Lair Of The Multimedia Guru

On the quest to improve and tinker with my 3d printer, one area to improve is noise. And a while ago i did buy a set of Stepper motor vibration dampers. The idea is quite obvious, the steppers produce noise and if they are rigidly attached to something solid and big theres alot of area that can radiate the noise. Adding a flexible damper between the source and the rest of the machine reduces the area that can radiate the sound and makes it less noisy.

The vibration dampers i got have two raised spots that have no matching holes in the 3d printers parts. They have to be removed or holes be added to where they are attached.

Filing them off by hand is very easy though, the metal seems quite soft.

Ive attached one on the X and one on the Y steppers, these 2 are the most active an noisiest steppers. The Z stepper moves so little that its inaudible except when the printer starts up and runs the auto homing sequence. The extruder stepper too is inaudible except during retracts. I plan to add a damper to it too when i take it apart for some other reason.

Testing with a microphone inside the enclosure printing a 20mm calibration cube before and after each damper addition

The difference after the 2 added dampers is quite noticeable. The top row is the original and bottom row is with the 2 dampers. The remaining noise is primarily from the hotend cooling fan and less so from the part cooling fan. I plan to replace the later with a noctua fan. The hotend fan is a 30mm fan though and 30mm fans seem rare, i am not sure from where to get a silent quality 30mm fan, noctua does not make one. I could use a 30 to 40mm adapter and different fan duct with a 2nd 40mm noctua fan though, have not decided yet.
Also it seems the addition of the dampers has slightly reduced the waviness of the sides on the printed cube. Its hard to say this definitive though as taking the stepper off and putting it back on changed things like belt tension which may have cause the difference too.

10 years ago, in 2007 3d printer prices broke through the 10000 USD barrier. Today in begin of 2017 you can get a 3d printer express delivered anywhere for less than 200 USD or € from aliexpress and probably ebay too. So obviously i had to get one :) iam not good at resisting “cheap” and cute tech.

The printer i bought was the tevo tarantula which at the time had the most orders in the price range i looked at on aliexpress. I got the version with a large print bed and auto leveling for about 250 €. I almost also got dual extrusion for free as the sloppy seller had a copy and paste error in the offer, sadly she insisted on not including that but she instead added some free replacement nozzles and more free filament.
There were not too many alternative options as i did not want a printer made from primarily acrylic plates (not strong yet brittle and not very hackable). One alternative would have been the flsun 3d i3 printer, my main reason i decided against that was its smaller build area and apparent smaller user base resulting in lack of reviews. I decided against delta style printers simply to keep the number of choices down and with the thought that i might buy a delta style printer at some point in the future.

The tarantula is primarly made of aluminum extrusions with a few acrylic plates. At the time when i bought it, it was shipped with DHL express for free. I was quite surprised about the express shipment and quickly found why, apparently express shipments appear to be subventioned in hong kong. Before receiving the printer i decided to buy a cheap set of random replacement parts for 3d printers, having read of quality issues and having experience with buying things from china ;).

The manual for assembling the printer starts quite good, the first page tells you how to put the base together suggesting to place the horizontal part in the middle, which is not optimal if you want to maximize the print area.

The 2nd page explains how to mount the y stepper motor so that it does not work with the included firmware, it needs to be mounted on the other side or the firmware changed and rebuild, also if you look carefull you will see that on the bottom there are 2 identical acrylic parts depicted, one serving no function and IIUC a left over from a older revission, they do include this part physically, its useless though.

A few pages in, the author apparently decided to stop annotating parts in the middle.

And 2 pages later all annotations are gone, and one has to use trial and error to find out that no included screw fits in some places.

Thanks to the community there are 2 video series on youtube though that explain how to put the printer together. Searching for “tevo tarantula assembly” finds these and might also find future ones. I recommand watching both and reading the manual before and while assembling, that way no mistakes should happen.

2 nuts included lacked threads entirely, one pulley was bent, the speculatively bought replacement parts included these luckily :)

The power supply works fine, sadly theres no real enclosure. The main wire terminals can be touched if the user puts his fingers on the power supply. Theres also no power switch, to switch it off you pull the plug from the wall. The fan of the power supply is quite noisy. Its output is 12V 25A (didnt test if its actually capable of sustained 25A thats just what the sticker says). I quickly replaced it by a random old ATX power supply which i had laying around, that way it has a nearly inaudible fan, no exposed mains voltage parts, a power switch and a few more voltages for free.

One of the first things i printed was a fan duct for part cooling, that improves print quality. I also covered the acrylic plate below the heated bed with aluminium tape as it appeared to soften from the heat and bend slightly requiring level adjustments between initial power on and when it had heated up. I also screwed the printer onto a piece of wood. That makes it independant of the flatness of the surface its standing on, it makes no difference in print quality though.

The LCD display as it comes with the printer isnt attached to anything and there seems no really great place to put it wthout extra parts, so i cut and drilled a piece of aluminum and attached it with that on the top. That location works. Slightly lower and in front of the al extrusion it would be in the way of the cables and tube from the print head if it moves higher up.

To better see what the printer is doing i added some 12V LED stripe with some kapton tape for isolation and stuck into the top alumiunium extrusion, it exactly fits. Powering this off the 12V line results in flicker as the heater elements being switched on and off cause +-1% voltage fluctuations. I thus stuck a cheap ebay voltage booster in line (12->13v) which fixed this until i powered it off and on, at which point the magic smoke left the voltage booster. Assuming that it didnt like the rather small boost of around 1 volt i took a new booster and this time added a fuse and fuse holder and powered it off the 5v line. After it worked fine over many hours and some aggressive power cycling i put it in a nicer box with ugly hot glue.

Ive also added a glass plate on top of the heated bed taken from a ultra cheap picture frame that was hanging on the wall, temperature cycling it to 130°C and printing a few things on it had no ill effects, no need for borosilicate glass here apparently.

And last ive build an enclosure for the printer out of wood and polycarbonate plates, some screws, silicon and 3d printed barrel hinges from thingyverse. I failed to find hinges in a shop locally that i liked. With these hinges one can also just simply remove the front door by just lifting it up. With the enclosure the print(er) wont get dusty, and is alot less noisy also it appears to have improved the results with ABS.

The door locking mechanism is build out of 3 times 2 screws and a ball neodymium magnet, and works very nicely.

A while ago i had the “need” to make a non removable “no advertisements” “sticker. To do that i tried several different methods to print on and etch metal. The methods where roughly based on various youtube videos for making other things. Its a while ago so i hope i dont misremember the details, i should have written this immedeately…
All the methods start out with a laser printer and then transfer the toner onto the object as a mask for etching.

Cold toner transfer

The image to be transferred is printed on normal paper. the object its intended to be transferred to is placed flat on a table and is wetted with a mix of ethanol and acetone something like 8:5 vol. Pure ethanol will do nothing, pure acetone will smear the toner. Then the printout is placed on top avoiding air bubbles and some timespan like 20sec is waited for the toner to soften. Next the printout is firmly pressed by some means (i used 2 pieces of wood and clamps) for some time (i waited 3 min). next the pressure is removed and one waits for it to fully dry. Next it is soaked in water for some time (3min in my case) and then with luck one can peel the paper off while the toner still sticks to the object one wants to transfer it too. Depending on the toner and paper different procedures are likely optimal. Using this to place a mask onto a piece of scrap aluminum worked so-so, some parts of the toner didnt like sticking on my first attempts. Also this method is only suitable for creating a mask for further processing, you would not want to use this to print onto metal as a final step as there is still paper sticking to the toner.

Hot toner transfer

The image to be transferred is printed on “toner transfer paper” (from ebay). The object to be printed upon is heated to slightly above the melting point of the toner (likely around 100°C) (i used a kitchen hot plate). Its important to get the temperature approximately right, too hot and the paper will be burnt. Also IR thermometers do not work accurately on shiny metal surfaces. The paper is then placed on the hot object and pressed firmly onto it (i used a silicon tube with a glass rod in it rolling over the paper several times). Next the object is taken off the hot plate and let cool. When cool the paper is removed, the toner mostly sticks fine, some individual tiny holes may be present in the transferred toner. To ensure good adhesion i reheated the object to >50°C above the melting point of the toner.

Heres an example of the result of this method using the last piece of scrap aluminum i had laying around:

Printing multiple times (if you can get the alignment right) or otherwise increasing the toner density improves the results of both methods. Also if there are defects, tiny holes or other you want to paint over them with something before etching. You also can apply some surface treatment like sanding or brushing to the metal before the toner transfer …

Etching

For the aluminum scrap pieces i had i used simple water and table salt as electrolyte, both anode and kathode where aluminum, separated by Plastic clothespins and held together by sticky tape. After several tries i learned that lower currents and voltages seem to work better. that is for the small piece i had something like 1.8V and i think 100mA for 2 hours. (Note, if you attempt to repeat this, you do so at your own risk, Electrolysis of water and table salt produces different things depending on the condition and electrode materials. Other electrolytes may be a better choice even though NaCl seems safe in this setup.)
After etching the toner mask needs to be cleaned off (unless it fell off already which it sometimes did and sometimes it stuck really
well) it can be removed with acetone or with patience also with other random things.

The electrodes with the cut up pieces of a clothespin and tape:

The results of several attempts

Transfer without etching

One can of course also skip the etching and keep the “mask” as the final result even with color or even as a addition to a previous etching step. This also works on glass (if you can heat and cool it without it shattering)

The results from my attempts for this:

After this i had no scrap pieces of aluminum left nor really time and the problem i was trying to solve (someone repeatly removing my fathers no advertisement sticker from his mailbox … to collect more free coupons or paper … solved itself as she stopped)

A few days ago i replaced my acer notebooks keyboard, several of its keys had become unreliable months ago I first attempted to clean it but that just broke some little plastic part off with no improvement. The process was a bit boing, 24 pages of the (well written) service manual 36 screws some epoxy and 2 hours later my note book was working again with new keyboard.
This notebook is definitely not built to be serviced, having to disassemble it partly from the bottom to get to the top. Some screws screw into plastic, many of them have the plastic cracked after screw removial making reassembly tricky. Some screws screwed into metal inserts, 2 of which broke off without me even touching them, requiring the epoxy to reattach the metal inserts onto the brittle plastic. There are also plastic latches before you disassemble things, the ones of the main door at the bottom are indestructable it seems but the ones deeper inside seem not intended to be reused judging from the smaller number of clicking sounds when reassembling …
My previous acer notebook i once dropped and it still works. It also still has its original keyboard and the hp omnibook i had before i could use until many of the keys on its keyboard had no readable symbols on them anymore. Though today that old hp notebooks plastic parts have also become extreemly brittle but its keyboard could be exchanged by just removing one or 2 screws IIRC.
In the distant past electronics seemed to last forever becoming obsolete long before failing. Now it seems most stuff fails long before becoming obsolete.

Both keyboards after the replacement:

And most disappointingly no parts where left unused after reassembly nor where any missing. I guess my workspace was too tidy.

DMMs are usefull but for some things they are a bit inconvenient and bulky. So for fun and less so for potential usefulness i bought the 8 in 1 voltage tester depicted below, smaller than a DMM, puts a small decreasing load on the tested circuit allowing things like GFCI testing and so on.

But when testing at 220V AC it produced:

In fact the 380V LED lights up down to 175V.
Opening the thing up without destroying it proofed to be some effort, the inside:

I was already starting to trace things and draw a crude schematic to debug this when i noticed:

A unpopulated component, for a fraction of a second i considered a optional features quickly discarding that in favor of the hypothesis of excellent quality management in this ultra high end (it cost almost 5 euro) tool.
So after a bit of thinking, guessing and testing i wanted to solder a 100k resistor in there but my 10-15 euro variable power soldering iron didnt work anymore. That one was even from a local shop not ebay. Luckily i still had my grandfathers soldering iron:

Which after exchanging the tip worked perfect:

and after that all voltages work fine, including 220v:

PS: Recommendations for a good and cheap variable power soldering iron are welcome! ;)

My grandmother has 2 mobile phones, both identical, they have an old style numeric keypad, tiny monochrome display. They are both old and look like they were used a lot, one works. The other sometimes works, there thus was need to obtain a new phone. Both phones she has have been bought by herself many years ago, they were phones intended for seniors and honestly they are just shit in every way IMO even when they were new, they are even hard and awkward to use for someone young.
I thus bought a cheap android phone for her, i was very curious if that would work out, she is 89 years old and AFAIK never used a computer or smart phone before. Going for a cheap phone that fits the requirements was done as this was quite experimental and i was not sure if she would loose the phone in a week or someone would steal it maybe. The phone needed a big battery as recharging had been a problem with her other 2 phones or possibly their batteries have aged too much.
The chosen phone was a cubot note s, 4150mAh 5.5inch IPS display 2/16gb mem, 4core, 3G, dual sim, dual cameras, … for less than 90euro. The 2 things the phone doesnt have is a notification LED and LTE support. Neither appeared important for the intended use.

On the software side, I installed

• Big Launcher and configured it so everything one needs is on the home screen, like buttons for directly calling family members.
  I also tried Phonotto, necta and other launchers Phonotto seemed not to fully work with android 5.1, occasionally dropping one out of the dialer without ending the phone call, which made it not ok. I chose big launcher as i had to chose one and it seemed mostly ok
• Missed call reminder, Which allows all kinds of vibration and led flash and screen on/off based notifications (due to missing notification LED on the phone) But even if it had a LED the bright LED flash and vibration should be better
• Ultimate Caller ID Screen HD, With all extra buttons disabled and the the screen with just simple buttons for accepting a call and hanging up.
• quick snap, as a simpler camera app but this wasn’t used sofar AFAIK
• automate, Used for giving spoken low battery alerts at <30% and similar if the phone charging is interrupted before reaching 60%. Some testing though showed that it did not work reliable (it got stuck when there was no internet connection) and thus was not enabled when i gave the phone to my grandmother, we also were unsure about the notification activating in inappropriate situations

The above, i believe was the initial set of apps when i gave the phone to her, the biggest problem was surprisingly switching the phone on (the lockscreen was also entirely disabled), the button is basically invisible under the silicon protector thingy that comes with the phone. Some sticky patch cut into arrow shape stuck onto the phone helped though.
When we called her on the phone for the first time after leaving she did not succeed picking it up, even though she could do it when we where there after some tries. So it seemed a failed experiment, but a few days later and corrected volume settings she made multiple phone calls with it alone :)
Further improvements we did were, that we installed some software to lock the volume settings (cant remember its exact name, but there are multiple that do the job), the volume buttons are next to the power button. Disabling the “telephone answering machine” as it picks up too quick and only adds the problem of dealing with missed calls, which was a problem with her previous phones already.Call Auto Answer & ReadItToMe configured so it automatically picks up calls from family members after 10 seconds. And we also enabled speaker-phone by default. We also considered to install Gravity Screen – On/Off but as she managed to switch the phone on it seemed more a potential way to switch it on unintended.

One thing that kind of annoyed me alot while configuring things is finding apps that arent full of ads. It seems everything for android these days is either spyware, ad-ware, or costs money. I wish the play store would have a way to search for things that are good old free no hooks attached type of ware. But i guess google wouldnt like how they then would have to mark their own apps.

Also for the case of older people with little smart phone experience, a somewhat more integrated UI for android would be nice. Not needing to install a dozen things that might interact badly or that then dont work with the latest android version.
Something that when randomly shaking or pressing buttons on a phone in standby mode would display an arrow pointing to the power on button. Some reliable and unobtrusive low battery notification would be nice too, and that one not just for seniors, the dim red notification leds are kind of easy to miss. Some easy always available help button that can explain the available buttons/options on any screen, …

A while ago searching around on ebay for geeky/nerdy toys i found some Thermoelectric coolers/peltiers for around 2$ with free shipping. So i bought a few of them …

They all worked fine, one had a hole in its silicon sealant though which ive “fixed” with hot glue (first heated the element up to reduce moisture inside then re-sealed it), i dont remember why i didnt use silicon …

I experimented a bit around with 1 and 2 stage TECs on a old heat-sink + fan that was laying around, the best combination interestingly was 2 stages first at 12V 2nd at 5V. though the gain for 2 stages over 1 stage was disappointingly small, IIRC a little over 10°C. Its also interesting to note that my chinese IR thermometer was not able to measure the temperature of the frosted top, it displayed way too low values. Actual real lowest value achieved was measured with a Type K thermocouple, frozen onto the TEC in a drop of water and frosted over for a while (the snowy stuff that forms should provides some extra isolation).

The 2 TECs in above are attached with cable ties, which was very limiting in what could be placed on top

For some reason yesterday i decided to test using the TECs for heating instead of cooling by reversing the input polarity.
That indeed worked and the same device happily boiled drops of water. I didnt think too deep about what the maximum temperature for the TECs was, i didnt expect failure below 180°C, but the top element died at probably around 120-130°C (K type thermocouple in drop of oil on top).
Not entirely believing the apparent facts, i picked another unused separate TEC1-12706 and retried, heating it to 160°C
which seems to have done no harm to it. Though i used the IR thermometer for measuring the 160°C, i should retry this probably with both thermometers but then according to the ebay article page they are max 70°C ;)

Breaking my TEC cooler toy i took it and the failed TEC element apart, Its failure mode was that it showed >10megohm resistance. Cutting its sealant away, it looked like this:

And separating it further with a tiny bit of heat and force (probably only heat was needed)

Also interestingly none of the remaining individual elements tested open, they all had low resistance. I know nothing about TEC failure modes but i wonder if one little part had just cracked from the heat and maybe mechanical stress. They are all in series so one cracking the wrong way should show similar symptoms …

To rebuild the TEC2-toy now ver2, i placed a piece of aluminum on top and tried to attach it with cable ties, but this proofed frustratingly unstable

My next idea of fixing it with screws, bolts, nuts or such wasnt an option as i lacked parts of sufficient length with non ridiculous diameter. So i cut 2 pieces of the same aluminum stuff and fixed it with 4 springs created out of a single larger spring separated by some foamy stuff for isolation:

In action:

Also i tested cooling and heating of a glass container with a liquid. (for cooling a drop of water was used as thermal component between glass and aluminum for heating a drop of minnaral oil). Without isolation, the temperature fell to +9.5°C in 1 hour and with some isolation to prevent the warm air from the fan hitting the container, to +2°C in another hour. Iam quite sure sub zero is achievable with a real attempt to prevent coolness loss but i kind of lost patience.
on the hot side i achieved 67°C with the TEC itself being at around 100°C, so if one would risk damaging the unit it might be possible to boil water in a container with it.

6 weeks ago (11th november) i switched both the tags i have on and put them in the same drawer in my kitchen, i then tried to connect to them when i remembered about it and tried to make them beep remotely. the itag failed to connect the next day but worked again after removing the battery for a moment, the day after that it failed again and no longer recovered after removing the battery (which was at 2.897V but apparently could not supply enough current anymore for the tag to power up), on last connection it showed 100% battery. Powering the itag off a bench power supply showed that it still worked fine.
Meassuring its current draw, shows 3uA when switched off, and around 1.1mA when on, considering that the tag has to be on to be of any use, that renders it useless as it eats batteries too quick.
the smart finder / “small lovely” continued working till when i tried it yesterday when a connection was no longer successfull, pushing its button it still produced a silent click which on repeated presses got weaker. so it too used up its battery after about 4-6weeks (i had last tried it 2 weeks ago when its battery was shown at 100% in bluthooths stuff).
Meassuring its current consumption, it draws 2.4uA when off, and when on after some initial higher draw fluctuates between 2.7uA and around 88 uA with an apparent average of 39uA.
Note, the current draws depend significantly on the voltage for the itag at least (i tested at about 3V), also the uA meassurements where at the edge of what my multimeter could show so they should all be considered approximate.

In summary, the itag i got eats its battery in 2 days, the smart finder thingy in about 4-6 weeks. I would have tested more tags but these where the only 2 i received. another one i ordered off ebay was lost in shipping apparently

A while ago i bought an old variac on ebay, it was in good shape but lacked any meter, originally that model had a analog voltmeter or something. That was missing, some cut wires sticking out of where it was. As i got it it also had a 6.5Amp fuse in a fuse holder marked as 4A and its output wires connected straight bypassing the fuse.
When i bought it my plan was to stick a cheap digital meter to it, which is what i did and also a modern and correct “fuse”.

The meter i found and got supported 80-250VAC, i failed to find one supporting AC voltages down to 0V. I originally had not planed to modify it, as it didnt seem a big issue, but it was just annoying that around 70V it dropped out and displayed junk and then went dark.

Inside it looks like this:

I saw 2 obvious ways to make this work with lower voltages, first is to make its AC->5vdc supply work with a wider range of AC voltages, the other is to split the voltage sensing off the supply. As my variac provides around 250VAC in addition to the variable and isolated output, using that seemed to be the easier solution.
But before i continue, a warning, do NOT try this unless you understand what you are doing, mains voltage can be dangerous and can injure or kill. Also not all similar looking such meters are neccessary identical and this modification might result in undefined behaviour in that case.
The voltage is sensed through R3 which is 1Mohm, removing it:

Results in a working amp meter with 0V:

Next we need an additional connector for the separate AC power and AC sense input, to get that we just need to clear 2 from solder and cut the 2 connected pins on the other side using a file. Note, if you try this modification double check that the new freed up pin is not connected to anything else by some tracks below, it wasnt in the meter i had but that doesnt imply its not in yours.

Now its tempting to use the same or a new 1meg ohm resistor for the new sense wire added below (and i did and it worked) but this is probably not safe, first you should clear the conductive parts of the logo which are below, off the board and use 2 resistors in series as there is about 230VAC over it, yes it was already before any modifications but still.


You can also slightly adjust the value of this resistor to adjust/finetune the volt-meter.
The other side of the resistor is connected with a mod wire to the newly freed up pin on the other side. Again using a file to make some cut in the board to nicely route the wire around.

The new connector is then connected like this:

1. Variac secondary tap 1
2. Variac secondary tap 2 and Load/Output connection A
3. Variac secondary tap 3
4. Load/Output connection B

Testing, works:

A while ago in coverity while fixing FFmpeg bugs there was a some kind of Nominate a bug, win a prize thing, i didnt ever nominate one but this was when i learned about the existence of tile which would have been the prize one could win. A BLE device that can be attached to something valuable and that can then be searched and found with a recent android or iPhone, or the other way around using the device to find your phone.
This seemed potentially useful to me, though i personally have never lost my keys or phone for more than a few seconds, i know someone who does have that problem. So i thought buy a tile or 2 they might come in handy for something but then i saw the price, non replaceable, non rechargable battery and thought ok, didnt expect someone would be that lame. I guess one should not expect any company not to attempt to rip its customers off to the maximum extend possible.

Lucky there are many similar devices, so the goal was to find the cheapest that works and is not just tied to a ridiculous business model. So i bought some of the cheapest i could find (they of course all have user replaceable batteries …)
First is something that identifies itself as

ITAG

The above one is one example of these, they come in many different shapes, cost less than 5$ with free shipping. The first i got had a different shape and came with a dead battery and also ate a new battery within a day. The second i got is the one pictured above, which worked more or less.
When Off, A long press on its large surface switches it on with 2 beeps.
When On or connected a long press switches it off with a long beep (this renders it useless as its easy to press by mistake)
When on but not connected its led also continuously blinks, draining the battery but making finding easier, it also at least once hanged and required the battery to be disconnected for a moment to function again.
On the BT protocol side setting immedeate alert to 2 results in 30 beeps and led blinks, setting link loss to 0 or 2 has no effect, the device always beeps on unintentional connection losses as far as i could figure out. pressing the button results in a notify with value 0x01 on 0000ffe0-0000-1000-8000-00805f9b34fb / 0000ffe1-0000-1000-8000-00805f9b34fb.
To make the itag only blink and not beep on immedeate alert, 0000fff0-0000-1000-8000-00805f9b34fb/0000fff1-0000-1000-8000-00805f9b34fb can be set to 0x00, this is remembered over disconnects but not over switching the tag off. All other values seem to cause blinking and beeping.
To identify it this may be helpfull:

• 0x2A29: CEVA
• 0x2A24: BT 4.0
• 0x2A25: 12x07x2012
• 0x2A27: SM-1
• 0x2A50: Bluetooth SIG Company: Ceva, Inc. (formerly Parthus Technologies, Inc.)
  Product Id:13330
  Product Version: 26369

Smart Finder

The above is another sub 5$ tag, which appears identical (minus the logos) to tags on amazon from chirotronix and ikee.
The official software for android (“small lovely”) has a rather long list of unneeded permissions like for the previous tag (“iTracing”) but for this theres also no inofficial sw i could find for android which supports these tags, which is why i reverse engeneered the protocol
When off a long press switches it on with a long beep, to switch it off again 5 rapid short presses are needed (resulting in 3 beeps).
When in On mode pressing the button results in 2 beeps this also causes the “#255 Manufacturer Specific Data” to change from 0x58,0x48,0x52 to 0x58,0x48,0xFF for a few seconds, apparently to identify which of potential several devices one wants to connect to. Switching the device off also seems not possible while it is connected. On connect and disconnect its led flashes once.
Protocol wise neither “link loss” nor “immedeate alert” have any effect that i could identify. To make the device beep and blink a command must be written to 0000fff0-0000-1000-8000-00805f9b34fb / 0000fff1-0000-1000-8000-00805f9b34fb. A single 0xAA results in some short beeps and blinking. Its also possible to write a 5 byte command 0xAA 0x03 count duration1 duration2. The count is the number of beeps, the 2 durations are the beep and non beep durations in milli seconds, i dont know what the 0x03 does or if there are other interesting commands.
To detect button presses the device can send notifies on 0000fff0-0000-1000-8000-00805f9b34fb / 0000fff1-0000-1000-8000-00805f9b34fb with a 3 byte value, it is either (0x01 xx 0x00) xx = number of short button presses or (0x02 0x00 xx) xx = number of seconds button is hold
To identify it this may be helpfull:

• 0x2A29: SIGNAL
• 0x2A24: BT A8105
• 0x2A25: 00001
• 0x2A26: F4F5V02
• 0x2A27: A8105F4
• 0x2A28: 1030627

The name of teh device is “AMIYJ_5B68”, i dont know if this is true for all these devices, google seemed not to have any hits on that.
It seems using a A8105, (the ITAG seems using a BK3431) datasheets can be found with google.
Interestingly theres also a entry for “Heart rate” on the bluetooth level, so i guess this shares some code with some other devices.

Hope something above is useful to someone

Update: 2015-11-09: corrected itags link loss behavior
Update: 2015-11-10: Added names of the official apps
Update: 2015-11-14: Added itag blink only info (found by and thanks to Joachim Schäfer)