Flashing LEDs - need comments/feedback

t06afre

Joined May 11, 2009
5,934
Have you taken into account the voltage drop in the NE555P output stage? this is about 2.5 Volt at 200mA. If you have calculated the LED series resistors without taken the latter voltage drop into your calculations. Each LED will have lower current than calculated. You will have less brighter LEDs. But your 555 will probably be inside the 200mA spec
 

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nerdegutta

Joined Dec 15, 2009
2,684
Have you taken into account the voltage drop in the NE555P output stage? this is about 2.5 Volt at 200mA. If you have calculated the LED series resistors without taken the latter voltage drop into your calculations. Each LED will have lower current than calculated. You will have less brighter LEDs. But your 555 will probably be inside the 200mA spec
Well, I got obviously stuck in one lane. And that was the battery lane.

Considering this, there is 125 Ohm difference with my resistors and the "new":

Now:
R = (6 - 3.2) / 0.02
R = 140 Ohm

With dropping 2.5v:
R = ((6 - 2.5) - 3.2) / 0.02
R = 15 Ohm

Hmm De-solder or make new board...?
 

t06afre

Joined May 11, 2009
5,934
It is hard to say what the voltage drop in your circuit actually is. Without measuring it. And for that a scope is needed. .Since you have such a sort pulses. A multimeter will show some sort of average. But the LED seams to be bright so I guess the voltage drop is lower than my 2.5 volt from the data sheet. instead making a new board. It should be quite easy to just put a FET switch on your board. And here I would perhaps use a P channel FET. Since it will invert the HI/LOW time from the 555.
http://www.electronics-tutorials.ws/transistor/tran59.gif
More easy to get short pulses that way with a 555 circuit. I think a about 50 mSec blink is enough.
 

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nerdegutta

Joined Dec 15, 2009
2,684
It is hard to say what the voltage drop in your circuit actually is. Without measuring it. And for that a scope is needed. .Since you have such a sort pulses. A multimeter will show some sort of average. But the LED seams to be bright so I guess the voltage drop is lower than my 2.5 volt from the data sheet. instead making a new board. It should be quite easy to just put a FET switch on your board. And here I would perhaps use a P channel FET. Since it will invert the HI/LOW time from the 555.
http://www.electronics-tutorials.ws/transistor/tran59.gif
More easy to get short pulses that way with a 555 circuit. I think a about 50 mSec blink is enough.
Pictures in post #76, is based on schematic in post #42. This gives me a short HIGH and a long LOW. However:

It should be piece of cake to make a new board, but I've stocked up on IRL2703...
 

t06afre

Joined May 11, 2009
5,934
If you are using the IRL2703 that is N FET you may perhaps do something like this If you want to stick with your original timing base from the first post. The transistor works as an inverter. You do not have to use a 2N2222 I think any NPN will do. I have simulated this. And it should be OK. But test it before making a PCB just in case
 

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nerdegutta

Joined Dec 15, 2009
2,684
Yesterday I put in brand new, really cheap, batteries. 4 AA 1.5v. And I turned it on at 12.22, and figured that it will last until 18.00. About 18.30 I turned it off, and turned it back on this morning at 07:00, when I started to "nerd".

Now, 13 hours later, it is still flashing...

For those who are a little bit beyond interested, I've set up an "live feed" with one of my pc...

http://www.nerdegutta.org:8081<snip>

I will have this on, as long as it flashes. When it dies, I will turn it off, and remove this link. We'll see how long it lasts.

Any bets?:)
 
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nerdegutta

Joined Dec 15, 2009
2,684
... so after almost a week, the LEDs has started to dim. I'm quite surprised it worked so long... I've turned the cam off, and removed the link from the previous post.

Thanks for all the help on this one.

I'm planning to oversize it a bit, with a 12v 4Ah motorcycle.

Any thoughts?
 

iONic

Joined Nov 16, 2007
1,662
I'm planning to oversize it a bit, with a 12v 4Ah motorcycle.

Any thoughts?

It will last much longer.
Hard to say not knowing the specific use of the device, or have you explained it and I missed it?

At least the lead-acid battery is rechargeable...better in the long run for your wallet.
 

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nerdegutta

Joined Dec 15, 2009
2,684
Hard to say not knowing the specific use of the device, or have you explained it and I missed it?
No, I don't think I've explained it... I've started scuba diving, and my navigation skills under water is... Not so good. (I know it will improve with practice and time, but for now...) Sometimes the water is not clear. We see only a few meters in front of us. The thought was to put this blinking device on the anchors rope/ hovering over the anchor, to more easily find the starting point. So far I've tested it a bit, and the theory works.

At least the lead-acid battery is rechargeable...better in the long run for your wallet.
Yes, and I can add some more LEDs:)
 

Wendy

Joined Mar 24, 2008
23,415
Last I calculated it was 120ma with intermittent use, so it is a safe route to use the 555 only.

If you need more LEDs you can always use either a logic level or conventional MOSFET, depending on the power supply level. You could also switch over to a CMOS 555 if you go this route, there will be a minor increase in battery life.
 

Thread Starter

nerdegutta

Joined Dec 15, 2009
2,684
If you need more LEDs you can always use either a logic level or conventional MOSFET, depending on the power supply level. You could also switch over to a CMOS 555 if you go this route, there will be a minor increase in battery life.
I was thinking of using the the same circuit, just adding a MOSFET. Which do you suggest?
 

t06afre

Joined May 11, 2009
5,934
Last I calculated it was 120ma with intermittent use, so it is a safe route to use the 555 only.

If you need more LEDs you can always use either a logic level or conventional MOSFET, depending on the power supply level. You could also switch over to a CMOS 555 if you go this route, there will be a minor increase in battery life.
Bill from the top of head. Is not the CMOS 555 max current about 100mA? I may be wrong here. And my mind is on one 1 week fishing trip/hike in the mountains. Logging out now for one week..
 
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