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- เผยแพร่เมื่อ 28 พ.ค. 2012
- Teardown Tuesday.
What's inside a Braun electric rechargeable toothbrush?
And some basic measurements on wireless power transfer and charging.
Chips Used:
EM6682: www.emmicroelectronic.com/webf...
TSM7401: www.goodexcel.com/new/download... - วิทยาศาสตร์และเทคโนโลยี
Dave, the transformer circuit is a simple split coil dual phase rectifier. For the positive phase one coil and one diode rectifies, for the negative phase the other coil and diode do the rectifying. In this way the efficiency is better and the distortion to the primary is less.
The 800Hz pulse is so that the microcontroller can read the battery voltage without the charging voltage interfering. Learned about that little gem watching bigclive tear down some battery charging units.
Huh, i'd like to see that one. Don't think i have.
You're supposed to push down on the tip to extract the whole assembly, this is shown on the bottom of the charging cradle.
It's called Teardown Tuesday for a reason. Each week is new tear down. Sorry for those who think it's maybe replacing other material. Obviously I can't do enough videos to please everyone all of the time.
The 2 little black thingies are pellets that neutralize chemical gasses that can be produced when a nimh cell is overcharged. I've heard of some cases of exploding devices that did not have these neutralizers, so most enclosures with nimh cells now contain one or two of these. See: www.generalchemical.com/assets/pdf/Potassium_Hydroxide_Pellets_ACS_PDS.pdf for more explaination :)
You can actually replace the battery inside, at least once or twice, until the sealing isn't good anymore. I actually "repaired" mine twice before I bought a new one, because the only part that actually dies is the battery, and it dies fast because of the constant charging.
I also replaced it with a NiMH one that had nearly twice the capacity than the stock one. It's a bit of a fiddling, with the soldered battery contacts, and really a shame that they don't bother to make it more accessible, but that is probably just planned obsolescence so you buy a new one at least every two years or so.
Bought a Braun on 2012 and has been using until now (2022 January). Still working like new. Top notch engineering and quality manufacturing.
is it nicad or nimh?
I think the ferrite beads are just permanent magnets to help hold the brush to the base.
I tore mine down when it failed, cleaned the guts up and put it back together :)
The charger on mine seems happy enough running on 120 volts even though it's a 240 volt model.
Great idea to tear down a toothbrush! I've nearly the same one and asked myself what's in there. Thank you!
The little ferrite beads in the charge receptacle are to kill the high frequency ringing on the edges of the 20 kHz waveform.
The pulsed charging is used to detect if the battery is fully charged, and then the charging will stop.
So the IC goes like I'll charge for 400 ms then stop 100 ms and measure the voltage, then repeat if lower than full charge.
and btw, it's nice to see the younger you :) we've all changed over the years
Nice teardown and explanation of working circuit .thumbs up
I always wondered what was inside an electric toothbrush.
Great video, Thanks.
I pulled one of these apart and all you have to do to get the whole lot out is to unscrew the bottom and pop it off like you did, and then invert it and push the shaft against a table top or the floor (whatever is hard and you won't damage the surface) and it will push the entire assembly out the rear end in one piece.
My guess is that pulsed charging is some sort of inteligent charging control, done by the micro, in order to extend the service life of the battery. Basicaly, every time charging stops, ADC can read the battery voltage and decide whether to continue or not.
16:24 it has 40 Bytes of RAM. That's even less than what the MIPS Altair had...
Interesting. I only gave them a cursory glance, they looked and felt like ferrites to me.
That FET needs to be off at 0 volt gate voltage, and decently on at 1 volt gate voltage. So I suppose it is not just like 'any power FET' would do.
instructions for taking the toothbrush apart are on the back of the charging unit - visible on the video too! - keep up the great vblog!
best regards from denmark!
"Now you can see the three wires coming off the coil there"
Dave, all i saw was how dirty the inside of your toothbrush was ^_^
Awesome video!!
Possibly that was just a convenient frequency to use in the uC program? Maybe the timers have a maximum period dependant on the clock speed of the chip...something like that
I would think the Ferrites are to ensure most of the magnetic field goes through the coil of the receiving coil.
One of the coils is for the positive, one for the ngative half wave. It´s basically one big center tapped coil. It´s providing full rectification while saving two diodes. More copper - less diodes, whatever is cheaper :)
only 1 diode drop too!
I think this is a situation of Dave not reading the manual, and by manual, I mean the diagram you describe on the bottom of the base. No need for percussive maintenance.
Quite thorough. I'd like to see the motor and how it converts from circular to oscillating motion.
I had to try out my hand-held scope:
with a single full ground wire loop, it showed perfect sine waves, 81kHz, Vpp was 408mV. The amplitude decreases as the brush is lowered on the charger pin. no glitches. My charger is one with the UV sanitizer. Cool teardown!
Wow, this is brilliant, love how your talking about all the individual components and are also testing it with the oscilloscope. As somebody who is relitivly new to electronics and who has just had an oscilloscope donated, this is an invalable teaching aid :o)
I love watching your videos after school. keep up the good work!
You're supposed to push on the tip and help push the whole assembly out. That's how mine came out anyway.
Dave dont always read instructions. It shows on base how to remove the inards. Funny as he read how to open it but ignored the second part
Dave I replaced the battery in my unit a few years ago and the motor and the shaft do come out you just need to push harder. Perhaps the o ring on the shaft is jammed up with old toothpaste.
I rather think that the pulsing the charger goes through may be designed to help keep the
battery in good shape as this has been found to restore batteries that will not take/hold a charge anymore. But, that's just a guess.
they must be pulsing the charging so that the cap keeps IC alive, then pause to refill the cap / check battery level, then pulse charge again, etc
Another great video by Dave. A very educational video that illustrated some interesting concepts new to me, particular the CRO probe mod.
Keep up the good work and thanks for re-sparking the electronics within me.
Could be the reason. But why 800 times per second?
Dave, the two coils and two rectifiers connected at cathode (common cathode) is used in some SMPS topologies where the secondary is center tapped to provide full-wave rectification with only two diodes instead of four.
I always wondered what was in my brush, woo 4-bit!
It sounds like you came to the conclusion (but didn't say it) - I rekon that the two coils are wound in opposite directions to perform the full wave rectification.
Also, whilst charging, you need to monitor the battery voltage, so I would imagine that it is being pulsed so that a reading can be taken at the ~800Hz to prevent over-charging. You may also find that the 'active' pulse shrinks as the battery voltage rises until it's just a trickle!
Items like this are what raise the overall noise floor so much in the average home. Many are not filtered well at all and have fairly high frequency switching frequencies. It's interesting to have a scanning receiver, do a sweep and then turn off the main breaker in your home and sweep in again to see how much quieter it has gotten.
LiPo's don't have a very long life; they only have a couple hundred charge/discharge cycles. Also, they can have to tendency to explode. Wouldn't want that in your hand first thing in the morning :)
Loved every bit. Really felt I am back to my favourite domain.
I would never have thought that toothbrush teardown can be this interesting!
Might be arbitrary delay, selected by software developer. As timers are very limited on this MCU, they might have just selected maximum possible delay, and it's still 700Hz... (freq/1024 or something). Datasheet was saying that there is 10-bit timers, hence the number.
I just happen to know how these toothbrushes actually work. For example: That pulse just tells to the mcu that it is in the charger, so it wouldn't turn pass MOSFET off. You could ask me some details more.
Petri Toivonen is the mcu the 1 that Dave found?
It's pretty interesting that a toothbrush has a micro in it. Lots of fun, thanks Dave!
Excellent, really enjoyed this, one of my favourites.
I really liked the trick of using the probe as an inductively coupled current loop. Who knew a toothbrush could be that interesting? Were you ever able to get the precise post-mortem verdict? Was the battery simply past its max charge cycle limit?
Love your vids. As a starting EE I appreciate all the pointers.
I have a completely different model (2 actually) that refuses to either run or charge. I managed to successfully disassemble it non-destructively this weekend. I thought I was at the end, but you've given me a few ideas on what to check next. Thanks Dave!
ps. I don't have a non-phone camera to post a reply/reaction, but rest assured I'll do my best Dave/DaveCAD impressions while working on it!
That's such a cweet method of getting readings on the coil through non-conductive material. So innovative
The reason for 2 coils is that each coil supply the circuit with half cycle via one of the diodes, there is saving in the components cost since the alternative would be a full bridge rectifier, standard bridge rectifiers are not suitable for this frequency, additionally since the induced voltage is very small and since there is a 0.7 volt drop across each diode therefore saving a diode in this configuration in compare with the full bridge can also save on power losses across diodes, as the charger is permanently plugged-in it makes sense to reduce the consumption to as little as possible.
Why do I get the feeling Dave just set in motion a world record spike in the number of toothbrush chargers hooked up to an oscilloscope? Madness.
Anyway, so when I tried it with my Phillips Sonicare, I was getting 82khz.
This post ist really old, but it'll get some clicks anymore. I think there are two coils to pick up both halfwafes and route each over one diode only. So the drop is only about 0.7V, not 1.4V it would be by using only one coil an a diode bridge.
Did I mention that they didn't do anything? At least not on the unloaded waveform. I didn't check again with the full charging current.
I was banging the thing on a hard surface with no result, so it's stuck good and proper somehow.
Don't Brushyateeth! Take it apart!
i would have expected a reed switch in the base which activates the charger only when the toothbrush is plugged in !
Another great vid Dave. Love your work.
I think both of you got it wrong. AFAIK the disassembly is done by removing a metal ring from the top of the case - it kind of fixes the water seal to the shaft. If done properly the inner part slides out very easily.
BTW: You missed a strange feature - the motor continously receives short pulses in off-mode (~1A for several µs at ~10Hz). Desoldering it stops the pulsing, but it won't turn on when put back together. Charging the device restarts the clicking and enables the toothbrush again.
Could the pulse charging be to monitor the charging process? Charge, turn off and measure the voltage, charge some more, turn off and measure, and so on.
You only need to look at the pinout of that SO8 to tell it's a MOSFET
I used one of these for 18 years before the battery gave out. The clue is to NOT put it on the charger when it does not need recharging.
It isn't full wave rectified, it seems to be half wave rectified, second wave comes from other coil
On my Phillips, the magnets create the vibration...the vibration has a sweet spot, calibrating the correct distance gives the correct vibration, apparently the spacer in between the magnet had been worn and is gone, I also think I found a flaw in the metallurgy connecting leading to the head, I suspect the metal may have cracked.
So, I mean that maybe it is a protection against wasting energy in case of improper thing laying on the base module or broken short-circuited toothbrush-module. And interrupting of charge current is basically for single-way communication purpose.
"Beep! You've been brushing for three minutes & your society is doomed."
Renewable Oilcan Rim Living closer to Germany, we are told to brush for 3 minutes _minimum_, though that number is based on manual brushing, not motorized brushing.
Another fantastic episode. It would have been interesting to see how much power the charger was drawing from the mains while it was charging the battery, just to see how (in)efficient the coupling is.
emcgon Maybe that's why my brand new Oral-B has a wonky pushbutton under a redesigned rubber cover, while the unreadable battery compartment labeling hasn't been improved since the old design.
Just before bedtime, great upload timing :)
Hey Dave,
the companys name is "Braun", which is pronounced like the color brown in german. ;-)
perhaps those ferrites near the base were cheap magnets, allowing the base cheaply beeing turned off via a reed contact.
(i own a braun3757 which keeps getting considerably warm even with now brush hooked on. So there will be some 2-3 watts of standby waste...)
Using basic office translucent tape (the milky white kind, not the clear transparent) allows to see ship IDs sometimes better. Just stick a piece on top, massage it a bit and it may show the text without reflections etc. that make it often very hard to read.
nice one mate. I am just discovering usage of my oscyloscope so it is helpful. Cheers
Hi Dave, I know this is a rather old teardown but I have only just found it. I was researching to see if there was anything on the Braun toothbrush and whether mine was repairable.
On mine the LED stopped flashing during charging but as you observed the problem could have been in the toothbrush itself or the charging base. I was fortunate in that I had an older model charging base from an earlier toothbrush which I knew was working at the time the toothbrush failed. When I fitted my current toothbrush to the old charging base, hey presto, the LED started to flash. After several hours charging the toothbrush definitely had more oomph in the motor so the fault was definitely in the charger base.
I used a modellers razor saw to cut around the join line on the charger base and managed to lever off the base plate. As you surmised the innards definitely are potted. Nothwithstanding, I decided to pick away the encapsulant (which was a semi flexible white opaque type) and eventually I uncovered several components on the pcb. There were 4 large smd diodes and a single MELF diode plus an NPN smd transistor. All diodes and the transistor checked out ok but the MELF unit was probably connected across the B-E of the transistor since it gave me 0.6V in both directions. Unfortunately, I suspect that trying to remove the pcb from the encapsulant will end up doing a large amount of damage but it would be my guess that the charging coil has a broken connection and is open circuit. I may still go ahead and try removing the board to see what is on the other side but I was a little surprised that the charging base circuitry was a little more complex than I first imagined.
they wanted to show off?
prevent interference from other sources? be high enough to not emit an audible whine?
not enough interrupt timers left for the uC to do it on a more reasonable basis?
Awesome. I didn't know you can change the battery. Thanks. You just saved me $50 Canadian. Or not.... Either way it's coming apart tomorrow.
Ferrites and catalyst pellets are made using very similar processes (the only real difference being the material), so it would make sense that they appear similar.
Dave..ur the only I have ever come across who can turn an oscilloscope probe into a transformer to pick up high frequency signals..wow..download all of the experiences u have come across thru ur time in the industry, onto a computer..put it up for sale and watch ur self make millions (with me being ur first customer :P)...just fabulous! keep it up !!!
Awesome video, @ 28:00 I presume that's the uC disconnecting the battery from the charger so it can test the battery level - and disable the charge once complete.
I've loved wireless toothbrushes forever - and understanding their circuit is awesome.
IMHO it's an usefull to see how those thingies are made. At least it saves me the effort on breaking up my own Brown when the Battery dies..
I know it's an old video, but right next to that recycling diagram, there was another one showing you how to take it apart by pushing on the toothbrush end.
I don't know whats inside baseunit, but my guess is that it's a way mobile-unit uses to tell to baseunit "hey, I am proper current consumer, and I am charging". Base unit monitors RMS current profile via primary coil and if it doesn't match predefined profile (e.g. RMS current is constant and doesn't going low 800 times per sec), then base unit decides: oups, something is wrong inside mobile-module, or may be it's even not a module at all, but someone just put metal ring upon basemodule inductor
also I was wondering if they made a voltage doubler with a capacitor and some diodes to run the micro when it was running off the 1.2V battery. 1.2V is not enough to power the LED (if it lights up when you're using it) or the FET's gate that runs the motor. As to charging, the resistance of the coils is probably plenty to limit charging current (they seemed to be really fine wire).
are you sure those "ferrite beads" aren't actually a chemical pellet that is used to absorb hydrogen, in case the batteries vent a little? lots of aluminum flashlights (maglites, etc) have these pellets in case the batteries vent; prevents the gas building up, at least for awhile anyways.
wonder why they did not add a resonant capacitor to the coil, from my little experience with building and testing a simple ZVS oscillator (the one usually used to make flyback drivers) and making a wireless thing, I was able to greatly improve the output by adding the correct value one based on the inductance of the coil. In fact, it went from simply tickling a 10W LED with a few mA's, to completely destroying it once I added the MKP 0.1uF cap! (shoulda had some proper regulation. Oops!)
Ah, Teardown Tuesday. Highlight of the week :p - Better than the crap on TV.
I bet the two coils are the same and here's why. You said it is full wave rectified and it is not. They have two half wave rectifiers and are feeding a sine wave in one and a cosine wave in the other to produce a highly inefficient full wave equivalent. You said some mysterious stuff about why they had two coils. They were just avoiding the $ of 2 diodes at the cost of efficiency. Right?
Jeremy Adair Almost. It's sine and minus sine, 180° difference, not 90° . In addition to saving the cost of 2 diodes, it also saves one diode drop and the associated power loss. Economically, the extra coil might be at least as expensive as two extra diodes, but saving one diode drop is significant in such a low voltage circuit.
I think this was a case of TLDNR...
Although 3 pictograms is hardly too long.
My experience with braun toothbrushes is that they sometimes get wet inside and electronics get corroded. Maybe that's what explains the two coils, some sort of failover mechanism...
You half the voltage drop. Its a classical center point circuit. You need only 2 diodes and the current flows always through only one diode. Cheap and efficient!
U_center_point_circuit = SQR(2*U_eff) - U_diode
U_full_bridge_circuit = SQR(2*U_eff) - 2*U_diode
Brilliant. One of the best yet.
Braun was part of the Gillette company until 2005. Braun is now a wholly owned subsidiary of Procter & Gamble. I'm living near the german headquarters and know two engineers worked there. Better call it "engineered in germany" cause it's definitely build elsewhere. I think not a single part of it is made in germany anymore.
Dave, I don't think you covered the portion on how the ferrite beads affect the input waveform. Maybe you could do it? Would be nice to see if the ferrite beads was just engineering bluff or the real deal.
What you can do is brush some talcum powder on these ic and then wipe it with your finger that will wipe off the powder from the surface leaving the particals stuck in the indentation and then youll be able to read it easily
They wanted a full wave rectifier with only half the diode drop of a rectifier bridge. The ferrites add some more metal to the flux around the coils to increase flux linkage and thus efficiency,
I read my comment and it really wasn't clear as to what I meant. At around 7m56s you cover its effects, but from the progression of the video I infer the testing was done by the probe RF loop. I want to see, and probably others too, is the effects of it when probing the circuit charging/no charging. Maybe current waveforms? Thanks.
"Don´t turn it on take it a part"
Dam i loved that..
Most likely some kind of compromise of Cpu power use and timers and A/D conversion. The system can't handle much more information with just 32 khz CPU (4bit) doing comparisions. And running it any higher than mandatory would be waste of power..
Thank you for this interesting video. In case there are any wrist watch fans out there (including our terrific host), it is interesting to learn that electric toothbrush charger bases can be used to charge a Seiko Kinetic Movement watch. These watchers, different from “automatic/mechanical“ watches, use kinetic energy to charge a capacitor and a battery which then drives a quartz movement. It requires 24,000 shake to fully charge no watch (ouch)! The watches can also use induced electric current for rapid charging, but Seiko does not seem to be marketing their OEM charger any more. The community has been coming up with interesting potential solutions, including adapting a Braun charger base. I find this whole technology (including toothbrush/watch interface) interesting and amusing. I’m sure there are many watch fans out there who would find an explanation of all this to be very interesting and helpful. Additional information can be found by searching TH-cam for “charging Seiko Kinetic” watch or “Seiko BFK diver watch”.
I did this exact same experiment with the same toothbrush(the toothbrush was a working model) and when I put the brush on the charger the amplitude reduced unlike yours
who would have thought that a teardown of a TOOTHBRUSH could be so interesting
It's just a coil and a magnet -- a transducer, or 'speaker' more than a motor. It relies on the resonant frequency of the armature with brush head so that it can just input a little pulse once per cycle to keep the oscillation going. On the phillips sonicare, it's tuned to (I think) middle C or 'A 440' (I forget which), so that it's aesthetically pleasing and won't sound awful or 'sick' compared to most music playing in the background.
Teardown tuesday is the best. I love to see what's inside everyday devices and of course to be taught how they work. :-)