Often, the only liquid level indicator you need is your eyes, such as when looking at your cold beverage on a summer’s day. Other times, though, it’s useful to have some kind of indicator light that can tell you the same. [Hulk] shows us how to build one for a water tank using a single IC and some cheap supporting components.
If you’re unfamiliar with the ULN2003, it’s a simple Darlington transistor array with seven transistors inside. It can thus be used to switch seven LEDs without a lot of trouble. In this case, green, yellow, and red LEDs were hooked up to the outputs of the transistors in the ULN2003. Meanwhile, the base of each transistor is connected to an electrode placed at a different height in the water tank. A further positive electrode is placed in the tank connected to 12 volts. As the water raises to the height of each electrode, current flow from the base to the positive electrode switches the corresponding transistor on, and the LED in turn. Thus, you have a useful liquid level indicator with seven distinct output levels.
It’s a neat build that might prove useful if you need to check levels in a big opaque tank at a glance. Just note that it might need some maintenance over time, as the electrodes are unlikely to remain completely corrosion free if left in water. We’ve seen some other great uses of the ULN2003 before, too. Video after the break.
Cool project, great if it solves a real problem at home.
But yeah nah, this has been done to death.
>>> If you’re unfamiliar with the ULN2003, it’s a simple Darlington transistor array with seven transistors inside.
And even if I AM familiar with the ULN2003 – which I am, because it’s a really old part and I’m an old(ish) guy – it’s STILL “a simple Darlington transistor array with seven transistors inside”.
Sloppy handling of IF statements can get you in trouble, even when they aren’t part of a computer program… ;-}
IF I remember properly, the 2003 was used in the Driver Circuit for the Apple ][ Disk Drive Interface..
I loved it when the Chip ‘Blew’ and turn on the Write Head!.. Re-Boot to try and Fix the Drive, with your Dealer Service Diagnostic Disk in the Drive, and would Erase a Spiral across the Face of the Disk, and sit and Spin ad Erase to Boot Track on the Drive..
Always have a Locksmithed Back up of your Dealer Service Diagnostic Disk Handy..
So I’ve been Told.. :)
Cap
Nope, if you aren’t unfamiliar with it, it’s fine if it’s whatever you previously knew it to be which may be equally or more detailed. This only minimally defines it if it’s currently undefined, which can be valid. In terms of crappyCode (TM, patent pending, shipping and handling extra, no returns, not liable for termite damage or acts of dog);
#ifndef ULN
#define ULN
struct uln {
trans darling[7];
};
#endif
Nah, jennings is being pedantic.
He’s trying to say that the part doesn’t care of you’re familiar with it and it certainly won’t change being what it is, depending on your familiarity with it.
Which is of course completely bollocks because that usage of “if” has been around since the birth of English or somewhere around that time.
He’s trying, but I’m trying to be even more pedantic than that, because sometimes that can be fun. I know the part doesn’t change depending whether I know about it or not, but I think that if you’re pedantic enough, then you can find that the original statement never actually implied that it does.
I think that the meaning of the original statement is that if someone does not know what this chip is, then Day defines it as an array of darlington transistors. But if they do know what it is, Day lets them continue to posses the information they already have. For instance, they may know that it has connections and extra parts which cause it not to be the same as seven *completely independent* darlington transistors, and Day doesn’t want to replace their superior knowledge with the simple and very slightly ambiguous definition he came up with. Even if nothing they know is in excess of this definition, he still does not need to replace what they know. So he only tells them what we know if they might not know it, or might know less than it, because they are not familiar with it.
I pull that dad joke level pedantry with waitstaff now and then. “Okay. Thanks, Edith. What’s your name if I don’t need anything?” Surprisingly, they don’t all appreciate the joke. But, I tip pretty well so it’s okay. ;-)
Decades ago I bought from J.C. Whitney (after market car parts company), a “low coolant fluid indicator”. IIRC, it consisted of an LED, a transistor, a resistor, a small housing to appiy to the dashboard, and 2 wires. One wire was placed in the coolant overflow reservoir and the exposed copper end was immersed in the coolant. When coolant level was low enough to expose the wire, the LED lit up.
Cool, but that still didn’t tell you if you were a little low or a lot low. THIS project can.
Serial to parallel chips and a string of these are able to drive pipe organ valves without any diode protection if I remember.
The circuit is simple but not so great by using DC on the electrodes and at high current. They’ll corrode but some metals can make enough voltage alone to turn on a Darlington, as an unintended 1/2 cell.
Running 12VDC to the common electrode means your circuit ground must be isolated, floating from earth ground or again- you get electrolysis.
Automotive low coolant sensors and better water detectors use AC, Corvette included.
Low windshield washer fluid is just DC to a CMOS gate input with 5MEG pullup, uA of current.
That’s what happens with those cheap rain / water / plant moisture sensors.
Capacitance works surprising well for stuff like this. Basically you run some metal (aka duct tape) down the outside of your plastic pipe; those are your plates and the water or air inside is the dielectric. Capacitance value changes with the water level.
OK. It’s real hack. We should give it that.
But that’s an awful choice for the detector amplifier. Even though it’s a Darlington, the base current is atrocious: Around 4 milliamps! Per input! And that’s lost current, not going to the LEDs.
It’s (as mentioned) going to have much more than necessary galvanic corrosion, but it’s also NOT GOING TO WORK in very clean water — it simply won’t be conductive enough (unless you use large electrodes, close together).
You’d be better off skipping the chip entirely here: just connect directly to the LEDs.
It’s have been said already, but corosion will be a problem.
To mitigate it tho, you can use carbon electrodes (like pencil leads).
Also, if you add a NE555, you can pulse the reading, reducing wear by a lot too.
Of course, other methods exists too.