• ​PCB. PCB never changes.

    George04/14/2016 at 07:46 0 comments

    Unless your parts are too small, then it has to change.

    After few weeks of trying to solder the chips correctly and get them working. I give up and re did the design of the PCB. This time with parts that didn't have 10 legs on 2,5mm^2 of space.

    Also i figure out, it's better to NOT solder the ESP8266-12 directly to the board, but instead use the breakboard. This way you can easily remove/replace ESP.

    Power management.

    Pretty much hell simulator. How do you get stable 3.3v and up to 300mA from li-pol battery ? The battery can have any voltage from 3.6v (can be lower) to 4.2v. First thing that comes in mind is simple linear voltage regulator. But i was having hard time to find any regulator with low enough drop voltage. Yes, you can find some very low drop voltage regulators, but i didn't have much time to wait month for regulators from china. So i was limited to what i could find on shops in my arena.

    So i came up with solution. Boost the voltage from battery to higher voltage, and then use regulator. How simple. So i've got myself a MCP1640 dc-dc booster, that can do from variable battery voltage a smooth stable 5v, this is then regulated down to 3.3V with LD117. Simple, not so effective but ESP is power hungry, so the difference between 300mA and 310mA is little (numbers rent real, just approximate).

    There was also problem with the ESP itself, on solderless board it behaved really strange and unstable. In the end, it was only need of large capacitor (470uF in my case). ALWAYS CHECK YOUR POWER SUPPLY FIRST, WHEN WORKING WITH ESP. This things are really sensitive to power.

  • The Fun part

    George03/18/2016 at 08:16 0 comments

    Design was done in Eagle CAD and transferred to PCB via photosensitive film, etched and soldered. And now comes the "fun"part. It does not work.

    when you connect lipo battery (4V~) to BAT connector, output from TPS61200 (connector 3.3V/ pads for ESP) is 6.01V (?!). Datasheet say that it can do MAX 5.5V (?!). But if you connect AA battery (1.2~V), the output is 3.3V. It seems like the booster mode works right, but the buck mode is somehow broken.

    Any idea what might be wrong ?