Habor  Freight giveaway DMM test - Page 1
Forum section: electronics / testgear

author: rhb
author_rank: Super Contributor
timestamp: April 08, 2018, 12:11:13 am
content: My free gift of choice at HF is the DMM. I've given away quite a few, but I have 8 of the current red versions. I just tested 8 of them against an LM399 voltage reference. I don't know the actual voltage, but my HP 3478A says is is 6.9113 V.Edit: I used a couple of 5% metal film resistors to make a 68K:1k divider for the 200 mV range.#90899 #1 6.92 V +0.14% 99.2 mV +0.02%#90899 #2 6.93 V +0.29% 99.0 mV -0.18%#92020 #3 6.88 V -0.043% 98.8 mV -0.38%#69096 #4 6.91 V 0.0% 99.2 mV +0.02%#90899 #5 6.89 V -0.29% 98.9 mV -0.28%#98025 #6 6.96 V + 0.79% 99.3 mV +0.13%#90899 #7 6.91 V 0.0% 98.8 mV -0.38%#90899 #8 6.88 V -0.43% 98.8 mV -0.38%3478A 6.9113 V 99.174 mVThere is a trimmer for adjusting the voltage, so I adjusted a couple of older ones I use on a regular basis to read 6.91 V. I'm going to leave the red ones alone and test them again later. These were sitting in an unheated space. I let them warm up, but I'll let them sit a warmer space for the next test.These all have the original batteries and some may be up to 3 years old. Claimed accuracy is 1% + 1 digit. So all are well within spec.I suspect that the AC performance is not as good, but I'll leave that test to another day. I've got a DMMCheck Plus on order, so I'll make more tests when it arrives.My reason for doing this is my concern that the voltnut aberration latent in many of us leads beginners on tight budgets to spend more on DMMs than they should. If you're building things using 5% resistors and 10% capacitors you don't need a 0.01% DMM.Edit: added HF item numbers.Edit: For the benefit of non-USA readers:https://www.harborfreight.com/7-function-digital-multimeter-90899.html

author: james_s
author_rank: Super Contributor
timestamp: April 08, 2018, 12:35:43 am
content: Imagine how impressive those specs would have sounded 30 years ago, a DMM that good would have cost at least $100, which was a significant amount of money back then.

author: rhb
author_rank: Super Contributor
timestamp: April 08, 2018, 12:53:11 am
content: I have a Radio Shack Micronta DMM I bought which now has a dead LCD. IIRC it was about $70. I did have the good fortune to calibrate is against a high end calibrator before the LCD died. Before that, my good meter was a 50k ohm Micronta VOM.The biggest deficiency of the free HF DMMs is they are only 1 Meg input impedance, so if you want an accurate measurement you need to take that into account in many cases.At just short of 65, I've finally loosened the purse strings and am buying things I've wanted for 40 years. Monday my spectrum analyzer, an HP 8560A should arrive. But I am acutely conscious of what it is like to not have access to the test gear you need. My degrees are in English and geology, so getting access to an EE lab was not an option.As I learned more, I realized that there are other ways of accomplishing tasks without fancy equipment. But a lot of people, my father was the worst, tell you all the reasons you can't, rather than how you can. And more importna, failure is OK as long as you keep trying until you succeed.

author: 001
author_rank: Super Contributor
timestamp: April 08, 2018, 09:06:43 pm
content: what is "Habor Freight giveaway DMM"? Is it local US meme?

author: james_s
author_rank: Super Contributor
timestamp: April 08, 2018, 09:10:12 pm
content: There's a store called Harbor Freight known for selling inexpensive Chinese tools, there's a similar place in the UK called Machine Mart. They often have coupons for a free item with purchase and one of the common items in the coupon is a multimeter that normally sells for something like $7.99. They're pretty handy as a backup meter, I keep one in my car that has come in handy on more than one occasion.

author: 001
author_rank: Super Contributor
timestamp: April 08, 2018, 09:26:01 pm
content: Is it "classic" ICL7103 based unit?

author: james_s
author_rank: Super Contributor
timestamp: April 08, 2018, 09:29:30 pm
content: I've never opened one up but I'd bet money it's a "classic" black blob of epoxy over an unknown die unit. Who can say what the IC actually is?

author: IanB
author_rank: Super Contributor
timestamp: April 08, 2018, 09:42:28 pm
content: Quote from: james_s on April 08, 2018, 09:29:30 pmIt's the most minimalist circuit board possible, with of course the obligatory black blob, and as few additional parts as ingenuity can manage. Every new revision has fewer parts than the previous one. One day, even the trim pots will disappear.Nevertheless, if you adjust the trim pot carefully, the meters are rather stable and usable.

author: rhb
author_rank: Super Contributor
timestamp: April 08, 2018, 09:58:02 pm
content: Here it is in all it's glory. It uses an "IC1". I have them all over the place. Toolboxes, battery drawer, etc. I prefer the older yellow P30756 which used the rotary switch to turn it off. I've had one actually die out of the large number I bought on sale for $2.99 before they started giving them away. The biggest problem is the test leads breaking.

author: james_s
author_rank: Super Contributor
timestamp: April 08, 2018, 10:01:58 pm
content: That is remarkably simple. I find it interesting that they have a pad layout for an actual IC there, I assume some of them must have had that instead of the blob.

author: rhb
author_rank: Super Contributor
timestamp: April 08, 2018, 11:01:12 pm
content: Here are two older yellow models. The first is the rotary switch OFF. The second is identical to the red one on the outside. It appears to be the same mold, just different color plastic.

author: rhb
author_rank: Super Contributor
timestamp: April 09, 2018, 02:28:50 pm
content: I was fiddling with a wonky Fluke 8000A last night. Probably dirty switch contacts, but I'm out of contact cleaner. The Fluke is a 70's vintage 0.1% DMM. It's really not worth fiddling with except as an amusement. People seem to ask ridiculous prices for them on eBay for some reason. But it got me to thinking about the calibration of these things.The traditional poor man's voltage reference is a new dry cell. So I measured a few with my 3478A this morning. The 3478A was last calibrated in 2004, so on an absolute basis the numbers don't mean a lot, but I thought they might be useful. The trim pot on the HF DMMs will get them to within 0.1% with a little fiddle. A 4-6 cell battery holder rewired to place the cells in parallel should do well. I suspect that Conrad Hoffman's mini-metrology lab series mentioned this. While technology has changed a lot, it's a great set of projects for the novice interested in electronics or anyone on a tight budget.1.631051.630721.630711.631451.631181.630751.631121.630661.631131.630341.631011.63173Mean: 1.630982StdDev: 0.000396It appears to me that this would be good enough to calibrate the HF DMMs to 0.1%. I find that quite remarkable for the price. They certainly did not give away Fluke 8000As with any purchase.

author: rsjsouza
author_rank: Super Contributor
timestamp: April 09, 2018, 03:51:20 pm
content: Quote from: james_s on April 08, 2018, 12:35:43 amThey were breakthrough - the Fluke 8020A cost US$169 in 1977 dollars (referencehere). Well, 40 years ago.Quote from: james_s on April 08, 2018, 09:29:30 pmDue to the external circuitry and the availability of some models in PLCC package that fit the pads, it is certainly an ICL7106 which is a slight variation of the Fluke-designed IC (and surreptitiously re-sold by Intersil) for the 8020A above - good storyhere.Quote from: IanB on April 08, 2018, 09:42:28 pmThey already did. Check:https://www.eevblog.com/forum/reviews/harbor-freight-cen-tech-90899-small-teardown/msg655719/#msg655719

author: rhb
author_rank: Super Contributor
timestamp: April 13, 2018, 01:09:33 am
content: FWIW I got a freshly calibrated DMMCheck Plus unit from Doug Malone today. Despite the cal sticker saying 2004, my 3478A was spot on 5.0000 Vdc so the HF DMM absolute errors I calculated are correct. Time to trim them all to 0.1%. I am quite amazed.

author: james_s
author_rank: Super Contributor
timestamp: April 13, 2018, 01:48:31 am
content: It would be interesting to leave one in the toolbox, keep one bouncing around in the trunk of the car, one on the bench out in the garage, etc and check them all a year later to see how the stability has held up.

author: rsjsouza
author_rank: Super Contributor
timestamp: April 13, 2018, 01:55:54 am
content: To have a baseline, find some Flukes and leave them on the same places. Then you can have a more solid base for comparison!

author: Brak
author_rank: Contributor
timestamp: April 13, 2018, 04:34:08 am
content: Quote from: james_s on April 08, 2018, 12:35:43 amHarbor Freight stuff has "Item Numbers". There are at least 5 different item numbers for these free meters, I assume there are at least 5 different manufactories making them and they buy from whomever offers the lowest price.I figured out how to add a trim pot to to item number 98025 if anyone's interested.It worked for me, no guarantee.

author: nanofrog
author_rank: Super Contributor
timestamp: April 13, 2018, 05:23:50 am
content: Quote from: 001 on April 08, 2018, 09:26:01 pmThey're commonly known as DT830/DT830B. Variations can include backlights or offer different means of turning it On/Off (some use a separate switch, and others use the range switch). Case colors vary too (seen them in black, yellow, blue, and red).Off position on the range switch:Separate On/Off switch (Cen-Tech is Harbor Freight's branding):Separate On/Off switch + backlight button in upper left corner:As per the IC, I think it may actually be aFortune FS970X.Regardless, they're usable in low voltage circuits and make great panel meters at little to no cost.

author: 001
author_rank: Super Contributor
timestamp: April 13, 2018, 06:29:59 am
content: Fortune chip is 5000 counts/ But dt830s are 1999

author: james_s
author_rank: Super Contributor
timestamp: April 13, 2018, 07:27:39 am
content: Quote from: rsjsouza on April 13, 2018, 01:55:54 amWe already know the Flukes don't drift. There are many thousands of them in harsh daily service with field techs and industrial electricians.

author: nanofrog
author_rank: Super Contributor
timestamp: April 13, 2018, 10:40:09 am
content: Quote from: 001 on April 13, 2018, 06:29:59 amI noticed that as well.Keep in mind however, it's possible to truncate digits. For example, some bench meters allow users to do this in order to obtain faster readings when additional resolution isn't necessary.FWIW, I found someschematicsthat indicated the IC was in fact the Fortune FS970X. Saw some others that indicated it was a 7106; assuming this is the Renasas/Intersil part (ICL7106), it's just an LCD driver that happens to be obsolete.I'm currently not aware of another chip that would allow them to meet the price point these meters go for.Would be interesting to know of if available though (I'm nosy).

author: 001
author_rank: Super Contributor
timestamp: April 13, 2018, 10:56:00 am
content: ICL7106 DIP is still avaliable at local store for about $2

author: Fungus
author_rank: Super Contributor
timestamp: April 13, 2018, 11:13:22 am
content: Quote from: nanofrog on April 13, 2018, 10:40:09 amIf you google "DT830B schematic" the chip you see is ICL7106.Quote from: 001 on April 13, 2018, 10:56:00 amThere's multiple manufacturers of that chip so you can bet there's Chinese clones, too.There's no way they can be paying more than a few cents for the IC in a giveaway meter.

author: nanofrog
author_rank: Super Contributor
timestamp: April 13, 2018, 11:38:35 am
content: Quote from: Fungus on April 13, 2018, 11:13:22 amFWIW, I hadn't seen any of the schematics (DT830B) using the ICL7106, but I didn't check all of them either.If there are clones of that chip that only cost a few cents (would expect so, but not aware of any), that would definitely make sense. As you say, these things are effectively giveaways, so have to be super cheap to manufacture (and still make a profit).

author: nanofrog
author_rank: Super Contributor
timestamp: April 13, 2018, 12:24:28 pm
content: Quote from: blueskull on April 13, 2018, 11:43:04 amOut of curiosity, who makes it?I ask as I've a really tough time figuring out Asian IC manufacturers and what they offer. So any clues/resources that would help figure this stuff out would truly be appreciated.

author: Fungus
author_rank: Super Contributor
timestamp: April 13, 2018, 01:09:20 pm
content: Quote from: rhb on April 08, 2018, 09:58:02 pmThe secret is to squirt some hot glue into the top of the probes (the open tube part).

author: rhb
author_rank: Super Contributor
timestamp: April 13, 2018, 01:12:10 pm
content: Quote from: Brak on April 13, 2018, 04:34:08 amThanks, That's the one with the worst error. It's also the higher priced version with the backlight which usually is not a giveaway. . I suspect that the item number is a single purchase order by HF. Manufacturer may or may not change. That provides everyone flexibility to modify designs and or suppliers.

author: james_s
author_rank: Super Contributor
timestamp: April 13, 2018, 05:01:24 pm
content: Quote from: blueskull on April 13, 2018, 12:33:02 pmLOL they clone the Intersil logo and then include a note that it's a fake part? How very polite of them

author: AtLarge
author_rank: Contributor
timestamp: April 14, 2018, 02:48:00 pm
content: The picture of the one with the backlight button is interesting. Never saw one like that before and I have been stacking them up for a few years now. I see you can get virtually the same DMM at Wally World now if you actually want to pay for one. They are in Chartreuse and marked as AllSun. They even had one on the rack with a GE logo but, exactly identical.Wonder if that was an authorized version.

author: IanB
author_rank: Super Contributor
timestamp: April 14, 2018, 04:00:03 pm
content: Quote from: AtLarge on April 14, 2018, 02:48:00 pmI've seen many of the backlight ones in HF in the past. Usually they are priced a few dollars more and sold alongside the ones with no backlight.

author: joeqsmith
author_rank: Super Contributor
timestamp: April 14, 2018, 05:10:19 pm
content: Quote from: rhb on April 08, 2018, 12:11:13 amIn many ways, these are much better than the first new analog meter the I owned. As a beginner, I was not concerned with static. Some of the cheap meters like these are easily damaged with ESD. I damaged the analog meter several times and was able to repair it where the modern cheap meters are disposable. No need for a battery to make voltage and current measurements was a plus as well.As a beginner, I certainly would have had no need for a higher end meter. I would say having a meter like the free HF meter may have inhibited my growth. If I knew every time I was going to play with it it may fail and I would need to replace it, I may not have played with electronics as much as a did.

author: rhb
author_rank: Super Contributor
timestamp: April 14, 2018, 05:45:10 pm
content: I've had one meter out of a dozen or so in regular use over many years (not the ones I tested). Only one died. No idea of the cause.They certainly are not susceptible to damage from being dropped. That's the main risk of damage to an analog meter. I'd toss a DMM to someone on a roof. I'd *never* do that with a VOM.

author: joeqsmith
author_rank: Super Contributor
timestamp: April 14, 2018, 07:11:25 pm
content: Quote from: rhb on April 14, 2018, 05:45:10 pmI would imagine how long the meter lived will has a lot to do with how it was used and how much. As a beginner, I did not have a lot of respect for the bits of equipment I had. The meter was still working when I finally pitched it. The case was badly damaged. The plastic lens over the movement had a large section broke out. It had been glued one too many times. I guess a testament to Radio Shack.For me personally as a beginner, it was the meter's resistors that took the blunt of my lack of an education. The leads took a fair amount of abuse as well.

author: 6PTsocket
author_rank: Regular Contributor
timestamp: August 25, 2018, 09:17:42 pm
content: Quote from: 001 on April 08, 2018, 09:26:01 pmYes. If you search "DT830"you will see the meter. They are sold World wide and there are quite a few variants. One article I found was from the UK.Sent from my SM-G900V using Tapatalk

author: 6PTsocket
author_rank: Regular Contributor
timestamp: August 25, 2018, 09:19:46 pm
content: There is a lot of info on that meter under DT830. That is the chip under the blob and there are plenty of schematics of the meter.Quote from: james_s on April 08, 2018, 09:29:30 pmSent from my SM-G900V using Tapatalk

author: 6PTsocket
author_rank: Regular Contributor
timestamp: August 25, 2018, 10:00:50 pm
content: Quote from: joeqsmith on April 14, 2018, 05:10:19 pmOne of my freebees, an old yellow one says Mastech on the pc board. There is a foil shield on the inside of the back cover and a spring on the pc board to contact the shield. At one time they gave a little thought to ESD.Sent from my SM-G900V using Tapatalk

author: rhb
author_rank: Super Contributor
timestamp: August 25, 2018, 11:15:10 pm
content: FWIW My most recent one doesn't have a trim pot :-(

author: james_s
author_rank: Super Contributor
timestamp: August 25, 2018, 11:19:17 pm
content: Is there a spot for one, or did they change the design to rely purely on tolerances of the components used or some kind of digital calibration?

author: rhb
author_rank: Super Contributor
timestamp: August 26, 2018, 02:25:43 am
content: Here's a family portrait. The two on the left are the most recent arrivals. I have 4 more of the 90899s and confirmed that all are the same as the example in the photo.While they generally look the same, all the front panels are slightly different except for the 98025 and the 90899.Also, the recent versions only go to 250 V. Some time when I don't want to do anything, I'll round up as many of the yellow ones as I can find and add pictures of those and measurements of my DMMCheck Plus.

author: rsjsouza
author_rank: Super Contributor
timestamp: August 26, 2018, 10:24:07 am
content: Quote from: rhb on August 26, 2018, 02:25:43 amThanks for sharing a more recent comparison. Those were my observations as well:https://www.eevblog.com/forum/reviews/harbor-freight-cen-tech-90899-small-teardown/msg655719/#msg655719Quote from: rhb on August 26, 2018, 02:25:43 amIMO this is a good change (also reported by someone on the thread I linked above), as it is a bit more honest about the device's limitations.

author: rhb
author_rank: Super Contributor
timestamp: August 26, 2018, 12:39:58 pm
content: I wouldn't be worried about using one at 500 V, but I wouldn't trust the probes that come with them.I'm a little disappointed by the loss of the trimmer. It will be interesting to see how accurate the 63759 version marked DT833 is. The high current fuse was reduced from 0.085" to 0.050" in the 250 V versions.

author: 6PTsocket
author_rank: Regular Contributor
timestamp: August 26, 2018, 01:38:47 pm
content: Quote from: rhb on April 08, 2018, 11:01:12 pmIn another post a fellow member displayed his red collection. There appear to be a bunch of production changes: fuse, no fuse, trim pot, no trim pot, board layout changes, circuit changes, etc. The same applies to the yellows. The early ones had a lot of film resistors instead of SMD's. There are also all the letter variants with features not offered at HF. From this site I learned about the "blob". I assumed they were hiding the chip. I never knew you could make a chip integral to the board, with no case and cover it with epoxy.Sent from my SM-G900V using Tapatalk

author: rhb
author_rank: Super Contributor
timestamp: August 26, 2018, 01:49:45 pm
content: All the ones I've seen are fused. I think people are confused by the 5/10 A fuse because it's not encased in glass. Though at 10 A I suspect the test leads provided would be the fuse if you were foolish enough to use them to measure that much current. More recent versions have a wire leaded fuse soldered in place.

author: besauk
author_rank: Contributor
timestamp: August 26, 2018, 02:53:02 pm
content: Quote from: Brak on April 13, 2018, 04:34:08 amWas the 10K resistor also needed?

author: james_s
author_rank: Super Contributor
timestamp: August 26, 2018, 05:22:54 pm
content: Quote from: 6PTsocket on August 26, 2018, 01:38:47 pmChip-On-Board (COB) has been around for many years. Loads of electronic toys from the 1970s on have been made that way, virtually all inexpensive calculators, musical greeting cards, etc.

author: rhb
author_rank: Super Contributor
timestamp: August 26, 2018, 07:48:07 pm
content: I just went through and did a cal on all mine that had a pot using my DMMCheck Plus. Much to my surprise, I discovered quite a bit of variation in units with the same lot #. I've attached a photo of the others.Most were already within 0.2% which is as close as they will read with a 5 V input. They are really tricky to trim as breathing on the trimmer is too much. I suspect that trying to do better would drive a person crazy.

author: IanB
author_rank: Super Contributor
timestamp: August 26, 2018, 07:57:22 pm
content: Quote from: rhb on August 26, 2018, 07:48:07 pmI have a few older ones with a trim pot. All of mine were a bit off at 5 V when tested out of the package and could be adjusted to do better.