I'd like to make a box which accepts 2 mains inputs and outputs mains
if either one of the inputs is on but not if both are on. Any ideas?

Failing this, how would I achieve the same effect with 2 low voltage
inputs?

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Mark wrote:

I'd like to make a box which accepts 2 mains inputs and outputs
mains if either one of the inputs is on but not if both are on. Any
ideas?

Failing this, how would I achieve the same effect with 2 low voltage
inputs?

Hi,
For low-voltage inputs to a low-voltage output, just buy a (VERY
cheap) XOR-gate IC, such as the 74135.

To use mains-voltage instead of ~4.5 volts, although there is perhaps
a better way to do this, I personally would convert the high voltages
to low voltages, use the IC, and then turn them back into a high
voltage output.

To turn mains voltage into a digital logic 1/0 signal, use a
transformer to drop it down to probably, say, about 12V, bridge
rectifier, and a filter capacitor of some kind, followed by a ~5V
zener diode. This'll give you 0V or 5V. You'll need one for each
input.

To turn the output back into mains voltage, use an optoisolated triac.
A basic triac switching circuit is shown he

http://computerchristmas.com/domains...-Schematic.jpg

although I would suggest connecting the input labeled "+5VDC" to the
output of your XOR gate, and the input labeled "to controller" to
common ground. Everything else can stay the same. The MOC-3010 is an
optoisolator; if you get a different optoisolator, you may need to
change the values of the resistors. TR1 is your triac; the diagonal
line is the gate, while the two vertical lines are the main
terminals. It'll probably only work with the main terminals connected
one or the other way around, so if it should be on but isn't, try
switching the main terminals. As the schematic shows, just put in
series with the circuit that would normally consist of the mains
supply and the load.

- --
Chris
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Feed input 1 to relay 1's activating coil which has normally closed contacts, the
input
2 power goes to the contacts of relay 1. Feed input 2 to relay 2's activating coil
which also has normally closed contacts, the input 1 power goes to the contacts of relay
2. If both power inputs are on, both relays will be activated and no power will be
received by the output which is connected to the contacts of both relays. If input 1
is off, relay 1 will not be activated and input 2 will flow to the output, and vice
versa.
QED Roy
"Mark" wrote in message
m...
I'd like to make a box which accepts 2 mains inputs and outputs mains
if either one of the inputs is on but not if both are on. Any ideas?

Failing this, how would I achieve the same effect with 2 low voltage
inputs?