Blinking LED's

Thread Starter

Hobby Bob

Joined Jul 27, 2020
14
Hi,

I'm looking to make a very simple device, nothing more than just a puck sized thing with a flashing LED on it.
The intention is to help my granddad who now has difficulty remembering where he's put his keys etc.

I've not done any electronics at school so I have a bit less than basic knowledge, but I expect this little project
should be easy enough. From what I've read on the www it seems that some LED's now have the circuit that
controls the LED {the circuit that controls the flashing} is integrated, my question is...

Is that all that's needed, an LED with an IC connected to a battery ? but how do I chose the right 5mm LED ?

Other than that, it seems LED's work from a wide range of voltages, from 3v to 12v so I'm not sure what battery
voltage to use, or what mcd would be appropriate, it would need to be bright enough to be easily seen without
mesmerizing the cat.

Does that voltage tolerance mean that a 12v battery would last 4x longer than a 3v battery ?
Any help / advice would be appreciated.
Thanks,

Bob.
 

mcardoso

Joined May 19, 2020
193
I've seen LEDs for sale that have built in flashing circuits. All you need is a battery and a resistor to limit the current. Could get fancy with a voltage regulator, but not needed. A coin cell battery would give an OK life. 100mcd chip resistors are plenty bright and I even added extra resistance to dim them.

https://www.adafruit.com/product/680
 

Thread Starter

Hobby Bob

Joined Jul 27, 2020
14
I've seen LEDs for sale that have built in flashing circuits. All you need is a battery and a resistor to limit the current. Could get fancy with a voltage regulator, but not needed. A coin cell battery would give an OK life. 100mcd chip resistors are plenty bright and I even added extra resistance to dim them.

https://www.adafruit.com/product/680
Isn't the resistor built in the IC ?
 

dl324

Joined Mar 30, 2015
12,792
Is that all that's needed, an LED with an IC connected to a battery ? but how do I chose the right 5mm LED ?
If you can find one, an LM3909 would be ideal. All you need besides the LED flasher chip is an LED and a capacitor. It will operate from a single 1.5V battery for months to years.

I built one in a 1"x1"x1/2" plastic box that ran from an N size battery.

Don't know if it will work with blue or white LEDs. I'll try one the next time I come across the thing. Or I'll wire up another because I still have some of those chips in my inventory.
 

djsfantasi

Joined Apr 11, 2010
7,628
Isn't the resistor built in the IC ?
Can’t tell you for sure, because your link asks me to open up a Rapid account. I’m not going to do that.

But from my experience, a 5V LED likely has the resistor built in, because there are no 5V LEDs. That means however, your battery needs to provide 5V. And there aren’t any 5V batteries.

I can’t tell how that LED operates on other voltages, because your link doesn’t work. Without more detailed specs, anything I say will be guesswork.

You could use a voltage regulator or a switching power supply to provide 5V. A constant current supply MIGHT be better, but once again, I can’t tell.

However, in any of these cases, it will take some power to use them, reducing battery life.
 

Thread Starter

Hobby Bob

Joined Jul 27, 2020
14
Thanks for the feedback guys, it's appreciated, I hadn't thought about needing a 5v supply, I'd thought the 5V wasoptimum voltage and that maybe a 3v or even a 9v battery would do the job, as it's current not voltage, far as I know ?

After reading a bit more on the topic it seems that the angle of dispersion and/or defusion are pretty important too.
Sorry that the link didn't work, here's the basics on the LED, seems some LED's draw 10-20mA and some draw just 20uA ?
I guess they must be very small LED's that aren't all that bright ?

Technical Details

  • 5mm diffused RGB LED
  • Two leads
  • Power with 3-3.4VDC
  • Current draw: 10-20mA depending on voltage and displayed color

Thanks Ci139 for suggesting the Key Finder, sadly I fear gramps would need a flashing light to find that too ;-)
What I'm looking at it a puck to attach his keys to, something that he wouldn't need to "look for" it would be hard to miss.

I really do appreciate the help you guys have given me, a fair bit to think about, including the timing of the flashes, the slower the better, I want it to look like a beacon rather than a fast flash alarm, looks like most IC LED's are fast flash, 1hz I guess 1hz is close to a flash per second, the ideal frequency would be a flash every 5 seconds, would that be 5z ?

If with your help I can get this done I might make it my High School Project, my guess is there's a lot of older folks who could use a "beacon" to find stuff.

Bob.
 

dl324

Joined Mar 30, 2015
12,792
looks like most IC LED's are fast flash
You can control flash rate with the LM3909. It's low drain, so you can operate from a coin cell battery if you wanted to. Just use ultra bright LEDs so you get more light at a lower current.

How are you going to get him to carry around a puck sized device to put it wherever he puts his keys? Wouldn't it be a better idea for him to have a routine? Then he'd only have a few places to check.
 

Thread Starter

Hobby Bob

Joined Jul 27, 2020
14
How are you going to get him to carry around a puck sized device to put it wherever he puts his keys? Wouldn't it be a better idea for him to have a routine? Then he'd only have a few places to check.
The idea Dennis is, the "puck" probably smaller though, but along those lines, would be attached to his keys, he doesn't carry his door keys around, he puts them down, and then can't find them, sometimes when he's just a few feet away from them, it seems at times that he doesn't recognise them, that's worrying, but if the keys were flashing like a beacon he would be drawn towards them. Seems a lot of older folks do the same thing, they are looking for something and although it's in plain sight just a few feet away they don't "see" it.

If I can get this "beacon" sorted out it could be useful for a lot of older folks, I was talking to a buddy about it and yesterday and he said maybe the idea could be adapted to remind folks to lock their doors at night time, seems that 2 to 3% of folks forget to lock their front door at night, that's as many as 1 in 30 doors left unlocked when folks go to bed, burglars know that and go round trying doors, just a matter of time before they find an unlocked door.

The adaptation would be a small "device" that could be stuck on the door near the lock that didn't just flash but it started to flash at say 9pm and stayed flashing until the door was locked and the device turned off, well, not fully turned off, but put in sleep mode until 9pm the next day. I guess that would be more complex, involving a timer, but still an achievable project ?

First things first though, back to the mini puck, am I right in thinking that the quoted voltage on a LED is just the optimum of say 3v, if the battery falls below that optimum voltage it would just call for more milliamps ? a sort of sliding scale, a new 3v battery calls for less milliamps but as the voltage falls it calls for more milliamps ? is that what happens ?
 

Bordodynov

Joined May 20, 2015
2,836
I'll put in my two cents. In order to use the three volt battery you need to use a red LED and a short pulse glow (50 ms) and a period of 50 seconds. You should also use an LED with low currents. You can use the MIC1557 small timer to set the pulses. With the CR2032 battery, 1000 hours of operation can be achieved. When using the CR123 battery, 10000 hours of operation will be achieved. If you need, I will develop several flashing beacon options. Using a micro power comparator will increase the operating time by several times.
 

MrChips

Joined Oct 2, 2009
23,239
The problem with this whole scheme is like tying a string around your finger. Now what the heck was I supposed to remember to do?

With a flashing LED how do I remember why that thing is flashing?

There are so many "beeping" things around the house and my poor sound localisation, when something goes beeping I have no idea what's beeping, the phone, microwave, toaster oven, TV? It took me a long time to learn that the first thing to do is go close the fridge door!

Ah! The joys of growing old!
 

dl324

Joined Mar 30, 2015
12,792
First things first though, back to the mini puck, am I right in thinking that the quoted voltage on a LED is just the optimum of say 3v, if the battery falls below that optimum voltage it would just call for more milliamps ?
It depends on how you drive the LED.

If you use the LM3909 that I suggested, it boosts the voltage from a 1.5V battery high enough to light an LED with a higher forward voltage.

With circuits that didn't boost the voltage, the LED would get dimmer as the battery voltage dropped.
 

Thread Starter

Hobby Bob

Joined Jul 27, 2020
14
It depends on how you drive the LED.

If you use the LM3909 that I suggested, it boosts the voltage from a 1.5V battery high enough to light an LED with a higher forward voltage.

With circuits that didn't boost the voltage, the LED would get dimmer as the battery voltage dropped.
Hello Denis, thanks for the explanation, much appreciated, it's a learning process so I appreciate your input.
Bob.
 

Thread Starter

Hobby Bob

Joined Jul 27, 2020
14
Hi Mr Chips,

MC: With a flashing LED how do I remember why that thing is flashing?

I guess the keys being attached to the puck would be a clue ;-)

MC: There are so many "beeping" things around the house and my poor sound localisation, when something goes beeping I have no idea what's beeping, the phone, microwave, toaster oven, TV? It took me a long time to learn that the first thing to do is go close the fridge door!

I hear you, I suppose it's a trade off, most of the things are helpful but we can finish up with input overload.

MC: Ah! The joys of growing old!

Gracefully, hopefully...

Bob.
 

Thread Starter

Hobby Bob

Joined Jul 27, 2020
14
dl324: If you use the LM3909 that I suggested, it boosts the voltage from a 1.5V battery high enough to light an LED with a higher forward voltage.

Forgot to mention, I'm following up on the above, Thanks again.

Bob.
 
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