to make an LED blink

[Mark Pitman]

Hi Guys,
I need to make an LED blink 5 seconds on 1 second off, power source 1.2 volt im looking to modify a garden solar powered night light.
Can any one tell me the component I need please.
Regards Mark

 

[Arouse1973]

The blinking bit is the easy bit. The hardest bit is finding an LED that will turn on at 1.2V. Is this an LED module you are planning on using which has a voltage boost circuit inside? What colour LED are you planning on using and the 1.2 volt source where is that coming from?
Adam

 

[(*steve*)]

You might be able to do it by placing a small capacitor across the solar panel and leaking a little of the LED voltage to it. As the circuit sees a voltage from the solar panel it turns off the light. When that leaked away it would turn it back on again.

 

[Mark Pitman]

The blinking bit is the easy bit. The hardest bit is finding an LED that will turn on at 1.2V. Is this an LED module you are planning on using which has a voltage boost circuit inside? What colour LED are you planning on using and the 1.2 volt source where is that coming from?
Adam

Hi Adam, the power source is a button battery 1.2volt charged by solar, the led is white but i was gona just paint it red, in normal use it comes on at night ( which is what i need ) i just need it to blink every 5 seconds ish through the night.
Regards Mark
Ps where abouts to install the component would be good to know too, there are only 4 parts to the hole thing!

 

[Mark Pitman]

You might be able to do it by placing a small capacitor across the solar panel and leaking a little of the LED voltage to it. As the circuit sees a voltage from the solar panel it turns off the light. When that leaked away it would turn it back on again.

It has to run at night! off the battery so no power to the solar cell.
Regards Mark

 

[(*steve*)]

It has to run at night! off the battery so no power to the solar cell.

Yes, that's the entire point. You start with an ordinary battery operated LED garden light.

You leak power back so that the circuit *thinks* there's light and turns off the LED.

You may notice how some of these lights tend to flash at dusk as light from the LED feeds back to the solar panel, this just does that in a more controlled way.

 

[Mark Pitman]

Ah got you now, so con you recommend a capacitor that i can get from say maplines?
Regards Mark

 

[kpatz]

Does your garden light have a photocell to sense daylight or does it use the solar panel?

Maybe "leaking" some of the LED's light to the photocell or solar panel will cause it to cycle on and off. Add a capacitor to slow down the rate of flashing.

Another thing I've noticed with the garden lights we have is when the batteries get weak they start to cycle on and off. Maybe a resistor in series followed by a parallel capacitor after the battery to make it "weak" will cause it to cycle.

 

[BobK]

If these methods worked at all, I don't think you will get satifactory results. Why not just use a blinking LED?

Bob

 

[KiwiSteve]

Hi Mark,

I'm quite new to electronics but I am a seasoned software developer. My approach would be to use an Atmel ATTiny chip and program it with the exact behavior I need. It would probably be just as cheap and use less parts. Just an idea.

Steve

 

[kpatz]

Most pre-packaged blinking LEDs blink faster than 5 seconds on/1 second off. An ATTiny or 6-pin PIC10F part would work great, but would probably draw a bit more current than the existing solar light circuit. You'll also need a boost converter since most electronics including LEDs need a bit more than 1.2V to run (there may be one built in to your garden light).

You might be better off finding a garden light that uses 2 batteries instead of 1, then you'll have ~2.4V to work with without needing a boost converter. If you replace the white LED with a red one, it won't need as much voltage to light up.

How accurate does the flash timing need to be?

You could use a LMC555 CMOS timer IC, with a 2-battery light, it'll work as low as 1.5V.

 

[flippineck]

don't know what this might be, it seems to be some kind of very compact, discrete 3-terminal semiconductor device. maybe something similar could help you, maybe someone might know what it is: http://www.hlj.com/product/hqpbl-unit/Sup

this one's 1.8Hz with a 50% duty cycle so, roughly one second on one second off - not much like the pattern you're after but how critical is it? http://www.optosupply.com/UploadFile/PDF/osxxxs5a31a-w1v_ver.a.3.pdf

this option needs 2.7V - google fairchild fan5646

 

[(*steve*)]

Ah got you now, so con you recommend a capacitor that i can get from say maplines?

This is all guesswork, and may not work at all.

Get a capacitor of between 1uF and 100uF and place it across the solar panel.

Then take a resistor (between 1k and 100k) and connect it between one side of the LED and one side of the capacitor (there are 4 options -- try all of them).

You *may* get flashing. The capacitor will determine how long the LED stays OFF, and the resistor/capacitor will determine how long it stays on.

There will be significant experimentation involved. If you find a way to place a completely light-tight cover over the solar panel (do not remove it) then you'll be able to do your tests other than in the dark.

If you get this working, the flash rate will also be strongly influenced by the ambient light level.