# looking for Circuit Design help

#### george0039

Joined Oct 15, 2008
158
Hello

I tried a search first but could find nothing to match my needs.

I would like to build a dark activated LED; Red, Green or bright white. It would be used for buoys for R.C Boat runs, so they would be in water.

I would like a circuit that would allow me to set the LED to flash and I set the rate OR leave them on constantly until light. It would work off of either a 9v or 2 C cells (good ballast weight).

Any help would be appreciated and I need the circuit to be as physically small in size to fit in the to be build bouys.

George

#### WBahn

Joined Mar 31, 2012
24,981

#### wayneh

Joined Sep 9, 2010
16,129
It seems like adding a flashing circuit to a standard solar garden light might be an easy hack.

#### blueroomelectronics

Joined Jul 22, 2007
1,757
Too bad they don't still make the LM3909

#### george0039

Joined Oct 15, 2008
158
Hi WBahn

Thanks for your reply and link. Ive had a bad few years, recovering from a bad car accident with head/memory issues, still a work in progress.

My therapist says that I should continue slowly with my hobbies and interests to see if it helps with memory and hands use, slowly typing this.

From what I remember, could a 555 I.C do this BUT I also wanted a dark sensor to activate this for night use so basically my club mates could take the bouys put them in a course pattern on the water and forget about them and they would then light at night and be off during the day. From what I read elsewhere, 9v or 2 C cells are used and the C cells are also great for ballast.

Hope someone can help me with a working circuit?

Thanks Again.

George

#### WBahn

Joined Mar 31, 2012
24,981
I would agree that adapting a solar garden light would be a good place to start. You merely need to place a flashing circuit inbetween the LEDs and the rest of the circuitry. Then you can put in a sufficiently large capacitor and/or a rechargeable cell and not have to service the bouys for years at a time.

#### george0039

Joined Oct 15, 2008
158
Hi WBahn

Would not the yard lights have large electronics and a volt. storage device?

I was hopping for a circuit, something in the size of 1" - 2" square ish? That could do what I listed above.

George

#### WBahn

Joined Mar 31, 2012
24,981

George

#### george0039

Joined Oct 15, 2008
158
Hello again

Thanks for the tip BUT like I said in my opening post. Sometimes the flashing would be turned to continuously on, depending on the r.c boat run and contest etc. our boat club desires.

George

#### MrChips

Joined Oct 2, 2009
19,774
Put any number of different colored LEDs, flashing and non-flashing and use a DIP switch to select the desired LED.

#### blueroomelectronics

Joined Jul 22, 2007
1,757
Simplest possible circuit would be a flashing LED, battery & ball switch. Turn it upside down to turn it off. Else if you can find them the LM3909 will run on a single battery for months.

#### george0039

Joined Oct 15, 2008
158
Hi
Im in Ontario, Canada

George

#### MrChips

Joined Oct 2, 2009
19,774
Last time I checked, Ontario, Canada is a pretty big place.

#### george0039

Joined Oct 15, 2008
158
Hi MrChips

Not to sound rude or anything. I dont know you or vice versa. Being asked about specific locations nowadays is a little "off".
George

#### Wendy

Joined Mar 24, 2008
21,914
Here is the link to the circuit I was telling you about. The second link can light the LED continuously by tweaking the first oscillator, but it is efficient enough you don't ever need it to turn off just because of sunlight. I suspect it would last over a year with C cells, more with D cells.

CMOS 555 Long Duration Blue LED Flasher

An even better circuit (but with a shorter battery life):

CMOS 555 Long Duration LED Flyback Flasher

This part of my personal blog on AAC...

Bill's Blog

If turning off with sunlight is a hard core requirement let me know, and I'll show you how to add a LDR (light dependent resistor, AKA CDS cell) to make it responsive to daylight. They are very cheap and easy to use, not to mention fun to play with.

For the other guys, the OP contacted me via email, where I told him I would help, but required a public post to respond.

Mr. Chips is an experienced hobbiest, like me. You will note my location is part of my profile, which helps other people recommend part houses. We usually recommend people do something similar. With my circuit any CMOS 555 chip will work, and you can merge the two CMOS 555's into one CMOS 556. A 7555 or 7556 are good alternate part numbers, and possibly more available.

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#### elec_mech

Joined Nov 12, 2008
1,500
Take a look at the schematic here entitled "LM 3909 Using Components". It's a little less than halfway down the page. You can use 2N3904 for the NPN and 2N3906 for the PNP if you'd like.

If you add a photo-resistor in parallel with the 100uF capacitor, you get a dark-activated circuit. I gave the circuit a try myself on a breadboard and it works well for a diffused red or green LED with 3VDC (didn't work at 1.5V). Didn't have much luck with a white LED, but perhaps adding a transistor to drive the white LED would do it. I can give it a go if you're interested. I found using a 100uF capacitor gave a good blink rate, but using two 100uF caps in parallel to get 200uF gave a much slower rate that you may find better simulates buoy lights.

You should be able to get this onto a 1-2 square inch board. One inch for sure if you opt to use SMT parts.

Some other thoughts are to use a blinking LED with a simple dark-activated circuit. This would reduce the size of the circuit - the only caveat is you would not be able to change the blink rate.

#### blueroomelectronics

Joined Jul 22, 2007
1,757
Hi
Im in Ontario, Canada

George
Me too. If you're in the GTA maybe I could cobble up a microcontroller based design that you could solder together.

E.g. A 8 pin PDIP 12F675 with a CDS or LDR could run a couple of LEDs off a pair of C cells for a very long time. It would be trivial to sequence 4 LEDs.

A store on College st in Toronto called Creatron carries everything you'd probably need. The trick will be the waterproof enclosure.

#### MrChips

Joined Oct 2, 2009
19,774
Hi MrChips

Not to sound rude or anything. I dont know you or vice versa. Being asked about specific locations nowadays is a little "off".
George
There is one member who was in the same building where we both worked. We chatted on AAC and still haven't met.

If you want to send me your location via pm that's ok. I'm in Ont.