On Tue, 03 Jun 2008 22:40:48 GMT, PCPaul wrote:
Because pneumatic or mechanical delay switches with outdoor fitting kits
are extortionately expensive, I was wondering if anyone had a good
circuit for making my own...
Ideally a single button press should start a delay timer that activates a
light for a few minutes (to light the way from the garage to the house).
I'm happy enough with digital electronics but my analogue is weak.. it
seems like there should be a way to use mains only for this, with a triac
or SCR to switch the load (1000W) and maybe some sort of rectified feed
to a CR circuit to do the timing. But I'm sure there must be a better
way...
The issue of it being outdoors (basically replacing a dead pneumatic
supposed-to-be-weatherproof switch) is also a problem, but making a
sealed rainproof box with a suitably rated momentary switch shouldn't be
too difficult.
Any ideas?
(I've seen motorised timers in an earlier thread but they were 110V
and in the US - I'm in the UK on 240V 50Hz).
---
View in Courier:
..MAINS-+--------------------------------[LOAD]-+----+
.. |R1 | |
.. [3000R] | |
.. | CR1 FODM [180R] |
.. O +-[1N4007]-+ 3053 | |
.. | | | R2 +-----+ | MT2
.. S1 | --O-|-[1N4007]-+--[30KR]--1|A MT|3-+ MT1
.. | | CR2 | | | /| Q1
.. | | |+ +-2|K MT|4----G |
.. | | [2000µF] | +-----+ |
.. | | CR3 |C1 | U1 |
.. +-|-[1N4007]-+--------+----------------+
.. | |
..MAINS--------+-[1N4007]-+
.. CR4
When S1 closes, the full-wave bridge CR1,CR2,CR3,CR4 charges C1
through R1 and triggers U1, a random-phase TRIAC driver optocoupler
through R2.
http://www.fairchildsemi.com/ds/FO/FODM3052_NF098.pdf
This causes the output of U1 to conduct, triggering Q1, a TRIAC chosen
to handle the mains voltage and the load current.
After C1 has been charged up and S1 opens, C1 then discharges through
R2, keeping the TRIAC driver triggered until the current in its LED
falls below 300µA. When that happens the driver's output will go
open-circuit and the Q1 will turn off with the next mains
zero-crossing.
Here's a little simulation so you can get a feel for the timing and
the values of components needed. Pay particular attention to the
wattages needed for R1 and R2!
Version 4
SHEET 1 880 680
WIRE 272 0 160 0
WIRE 400 0 336 0
WIRE 16 96 -64 96
WIRE 160 96 160 0
WIRE 160 96 96 96
WIRE 272 96 208 96
WIRE 400 96 400 0
WIRE 400 96 336 96
WIRE 576 96 400 96
WIRE -64 160 -64 96
WIRE 576 160 576 96
WIRE 400 176 400 96
WIRE -64 320 -64 240
WIRE 208 320 208 96
WIRE 208 320 -64 320
WIRE 272 320 208 320
WIRE 400 320 400 240
WIRE 400 320 336 320
WIRE 576 320 576 240
WIRE 576 320 400 320
WIRE 160 432 160 96
WIRE 272 432 160 432
WIRE 400 432 400 320
WIRE 400 432 336 432
WIRE 400 512 400 432
FLAG 400 512 0
SYMBOL voltage -64 144 R0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value SINE(0 350 50 0 0 0 500)
SYMBOL diode 272 112 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D1
SYMATTR Value MUR460
SYMBOL res 112 80 R90
WINDOW 0 0 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R1
SYMATTR Value 3000
SYMBOL cap 384 176 R0
SYMATTR InstName C1
SYMATTR Value 2000E-6
SYMBOL res 560 144 R0
SYMATTR InstName R2
SYMATTR Value 30K
SYMBOL diode 272 16 R270
WINDOW 0 32 32 VTop 0
WINDOW 3 0 32 VBottom 0
SYMATTR InstName D2
SYMATTR Value MUR460
SYMBOL diode 336 304 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName D3
SYMATTR Value MUR460
SYMBOL diode 336 416 R90
WINDOW 0 0 32 VBottom 0
WINDOW 3 32 32 VTop 0
SYMATTR InstName D4
SYMATTR Value MUR460
TEXT 406 480 Left 0 !.tran 200 uic
Also, that cap is going to be pretty pricey.
http://www.newark.com/jsp/search/bro...questid=209120
JF