Colin,

Why no uP? that were a low pin count uP is the best.
a six pin uP and 3 MOSFET with 3 resistors would fit the bill





> On Apr 1, 2017, at 8:30 PM, CDB <colin@btech-online.co.uk> wrote:
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> I was chatting with someone from work the other day and the conversation=
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> turned to them wanting to put an LED on their quadcopter which had a=20
> strobing light similar to the navigation light on an aircraft, the one=20
> that appears to make quick succession flashes that increase in frequency=
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> making it look like one flash-pause pause next flash - pause -flash.=20
> This would be easy to do with three LEDs in parallell, light LED 1 then=20
> LEDs 1 and 2, then LEDs 1,2,3
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> This got me thinking on how to hypothetically come up with a circuit.
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> The criteria would be:
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> No uP to be used.
> Vcc =3D 5V
> One white high brightness LED
> Flash rate unsure but I suspect around 1 to 2 Hz
> As few components as possible
> Small footprint.
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> Now as I tend to come up with complicated ideas and then work backwards=20
> to simpler ones, I'm looking for comments and other ideas on what I have=
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> thunked up so far.
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> 1. The obsolete LM3909 might fit the bill (still available on Ebay)=20
> except I need 3 flashes per period=20
> (https://www.digchip.com/datasheets/parts/datasheet/321/LM3909-pdf.php)
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> 2. CD4017/74LS90 decade counter + CD4093/74LS00 NAND gates for=20
> oscillator + 1 74LVC1G27 single triple input OR gate chip connecting the=
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> decade counter outputs to the LED.
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> 3. 74LS196 decade counter +  CD4046 PLL driven by  unijunction=20
> transistor the idea being the frequency will change with the sawtooth=20
> pattern and hence the light pattern will change.
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> 4. CD4048 dual retriggable monostable + 555 as oscillator then OR the=20
> two outputs together.
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> 5 Pulse generator using an 74LS10  quad NAND gate + 555 as a clock=20
> generator and OR gate at the two pulse outputs driving the LED.
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> I've just thought, I suppose I could use a dual 555 timer + driver=20
> transistor.
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> I'm sure back in the 80s there were special one chip flasher chips aimed=
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> at toys which did exactly what this circuit needs, but I threw my lovely=
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> paper based Maplins catalogue out years ago (1999 to be precise).
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> Comments welcome.
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> Colin
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> --
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> colin@btech-online.co.uk
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Just my $0.02,

Jean-Paul
N1JPL



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