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Old 28th Feb 2019, 11:14 pm   #21
Robsradio
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Default Re: Are there any Ex GPO engineers here? Dorman Lamps

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Originally Posted by julie_m View Post
I'm fairly sure the subject of my little impromptu teardown did not have a light sensor in it; I think the transistors might have been wired in a deadly embrace, dumping the capacitor's contents into the lamp filament and resetting it for the next cycle.

I'm probably going to have to try breadboarding a few circuits now, just to see if I can reproduce it .....
Let us know the results of the breadboard tinkering
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Old 2nd Mar 2019, 4:25 pm   #22
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Default Re: Are there any Ex GPO engineers here? Dorman Lamps

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So near, and good recall, they are 5v 0.09A. I assume they went for 5v to allow for the volt drop within the flasher circuit, I guess the static lamp's bulbs were slightly overdriven.
I seem to remember that torches that ran on 2 D cells had a 2.5v bulb, so maybe that was the practice to slightly overdrive them, maybe for a whiter light?
Yes, most of these road lights used a 5 volt 0.09 amp bulb, miniature centre contact type.
Under a modest load the battery voltage would probably average about 5.5 volts, which together with a little voltage drop in the transistor would run the lamp at about 5 volts.

Various version of flasher circuit existed, many were potted in ordinary candle wax, this being much cheaper than proper potting compound and still fairly effective for a low cost product.

Perhaps surprisingly these bulbs are still available. Apart from the intended use, they are useful whenever a long running light is needed from a 4 cell dry battery. The bulb life is fairly short, but that is actually preferable since it improves the efficiency and gives the most light from the limited and very expensive energy in dry cells.
A single zinc carbon 996 lantern battery should give 100 hours service. Most useful before the LED age.
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Old 2nd Mar 2019, 10:56 pm   #23
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Default Re: Are there any Ex GPO engineers here? Dorman Lamps

I can't remember what I did yesterday, but I can remember the 1970's square metal sided version used 2x ztx500 transistors in a flip flop, no ldr in the circuit by then.
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Old 3rd Mar 2019, 7:49 pm   #24
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Default Re: Are there any Ex GPO engineers here? Dorman Lamps

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Various version of flasher circuit existed, many were potted in ordinary candle wax, this being much cheaper than proper potting compound and still fairly effective for a low cost product.
Yes, I remember 'unpotting' the circuit from the candle wax in a DS Trafilamp back in the late 70s, as I wanted to make indicators for my push bike and for covers I remember using some car wing repeater lights from an Austin 1300 a mates dad was breaking. Happy days
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Old 5th Mar 2019, 1:45 am   #25
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Default Re: Are there any Ex GPO engineers here? Dorman Lamps

Does anyone know about the modern version that you frequently see on long stretches of roadworks? What intrigues me is that they seem to be synchronized such that each one lights after the previous one has. I'm assuming there must be some kind of sensor to detect this as there is surely no way that they have to be placed in the correct order to achieve this effect.
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Old 5th Mar 2019, 9:37 am   #26
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Default Re: Are there any Ex GPO engineers here? Dorman Lamps

I don't know the answer to your question, but I have always assumed that each one (except the first) is triggered by a signal (IR?) from the one in front. If the sequence ran in the other direction (i.e from back to front - not very useful) the next could pick up the light flash from the one behind, but I'm not aware of light being shone on the next one behind.
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Old 5th Mar 2019, 7:42 pm   #27
Brigham
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Default Re: Are there any Ex GPO engineers here? Dorman Lamps

The number of these I've seen running in the wrong order suggests that they are simply timed individually, and lots of folk can't be bothered setting them up properly.
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Old 6th Mar 2019, 5:06 pm   #28
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Default Re: Are there any Ex GPO engineers here? Dorman Lamps

Many of the modern ones are intelligent and form a self-defining mesh network to talk to their neighbours to do the 'strobe' flashing.

They can also be turned-on-and-off, have their colour switched between amber and red, and can report their battery-status wirelessly - rather than needing to be fiddled-with individually by an individual-in-a-hi-viz jacket. The electronics needed to do all this are implemented as a single resin-encapsulated 'blob' fitted to the PCB which also forms the battery-connection plate.
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Old 7th Mar 2019, 11:38 pm   #29
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Default Re: Are there any Ex GPO engineers here? Dorman Lamps

Off topic I'm afraid (only slightly, on basis of their colour!), but I'm sure there's one or maybe two blue Dorman/Unipart Ex-police (presumably) versions of these lamps somewhere in our house. Unsure of their age but they definitely have no light sensing circuit, Use an incandescent lamp and are switched by a push button under a stiff rubber membrane & are made of plastic. They were here when we moved in, I must try and dig them out and see what version of the circuit they use.

Last edited by ekjdm14; 7th Mar 2019 at 11:49 pm.
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