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Assembling

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zkemble edited this page Oct 15, 2014 · 3 revisions

Assembling

WIP!

For pictures see here (will be put in the wiki sometime) - http://blog.zakkemble.co.uk/nwatch-wristwatch-kit/

Tinning

If you're using untinned PCBs, like those from OSHPark, you may find that tinning the pads for the USB and OLED pins and battery pads will make them much easier to solder. Only a thin layer is needed, just enough to cover the copper (use some solder wick to remove excess solder).

USB connector

Be careful not to let solder wick its way inside the USB connector, if that happens it'll end up blocking the USB cable from being plugged in! You'll also have to get a new USB connector.

Flux

Use it! It makes SMD soldering so much easier. Some fluxes require cleaning afterwards, I use 99.9% Isopropyl Alcohol.

Before applying power

Make sure no conductive liquid (flux, alcohol etc) is left under the OLED cable, if there is the display will probably die fairly quickly.

Recommended order of soldering

  • USB1
  • SW1
  • SW2
  • SW3
  • U3
  • C1
  • C2
  • D1
  • C7
  • Q1
  • Q4
  • C8
  • C9
  • C3
  • C10
  • R4
  • C12
  • C11

Turn over

  • U1
  • RN1
  • C5
  • D2
  • RN2
  • C4
  • R3
  • U4
  • R1
  • RN3
  • C6
  • R2
  • Q3
  • Q2
  • LED1
  • LED2

Now, before soldering the last 2 components (OLED and RTC) we want see if the watch turns on. If the microcontroller is already programmed then plugging in USB will make the red LED flash a few times (that's the bootloader) then the green LED will flash and the sounder will beep. Pressing the select button should also make it beep and flash as it enters the Main Menu.

So that seems to work? Great! Now to solder the last 2 components:

  • U2
  • OLED1 (remember to feed the cable through the strap hole)

Turn it on and check that the OLED works and seconds are incrementing.

Now the battery. First solder just the positive side to the + pad. Now with a multimeter and some crocodile clips attach one end of the multimeter to the battery negative cable and clip the other end to the USB connector socket (socket is connected to ground of the watch and it's easy to attach a crocodile clip to).

Turn the multimeter the the 20mA range and the watch should turn on. When the watch is on the current draw should be around 8-11mA and in sleep mode should be less than 10uA (switch to 200uA range). You may find it jumping around a bit, that's just the RTC doing its temperature measuring and compensation.

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