# looking for Circuit Design help

#### blueroomelectronics

Joined Jul 22, 2007
1,757
I'm game for a meet up over coffee in Toronto.

#### george0039

Joined Oct 15, 2008
158
Hi Mr. Marsden

Thank you for the circuit help. One thing Sorry for the trouble BUT could you include a LDR in your circuit and PLEASE can the circuit shown only operate ONE LED, either Red, Green, Bright White and the circuit could either be adjusted by the user to be flashing OR continuously on until day light and on at dark.

I would like to make several of the circuits for a ed LED and several for a Green LED and some for a bright white LED. So I guess I need one circuit for each.

Thanks again for ALL the Help. Eagerly wanting to start this.

George

#### blueroomelectronics

Joined Jul 22, 2007
1,757
Well lets get some specs and details.

Flash i.e. 2sec on 2sec off.

caveats: an LDR (any analog device) will draw more power (it's got to be monitored and that drains power) than a digital equivalent such as a pushbutton. If a pushbutton could be used to start the device it could go to sleep automatically after several hours, would that be acceptable?. Also an LDR can be fooled when you store the things.

How do you plan to adjust the flashing? What range do you want? How bright do you want them? Remember high power 1-3W LEDs will chew through batteries in hours and require slightly more circuitry where standard 20mA LEDs could last for days.

Note: White LEDs need 3.2V I'd recommend using 3xAA batteries for the supply.

Have you considered just buying solar powered dock lights and putting them on floats?
http://www.solardocklightsonline.com/solarmarinesafetylights.html

#### george0039

Joined Oct 15, 2008
158
Hi bloomroomelectronics

Bill is it? You give me lots to think about. Lets start with the LEDs, I will go with the Regular ones, 20mA. Red, Green, Bright White. I wanted to use the LDR so our club members could just place them in the pool or pond in a course pattern and have them set to turn on at dusk/night then off at light OR if they are retrieved a manual operation of opening the bouy and pushing a switch to turn the circuit off. Then again on for the next time and then view the lights. I think for flashing, I think the 2sec. on and 2 sec. off should be ok as long as you can see the LED on and fully off OR if set by me the LED is constantly on. I guess a flash rate adjuster pot would be great as well as a switch for constantly on at dark.

George

Lots to think about. As for the solar dock lights, well cost, plus wanting to work with circuit construction - wins out.

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#### blueroomelectronics

Joined Jul 22, 2007
1,757
Well if you think it's going to be cheaper...

Anyway lets start with something common, a $20 USB rechargeable bike light from MEC. It has a very bright LED, and 3 modes, normal, bright, flash & off all set with a simple push button. In low quantity and without circuit boards (hand wired) your costs will probably be higher. Case, battery holder, electronics all add up. Plus prototyping, your first device is called a proof of concept, and you'll want to test it before making more. My solution would start with a$1.50 PIC12F629 microcontroller as the support components are simple and few, plus it's a very flexible solution that would be difficult to do with a discreet solution. Something like this.

http://www.talkingelectronics.com/projects/StartHere12F629/StartHere12F629-P2.html

I would make it so the power switch would be a mode switch just like typical bicycle lights, avoiding pots & LDRs.

#### Wendy

Joined Mar 24, 2008
21,914
Sunlight shut down, got it. OK, is being able to switch it on continuously also a hard core requirement?

At a unit cost of 40¢ and no programming I think a 555 or a 556 would be hard to beat. It is the programming, as usual, of the PIC that is a show stopper for beginners in electronics. PICs only seem simple to folks that know them.

#### george0039

Joined Oct 15, 2008
158
Hi Mr. Marsden

If it is possible, YES the option of being switched on at dusk/night, would be great BUT it still has to be able to turn off at daylight or manually be turned off. Not sure if I mentioned that last part? SORRY

George

#### Wendy

Joined Mar 24, 2008
21,914
The question was about continous lighting of the LEDs. This has more significance than you might realize. Red LEDs need 2.5VDC just to turn on, green is a shade higher but close enough, while blue needs 3.0 to 3.5V. With a 3V power supply this is a problem, as you can see. It can be done however.

So, what I would recommend is to have one circuit for red LEDs, and another for blue LEDs, the red LED circuit being the simpler of the two.

Would this work for you?

#### george0039

Joined Oct 15, 2008
158
Hello Mr. Marsden

Slight confusion on my part, I think, I wanted to work with Red, Green, bright white LEDs BUT for each one it would have its own circuit BUT is it possible to run all the circuits from a 9v battery for each one? That would give the ballast weight, somewhat what is needed for a bouy.

I am open to ONLY having the circuits having adjustable flash rates, if that makes things easier? That way at max. adjustment the LEDs would look like their on continuously and could be adjusted down a bit to give them the flashing effect.

George

#### Wendy

Joined Mar 24, 2008
21,914
The thing I was after was long duration. When I think buoy I think in terms of months or years. A larger power supply makes things simpler but won't last as long, a day or two (maybe a week) at most. I have the other parameters set in my head, so the power supply is the last one. You could also go with 3 1½V batteries and it can be both simple and long lasting.

Finding out exact specs needed is always the long part for me. I hate to draw something up and then be told "I need this feature". Often as not it requires a complete redesign.

So, here are the specs as I see them.

1. 1 flash per second, 0.03 seconds long. I can make the flash rate per second variable, pot required. Define the range.

2. LDR Sensor for automatic shutdown during daytime. As far as turning it off a simple switch would work.

3. A 4.5VDC power supply, 3 C cells would last months, perhaps years, AAA batteries would last a fair amount of time, possibly up to a month to several months.

You might want to show me a quick sketch of what the LED setup will look like on a single buoy.

#### george0039

Joined Oct 15, 2008
158
Hello again

Your specs are ok with me, just want to make sure about the flashing rate. Can I have the ability to adjust it so the LEDs will flash on & off noticeably?

As for run life, our club only runs course events for a day/evening or two, the bouys would be removed at the end of each run for security, in a public place you know and put back the next day and used at night.

It would be helpful for longer battery life instead of just lasting a couple of hours then have to change the batteries. A few days of weeks is ok.

George

#### Wendy

Joined Mar 24, 2008
21,914
OK, I'll draw something up. It will probably be done tomorrow, it is Friday night after all.

#### Wendy

Joined Mar 24, 2008
21,914
OK, first effort...

Since I have not built this circuit directly I have a few qualms, which I will explain. It is a direct spinoff of the CMOS 555 Long Duration Minimum Parts LED Flasher, most of the parts are the same.

If you are willing to either remove the batteries or add a simple on/off switch you can use a 2 way switch (DPST), which are much easier to get, and eliminate the off position all together.

R3 is a test select resistor, you find out what works. If the power supply were 9V (as in a 9V battery) then it becomes much more predictable, as it is I am pushing the limits here. While more reliable, the 9V will last much less time. For your needs it may be adequate.

Procedure to test select R3.

1. Calculate R3 with the following formula;

R3 = (4.5V - Vf) / 0.02A

If the battery is 9V then the 4.5V becomes 9V. Red and green LEDs typically drop 2.5V (which is Vf, forward dropping voltage), blue and white LEDs typically drop 3.5V, but there is a wide variation in LED families, even if they are the same part.

2. Get the closest resistor to the calculated resistance. For a blue or white LED this would be 50Ω {(4.5VDC - 3.5V)/0.02A}, which would be 47Ω as a real part. For red or green LEDs this would be 100Ω {(4.5VDC - 2.5V)/0.02A}, which has an exact value. See attached standard values.

3. Switch the circuit to continuous mode, then measure the voltage drop across R3. This will give you the real current with the formula ILED = VR3 / R3. Adjust R3 if more than 0.005A off.

As I said, using a 9VDC makes things more predictable. It is a trade off.

I used a default of 0.03 seconds for on time. This is calculated by
R1 = Ton /(0.7*C1), or
0.03 Sec/(0.7*1E-6) = 42.9KΩ ≈ 43KΩ

I would not use less than 10KΩ for this part. Given that I figured minimum light duration already, it will not be a problem.

Both R1 and R2 sets the off time, using the formula
R2 = (Toff / (0.7C1)) - R1, or
(1 Sec / (0.7 * 1E-6)) - 43,000Ω = 1.39MΩ ≈ 1.5MΩ

So if you increase R1, you increase the on duration of the LED, and shorten the battery life.

If you increase R2, you decrease the flash rate, which increases battery life (but not as significantly).

I may yet build this as a prototype to check its reliability, but then, maybe not. The only reason I have any doubt is as the power supply voltage goes down on the CMOS 555 the drive decreases significantly. See the original article, it explains this in detail.

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#### blueroomelectronics

Joined Jul 22, 2007
1,757
That's pretty nifty. What's the average current draw?

#### george0039

Joined Oct 15, 2008
158
Hi Mr. Marsden

I will go with the removing of the battery, 9v and JUST use the switch for both Flashing and continuous. I just have to make sure I get ALL the parts for a trial circuits, one for RED, one for GREEN and one for Bright White LEDs.

I will be rereading your last post and blow up the circuit in it at the top so that I can see it clearly.

If there is anything you can do to help me with the prototyping of the Three circuits, I would appreciate it.

Can you confirm the parts list, from your post the parts list is:

Battery Clip (Radio Shack catalog # 270-398B)
• One CMOS TLC555 timer IC (Radio Shack catalog # 276-1718 or equivalent)
• C1 - 1 µF Tantalum Capacitor (Radio Shack catalog 272-1025 or equivalent)
• C2 - 100 µF Electrolytic Capacitor (Radio Shack catalog 272-1028 or equivalent)
• R1 - 1.5 MΩ ¼W 5% Resistor
• R2 - 47 KΩ ¼W 5% Resistor
• D1 - Red light-emitting diode (Radio Shack catalog # 276-041 or equivalent)
What is U1 7555 ??? I know its an I.C but its full number ??

Finally, Thank You for ALL your Help and guidance.

George

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#### Wendy

Joined Mar 24, 2008
21,914
That's pretty nifty. What's the average current draw?
Not sure, it is the average that counts. When I ran these experiments back in, what, 09? I measured it but that memory is long gone.

To the OP, the Radio Shack TLC 555 and the 7555 are both CMOS 555s, and are interchangeable (different manufacturers). The battery capacitor will extend the battery life a lot, by removing the surges from the battery and putting it on the capacitor.

If R4 were dropped in value you could probably use a conventional 555 with no problem. I'm thinking 1KΩ to 10KΩ. The life would be very short, a couple of days at most, but it would work.

A common trick for making large prints (in Win XP) is use the photo-viewer that originally brings up the saved image. When you print it it will be a larger image, not to mention it having a zoom feature.

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#### george0039

Joined Oct 15, 2008
158
Hi

Thanks for the update and ALL your help.

George

#### Wendy

Joined Mar 24, 2008
21,914
I want pictures when you are done.

#### george0039

Joined Oct 15, 2008
158
Hi

Posted here? When Im ready, I will then need help to do that as I have no clue how to post pictures here. When Im ready though.

Thanks Again

George

P.S. Been trying to post a new req. for another crt. but the sys. wont do it just goes into limbo??????

#### Wendy

Joined Mar 24, 2008
21,914
Title length is the usual issue, it is a known bug. Put something in shorthand and a moderator (or you) can change it after the post is established. Please PM Bertus about getting your user ID changed.

To attach a document or picture to a post

One of several options will pop up,

Click "Manage Attachments" much further at the bottom of your post,

To upload a file from your computer click "Browse", then select the file.

Schematics should be .gif or .png format, pictures should be .jpg. .jpg formats will fuzz out schematics, and should not be used for that purpose.

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If you want to display this file there is an old thread I made,

How to Display Attachments Full Size