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--|>|-- = DIODE
A bit heavy on component count but lights evenly independent of lamp
load, choose diodes to match full lamp current. LED is low current
All parts are live, including the LED. For safety don't poke the led
thro the panel, use a plastic holder.
Extra components would be required to meet BS/VDE safety.
I should have said that a low current red led was intended, which will
only drop about 1.5V, should give about 5mA pk.
Power zener good & removes the need for the reverse diode, but I was
thinking of cheap & easily available comps - none at maplin under 5.1V.
. . . but RS do a 5W at 3.3V, so here it is for that option:
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LED - red, low curr
ZENER - 3.3V 3W or greater
eg http://rswww.com code 447-2061 3.3V 5W zener 49p + vat but sadly min
Suitable for use up to 250W load.
Yes. Its horrendously inefficinet tho. You need a diode in addition to
the LED wired in series, and a series resistor. about 22Kohms will do
and at LEAST 2W rated. It will get hot.
Alternatively a capacitor can be used, but tis late and I can't be
bothered to calculate teh value...,
This sounds similar to a concept I used for a fermentation cupboard thermostat.
IIRC it employed the reactance of a polystyrence capacitor placed in series with
an electrolytic capacitor across live and neutral, followed by a diode from their
junction with another electrolytic from diode to neutral. I think it supplied
about 12 Vdc to the temperature controlling chip. Does any of that sound fesible
- and yes it is late here!
Why not use a neon lamp like the ones used in cooker units ? These don't
have to be wired to anything fancy like diodes or heavy resistors. They are
easily obtained and very cheap, and can be wired to live and earth if your
not using an RCD breaker. It can be done remotely from one room to another,
which I do quite regularly to indicate when water heater thermostats are
switching on and off.
Like these ones:
Outgoing mail is certified Virus Free.
Perhaps it is to tell him whether the switch is off before he takes the
blown GLS lamp out to change it?
I've replaced all the filament lamps in the indicators on the machines in my
factories with mains rated LED 'lamps', supplied with the same fittings.
They are a lot dearer, but they are also far more reliable and the savings
on maintenance (most take a disproportionate amount of time to change)
covers the extra cost.
Possibly an indicator for a loft, attic, cellar or cupboard light....
Or perhaps it's to stop the electricity usage when the (unobserved) light is
both off and on simultaneously (junk science meets Schroedinger)
email me at
richard at olifant d-ot co do-t uk
Do you want the indicator to be on when the lamp is on, or would on when
it's off be OK?
I think it's the former you want since you mention an earth. What the
regs say about using the earth as a return for the tiny amount of current
required, I'm not sure, as plenty of electronic equipment uses this method
for RFI suppression.
*Some people are only alive because it is illegal to kill.
Dave Plowman firstname.lastname@example.org London SW 12
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