The Final Walk (part 2)

The day came. I couldn't.

This is continuation for this.

He reached age of 12, which isn't too bad for a dog of his size. In the end it was cancer. He just crashed one day, and quick prognosis from doctor was that he might have maybe few more days, at best.

I wasn't there for his final moments as I was talking care of our (human) kids, but nevertheless, it hurt Bad, Seriuously Bad. 

We have other dog, 5 years old, and he was and still is confused of the situation. At least we have him, and will get another (later), but I won't be looking forward of next time this happens either.

This is part part of the bargain we get. They love us all their life, and we must love them back - and accept that they will leave us so soon.

 

Radio headphone teardown

These Philips wireless headphones - model SBC HC8545 specifically - were really nice - when they worked. I bought them maybe 2006 or 2007, and I remember using them quite a lot when our kid was small. Unfortunately they started acting up more and more - specifically headphones did not pick up then wireless signal until maybe after many on-off cycles - until later they just would no longer pick up the signal at all. Bummer, because they offered a lot of freedom and, unlike many headphones, were actually comfortable to wear even with glasses.

They have been sitting on my shelf for a long time now, and since I had some unexpected free time last week I decided to see what's inside.

Headphones had rechargeable batteries (two, AAA size, 1.2v 550 mAh NiMH) and they were charged when on the base station. 

Base has two screw on bottom, and after that top part comes loose - interesting design choice.

RF can has PCB in it, with seemingly just passives and few (likely) transistors in it. U5 at the right is EM78P156 - apparently simple microprocessor. I guess it controls charging, FM transmitter, status LEDs and maybe thing or other thigs. Wires you see at bottom go to charging contacts on top part.

I was looking for chip datecodes until I saw huge date stamp marking on it, placing manufacturing date to november 2006.

Unfortunately for me almost all built-to-price RF circuits are effectively black magic; I can work out how, say, spectrum analyzer RF front end works, as you can clearly see all chips and radio path involved, but these things where oscillators are built with just few passives and maybe a transistor are something I've never managed to grasp.

I thought that is might be possible that the problem might be transmitter or receiver frequency slowly crawling off the spec so receiver could no longer lock on to it.

Headphones opened up. It appears that other cup has mainly power and charging related parts (including batteries), and other has RF parts, and there is nothing tunable on RF side. Copper wire on lower right functions as antenna here. Under the RF cover is RS832U chip; I could not find any information about it. I don't think those blue ones (brown board) are related to RF stuff; brown board is connected to RF board with two pairs of wires, other being power and other audio.

This thing has been sitting on my shelf, unused, for close to ten years. But since I now had it open (previously I had opened only headphone part, finding no adjustments and given up) I thought I might as well try to adjust it, assuming it were the RF being out of tune.

My plan was: I use function generator to enter 1 kHz sine wave to one audio channel, and spectrum analyzer (with very narrow span and resolution bandwidth setting) to find RF carrier at specified frequency (helpfully frequencies - selectable, in case there are multiple devices operating at same area - are listed at bottom of base station) and try adjusting those yellow resistors on transmitter.

But guess what. When I try this, frequency seems to be spot on  (granted, considering that I do not have exact 10MHz reference for analyzer, this isn't exact science) and headphones lock on to signal immediately. 

This was with fresh non-rechargeable AAAs though. I switched back to rechargeable NiMHs (new ones, original ones were totally dead) and no more audio. Hmm. Curious. 

At this point I switched to adjustable desk power supply. Headphones would lock to signal at around 2.5v voltage level, and lose it below that. That's on a bit high side (considering NiMHs are 1.2v nominal), so I now focused to those blue adjustable pots on power board.

After a bit of experimentation I figured out that one very likely adjusts undervoltage sensitivity; I guess that under a specific voltage it cuts power completely from RF board. Other adjusts LED behavior, at which voltage it starts to flash. 

So, new plan: Set my desktop power supply to around 2.3v and start adjusting those two pots so that audio and LED drop out just below that voltage (1.15v being around 10% left on NiMH according to voltage curves, leaving a bit overhead). This turned out to be less than exact science, though, so eventually I ended up just tuning them to "works, plus some" level.

So, now I again have working headphones. If they last for year or so I consider this a big win.

A bit warning if you plan to do this yourself though: Although adjustment takes only a phillips-head screwdriver, those wires inside headphones are very fragile and are torn off the board very easily. Be very very careful with them if you choose to open your headphones up, as soldering them back can be challenging without proper tools.

Email (not!)

Last evening, maybe around 20 or 21 clock, I checked my mail (mainly to get rid of spam, I try to not reply but to shortest and clearest messages on evenings) and tried to send a quick reply, which failed. Server had went down for whatever reason (probably server was already down by that time; laptop very likely had loaded those few messages on standby earlier on evening)

Now, some 16 hours later the email is still down.

You never realize how often you need something until it's gone - albeit this is but temporary problem, but nevertheless. 

"Good, new software build works, I'll just email the details [to a guy] for testing... awwdamnit"

"So I'll just open the mail which had device serial  numbers I need to...crap"

And so on. Over and over again today.

(side note; I absolutely hate Slack (which I only used briefly for a side project once, fortunately) and other similar online messenger type software for work; there is implicit requirement of responding right now which is really disturbing for my work flow)

Not a rant (above tangent aside). It's just a bummer not being able to do so many things due to old, but apparently all-so-critical tool being unavailable. 

Crimp connectors

Crimped connectors are nice for production, but for hobbyist or even prototyping a real pain in the behind. While crimps and crimp housings are cheap, the tools to actually crimp them usual may cost several hundreds of euros easily. 

In this case I wanted to test a module which used Molex Micro-Fit type crimp, which I of course had not used before so I didn't have tools for it. Since I needed to make exactly one cable (to test that the cable drawing is correct before pushing it to production who have proper tools ready), I didn't feel like paying 150€ for tool I was going to need for just one connector.

Fortunately it is possible to "manually" crimp these by using suitable pliers. Place wire so that exposed part of wire is on inner contacts and insulation on outer and bend one side after other so that exposed wire is wrapped inside, and after that, bend outer contacts over insulation. Make sure that crimp contacts are properly wrapped around wire; if they point outwards, crimp will likely not fit in housing.

Here brown is ground that is in two places in connector, which is reason for ugly split there. And, again, this is one-off, for-quick-test-only cable so I didn't give a hoot about quality, only thing I was interested was whether designed connections are correct so that production can built it in volume without need of (expensive and annoying) rework afterwards.

You may want to also solder the wire to crimp too, to make sure that wire has proper contact. Only use just enough solder to make sure wire is soldered as a large solder glob will also prevent crimp insertion to housing. (above picture is taken before soldering)

A crimp made this way is way inferior to properly made crimp in just about every way, including but not limited to current handling capacity, mechanical reliability, aesthetics, and environmental reliability, so keep that in mind. 

This quick crimp job was nevertheless sufficient for me to test cabling (and yes, make corrections to drawing), and hopefully it will be useful for you too.

Testing new design

Whenever I design a new circuit, I order set of prototype boards (those 10 boards for 10 bucks or so services are really useful) and hand-assemble the first one testing it as I go. This means that I usually start from "outside" - power converters and thus are first parts so I can test them without risk of blowing up PITA-to-solder MCU due to bad output voltage, then proceeding inwards adding components. This is when I am building full board and not just testing specific parts of it separately, like building just MCU and parts it requires to see that JTAG works and MCU runs.

This is the main reason I don't use BGA packages - I don't have suitable tools to solder them, so I would have to order manufactured boards which can cost easily thousand or so for even small batch.

I just recently made a small new board which works as "glue" part for larger interoperating system, containing just power converter and needed connections to both directions. So as usual I built it up and tested it quickly. First attempt is success - I get correct output voltage from device so I am happy. But then it was time to go home for the day.

On morning I arrive and fire up my BK Precision 8540 electric load. As a side note, this kind of load is incredibly useful if you even semi-routinely design power supply parts. No more fiddling with resistors or lamps as load, I can actually properly test the damn thing so very easily on various voltages and loads!

For this design I used a buck converter chip I haven't used before as I needed more output current as usual, meaning this is "all new design" (well, as new as basic buck converter can be) so I start easy. 50 milliamp load? Ok. 100mA? Still ok. Up to 300mA ... and regulation just falls completely apart. And this is design that is supposed to handle up to 2A loads. Fsck.

I start probing the circuit, trying to figure out what is wrong. Bad inductor? It was quite small one, just 1.5uH, which I though to be too small for rated current, so switch 10uH one in. Issue continues. Diode? Feedback? All good. Damn it.

Finally - after hour or so - I remember to the check power supply. Which is set to 13v, but limited to just 100mA or so. Just like I always do on first try - if I expect new board to consume specific amount of current, I set the first try limit to just above that to make sure nothing blows up if there is for example short somewhere. I happily managed to forget this limit over night.

Now up goes the current limit and what do you know, now the boards works just fine up to 2.5 amps output current, well past rated maximum output (I upped inductor to 3.3uH from original, though, as tests told me that it gives better overall efficiency than originally calculated one. Might try 4.7uH if I had one to test it with.)  

That is, until converter chip gets to 130+ degrees C and starts cutting power output. This was not unexpected either, since this chip has thermal pad on bottom which is PITA to solder (read: it very likely isn't soldered at all) so thermals aren't as good as they would be on properly manufactured board. Unfortunately that isn't something I can check until I get first batch of said properly manufactured boards, so that will be the next step.

Different kinds of holiday travelers

Travel-related stuff follows.

Some ten years ago I was on a package tour in Sri Lanka, in a hotel that catered primarily for all inclusive tourists. We were there mostly because at the time the selection available via our local travel agency was severely limited, I might have otherwise chosen somewhat different hotel.

This was two-week trip. As usual, we went out just about every day to see what's around us, and for lunch and dinner at some nearby restaurant - breakfast we had in hotel. We did also book some local tour trips, especially one single-day animal-sighting tour to jungles at the center of the island. And damn, those leeches there were something else! But I digress there..

After a week, halfway through the trip we had group trip to southern part of island. What was exactly visited is not important, but part of that trip was lunch at local restaurant there. A couple next to us though that food was too hot - to me it was kinda bland, and guide confirmed this, they had especially made extra mild portions for our group. I don't blame this couple, not everyone likes their food hot, but I started discussing with them of other things, and found out that they had not left the hotel - not even once! - during that entire week. They were just there enjoying their all inclusive catering.

For me this is absolutely baffling. I could not imagine staying in a hotel for week or two, as for me sightseeing - on our own, that is - and eating out is essential part of the travel. And part of the latter is to just walk around, looking for a nice restaurant where to eat this time. Preferably different each time.

This is how we have always traveled. Before kids, and even with small kids. They follow along, in stroller when small, and we bring their food (if they can't eat "normal" food) with us. After growing a bit they follow on foot. We have never had any problems there. Yes, kids are too tired sometimes and I have to carry them back to hotel, but that's just normal.

Some other people I know on the other hand prefer all inclusive traveling with kids. Hotel absolutely must be 'all inclusive' kind and they rarely, if ever, go restaurant outside hotel to eat or do anything else either. "Too difficult" they say, but as far as I know, they have never even tried. But that's okay, it's not my problem. It's just weird to me, to me these people are missing half of the travel experience!

Of course there are not two exclusive types. Some like to rent a room/condo/apartment and even cook themselves. And that's perfectly okay too. To each their own.

I am a bit bothered though because these days it seems that at some locations you can't even get anything but all inclusive-type places (when going through agency, wife isn't too excited with idea of doing arrangements ourselves.) This itself isn't an issue, but often these are located far away from towns, locations where there is nothing but other all inclusive places nearby. So nothing to go to. I once accidentally booked a trip at such a hotel once, so we had to get all inclusive at the location, which was a bit of a bummer.

What kind of traveler are you?

ATV Electronic conversion: Final part (part 2)

Previously in the story, I had finished winter-long update of cheap Chinese kids' ATV whose 2-stroke engine gave up way too soon to electric one, and then kid overloaded and burned out electric motor in less than 20 minutes of driving.

So I ordered a few more parts. I got new motor, 300 watt one now (previous 350 watts) to lessen load to battery a bit, and larger (104-tooth IIRC) rear sprocket to replace previous one, to bring gearing down even further (and to reduce load to motor, also upping drive torque a bit).

Sprocket was more challenging to change, as compatible sprockets with three-point attachment at radius I needed wasn't available in larger sizes. In the end, I just driller holes to old sprocket (original one, for different chain) and bolted that together with new one. This moved chain line a bit, but adding a spacer to motor sprocket fixed this.

Replacing motor was also simple, take old out, new in. This time I however added a thermal fuse in between motor and controller and zip-tied it against motor housing. Thermal fuses are handy as they permanently blow out when temperature rises too high, protecting the motor from overheating. Of course I used handily available Abiko connectors for that so it can be easily changed (also, soldering thermal fuse to a wire is very, very difficult; heat from soldering iron will blow it very easily!).

And now we're rolling again. Thermal fuse blew relatively soon (30 min or so), but that's okay; I used fairly conservative (low) temperature value at first. And it's easy to change so I think we're good to go now.

Now, for next iteration (if I were to make one, I'm not planning to anytime soon!) I'd look for more powerful engine; 500w 48v or something like that, and try to work out gearing so that top speed would be about the same (20 km/h). This would hopefully make the load on engine lower, allowing driving in more difficult terrain.

I did dream about converting a motorbike, something old 250-500cc bike like Suzuki GS500 to electric, but based on my calculations I'd need about 10kW of power to have nice "city-bike" with top speed of around 100km/h. I'd be okay with that power figure, but such motors, along with suitable battery packs for it, are just impossible to get here, so guess I'll be buying a ready-made bike sometime in the future - when they start bringing those here, that is.