Reworking the AI Thinker T5 board

You’ll have seen from a previous posting that I was less than impressed with the AI Thinker’s “Black board T5”.

T5 board, minus QFP chip
Look Ma, no legs!

I was completely unable to get it to do anything other than make an extremely annoying noise and, judging from comments from others and postings to the AI Thinker (Non-)Support forum, I’m not alone. ¬†However, I did mention at the beginning that the board looked worthwhile just for the parts alone, so having wasted enough time trying to get anywhere with the stock item I’m going to fire up the soldering iron and massacre the damn thing (insert evil chuckle here). ūüôā

So, looking at the circuit diagram (which is just about the only document from AI Thinker that I can understand, crap though it is), it seems as though a good starting point to make something useful out of this would be to wire the DHT11 to one of the spare GPIO pins on the ESP8266 and turn it into a temperature and humidity monitor. ¬†Not exactly novel, but better than letting a perfectly good WROOM-02 gather dust. ¬†Oh, and along the way we’re going to rip that QFP micro off the board, too. ¬†So, if anyone else wants to follow along here are the relevant steps.

Before starting, please take the batteries out, or disconnect the DC supply, if you were using one.  If you have anything  else connected up to the board (USB RS232 adapter, Van de Graaff generator, auxiliary power cord from a UFO, etc.), disconnect it now (or there will be tears!).

Break out the precision, surgical instruments. ¬†Nah, forget the scalpel. ¬†That chip is the thing that’s been beeping at us incessantly for the last couple of weeks. ¬†We’re going to make it suffer (retribution is the name of the game!). ¬†Grab yourself a box-cutter (or craft knife, or disposable hobby knife, or whatever they call them in your neck o’ the woods). ¬†Nah, not that puny little pencil sharpener variety, get a nice sturdy 18mm (3/4″) one (we don’t want to hurt ourselves, we want to hurt that chip!). ¬†Put the T5 down on a solid, non-scratchable surface (-don’t- use the coffee table – I have enough trouble with my own significant-other, I don’t need yours chasing me with a meat cleaver). ¬†Take the jumpers off the pins in the middle of the board so that you have better access to the chip (and just to be clear here –and I’m talking really slowly now — the chip we’re referring to is the black square, about the size of the nail on your little finger, with 32 pretty little legs, sitting squat in the middle of the board, between the jumper block and that oh-so-annoying beeper). ¬†Now take your craft knife and cut every single one of those 32 pretty little legs right off. ¬†Take your time. ¬†Enjoy yourself. ¬†Just run the blade along the top of the legs as close to the body of the chip as you can. ¬†Use a little downward force (you won’t need much) as you cut. ¬†You’ll be able to feel the satisfying twang as each leg parts under the onslaught. ¬†Fun, isn’t it!?! ¬†Work your way round all four sides of the chip. ¬†Take your time. ¬†You’ll need to reposition the T5 board to get better access as you work (that beeper is being awkward again and the 1000uF cap and DHT11 are ganging up with it on the other side). ¬†After working round all of the sides, you should be able to turn the board upside down and have the legless chip drop off. ¬†If it doesn’t, you can pry the sides of the chip gently, just to find out where the stubborn connections are (don’t try to force the chip up, or you’ll damage pads and tracks) and then have another go on that side with the knife. ¬†If all goes according to plan, you should end up with four neat rows of pins, but no chip (if you have a small, square hole in the middle of the board, you were using too much pressure on the box cutter — or you’re rich enough to afford a decent laser).

If the legs are all still neatly lined up (and none of them are touching their neighbours — nice, civilized little leggies), you can take a chance, pop the batteries back in (or reconnect the UFO) and switch it on. ¬†You should be rewarded with blissful silence and a lit red LED. ¬†If instead you are presented with magic smoke, loud Anglo-Saxon expletives and singed fingers (or interplanetary warfare), you should make an appointment with an Optician.

To finish off this instalment of chipocide you need a decent soldering iron with a clean tip (and, if you did the switch-on test in the last section, you should remove the batteries again now; mainly because the battery holder always drops off the work bench, dragging the T5 with it,¬†at the most critical points of the rework operation). ¬†As long as the iron is up to temperature, you should be able to “wipe” off the complete row of disconnected legs on each side. ¬†There is at least one pad without a connection which may lift with its associated leg, but as long as you don’t leave the iron in once place for too long, all of the other pads should stay firmly in place. ¬†Wipe the dead legs off the tip of your iron by running it over a very slightly damp rag before starting on the next row. ¬†You can use your cleaned and tinned iron to clean up any solder bridges after you’ve taken off all of the legs (don’t use solder braid unless you’re really desperate; the heat needed to activate the braid will almost certainly lift the pads and permanently damage the board). ¬†Once you’re happy with the cleaned-up pads, try the switch-on test again, before moving on to the next stage.