techie question.....

[ean_p]

OK so it may be a sad posting but could some techie out there suggest a circuit that draws almost no currant that could be put in line or parallel to a circuit so as to drive a neon or similar which would indicate when current was flowing and hence show if a mast head bulb was lit or not for example......
thanks
Ian P.

 

[Guest]

I think if you were to wire a small red, yellow or green indicator light in parallel in the circuit, it would indicate that
the circuit or masthead light had burnt out by not being lit itself. Does that make sense? I have this picture in my head but
I'm not sure I'm conveying the right description. Any EE's out there?

 

[salamicollie]

Place a small LED across the positive (after the switch!) and negative. Either use a 12V rated LED (assuming 12V electrics) or use suitable bias resistor.

Suitable LEDs and holders are available from Maplin (www.maplin .co.uk) etc. Draws miniscule amount of current!

 

[jollyjacktar]

What if it was bown?

If it works you can tell by looking at it at night, if it is not working, are you going to climb the mast at night to fix it? Better still carry a spare light that can be hoisted in emergency, can also be pressed into service as a trouble light or emergency lighting. If you have to fit a low powered indicator light use a LED with a 680 ohm resister in series with one of the LED terminals. Note that LEDs are polarized and will not light if connected the wrong way round. This will use practically no power at all. Well it will look pretty and give out a cheerie glow but the best solution is in my first sentence, uses no electricity at all. Good luck.

 

[rogerm]

Sorry, wiring anything in parellel to something else is not going to tell you what the other half is doing. Wiring things in series will but the problem is to keep down the volt drop across the monitoring bit so that as much energy as possible gets to the main bit.

No doubt more than one way can be found of doing the monitoring but one of the 'best' ways is to use a reed switch. This only works well as long as the main thing (masthead light?) draws a fair bit of current, say more than 0.5A.

Buy yourself a (or several) reed switches from Maplin, RS, Farnell. For the lowest current consumption get a 'normally closed' reed rather than the more common 'normally open'. Find (or make) a small cardboard tube which the reed will just fit in. The next bit you need to experiment a bit with since it depends on how much current the load draws and how sensitive the reed is (they vary).
Get some enamelled copper wire of about 16-18SWG and wind (for starters) two to three layers along the cardboard tube.
Connect one end of the copper wire to a 12v source (eg. battery), the other end to your load (bulb or whatever) the otherside of the load to the other side of the 12v source ie all in series. Put a meter across the reed connections (the reed is in the cardboard tube) and check that the reed is off. Disconnect the load and check that the reed switches back on.
If it doesn't work then wind on another layer or two of copper wire. If it works fine then (if you want to 'tune' it) try unwinding some of the copper wire until it doesn't work and then put some back on. Remember not to 'tune' it too tightly or it will stop working when the battery starts running down....

You should find that it will work with a quite small volt drop, well under a volt.
Arrange for the reed switch to operate a peizo sounder or a LED and there you have it.
Roger