I thought I might be able to simulate this circuit to teach myself how to amplify voltage, but I can't seem to get it to work correctly.

RL1 is a 12v Relay for those attempting to assist me.

I found that even with the 'darlington pair' the voltage is still not enough to activate the relay.

Why is it the more transistors that I place in the array the less the voltage?

How could I get this circuit to work?

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The relay is in the wrong place. It must be connected between 12 V and the collector of the transistor (you need just one). The cathode of the battery and the emitter must be tied to ground (insert a GND symbol). The resistance depends on the collector current, you probably need some kohms.

 

I understand what you're trying to do, but even when I do those things I still can't get the relay to switch.

I can however get it to switch using 3 transistors, like an extended darlington pair.

 

That's because 10M is too high a value, adding a further transistor works because you've then got so much more gain.

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The 10M resistor is to simulate water.

 

So why did you choose 10M?, water is likely to be far lower than that.

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That's what I measured the resistance at.

 

And I bet you used a digital meter to do so!.

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Well I done a fair bit of googling first, but couldn't find anything.

So yeah, poured a glass of water and put the probes of my digital multimeter in.

What's wrong with that?

 

why don't you try fixing your circuit arrangement (moving the relay), changing the 10M resistor to a much lower value, and then using that to get an actual idea of how the circuit is supposed to work, and then put something together and just trying it out?

Your measurement of 10M ohms seems high, unless you are using distilled/deionized water, and/or a terrible electrode setup, in which case your simple transistor setup is probably not going to cut it anyway... A pair of electrodes very close together (or better, overlapped finger pairs on a PCB) would probably be much better.

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Digital meters are pretty useless at measuring resistance, 10M is far too high, unless it's distilled water (and probably too high then as well).

Get the two probes from your darlington, and place them in the water, ensure the relay is in the collector of the transistors, and not the emitter - see if it works then.

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Perhaps you should throw out your meter. I've never had a prolem with measuring resistance on a digital meter, all the resistors I've measred read true to their value and I've even measured 10M reesistors without any problem whatsoever.

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My Fluke digital meter measures resistance perfectly. Its max is 40M and on its lowest range it can automatically subtract the 0.4 ohms of its leads.

My tap water measures 225 ohms. Acid rain might measure higher. Distilled water is nearly an insulator.

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Measuring a resistor out of circuit is fine, but measuring water (or resistors in circuit) is a completely different thing!.

And you don't think that seems rather low?.

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hi,

Using a DVM, measured tap water as 13K to 15K for 1cm probed separation, insertion depth about 1cm.

Measured filtered water [ Brita ] about 1K lower ???

EricG