Category Archives: electronics

Cheap power banks and why don’t they charge my Samsung S4 Active

Yesterday I bought cheap iWalk branded power bank to make my Ingress (read – working out) sessions last longer and to my dismay this power bank did not charge my phone while I played Ingress. Since not so long ago I developed this universal USB charger, I am well aware that at large charging currents (1A and more) there is quite a bit of a voltage drop in USB cable and at least modern Samsung phones sense this drop and reduce charging current. I cracked open iWalk and no surprise there, output at USB connector on bank side was 5.06V. Solution to this problem is to bring up output voltage to about 5.2V, which is still within USB specifications, but compensates for the voltage drop caused by thin USB cables.
Luckily iWalk used two easily identifiable adjustable switching step-up converters with resistor voltage divider feedback network, so all it takes to fix the issue, is to replace those resistors with new ones and see if that helps.
Stay tuned while Farnell delivers my resistors, once that happens, I promise to write a new blog post with some images.

Update – apparently that post I promised is not going to happen because there is something fishy going on with that power bank and I do not have time and/or will to figure what exactly.

Dear Atmel, Texas Instruments, Intel,…

… you all are big companies, you all say you support makers and hackers alike and you all are members of USB-IF. Maker community has a problem with USB-IF, which is probably best described in this blog post by Nick Johnson, so I thought, you, as members of this organisation and as supporters of maker community, could help convince USB-IF executives to be more open-minded and collaborative?

Thank you in advance,
Raivis Rengelis, one of makers

TCS34717 break-out or #SecretProject revealed [updated]

Jayson Tautic of TAUTIC ELECTRONICS LLC has teased his followers on twitter with some #SecretProject for a while and today was the big revelation – that is TSC34717 color/light sensor breakout.
Chip itself is a nice little gem by ams, first, it looks cool, second, it is capable of measuring R, G, B and overall luminosity with 16 bit precision each and has high dynamic range.
But there is a catch – it has weird power requirements, 3V supply and 1.8V I2C bus and it is very small. I made a decision to make the breakout 3.3V-5V compatible, so that it can be used with most popular development boards out there. Yes, I made that decision, because that was me who designed the breakout and pushed Jayson into producing and distributing it. Reason for not doing that myself is that I live in Latvia and small production runs of things like this is way more expensive than doing the same on the other side of Atlantic.
So there you are – 16bit color/light sensor with high dynamic range, compatible with 3.3V-5V hosts and communicating over I2C.
After getting first working prototypes done, joint decision was made to go on tindie with fundriser. That would let us find out if there is interest in this sensor and hopefully fund first production run. Meanwhile, I am working on Arduino library, so that break-out is usable from the day one with ever so popular prototyping platform.

The cool thing about this project is that I live in Latvia, Jayson lives in the USA and we have never met in person. Our only contacts are on internet, on twitter and tymkrs IRC.

the board is now on tindie – TSC34717 break-out fundraiser

cheap signal generator? yes please!

Who does not want a VNA and/or Spectrum Analyzer? I do, but those are a bit out of my budget right now. But I still want to play with some loop antennas for the project that is in the works, so I need a way to measure loop antenna parameters. How is it done? Well, you put known signal into loop and measure response, that’s what VNAs and SAs do, but those are expensive…

Cheap AD9850 breakout to the rescue. China made AD9850 breakout boards are available on eBay for ~6USD shipped (I wonder how they do that if chip itself costs ~15USD in 1000 quantities from DigiKey). Those things are capable of putting out 0-40MHz in sub-Hz steps of quite nice and clean sine wave, but you need a way to control them. And so “somewhat useful” Arduino sketch was born. It uses AD9850 library from ELECFreaks, one can set specific frequency with it, make AD9850 sweep through frequencies tracking generator style or sweep through frequencies in oscillating manner – back and forth.

It is probably good for testing AD9850 breakouts too, enjoy – somewhat useful AD9850 Arduino sketch.

A bit of background info. Serial control is used, see the datasheet what pins need to be pulled up and what pin needs to be pulled down to enable that and since there is no information on module available, some nice guy called Andrew Quinn has documented pinout of these little neat boards on his blog.