Message 26516 in TECH.WW
From: G8MNY
Date: Fri, 24 Jul 26 06:44:00 Z
Newsgroups: TECH.WW
Subject: Night Light Switch
Message-ID: <140_GB7CIP>
Path: N2MH4|GB7BED|EI2GYB|GB7CIP
R:260724/0653Z 34281@N2MH4.#SENC.NC.USA.NOAM LinBPQ6.0.24
R:260724/0653Z 14775@GB7BED.#21.GBR.EU LinBPQ6.0.25
R:260724/0652Z 56765@EI2GYB.DGL.IRL.EURO LinBPQ6.0.25
R:260724/0644Z @:GB7CIP.#32.GBR.EURO #:140 [Caterham Surrey GBR] $:140_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (New Jan 16)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
This is one of my simple designs to turn on a low power mains lamp when dark.
The Light Dependant Resistor sensor of course, must not see the echonomy lamp
or other lights if it is to work properly.
CIRCUIT
X rated
C1 0u1 4x 1N4001
HOW IT WORKS
The small value of C1 a mains X rated Cap is used as high impedance current
operate the relay. So C1's value all depens on your relay ratings, (C2 50V can
coil. The 100uF C3 gives a slow operation of a second or so, & also damps out
any mains surges with a flame proof 820R surge R too.
The NPN was a BC337 for my >7mA @ 50V needed to drop the high impedance PSU
below the relay hold voltage, but any transistor will do for your V & I and
ratings and high current gain. If higher currents are needed, a darlington or
pair of transistors may be used for low light sensitivity.
Day light striking the LDR causes it to change from a few 10s of Meg ohms down
relay supply voltage gets reduced to just the few volts & then the relay
releases turning the lamp OFF. There is a large hysterisis to this ON/OFF
action, so slight lamp light pickup is not too much problem. The 18K can be
changed for different sensitivities.
The power LED lights all the time, brighter when in daylight. Total Power is
quite low due to the use of C1 as the "power less dropper".
CONSTRUCTION & TESTING
This is a 230V MAINS circuit! Use an isollated supply for testing, and still
keep 1 hand behind your back when you fiddle with it! As drawn most of the
circuit is only at +/- 50V AC above Neutral.
It must housed in a proper insulated box Box and connections insulated too, or
use an earthed metal Box etc. Extra precautions needed for outdoor use, eg.
sealing holes and (or) drilling holes to let water out and box breath etc.
QRM FREE
With no Mains switching Traic, there sould be loaded noise with this unit.
(Other than what the Economy lamp makes!)
See my TECH bul on "Christmas Mains Light Chains" & "Fairy Light Flasher".
Why don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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