use of diodes it's able to light the LED and differentiate between three separate buttons using only 2 wires to the remote unit and no fancy digital interface.Something to keep in mind with the mcd ratings of LEDs, they are affected greatly by beam angle. An LED with a really narrow beam will have a much higher mcd rating than the same LED chip with a diffuse lens but it's the same amount of light. It will look brighter if you look directly at it but off axis it will be dimmer. If you want max brightness and cannot change the drive current, look at some of the high efficiency green LEDs, they're right near the peak sensitivity of the human eye and can appear quite bright on just a few mA.

author: brucehoult
author_rank: Super Contributor
timestamp: May 12, 2021, 07:44:31 am
content: Quote from: machinehead on May 11, 2021, 02:24:42 amThat has got to be a higher voltage with a lowish duty cycle. You should check with an oscilloscope not a multimeter.

author: james_s
author_rank: Super Contributor
timestamp: May 12, 2021, 06:50:45 pm
content: No need to check, just try connecting a different LED and see if it's brighter. LEDs are cheap and modern ones tend to be higher efficiency than older ones.

author: machinehead
author_rank: Newbie
timestamp: May 14, 2021, 02:38:22 am
content: Thanks for the inputI'm using a Klein MM600 cheapo, no true RMS available.I did remove the LED and measured 1.41VAC across the leads.I did use the Frequency function and measured 150Hz.Since my last post I've tried two other green LED's with no noticeable gainin brightness and to clarify this is the clearance sensor.I'll try ordering a few others online tomorrow.Thanks a bunch

author: rdl
author_rank: Super Contributor
timestamp: May 14, 2021, 11:09:22 am
content: I bought one of these a while back to use as the power on indicator in a PC I was overhauling. I wanted a "true green" color not that snot yellow-green type. These must be intended for making traffic lights. I had to use something like a 50k resistor to get it dim enough.Kingbright WP7083ZGD/GI got mine from Mouser.https://www.eevblog.com/forum/beginners/how-can-i-determine-the-resistor-value-for-an-unknown-type-of-led/msg2893554/#msg2893554

author: james_s
author_rank: Super Contributor
timestamp: May 14, 2021, 07:22:42 pm
content: Quote from: machinehead on May 14, 2021, 02:38:22 amYou mean the photo beam sensor that reverses the door if something breaks the beam? I don't know if those are all the same but several years ago I reverse engineered mine so I could bypass it as I find those things obnoxious and totally useless as long as you properly adjust the mechanism that reverses the door if it senses excessive pressure. Anyway the way mine worked is the transmitter and receiver are both wired in parallel powered by a current limited source. The transmitter has an oscillator that pulses an IR LED, and then when the receiver receives each pulse it shunts across the supply. A capacitor in the transmitter keeps it powered during the brief moments when the receiver has shunted the supply, and the microcontroller in the opener monitors for a pin toggling so you can't defeat it just by disconnecting or bridging the wires. I wired up a 555 with a transistor to simulate the output of the receiver and mounted that inside the opener itself, it has worked perfectly for years now, no more messing with those stupid sensors that get knocked out of alignment or get covered in cobwebs. The whole requirement for those was a knee-jerk reaction based on one single incident where the opener was improperly adjusted and someone died and suddenly those sensors were mandated everywhere. I hate the things.

author: TimFox
author_rank: Super Contributor
timestamp: May 14, 2021, 08:34:59 pm
content: The rms current into a non-linear load (such as the LED) is less relevant on a pulsed drive than is the mean (average) current. RMS is good for resistive loads. The peak voltage across the LED is a weak function of the peak current, and the mean voltage is useful only for estimating the pulse duty factor. The mean current should correlate with the average optical output.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: May 14, 2021, 10:30:39 pm
content: Green is the color most humans see best. Google said so.

author: machinehead
author_rank: Newbie
timestamp: May 15, 2021, 12:56:52 am
content: Quote from: james_s on May 14, 2021, 07:22:42 pmExactly. I removed the LED from the PCB and moved it to the wall in front of the vehicles.This allows a simpler verification that the vehicles are inside far enough for door closure.Thanks rdl for your suggestion.

author: james_s
author_rank: Super Contributor
timestamp: May 15, 2021, 02:33:11 am
content: Quote from: machinehead on May 15, 2021, 12:56:52 amAnother option is to replace that LED with the LED in an opto-isolator and then use the output of that to control whatever type of indicator you want. There may be enough voltage headroom to put the opto in series with the original visible LED so you get both. You could even use a triac driver optocoupler and use that to control a line voltage lamp mounted in front of the parking spot. A non-invasive solution would be mounting a phototransistor in a light proof box over the indicator LED.

author: machinehead
author_rank: Newbie
timestamp: May 22, 2021, 12:46:47 am
content: Hi All,This update will mark this thread as solved.The replacement LED is a VCC L65DG2L. It's diffused, but the output isexactly what I was looking for.Thanks All