# I'm going to build a long-life single LED flasher, can you verify my part list?

#### judoGTI

Joined May 26, 2005
25
Hello -

We have had a lot of break-ins in my neighborhood, and although I do have a home alarm system I'd like to setup a single red LED to blink in the windows, to give a visible cue that I have an alarm system to would-be burglars.

I found this circuit design:
http://pigeonsnest.co.uk/stuff/picprog/single-cell-led-flasher-two-year-battery-life.html

And it appears to fit the bill perfectly for what Im looking for. Few parts, long life, could be built very compactly.

The question I have regards some of the parts listed:

LED Flasher Partlist:
100k resistor (1)
1M resistor (1)
10k resistor (1)
4k7 resistor (1)
1M8 resistor (1)
100 resistor (1)
27k resistor (1)
1u capacitor (1)
100u capacitor (1)
2u2 capacitor (1)
BC557 transistor (1) where can I find this? Or suitable replacement?
ZTX869 transistor (1) http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=ZTX869-ND

Is digi-key the best place to get the ZTX869? Looks like I can get 20 of them for about 30 bucks. A little high, but I can live with that.

As for the BC557, it looks like they may not be made anymore? Is there a replacement I can get for this?

I'm a bit of an electronics newb, but I do know a little so I apologize for any beginner questions or mistakes I might make (Ive made my own solar yard lights with a diode, PNP transistor & solarcell & LEDs, but my knowledge doesnt go much beyond that). I appreciate any help/tips you guys can provide. Thanks!!

#### ELECTRONERD

Joined May 26, 2009
1,146
Hello -

We have had a lot of break-ins in my neighborhood, and although I do have a home alarm system I'd like to setup a single red LED to blink in the windows, to give a visible cue that I have an alarm system to would-be burglars.

I found this circuit design:
http://pigeonsnest.co.uk/stuff/picprog/single-cell-led-flasher-two-year-battery-life.html

And it appears to fit the bill perfectly for what Im looking for. Few parts, long life, could be built very compactly.

The question I have regards some of the parts listed:

LED Flasher Partlist:
100k resistor (1)
1M resistor (1)
10k resistor (1)
4k7 resistor (1)
1M8 resistor (1)
100 resistor (1)
27k resistor (1)
1u capacitor (1)
100u capacitor (1)
2u2 capacitor (1)
BC557 transistor (1) where can I find this? Or suitable replacement?
ZTX869 transistor (1) http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=ZTX869-ND

Is digi-key the best place to get the ZTX869? Looks like I can get 20 of them for about 30 bucks. A little high, but I can live with that.

As for the BC557, it looks like they may not be made anymore? Is there a replacement I can get for this?

I'm a bit of an electronics newb, but I do know a little so I apologize for any beginner questions or mistakes I might make (Ive made my own solar yard lights with a diode, PNP transistor & solarcell & LEDs, but my knowledge doesnt go much beyond that). I appreciate any help/tips you guys can provide. Thanks!!
They still make the BC557, at least Phillips does. You don't have to get the ZTX869 at Digi-Key but if you wan't you sure can. Also, note that the 4k7 represents 4.7k in English (Originally British). Don't feel bad for not knowing any of this, I was the same way once in my life too. Never be afraid to ask questions!

#### Audioguru

Joined Dec 20, 2007
11,251
A 2N3906 is the same as a BC557 except the pins are reversed.
Just about any little NPN transistor can be used for the rare Zetex one.

The circuit will not blink an LED brightly, so that its battery lasts a very long time.
For the warning LED on an alarm system you want a very bright blinking lED.

#### Bernard

Joined Aug 7, 2008
5,229
BC557, 10/ $1.00 ; PZT3904 C-E sat 200mV @ 50 mA, gain 100-300, 25 @$.16 ea.[ surface mt.], from The Electronic Goldmine.Prob. dont want SM, but just to show $advantage. #### Wendy Joined Mar 24, 2008 21,840 #### Wendy Joined Mar 24, 2008 21,840 Compared to a circuit designed for the job they actually do draw a lot more power. They are simple though, which will make them attractive for a beginner. Basically all these transistors are operating in the digital mode, which means they are pretty easy to substitute. Thread Starter #### judoGTI Joined May 26, 2005 25 Wow, thank you for the replies. Let me see if I can ask all my followup questions to the right person: ELECTRONERD said: They still make the BC557, at least Phillips does. You don't have to get the ZTX869 at Digi-Key but if you wan't you sure can. Also, note that the 4k7 represents 4.7k in English (Originally British). Do you know where I could find a Phillips BC557? Would it be called just that a 'Phillips BC557'? And 4k7 = 4.7k so does 1M8 = 1.8million? I know probably a dumb question but this is sort of one of those 'measure twice, cut once' things for me. Thanks! Audioguru said: A 2N3906 is the same as a BC557 except the pins are reversed. Just about any little NPN transistor can be used for the rare Zetex one. The circuit will not blink an LED brightly, so that its battery lasts a very long time. For the warning LED on an alarm system you want a very bright blinking lED. The 2N3906 is the same but reversed pins? Im not sure I follow if the transistor has 3 pins how could they be reversed? Or do you mean its a PNP v. NPN thing? How dim do you think the LED will be? Not-usable dim? (of course Ill find out when I build one, but maybe there is a way I can make it brighter and still have a 1 year batt. life?) Benard said: BC557, 10/$1.00 ; PZT3904 C-E sat 200mV @ 50 mA, gain 100-300, 25 @ $.16 ea.[ surface mt.], from The Electronic Goldmine.Prob. dont want SM, but just to show$ advantage.
Im not sure I follow you post at all. Are you saying that a BC557 is the same as a PZT3904? I definitely do not want a surface mnt but would rather have the pin-thru. Can you explain your post a little more for me? Thanks.

Bill_Marsden said:
I have seen several of your posts on here. The reason why I didnt choose your designs is because the first one looks like it was down to less than 10% brightness in less than 1 year. Do you think the same will happen with the link I posted? You contribute a lot to the forums so I'm definitely interested in your opinion. I would be happy with a circuit that would last 12 months and use 2 AA batteries, anything extra would be bonus. Do you think the circuit I posted will exhibit the same dimness after ~6months of usage?

Thank you everyone for your replies.

#### Wendy

Joined Mar 24, 2008
21,840
You did notice it was using AAA batteries? There is a bit of a diff between those tiny suckers and a D cell.

#### judoGTI

Joined May 26, 2005
25
You did notice it was using AAA batteries? There is a bit of a diff between those tiny suckers and a D cell.
Well its using a single AA. So if I throw a D cell (9v right?) I'd be golden?

#### Wendy

Joined Mar 24, 2008
21,840
A D cell is 1½V cell, you will fry this circuit (or any of the LED flashers) with 9V. You will get over a 1 year at 1Hz or less with the D cell, but there are some provisos. The circuit will not work with modern LEDs, unless you're using 2 batteries (both 1½V). The CMOS 555 Long Duration Blue LED Flasher is loosely based off the LM3909 circuit (which is what you have), I explain how it works in the Theory of Operation.

With a AA battery you will not get several years, but several months. The original rating for this circuit was a D cell, which lasts around a year and a bit more.

The reason the LM3909 was retired is LEDs themselves changed. Back when it was invented a red LED dropped around 1.5V, so the LM3909 slight voltage boost (1½V battery to a 2V pulse) lite them just fine. New red LEDs use a different manufacturing process, are much brighter, and drop around 2.5V (sometimes a couple of tenths more). The LM3909 simply won't work with a new LED and a single battery (2 batteries might work).

I think you'll find the flashers I've designed are actually more efficient than a LM3909, in context that they are different technologies, and will last as long with similar batteries.

If you have a source of the older LEDs go for the LM3909 emulation, I am not one to discourage experimentation. If you want to use a modern red LED you will need two batteries.

The CMOS 555 Long Duration Red LED Flasher and a couple of D cells will last for well over a year.

#### rspuzio

Joined Jan 19, 2009
77
> The 2N3906 is the same but reversed pins? Im not sure I follow if the
> transistor has 3 pins how could they be reversed? Or do you mean its
> a PNP v. NPN thing?

I think he's referring to the pinout --- namely which pin on the case connects
to the emitter, which pin to the base, and which pin to the collector.

#### judoGTI

Joined May 26, 2005
25
A D cell is 1½V cell, you will fry this circuit (or any of the LED flashers) with 9V. You will get over a 1 year at 1Hz or less with the D cell, but there are some provisos. The circuit will not work with modern LEDs, unless you're using 2 batteries (both 1½V). The CMOS 555 Long Duration Blue LED Flasher is loosely based off the LM3909 circuit (which is what you have), I explain how it works in the Theory of Operation.

With a AA battery you will not get several years, but several months. The original rating for this circuit was a D cell, which lasts around a year and a bit more.

The reason the LM3909 was retired is LEDs themselves changed. Back when it was invented a red LED dropped around 1.5V, so the LM3909 slight voltage boost (1½V battery to a 2V pulse) lite them just fine. New red LEDs use a different manufacturing process, are much brighter, and drop around 2.5V (sometimes a couple of tenths more). The LM3909 simply won't work with a new LED and a single battery (2 batteries might work).

I think you'll find the flashers I've designed are actually more efficient than a LM3909, in context that they are different technologies, and will last as long with similar batteries.

If you have a source of the older LEDs go for the LM3909 emulation, I am not one to discourage experimentation. If you want to use a modern red LED you will need two batteries.

The CMOS 555 Long Duration Red LED Flasher and a couple of D cells will last for well over a year.
That is awesome info. I think I'll give that a shot. In your design you are using 2 AAA batteries. I read on wikipedia (http://en.wikipedia.org/wiki/D_battery) that D cell has about a 12,000mAh capacity, and a typical AA has 2400mAh. If wanted to adjust for size, could I use 4 AA instead? that would bring the capacity to ~9600mAh right? I think this would work better if I could line up 4 AA side by side, instead of 1 (or 2) round D cells. That will still provide the correct voltage right, but give me extra capacity?

EDIT: Also what is a "One DVM or VOM", multimeter?

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#### Audioguru

Joined Dec 20, 2007
11,251
A D cell is 1.5V just like an AAA cell. But a D cell is huge and heavy and will last 15 times longer than an AAA cell.

An AA cell lasts 2.5 times longer than an AAA cell.

A 9V battery has tiny AAAA cells that last half as long as AAA cells.

#### Wendy

Joined Mar 24, 2008
21,840
DVM = Digital Volt Meter

VOM = Volt Ohm Meter

The VOM was around long before the DBM, both do the same job. One is analog, one is digital. A lot of techs have both.

#### judoGTI

Joined May 26, 2005
25
EDIT: Nevermind! I had a few pins off, corrected those and it works like a charm! Thanks! I have no idea how it works... That will be the next part for me.

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#### Wendy

Joined Mar 24, 2008
21,840
Does look kinda familiar. Are one of the transistors backwards?

Look at Q1.

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#### judoGTI

Joined May 26, 2005
25
Does look kinda familiar. Are one of the transistors backwards?

Look at Q1.
Yeah not its correct. I thought that too but I had to go to a different store for the Q1 because radio shack was out of them. But I verified the EBC all lined up correctly.

It works well. Next im going to get some breadboard and solder up a real one and see how small I can get it to mount in my windows.

#### Wendy

Joined Mar 24, 2008
21,840
OK, the parts list isn't critical. What transistor did you use?