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Lighthouse Flashing Circuit

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NewcastleSAR

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Hi Folks..

Just joined the form and looking a bit of assistance.

Basically, due to family connections, I'm looking to build a circuit that will simulate the flashing of a lighthouse using an LED. I know there are some circuits on the forum and elsewhere but this is slightly different.

What I would like to use is the solar panel and charging circuit as used in garden lighting with the inbuilt 'dusk' switch so the circuit for the 'flashing' bit basically has to work around 2.4volts. Things get really interesting now as I would like to use a PIC to control the light flashing.

The reason? I know it may be overkill to use a PIC but as most people will know, every lighthouse has its own characteristic 'flash' e.g 2 Light flashes every 6 seconds or 4 flashes every 8 second followed by a 16 second pause before repeating itself.

I've been told that I could use the 16LF628 PIC as it works down to 2.0v I'm interested in peoples views on this.

Am I talking drivel in trying to get this to work. Basically, rather than just having the Garden Light switch them selves on at dusk, I'm looking to add a different slant by have 4 or 5 of thes garden lights flash the sequence of selected 'lighthouse' characteristics as soon as dusk approached. Thes units will all be self charging and activating

Regards

Declan Barry
 
Are you looking to build an a new circuit or just modify an existing garden light?

I recommend you do the latter since it'll be far easier to do.

Why do you want to use a PIC?

You could quite easilly use a CMOS 556 timer to do this, the TS556 will work down to 2V and probably use less current than a PIC.
 
Hero999 said:
You could quite easilly use a CMOS 556 timer to do this, the TS556 will work down to 2V and probably use less current than a PIC.

Would it?, PIC's are also CMOS and use very little current - but either would use so little as to be completely insignificant against the pulsed LED.

Would a CMOS 555 work on as low a voltage as this?.
 
1. You have a valid point.
2. Read the datasheet I linked to in your quote.
 
Hero999 said:
Are you looking to build an a new circuit or just modify an existing garden light?

I recommend you do the latter since it'll be far easier to do.

Why do you want to use a PIC?

You could quite easilly use a CMOS 556 timer to do this, the TS556 will work down to 2V and probably use less current than a PIC.

Hi Hero999..

Basically I'd be looking to modify an existing Garden Light. As it stands, the Garden light charges 2 x 1.2V AA Batteries during the day then when daylight falls below specifc point, the Light comes on. What I am aiming to do is replace the existing LED connection with a circuit which will switch on and flash the characteristics of my chosen lighthouse and at the same time, use the solar cells to recharge the batteries.

This is where I thought the PIC would come in. I'm not well clued up on the design stages but I thought that due to the number of times (or combinations) the circuit had to flash a light and then had a 'timeout' period before repeating the flashing sequence, it may be easier to use a PIC. I've used a program in the school called 'PIC Logicator' which is like a logic flowcharting program along the lines of light on - wait 1.5 secs - light Off - Wait 1.5 secs - Light on - wait 1.5secs - Light Off - wait 8 secs then repeat. This is then transferred to an actual PIC and plugged into the circuit.

Does this make sense or am I using a hammer to crack a nut? Possibly I could use 555 timers with one triggering another and such like but its the 'odd' style of the flashing sequences that may prove awkward with 555 Timers

For instance, if you go to www.cil.ie and click on 'pictures' on the left menu screen and select 'Set 4', Click on the lighthouse St John’s Point, Co. Down You will see that it flashes 2 white lights every 7.5 seconds. Would that be easy to do with 555 Timers? Using the PIC Logicator program, thats easy to do.

Declan
 
I would use the 555s myself though I can see why you like the PIC idea, I personally wouldn't do it as I don't have the tools to program it with.

A 555 is pretty easy, you set one with a one second pulse every 6.5 seconds and the other to a frequency of 2Hz, that'll give you what you want.

The PIC will be more accurate though as it's crystal controlled, but this kind of precision isn't required for this application.

I don't know which works out cheaper though, how much is the cheapest PIC compared to a TS556 + timing capacitors and resistors?
 
Hero999 said:
I would use the 555s myself though I can see why you like the PIC idea, I personally wouldn't do it as I don't have the tools to program it with.

I don't know which works out cheaper though, how much is the cheapest PIC compared to a TS556 + timing capacitors and resistors?

555 would be my PICk too, but I can program a PIC, and have 32Khz xtals for low power (battery if needed). The last couple PICS (not cheapest) I bought were $0.63 US.

So if you can burn a PIC it is not a bad option. You can add extra things to the lighthouse as well. But 555 was the first thing that came to mind.
 
Hero999 said:
I would use the 555s myself though I can see why you like the PIC idea, I personally wouldn't do it as I don't have the tools to program it with.

A 555 is pretty easy, you set one with a one second pulse every 6.5 seconds and the other to a frequency of 2Hz, that'll give you what you want.

The PIC will be more accurate though as it's crystal controlled, but this kind of precision isn't required for this application.

I don't know which works out cheaper though, how much is the cheapest PIC compared to a TS556 + timing capacitors and resistors?

Heh..heh!!

Looked at the price at Farnell - £2.21 for the PIC. May try one anyway. Would you have a circuit that roughly explains what you described above in the quote for the 555?

Regarding the PIC, I have the facilities in the school for programming the chips (technology Department)

Declan
 
NewcastleSAR said:
Would you have a circuit that roughly explains what you described above in the quote for the 555?
Not at the moment, I'll draw one later when I've got the time, but for now here's a clue. Build two monostable circuits with the frequencies I talked about earlier, connect pin 3 of the low frequency one to pin 4 of the higher frequency one. By the way the low frequency one needs to give a one second negitive pulse every 6.5 seconds.

**broken link removed** will help you with the calculations.
 
Cheers..

I'm going to dissasemble the Garden Soalr Light to see what makes it tick and how it can be incorporated into the circuit. Is there any way of getting the 3.6volt solar panel to charge either 3 or 4 AA cells? so that I could use the 555 timer IC?

If I read correctly, the 555 Timer IC works only down as far as 4.5volts so in actual fact I would have to use 4 AA cells if using the 555 IC. In saying that though, I could use 2 Solar cells. They solar panels don't actually have to be enclosed in the same unit as the lighthouse circuit (but would prefer) so they could be set in the garden in such a way that they get maximum sun exposure but don't have long cable runs. What sort of voltage drop would occur this way?

The other thing I was looking at was a voltage doubler. I noticed one on the forum but it was for up to 12v - 15v (LM1577 (LM2577))

Is is feasible to adjust the circuit in th datasheet to use the 3.6 volts from Solar Panel to convert up to 6 volts (or whatever is necessary) to charge a 4.8v battery pack. Sorry if this sounds stupid. I'm just trying to decipher replies regarding voltage doublers.

Declan
 
Last edited:
The original 555 needs a minimum of 4.5V to power it. A Cmos 555 (LMC555, TLC555) operates down to a 1.5V supply voltage and 15V is its max.
 

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How about a 555 to clock a cd4017. You would have 10 outputs to choose your flash/pause pattern from. I think a 4017 needs around 3 volts. All the garden lights I have are 2 cells, or 2.4 volts. I replaced the batteries on one with a 3 cell pack 3.6 volts, works fine. Even replaced the amber LED with a flashing RGB LED, but after about 2 hours, it just flashes red.

I'd stick with the amber LED for you lighthouse, white LEDs are around 3 volts, they'll work, but not very long before the batteries are drained.

Never tied the outputs together on a CMOS chip, so not sure if that's allowed, might need blocking diodes.

Personally, I would stick to the garden light's charging/switching circuit. I built two different designs, but work about the same. When it starts getting dark, it slowly switches in the load. Wastes battery power. If find a circuit that switches between charge/load quick and clean, will post it. Had an idea once about using a voltage reference of the solar panel, and just getting rid of the Cds sensor, but couldn't find the part I was looking for.
 
A 74HC4017 is guaranteed to work down to a 2.0V supply. You can't short outputs together but series diodes can be connected together to make patterns of flashing. Then the diodes drive the base of a transistor through a resistor to turn on the LED. Use a Cmos 555 as its oscillator and the original batteries and charger.
 
Here's a quick circuit on LiveWire. For longer delays between flash might cascade a second 4017 off the Carry. I don't have models for the low voltage versions of the 555 or 4017, this was just illistrate the function. The pin-outs are most likely the same.
 

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HarveyH42 said:
Here's a quick circuit on LiveWire. For longer delays between flash might cascade a second 4017 off the Carry. I don't have models for the low voltage versions of the 555 or 4017, this was just illistrate the function. The pin-outs are most likely the same.

Cheers.. Thanks for that. Must allocate Livewire to my computer at work and see how things progress.

Declan
 
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