EEVblog #813 - Mailbag - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: November 03, 2015, 04:58:50 am
content: Bumber Mailbag.Guest appearance by SaganSPOILERS:Sinclair / Thandar SC110 10MHz portable analog CRT oscilloscope form the 1980's!Makerbeam by Chartup:https://www.chartup.com/index.php?cPath=1_2A mystery device from a Police auction from Rossin Corporation10MHz TCXO reference clock generator:http://www.bloguetronica.com/2015/08/gerador-de-relogio-gr10m.htmlAST3TQ TCXO datasheet:http://www.abracon.com/Oscillators/AST3TQ.pdfCC2541 Bluetooth microcontroller datasheet:http://www.ti.com/lit/ds/symlink/cc2541.pdfFitbit ripoff teardownMMA955L Motion sensing pedometer datasheet:http://www.freescale.com/products/sensors/intelligent-sensors-and-sensor-hubs/motion-sensing-pedometer-platform:MMA9555LHarbour Freight Cen-Tech multimeter teardown!

author: crispy_tofu
author_rank: Super Contributor
timestamp: November 03, 2015, 06:07:40 am
content: Those Thandar/Sinclair SC110s (also called Thurlby SC110) show up on eBay once in a while for about US $50, some of them are even RS branded!http://www.ebay.com/itm/Vintage-RS-SC110A-Thandar-Portable-Oscilloscope-/221840075629Manual:http://www.kevinchant.com/uploads/7/1/0/8/7108231/thurlby_sc110-instruction-manual.pdfAnd that cheapo multimeter is really similar to the DT-830, there are a lot of rebrands (there's a lot of them, some don't have transistor tester, backlight, etc.). They use the ICL7106 IC in these metersThere's one at Jaycar (Digitech, $10) and one at Dick Smith (Digitor, in a shiny silvery plastic for$22).There's even one that's UL listed, in case someone wasn't sure about the quality(Interestingly, it has CAT I on the front, unlike the Harbour Freight meter)

author: tec5c
author_rank: Frequent Contributor
timestamp: November 03, 2015, 06:15:54 am
content: Is it just me or does Sagan sound a tad British?

author: EEVblog
author_rank: Unknown
timestamp: November 03, 2015, 06:55:09 am
content: Quote from: crispy_tofu on November 03, 2015, 06:07:40 amJust like the Batteriser is UL tested!

author: Dr Bob
author_rank: Contributor
timestamp: November 03, 2015, 07:59:20 am
content: The mystery sensor looks a bit like this patent from the same time frame:http://www.google.com/patents/US4468658dB

author: Dr Bob
author_rank: Contributor
timestamp: November 03, 2015, 08:03:42 am
content: The first thing to do with those Harbor Fright meters is to delete the included battery before it leaks all over the place. I have a few of these meters that I've received for free at HF. They are handy to toss in a glove box or tool kit to have about for a bit of quick troubleshooting.dB

author: jwm_
author_rank: Frequent Contributor
timestamp: November 03, 2015, 08:15:05 am
content: Quote from: Dr Bob on November 03, 2015, 08:03:42 amThe battery isn't even alkaline, it is heavy duty meaning carbon-zinc construction. At least you can pull out some nice inanimate carbon rods from the batteries. They can save the day in a pinch.

author: mrkva
author_rank: Unknown
timestamp: November 03, 2015, 08:30:04 am
content: Dave, I've sent you an item in August from Slovakia - did it arrive? Cardboard box, around 15x15x5 cm I have a tracking number, but all I get is that it left Slovakia.

author: vk3yedotcom
author_rank: Frequent Contributor
timestamp: November 03, 2015, 08:32:36 am
content: My very wild guess for that sensor thing is a window microphone that could activate a tape recorder when someone talks.Or maybe it could be pointed at a mirror and detect any small movement due to talking?Colin Mitchell might know

author: SteveLy
author_rank: Regular Contributor
timestamp: November 03, 2015, 10:06:44 am
content: Child labour - done right.

author: EEVblog
author_rank: Unknown
timestamp: November 03, 2015, 11:06:58 am
content: Quote from: tec5c on November 03, 2015, 06:15:54 amProbably Pepper Pig & Mr Maker!

author: Deathwish
author_rank: Unknown
timestamp: November 03, 2015, 12:00:13 pm
content: Quote from: Dr Bob on November 03, 2015, 07:59:20 amDifferential pyrolectic sensor ?

author: Deathwish
author_rank: Unknown
timestamp: November 03, 2015, 12:05:19 pm
content: Having watched Sagan take the nut driver from dad's hands and listened to him articulate himself I can only say this to him.Dont worry mate, it wont be long before you can park dad in his wicker chair on wheels in the corner and watch him as he drools when you take over the show.

author: mikerj
author_rank: Super Contributor
timestamp: November 03, 2015, 12:35:31 pm
content: Quote from: Dr Bob on November 03, 2015, 08:03:42 amHow do you delete a battery? I never use cheapo included batteries in anything I actually care about keeping.

author: WN1X
author_rank: Unknown
timestamp: November 03, 2015, 01:32:59 pm
content: Quote from: crispy_tofu on November 03, 2015, 06:07:40 amI love how the Cen-Tech meter is marked as being Cat II rated

author: Fungus
author_rank: Super Contributor
timestamp: November 03, 2015, 02:49:15 pm
content: Don't complain, your meter has a fuse in it!When I did my teardown video there were no fuses at all in either of mine....and an on/off switch! Luxury!!PS: Yes, they're pretty damn accurate,rugged, too!I want to know why they bother with the transistor tester. It's totally useless and costs them money. You'd think that would be the first thing to go when they look at the build cost.

author: max666
author_rank: Frequent Contributor
timestamp: November 03, 2015, 03:53:15 pm
content: Quote from: Fungus on November 03, 2015, 02:49:15 pmSome bloke having a swim with his meter. Where have I seen this method for testing multimeters before?

author: djQUAN
author_rank: Frequent Contributor
timestamp: November 03, 2015, 04:17:51 pm
content: AFAIK Cen-Tech is the HF brand for their tools or something like that.The multimeter PCB is not actually routed. It is cut (stamped?) with a cutter and die. Have a look at the PCB edges and they are kind of frayed, not the clean, smooth edge you get when they are milled.It costs more to make the cutter but only a one time cost. Then cutting the PCBs is just stamping them out like cookie cutters.The entire PCB outline is cut including the slots, large and odd shaped holes in just one step.We did this where I used to work. The prototypes are done as we are all familiar with using milling and drills but once the PCB shape is finalized, the mass produced product will use the cookie cutter thing. I forgot what they call it in the industry.

author: free_electron
author_rank: Super Contributor
timestamp: November 03, 2015, 04:48:26 pm
content: thermal intrusion detectorhttp://www.ebay.ca/sch/sis.html?_nkw=Rossin%20Thermal%20Intruder%20Sensor%20107255&_itemId=141154781502

author: Towger
author_rank: Super Contributor
timestamp: November 03, 2015, 06:06:15 pm
content: Those multimeters cannot be too dangerous. My father managed to blow the tips off his probes, trying to measure the voltage across an immersion element...He lived to tell the tail, but he still thinks there was something wrong with the meter, rather than 'user error'...

author: woox2k
author_rank: Regular Contributor
timestamp: November 03, 2015, 07:18:56 pm
content: You can't argue the fact that these free multimeters are great value for money. They still are reasonably accurate for everyday use. I agree that these shouldnt be used as a mains testers but for <50v everyday measurements they are fine.About the safety, i own similar looking unbranded and even unfused meter. I once foolishly tried to measure a car battery when probes were in 10A plug...Needles to say i am still here to tell the story because apparently those "patented safety probe leads" acted as a fuse and the lead just broke in the middle instantly, i barely even saw the sparks coming off the battery terminalsI still use that meter sometimes, with new cheap probes.

author: Ampere
author_rank: Regular Contributor
timestamp: November 03, 2015, 07:47:18 pm
content: I have a few of those Harbor Freight meters. I keep one in my trunk. I wouldn't use them to measure any amount of current, but they're still quite useful to keep around for voltage or resistance measurements.

author: Christe4nM
author_rank: Unknown
timestamp: November 03, 2015, 08:28:42 pm
content: That intro with EEVblog junior mark 1 is a keeper!I instantly gave a tumbs up before watching the rest of it.About that multimeter; how about a high voltage test? It's been too long since we saw something being blown up

author: Don Hills
author_rank: Regular Contributor
timestamp: November 03, 2015, 09:43:56 pm
content: Quote from: jwm_ on November 03, 2015, 08:15:05 amHave you seen any carbon-zinc 9v batteries with cylindrical cells inside? All the ones I've seen have a stack of "pancake" cells inside.

author: wojteks
author_rank: Newbie
timestamp: November 03, 2015, 11:07:24 pm
content: On the topic of oldschool miniature CRO's - my recent eBay score:https://www.eevblog.com/forum/testgear/oldschool-1972-polish-oscilloscope-ebay-score/

author: Don Hills
author_rank: Regular Contributor
timestamp: November 04, 2015, 12:07:41 am
content: On the subject of the Thandar scope:The blue wire wrap winding on the transformer is almost certainly the filament power winding for the directly heated CRT tube.

author: jnissen
author_rank: Regular Contributor
timestamp: November 04, 2015, 01:46:23 am
content: Quote from: WN1X on November 03, 2015, 01:32:59 pmJust depends on your definition of CAT! Meow!

author: gordo51
author_rank: Contributor
timestamp: November 04, 2015, 02:07:53 am
content: I can see it will not be too long before Dave2 is laid off and Sagan takes over. Pretty clever and articulate for a 4 year old.One problem I have had with cheap multimeters is that they do not have a Lo Batt indicator. I was tearing my hair out once checking something with a cheap meter, Radio Shack I think, and finally concluded the meter was wrong. Turned out the 9v battery was way low. No cheap meters any more, just Fluke or Tektronix.

author: crispy_tofu
author_rank: Super Contributor
timestamp: November 04, 2015, 02:16:10 am
content: Quote from: gordo51 on November 04, 2015, 02:07:53 amI'm pretty sure the DT830 has a battery indicator on the bottom left of the LCD, but those multimeters tend to drift a lot when the battery is low, exactly what you describe.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: November 04, 2015, 03:53:23 am
content: Quote from: free_electron on November 03, 2015, 04:48:26 pmYup, looks like Dave has later model of it. Senso still looks like one on the patent:https://www.google.com/patents/US3839640?dq=3839640&hl=en&sa=X&ved=0CCYQ6AEwAWoVChMIwv61uu31yAIVDsljCh23ngM3That thing deserves separate video with tests and experiments!

author: djQUAN
author_rank: Frequent Contributor
timestamp: November 04, 2015, 04:12:53 am
content: I have seen a glass breakage detector with an internal lithium coin battery.The battery runs the circuitry and the two wires are simply a normally open contact (open collector).Maybe that is the case with the cell inside the intrusion detector.

author: bills
author_rank: Frequent Contributor
timestamp: November 04, 2015, 05:49:18 am
content: What ever the battery is for it is no doubt dead by now,so it's purpose is moot.

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: November 04, 2015, 08:30:06 am
content: Quote from: EEVblog on November 03, 2015, 11:06:58 amLMAO! I knew that when I heard him speak!Don't let him park his car on a 50 degree slope like Peppa Pig does though!

author: bookaboo
author_rank: Frequent Contributor
timestamp: November 04, 2015, 11:23:12 am
content: Quote from: EEVblog on November 03, 2015, 11:06:58 amWas thinking exactly that, we have the same problem here. The word generally used (slang if you want to call it that) for mother here was "mammy", now all the 5 year olds including mine refer in an oxbridge tone to their "mum".

author: f4eru
author_rank: Super Contributor
timestamp: November 04, 2015, 12:35:03 pm
content: Quote from: jnissen on November 04, 2015, 01:46:23 amProbably it can hold the weight of two stacked cats.

author: kfitch42
author_rank: Frequent Contributor
timestamp: November 04, 2015, 03:24:58 pm
content: Hearing about Kindergarten orientation, then watching Sagan play with those Makerbeam thingys made me think about what will happen the first time he gets a homework assignment along the lines of "Using common household object build a diorama of your community."I suspect Sagan might end up leaving a wake of "reactive rules" as he progresses through school. The year after him will have lots asterisks on their assignments like "* High voltage power supplies and nixie tubes are NOT common household objects."

author: Towger
author_rank: Super Contributor
timestamp: November 04, 2015, 03:35:51 pm
content: Quote from: bookaboo on November 04, 2015, 11:23:12 amThat depends on the area you are from. We never said mammy, my 5 year old says mummy and the 8 and 9 have progressed to 'Mother', in a posh accent...

author: Stonent
author_rank: Super Contributor
timestamp: November 04, 2015, 05:00:37 pm
content: We can't have Sagan getting a British accent, we need to start him watching old episodes of Mr. Wizard and we can Americanize him.Heathkit Hero 1 Mini Teardown:Sounds like Hero has a Votrax SC01 accent.

author: SeanB
author_rank: Super Contributor
timestamp: November 04, 2015, 05:33:46 pm
content: Thandar/TTI/whatevertheyarenow made a whole range of test equipment in that same case, all using the same front panel switches and knobs. The scope was the one, and there was a function generator as well. All battery powered.I still have a SC110A I got in school many years ago. It worked well for many years till it finally died. I should look to see if I can fix it some day, as I can now get the manual online for it. IIRC it was a $200 scope, my dad bought it in Hong Kong on a business trip to Japan when he went to Toyoda to see the Toyota works. Still have a paper picture of Mt Fujii on the wall, apparently they are collectors pieces now. He went on a tour there with Toyota, and this was one of the places he visited and this was a gift.

author: apis
author_rank: Super Contributor
timestamp: November 04, 2015, 11:46:55 pm
content: I got a couple DT830 from ebay for 1$ including shipping (each), what surprised me was that there are different versions, some crappier than others. They probably use the same chip but circuitboard and the cases were different, one didn't even have a trimmer pot.And wrt the alcohol tester, Iv'e seen a teardown of a alcohol tester that works, it had an air pump so it could sample a known volume of air and the sensor had to be calibrated regularly. That one from ebay must have had some very nice sensor in it, or maybe not.

author: bookaboo
author_rank: Frequent Contributor
timestamp: November 05, 2015, 10:31:13 am
content: Quote from: Towger on November 04, 2015, 03:35:51 pmIm in the north west, I always thought Mammy was standard across the board? Im thinking south Dublin the exception. Certainly never heard "mother" or "mum" until recently

author: Robomeds
author_rank: Frequent Contributor
timestamp: November 05, 2015, 03:36:59 pm
content: There are many many different 830 meter designs. The HF ones seem to be the cheapest (price and construction). But even the HF meters vary quite a bit. Just from threads around here...https://www.eevblog.com/forum/reviews/harbor-freight-cen-tech-90899-small-teardown/msg181243/#msg181243https://www.eevblog.com/forum/reviews/harbor-freight-cen-tech-90899-small-teardown/msg181264/#msg181264Non HF versionshttps://www.eevblog.com/forum/testgear/world's-cheapest-multimeter-teardown/I've wounder if the meter in question was adjusted before being sent to Dave. I've tested perhaps 6 or 7 of these things against other meters (Fluke 87-3 and 87-5, not true calibration equipment) and found none out of spec and most within a few counts. That does speak well of the IC used in the things. Currently I have I think 5 of them. 3 in the pile, one in each car. The local school was throwing them out (maybe someone pointed out the near total lack of safety circuitry) so I picked them up as give aways and back of the car meters. I see them as better than nothing if you know their safety limits. Never my first choice.

author: bloguetronica
author_rank: Frequent Contributor
timestamp: November 07, 2015, 06:52:12 pm
content: Dave, first of all I want to thank you for the excellent review you've made on the GR10M board I've sent you.You did point some valid aspects, some of which I can't implement due to the nature of the project and the enclosure used of it, which is an Hammond 1455D601. I guess where won't be space for holes (nor need to) or BNC connectors. I know the SMB connectors are not very durable, but the other option would be to go for SMA, which is even worse IMHO. However, the voltage rating idea printed on the silkscreen is a nice feature that I've already implemented on my next project, and all thanks to you.I'm worried about the state of your board, since F1 seems chipped to me. I could swear the board seemed to be fine when I sent it to you. Since I never wished to sent you something that is broken (or got broken during transportation), I can send you a replacement polyfuse. Please, could you confirm if F1 is damaged? Thanks in advance.

author: twice11
author_rank: Contributor
timestamp: November 08, 2015, 01:37:06 pm
content: Quote from: crispy_tofu on November 04, 2015, 02:16:10 amActually, the 7106-based 9V multimeters are quite good at handling low battery. The configuration is basically a zener diode for the reference voltage which is tapped by the pot together with fixed resistors to produce 100mV. Typically the LCD gets unreadable before the values get inaccurate (only exception: on a weak battery, the current drive in ohms range may fail early, producing garbage readings, even if the leads are open-circuit).I really got bitten by a much higher-priced 3.75 digit autoranging multimeter that displayed "-3.785 V" or something like that in auto-range volts with -7V applied. When manually switchted into the 40V range, display was OK. Obvisously with the low battery the output common mode range of the input ampliefier (the 7106 don't even have such a thing!) was exceeded before the output voltage was low enough to trigger the range switch. The "lo batt" indicator of that meter was *NOT* turned on at that point. Utter fail! (I fail to remember the brand or model, though. The case was yellow...)

author: Poe
author_rank: Frequent Contributor
timestamp: December 31, 2017, 07:54:50 pm
content: Sorry for bumping an old thread, but I wanted to add some points regarding the cheap meter.The small/large PCB arrangement not only improved PCB area usage, but also reduced the main board's copper weight to half ounce or less. The small board appears to be 2 or 3 ounce copper for the current shunt.Not that they needed that thick copper, the probe wires have fewer than five strands of 30AWG wire! I had one with only three strands in each wire. 10A results in 5 to 8W of heat before the wires melt.V-score is cheaper than routing, but even that would be too expensive. Both of these boards are punched, including the plated through holes.