water detector

[spindown]

I have a water detector that lies on the basement floor and sounds an internal alarm if water is present. Problem is I can't hear alarm up in the house. It is powered by a 9 volt battery and the alarm draws 2ma. Can someone refer me to a circuit that would detect the 2ma. current draw and activate a relay that will sound a remote alarm? Thanks Paul

[Chris Smith]

A SCR would do this like a relay. <p>The SCR is actually very much like a relay, in that it triggers with very little effort, dosent draw any power away from the original circuit, and can handle large loads on the out put. <p>The GATE [trigger]is placed into the original signal line, [possibly with a resistor?] and the IN/Out lines can control long leads and larger loads to set off bells and or whistles up stairs.<p>Its a little more complex than this, but its simple to work out.

[philba]

a relay might be a bit of problem as there aren't any, afaik, 9V relays. 12V relays probably wont work and you'll need to drop quite a bit to use a 5 or 6V relay.<p>Here are a bunch of water sensor circuits.
http://www.discovercircuits.com/S/s-water.htm<p>Phil

[haklesup]

Depends on how you plan to sense the 2mA. If you are willing to modify the circuit you have any number of options but usually you need to put a resistor somewhere so you can detect a voltage change. <p>For a non contact or single wire contact, I don't see a simple solution. Another problem is that a relay would kill a 9V battery in no time, the voltage is higher but they tend not to have much capacity. <p>What I would suggest is that you get a Piezo buzzer (high impedance won't use much more current) and simply parallel it with the built in buzzer. You will need to run a wire upstairs though. Possibly use some spare conductors in your phone wiring?

[sofaspud]

I believe Coilcraft manufactures a line of current-sensing inductors. Not sure if they have a 2mA device but it might be worth a look.
If you're not deadset on the current sensing solution, a sound activated switch would likely do the trick.

[philba]

Current sensing transformers would only work if the signal is some sort of oscillation. Also, most magnetic current sensors I've seen have a reasonably high lower bound (1 A). I'm not sure an inline current sense resistor would work at all well - a 1 ohm sense resistor would only develop 2 mV which would be indistinguishable from noise. I'd think that you'd need at least 50-100 mV to reliably sense the signal. 50 mV would take a 25 ohm sense resistor.<p>Given that we don't know anything about the current equipment, its hard to say but if it were up to me, I'd just get a new unit that met my needs (or build one).<p>Phil

[sofaspud]

You're right, philba. I took a quick look at the Coilcraft site and 500mA was the smallest I found, designed for 50/60 Hz and up. I was thinking that the transition from 0 current to 2mA could be detected but that is probably stretching things a bit much. I'd go with the VOX switch. The input transducer could be placed close enough that the threshold would be set above virtually any ambient noise.

[dyarker]

If you mean 2mA with water present, 0mA with no water-<p>Put base-emitter of 2N2222 in series with the 2mA line (watch polarity, base positive relative to emitter). Two wires go to upstairs. One connects to 2N2222 collector, other to emitter.<p>At upstairs end, negative terminal of 6V DC buzzer to collector wire. Positive terminal of buzzer to positive of 4 AA cells in series. Negative of AAs to emitter wire.<p>No resistors needed. The 2mA current won't hurt the transistor, and 0.5 to 0.6V drop of base-emitter shouldn't upset original detector anymore than normal aging of 9V battery.<p>The whole thing is still battery operated for safety, and no common with AC power lines should prevent electrical noise problems (false alarms). To further reduce noise, use twisted pair wire and do not run closely parallel to AC power lines.<p>Cheers,

[Edd]

I also second the pre-suggested idea on the use of a hard wire run of a remoted Piezo sounder. Since with a mere 2 ma current drain on a 9 Vdc supply, that’s what they are using now. However, with this variant, the salvaging of that piezo element from a thrift store $1 smoke alarm unit (Take a battery along to test its voicing), It WILL wake. the dead. You then will only need to differentiate whether its signaling time for a wiener roast or time to get out your hip wading boots.
As also suggested the ring line pair of an already installed basement/upstair phone might be available to utilize …being with the demise of POT’s and their ring line requirements.<p>
73's de Edd
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[spindown]

Thanks to all who replied. I will try your suggestions and get back with you. Paul