What's inside a digital scale & how does it work
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- เผยแพร่เมื่อ 22 ต.ค. 2020
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Today, let's open a cheap digital pocket scale to see what's inside and how does it work. This one goes up to 500g with 0.01g resolution. It seems to contain a load cell with 4 strain gauges set up in a Wheatstone bridge configuration. - วิทยาศาสตร์และเทคโนโลยี
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Hiya, just wanted to let you know, you're one of the best educaters I've ever encountered. Thank you kindly
important tip when putting back screws in plastic components. 13:32
Yes, I agree with you, a good tip on screws in plastic.
I get the notification for this video 4 days after buying this exact scale. Perfect.
you filmed this video in 1080p. thats niiiiiiiiiiiceeee:)
wild diode is yt legend :)
naaajjss
i was gonna say that and you forgot to say its in VP9
scales like this are used for postage and marijuana(i would LOVE to hear you pronounce this word) and are 1 of the only reasons americans know how many grams in an oz
Am an american cannabis user can confirm. And can also confirm every stoner in america and canada has similiar scale. Really any consistent drug user tbh.
not just Americans. people everywhere learn this from these..
Back in the 80s, in England, Amphetamines were always sold by the gram but Hashish and Marijuana were sold by fractions of an ounce.
Exactly. The proliferation of drug culture created demand for small, accurate, affordable digital scales. That's a handy thing for us amateur science people who need them for different purposes. Getting a chemical balance 30 years ago would've been far more costly. Mass produced electronics have made a lot of hobbies easier to get into.
American Weigh Gemini-20, cheapest scale on the market with milligram precision. It used to be pretty entertaining to see the "people also bought" on amazon.
Very informative. The accent is a bonus.
Thank you for this teardown and explanation. I did not know how a digital scale works. I'm thinking to support you on patreon, you really deserve it!
Wow! I didn't expect the traces on the sensors to be visible. It's amazing to me that just bending those a tiny bit causes detectable voltage change. I mean, it's very tiny voltage change, but more than I expected. Super cool!
Very sensitive measurement needed; remarkable it so cheap.
It's a consequence of precision mass production. As long as you can make the sensors as identical as possible, from then on all the laws of physics are in your favour. The impedances are low and the wires are short and close together, so noise pickup is minimised. The components on the chip which make up the amplifier circuit are close together, so at the same temperature, which means everything is affected equally. And the analogue circuitry is symmetrical, basically three op-amps: one to provide a buffer on each input to minimise the influence of the other input on it, and the third to amplify the difference between the two to match the analogue to digital converter. This symmetry naturally rejects noise. All the rest is straightforward digital stuff well within the capabilities of a modern microcontroller.
@@bluerizlagirl Thats a good analysis. I wonder if a generic op-amp like LM324 can work like a instrumentation amp you mention. The figures measured in the video seem to in the millivolt range; maybe the input offset of 2mV of a generic op-amp would be the limitation. I've checked these low cost Chinese digital scales- the construction are with the cheapest materials possible, and even the finish is lousy. However surprisingly the measurement is precise and repeatable over months. I imagine that someone has mass produced these as an SOC, and selling it off cheaply in bulk to anyone interested in building a product around it.
@@rtos As a general rule, the smaller you make something, the fewer ways there are it can go wrong. What's most important in making both instrumentation amplifiers and A-D converters is close matching of the ratios between resistors, and that's actually easier to do in silicon than to get an exact value. The programmable gain and offset circuits also depend on closely-matched resistance ratios. Also the close thermal contact helps compensate for temperature changes.
I'm expecting it to be using software calibration to tweak out DC offsets (knowing there is nothing on the scale pan when first switched on, so the weight should read 0g.) and set the gain, and some sort of averaging over multiple readings. These cheap scales do tend to drift a little over time, but that's probably why the automatic power off is so aggressive!
@@bluerizlagirl how does a cheap knockoff like this compare to original one like lyman or hornady, frankford arsenal ?
i heard guys explain these before using basically a resistor, but never fully explained... the Wheatstone configuration makes perfect sense to get a voltage reading of. Thank you for this little bit of knowledge...
I have one exactly like this. Thanks for the teardown. And thanks to you, now i know whats inside of it and how it works.
you can probably put a 500g weight then compansate it. When you remove the weight it will say -500 after that you can measure up to 1kg in teory.
Yes, that's right, because it has full capacity tare.
This often works, although there is a chance the load cell will be bent/changed permanently, making it less accurate.
Tried with my cheap kitchen scale and it don't work.
Probably the chip can only read (example values)maximum 0,6V (600gr) and it can't read it correctly
Different is if the cheap display can only shows (max) 199.99grams. In that case the trick will work
@@thefighissimo I doesn't work for all of them but works in mine.
Yes, in theory you should be able to weigh anything from 500g. to 1kg. by this method, or even up to 1.5kg. by zeroing it again with 1kg. on the scale pan; but in practice you would have to watch out for (1) the voltage difference exceeding the input range of the amplifier and (2) the force applied exceeding the elastic limit, so some part of the sensor does not spring back to the shape it was before but is permanently deformed.
A good design engineer would never let that happen, probably allowing for the system to withstand up to 2.5kg. before non-elastic deformation if it said maximum 0.5kg. and the amplifier to remain linear all the way up to 1kg. But a sales manager will insist for everything to be made as cheap as possible in order to get maximum profit, so the metal beam may not be strong enough to take much overload. And it is a bad idea not to use the full linear range of the amplifier for meaningful measurements. The smaller the wanted signal, the greater the influence of any noise upon it. The analogue to digital converter also has a limited number of steps, which must be a power of two; probably 65536 steps, to cover the range 0-500g. in 0.01g. steps. Once you exceed the maximum input voltage, it will never read any more than 65535.
(It is possible to use two analogue to digital converters together to obtain a wider range but with less precision at higher readings. This is often a good compromise between maximising precision on small readings and using an analogue to digital converter with a higher resolution (more bits = more £€$, and in any case you are often restricted to what is available on a chip). For instance, two 8-bit converters are fed with a signal x and an amplified copy 16*x. The converter receiving the stronger signal will max out at 255 (which is really 15.9375, since it has been amplified by a factor of 16) but the converter receiving the weaker signal is still only reading 15 at this point, and can go all the way up to 255, just in coarser steps. What the software has to do is read input 1 and if it is 16 or greater, then multiply it by 16 to get an answer from 256-4080; otherwise ignore it, and use the reading from input 2 directly to get an answer from 0-255.)
Information about battery life and behavior with dead batteries:
Current when OFF: 0.4 uA (virtually indefinite shelf life - no need to take out batteries)
It gives Low battery warning (refusing to work) bellow 2.5 V so it will use up only around 50% of capacity of normal primary cells and maybe 10% (!) of NiMh rechargeables at best.
Current when ON, without backlight: 3.5 mA (ca. 140 hours of continuous use, assuming using up 50% of an AAA capacity)
Current when ON, with backlight ON: 14 mA when running from 3.2 V (fresh batteries), 7 mA @ 2.8 V and 3.5 mA @ 2.5 V (backlight goes very weak). (hard to guess - few tens of hours, maybe???)
The low battery warning seems to be reliable and the scale doesn't read nonsense with low batteries.
Interesting addition, thank you!
Not sure how I managed to miss this video first time around DGW, but it's amazing. Describing a tear down video as spellbinding is a bit ott, but this one is close. Incredible.
Thanks for another great video! I have used a 'window comparitor' made using 'op amps' to achieve something very similar to this.
Surprisingly decent scale weight for its price. I have 200 g model and it works great so far even with rechargeable NiMH cells :)
Very cool - I thought the sensing would be some crazy physics effect but it turns out to be pleasingly simple!
I just really want to say thank you a million. This was so useful 🙌 why can't people make more video like this fantastic information.
Nice tear down, quite deep with the explanation and principle. I appreciate!
Thank you so much sir , you explained very rhyming rhythmically-superb presentation and technically sound
its amazing how they can make it so cheap yet be able to measure down to the microvolts
Diode always useful information, thank you 👍
Excellent video as always. Glad to see you upload videos more often :)
Also nice to see you upload videos in 1080p
very accurate description
best channel ive seen
Thanks for your explanation. Was very interesting!
Fabulous video, terrific explanation. Very informative.
Great explanation! Love your way of teaching
Really nice video about digital weight measure device working principle! Thanks a lot and blessing.🙏
The design of these devices blows my mind because it's all done along the same lines as the internals of a two dollar pocket calculator, with the addition of that sensor. An ironic thanks goes out to the War On Drugs for this gift of cheap tech to the masses.
I couldn't weight to see this video about measuring waits. Thank you
Thank you so much for the explanation! I was really wondering 😮
the most amazing thing is it still works
Informative as always. Thank you.
👍👍🙏 Thanks for your comment on the blue light... I really dislike blue backlights... personal preference: Orange :)
That Auto off in some scale like this is one of the biggest annoyances in my life. When you do not got all ingredients of the cake at hand, it will turn off just the moment you are back, and you are lucky if you can figure out what's already in the bowl.
smoke atleast 1 bowl of cake ingredients but no more than 8 bowls while weighing cake ingredients or you will forget easier
I was just about to comment about this.
I wish i could find out how to bypass the Auto off feature!
@@jayytee8062 No problem, the blob can not be accessed, but a pulse generator with a relay could connect resistors to the bridge shown in the video, this would simulate something is happening on the scale. Will make this happen after I finished the other 100 ideas I have...
@@timtim8468
Thank you!
Finding a completely flat battery in equipment with no auto-off is even more annoying :D.
SUPER! Просто молодец, даже продемонстрировал как правильно винтики-шурупчики обратно закручивать. Спасибо за Ваш труд.
That's a nicer/cheaper way to get a beam sensor than actually trying to buy the sensor on AliEx.
Very nice - well done!
Fantastic video
You very smart guy! I love how you write it’s the same as you speak~ ❤
☺ Ni-i-ice! ☺
:)
Helpful video 👍
That electronic sensor was art
A well balanced teardown.
Very nice explained. Mr. Teacher :)))
Troy Ounce is one of the settings. I use it to weigh gold.
Thanks for the info..👍
You take apart "my" digital scales, so that I don't have to. :)
I love that tin of big "old style" resistors on your bench... I've seen it in a few videos now, It's like a time-capsule into my childhood.
Great explenation, keep it up
This guy's a freakin' genius (at least to guys like me who are scientific ignoramuses he is)!! And his inimitable accent is the cherry on the cake. Brilliant!
Great vid.
There is an other kind of digital scale, that was used in low budget digital personal scales 20-30 years ago. It has the same mechanism as an analog personal scale with the rotating number disc, but the number disc is replaced with a slotted code disc and an optical gate, like the optical encoders in old ballsy PC mice. They are horrible. You stand on it three times, and it gives three different values with about 5% or higher inaccuracy :)
Very interesting so far! (I'm still watching)
And I love your English. My spoken English is bad, too.
His English is very good, he just has a strong accent. I didn't hear any incorrect words, and I heard several English idioms used correctly.
@@PablumMcDump With his "Bloody Hell" and "Very Dodgy", it sounds like good English-English too, not American-English.
@@edgeeffect - the Bloody Hell and Dodgy make him sound like Australian English. Yet he doesn't say "mate" LOL
@@johncoops6897 Both Aussies and Brits use "bloody hell" and "dodgy", I think it's great that DGW uses them too, I love his accent but I have no idea what his nationality is!
Does anyone know where he's from? I can't place the accent.
Should have changed the backlight before assembling 😂
I had this plan, but I got demotivated when I discovered that it's not a through hole LED, just a super tiny SMD one.
I understand how the resistive sensors work, but I'm puzzled of their layout. They look like they go across the bar rather on the length of the bar where they could stretch or compress. I don't see how they can stretch or compress across the bar. Anyone has a good explanation?
Great explanation.
I have a question, hopefully you can help me.
I have a mini scale, if I put the weight in the exact center the measurements are accurate. But if I don’t and move up/down-left/right even a little the values change a lot. Is there a way to fix this?
Thanks in advance for your time
Thank you
Great video
very nice video
Do you know from which material are the sensor conductive traces made of? Is it some kind of resistive alloy?
I have a nice and fairly expensive kitchen scale I am attempting to fix. everything seems fine so I think my issue is with the backlight or the connection pad onto the display glass. Is there a way to re-adhear the display glass to the small connection rubber piece if it fell off?
I have one question if battery discharges it voltage get down so it's effect on measurements or not?
I've gotten my scale fallen down and all the wires are cut inside it. I don't know if I can soldier it again, I need to understand which colors go up and down.
It has 4 wires whitr red blue, and black.
Is there any hope tobfix it again?
Very interesting !
Hi are you read my comments of last two videos???
Your all videos are nice and very very informative.
Nice. 4 wire measurements of the resistance in the strain gauge. That helps a lot with accuracy and temperature stability. The opamps, voltage reference and ADC (22 / 24 bit maybe) also need to be pretty accurate and linear, because I don't think these scales are individually calibrated at factory to compensate for all inaccuracies. It is quite amazing that you can produce so precise device basically for less than 1$.
I think they *are* all individually calibrated, to take out the random variations between units. The gain and DC offset will be set by D-A converters, from values stored in E2PROM.
@@bluerizlagirl you are right. You can even do it yourself, they do have guilting calibration function, some long button presses and one or two test weights and you are done. Quick to do.
@@bluerizlagirl Yes at 11:41 you can see a VPP test pad on the circuit board for the Antifuse/EEPROM programming voltage. There are also 4 test pads near the LCD connector which are probably intended for programming calibration data.
@@atmel9077 I guess that would be for the initial programming of the micro. It probably contains just standard UV EPROM like the classic 27128, but of course the black resin blob prevents it from being erased. Although you probably could use X-rays to reset its contents to all &FF, if you really wanted to reprogram it! There probably will be a separate area of EEPROM to store the calibration data; and some hard-wired ROM containing a special loader program to allow a program to be read serially through the 4 pin interface and written to the main EPROM.
I can see at least 28 tracks going under the blob, so maybe there is also a version of the same chip in a 28-pin package ..... perhaps with a glass for UV erasure.
I can think of many situations where you might want to measure a voltage and display a reading which can be got by simple maths from it. The IC probably is a very generic one that could be used with many different kinds of sensor, not just for weight but also light, sound level, pressure ..... just by programming a different gain and offset, and a microcontroller with enough I/O pins to drive the LCD, read the buttons and control the power to the sensor so it is only connected to the battery when a reading is wanted.
@@bluerizlagirl I've got one possible candidate... www.holtek.com/documents/10179/116711/HT67F5630v120.pdf
It's got an LCD driver and a 24-bit delta sigma ADC with 19.5 effective bits @ 5 Hz and a differential programmable gain amplifier with a gain of up to 128 so probably good for this kind of application.
Thank you sir ,how I can balance sensor
Your channel is so great and informative! Thank you keep up the great electronics tear downs!
Does anyone happen to know that if any of the sensor wires are cut shorter, would that throw the entire calibration out and cause an ERR to be displayed?
Sir,please make a video of how light ray/lesser Rey could measure the distance.i really wanted to understand and make one.
Does it die during weighing like some of these cheap weights? and does it weigh from 0.01g or it only starts at 0.5,0.7g and so on?
There is on extremely annyoing thing with almost all digital scales, the auto power off function. If you take too long when you are mixing your ingredients, the scale shuts off on you and you have to start over again. Is it possible to identify which component on the circuit board that is responsible for the auto shut off function, and somehow disable it so that the scale will stay on until you press the power off button?
Woooow I have that exact scale
10:57 how that connector are made ??
Very nice video. Link of product?
Japanese scientists: invent blue led
Nobel academy: Yay, love it!
Electronics industry: Yay, love it!
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I like the way you sing bro
@13:10 I do not think so, I believe they used a Differential op-amp To increase the voltage after ADC.
This dude talks like Roswaal from Re:Zero.
Subscribed!
Since you already opened it, It will be just awesome if you changed the color of the lcd.
I have a hanging type luggage scale with a very small backlit digital scale that reads in grams,,lbs,and kgs,,to hang heavy packed suitcases on it to check weight to b sure I,m not exceeding 20 kgs b4 travelling on any long hauled public transport including domestic and international air flight travel journeys.
Gee, wow. I have a white cupboard style device that uses an electric motor to pump refrigerant gasses and move heat from inside to the outside. That reduces the internal temperatures, making it ideal to store perishable foods, to extend their edible life. I use it for dairy products like milk and cheese, for meat, and for vegetables as well. It can also be used to store previously cooked foods, and to chill liquid refreshments like juices and beer..
If the plastic is ABS and you've stripped the threads... A drop of acetone in the hole can remelt the plastic and allow you to recur a thread.
@8:52 the torus "donut" sensor. Comprehend and copy nature and you get results.
how did you assembled it so the display works?
I should've watched this video when I learned sensors at University.
I like it!
Could you explain why scales can detect RF in the microwave range? Mobile phones during a call, WiFi routers and microwave ovens effect scales. Grammes for example jump around -5 to 10 when I heat up food, it's dependent on proximity. Just a few inches reduces the measurement greatly.
PS: the second unit tl is teralitre, 1 tl = 1 trillion liters.
9:55 could that bridge be acting like a transducer? tl or gn on your scales would show a better resolution.
Hi, thanks a lot for your video and your channel too.
I have a question for you, I have same model of pocket scale, I have calibrate it I think 5 or 6 times and now don't show me PASS screen but show me word FULL and never calibrate more, you know in what way can I delete memory of calibration, cause I never calibrate more and the screen it block with word FULL. I have try removing battery but nothing....
Thanks!!!
Same thing... did you ever solve it?
@@kicon7714 No, I haven't solve it, I think something in chip is broken, cause none have talk about this in the web, and every peoples can calibrate it when they want.
I think I have to buy another one (and not chinese looseless like this if I can).
@@teodiofauss5806 Yes... I will probably buy another as well ... Shame that "Full" cannot be cleared so that we can recalibrate...
my scale keep showing different measurements even without anything being placed on it. I tried calibrating the scale but the problem still persisted. what can I do to fix this?
Buen video..Saludos..
I have the exact same scale
It's thrown in the recycle by someone but the only faulty thing is the tack tile click switch on the on/off
*tactile - and it's neither a click switch nor a tactile switch.
@@johncoops6897 mine have a tactile switch
@@lifeai1889 Then you DO NOT have the "exact same scale", do you? Clearly at 10:43 ou can see that this scale DOES NOT have a tactile On/Off switch.
@@johncoops6897 not exact the same but almost
They looks the same and even have the same frimware
Just the switch is different
you are great, i love ur accent
can you show how to fix the screen if it’s cracked
That's how my scale works eh. Nice.
Nice
hey man i have the same scale. but i cannot calibrate it. it goes upto 300gram. but no matter what i use to calibrate it its not working. i tried calibrating with 1gram and now it doesnt go up more than 25 grams.
A 24-bit ADC costs a lot. A high CMRR in-amp costs some. Those two packed together for the purpose of portable scales? They cost mere cents!
Nice...
nice
The name of the sensors is "strain gauge"
Interesting explanations, thanks. But damn, where is your cat ??