Power Amplify Circuit

[Hero999]

Why is that so?

Is it something to do the the voltage used?

 

[Nigel Goodwin]

Why is that so?

Is it something to do the the voltage used?

I've always assumed so?.

 

[ScuzZ]

Updated Circuit

Well with all the elements of the circuit staying the same, I still have not managed to get the relay to switch. It will switch with a current of 100mA, but alas I can not seem to get enough current without using three transistors.

Can anyone help?

 

[Nigel Goodwin]

Well with all the elements of the circuit staying the same, I still have not managed to get the relay to switch. It will switch with a current of 100mA, but alas I can not seem to get enough current without using three transistors.

Can anyone help?

Have you tried the probes in water?, like I said 10Meg is far too high.

 

[ScuzZ]

Yes. That's the value I get. The probes are 0.4mm apart. Made of galvanised steel.

 

[Nigel Goodwin]

Yes. That's the value I get. The probes are 0.4mm apart. Made of galvanised steel.

Are you using distilled water?, simple two transistor darlington circuits have been used since the 1960's and 70's to detect water in just this way. However, trying to drive a relay directly means you need a LOT more output current, perhaps using a third transistor as a relay driver would be a good solution?.

 

[ScuzZ]

It's actually spring water.

I can get Livewire to make the relay go 'on' with three relays. I just thought I made it work with two a while ago. But then had to leave the project and forgot.

 

[audioguru]

The collector of Q1 is not connected to the positive supply, so it doesn't do anything.

 

[ironmanmill]

IS there a difference when using a digital vs a analog ohm meter to measure resistance? No, not according to a guy that calibrates them, they are designed to measure exactly that resistance. N.I.S.T sets the standard! Now are there ones made better? Simply yes, tolerances very, but for 10 meg, Hummm?

 

[Hero999]

ironmanmill,
Nigel_Goodwin is claiming that water doesn't behave like a resistor. Many things don't have a linear relationship between voltage and resistance. Take a red LED for example, try measuring its resistance at 0.6V and it will be very high, measure its resistance at 2V, it will be very low, so low in fact that it might damage the LED.

 

[BeeBop]

Think about what happens to an ionic solution when a DC current is passed through it. You will not get an accurate resistance reading, because the current will affect the ions in solutions. You need to use an AC signal. Water will only conduct when there are dissolved salts present.
Also, your electrode material, depending on what it is, may take part in the reaction. Galvanized (zinc coated) steel is not the best choice - gold would be much better.

 

[Hero999]

I thought carbon wat best since it's the most innert.

I don't know about the AC vs DC argument though other than the fact that electrolysis is unlikely to happen at higher frequencies ad the ions might not have enough time to migrate. Pure water is a pretty good insulator, therefore I would imagine it would behave like a capacitor so at AC the impedance will be a function of the frequency.

 

[BeeBop]

I thought carbon wat best since it's the most innert.

You just might be right about that, I'll have to give that a try.

I do know, that you cannot do it with DC. I tried it until 'I was blue in the face,' and it just wouldn't work. Somewhere on the net, and it was a long time ago when I came across it, there was a molecular simulation program. I used it to pass a current through a NaCl solution, and the result was that the current changed the concentration of ions.

I have a circuit somewhere, but not sure I can find it.

I found this to be true:

t higher frequencies ad the ions might not have enough time to migrate

but even at 1 kHz it worked.

 

[Hero999]

I don't know how long it takes the ions to propagate, I imagine that 10Hz will cause electrolysis but 100kHz doesn't. I don't know what the cut off point is or whether electrolysis just becomes less and less with increasing frequency.