Cheapest multimeter ever!

[128er]

I have one of these cheapy multimeter... the wires going to the leads detached themselves internally from the probes.   

The same happened to my probes. Cheap crap . . .

[Stonent]

Just worth mentioning, the ones that Harbor Freight sell (the Centech brand) have a battery tester position, so I think they drop one of the higher voltage ranges to make room.

[dannyf]

I have used those meters since the 1980s (DT830). They rock in terms of accuracy, as well as value. I still have one with me, with a half detached back cover. This thing gives me no excuse to throw it away.

[Stonent]

I have used those meters since the 1980s (DT830). They rock in terms of accuracy, as well as value. I still have one with me, with a half detached back cover. This thing gives me no excuse to throw it away.

I've had a couple that just seem to wander aimlessly on the ohms range.

[MatCat]

I have a handful of the harbor freight freebies, they do actually work well for basic spot checking voltages and such, never tried measuring 10A through it, I think that would be a bit pushing it, but for a second / third / fourth meter just checking logic voltages, it works just fine.

[dannyf]

I just checked my tool box and I got actually two of them, one DT830B and DM301 (Made in Korea). On a few 2.5v Vref I have (REF3325, LM4040, and two others), the DT830B reads 2.50v spot on, and the DM301 2.48v.

Pretty respective for a meter from the 1980s.

never tried measuring 10A through it

The leads on my DM301 have a resistance of over 1ohm, and super-flexible, . The DT830B leads on the other hand are well made.

[dannyf]

7106 (and 7107) are those chips that totally revolutionized an industry and left in its wake lots of dead analog meters.

Think about what those $5 meters could do, vs. analog meters 10x or 100x of their prices. Not to mention the consistency of those $5 meters: it is tough to mess them up,

[dannyf]

Here is one example of alternative uses of those $5 meters: a digital milliohm meter.

7106 works by converting input voltage to 1000 count proportional to its Vref (100mv). So if you use a reference resistor in serial with your DUT and the Vref is tied to the voltage drop off the reference resistor, you have gotten yourself a resistance meter. If the reference resistor is a precision 1ohm resistor -> a cheap and accurate milliohm meter is yours, for $5 + some soldering.

[facumedica]

That multimeter was my first one! It was rebranded and costed me about $30 (argentinean pesos) like 3 or 4 years ago.  I changed it for a ExTech Ex-330 

[AlphZeta]

Well, I have two of those. One was bought 15 years ago while I was in China, the other one I got from Harbor Freight a couple of years ago. While PCB design changed quite a bit, they are both variant of the good old DT-830 (Mastech/Centech etc). The accuracy of these meters are pretty awful right out-of-box, but can be adjusted (via a trimpot) to be reasonably decent.

For less than $5, they are actually surprisingly forgiving. I think I mentioned it in a thread somewhere on this forum (a while back) that once I was trying to measure mains voltage but forgot that I had left the lead in 10A.... there was a huge spark and a loud bang.... but when everything was said and done,  the only thing that went was the fuse, the meter survived and everything is functional till this day. Because it's cheap, I tend to be quite rough with it... And after 15 years, it's still working!

[dannyf]

the meter survived and everything is functional till this day.

Because those meters usually have a 1Mohm serial resistor on the input.

And after 15 years, it's still working!

They are the best value out there, bar none.

Most of the issues come from crappy Vref generator - sometimes they are simply a pot to the battery. A LM385 or even a TL431 would fix that.

[Rick Law]

There was another post about the DT830 not so long along when another forum member was talking about decoding the LCD to log the data.

Did anyone try that yet?

I am itching to try, I would mind hearing from someone who tried before.

[dannyf]

It is doable to decode multi-com lcds but that not easy;

Two simpler alternatives:

1) use a display adc with pwm output;
2) use a display adc with bcd output - 7135 for example is fairly easy to decode with a mcu. The mcu can then transmitt the data out via a uart. You then have a 20,000 count data logger!

[mariush]

The multiplexing of the lcd segments plus the various levels of voltage would make it hard to actually process and record the segments active on screen.

The old ICL7106 is cheap in quantity (<2$ in 100+) and has seven segment display driver, so it would make it much easier to tap into it and get the value.  But then again, there are others that have built in i2c/spi output for about the same price so why bother (other than a fun spare time project)

[Rick Law]

It is more so for fun.  I have enough 1-2% accuracy logger to use for now.  If the DT830 is 0.1% accuracy, that would be a different story.

I plan to start with a dead calculator.  See how that LCD works and see if I can adapt it to some use.  (It would likely be cheaper to get a 1602 LCD from eBay than revive an 8 digit calculator LCD, but that wouldn't be much fun)

[KC0PPH]

My father bought 10 of them from Harbor Flake for around $2 a piece...

He was able to adjust them all and they are decent little (low precision) meters. IMO the hobbyist should have a few of them for when you need a) a cheap meter, b) something to keep in the car, c) using 500 meters while building/testing/fixing things. I just would not be measuring mains or anything with them... As i recall the transistor testers worked alright as well... Just make sure you keep other quality meters around...

[dannyf]

It is more so for fun. 

The 7107 datasheet suggests that it is a static lcd (single com / backplane). So it is fairly simple: on the polarity change of that com, read all the pins and you should be OK. The lcd shouldn't run very fast so it should work - just lots of pins to connect.

I plan to start with a dead calculator.  See how that LCD works and see if I can adapt it to some use.

You can start with a new calculator: most of those tool shops or large box retailers sell 8/10 digit calculators for a dollar or so -  they have been my preferred source of lcd panels,

[Rick Law]

It is more so for fun. 

The 7107 datasheet suggests that it is a static lcd (single com / backplane). So it is fairly simple: on the polarity change of that com, read all the pins and you should be OK. The lcd shouldn't run very fast so it should work - just lots of pins to connect.

I plan to start with a dead calculator.  See how that LCD works and see if I can adapt it to some use.

You can start with a new calculator: most of those tool shops or large box retailers sell 8/10 digit calculators for a dollar or so -  they have been my preferred source of lcd panels,

Great mind think alike!   I just came back from Walmart and got their $1 calculator, and I then saw your note.  I thought that was worth a try - at least I can decode what is on the display with the display ON on rather dead. 

...then, after I make that one work (or not), with a bit of experience under my belt, I can try the "red-melon" calculator.  (Yeah, is a kid's toy, looks like a red slides of some melon.  Coming from kid/baby toy store,  it probably costed more than a 20x4 LCDs.  Kid/baby store is awful place to find good deals..)

[Rick Law]

My father bought 10 of them from Harbor Flake for around $2 a piece...

He was able to adjust them all and they are decent little (low precision) meters. IMO the hobbyist should have a few of them for when you need a) a cheap meter, b) something to keep in the car, c) using 500 meters while building/testing/fixing things. I just would not be measuring mains or anything with them... As i recall the transistor testers worked alright as well... Just make sure you keep other quality meters around...

I have two of them, normally attached to my power supply - one for Voltage and one on a .1ohm shunt for current.  They run off individual isolated power brick and a 7809.  The AC power adds some inaccuracy, good enough (+- 2 digits max comparing my UT61E running on battery - I am very surprise at how good they are.)

[dannyf]

I am very surprise at how good they are.

Amazing feat of technology,

[morpheus]

Yah, that's the one i have to use.