Friday, August 28, 2009

Assembling Wiseduino

Updated Feb 11/10

This is the documentation with instructions for assembling the Wiseduino board.
Basically, this is a list of the steps for preparing, placing and soldering the components.

I assume that Wiseduino is not the first board you solder and you have more than basic soldering skills.

I have to be honest and acknowledge that, trying to follow the high standards set by ladyada in her tutorials, I failed. Now I appreciate those tutorials even more. (I suspect that a second person took photos of her soldering; otherwise, using the timer is a gamble.)

So, let's just say that you already know, from previous projects, how to bend the IC's terminals before inserting the ICs in their sockets, you already know to cut the terminals that stick out (resistors, transistors etc) on the soldering side, you already know that polarity is important for some components (e.g. polarized capacitors) etc.

Here is the assembly process, step by step:
  1. If you have the SMD version of the EEPROM (24LC256) or RTC (DS1307), solder those first. To make it easier, flux the pad(s) with the flux pen. If not soldered first, it will be harder to access the SMD pads later. Pay attention to the orientation of the chip. Pin 1 is marked with a dot, on both the chip and PCB.
  2. Next, solder the sockets for the microcontroller, EEPROM and RTC (if you have the through hole chips). The notches on the sockets should match those in the silkscreen.
  3. Solder the battery holder. Make sure it is inserted all the way.

  4. Next, solder the power connector, then the 6-pin FTDI header.
  5. Place the micro switch on the pads and solder the middle terminal so that the switch's lever is just 1 mm out of the board's edge. After the micro switch is positioned correctly, solder the other 2 terminals.

  6. Next step is soldering the resistors. All 4 of them need to be inserted and soldered vertically. For this, one of their terminals needs to be bent 180 degrees.
  7. Insert and solder the 4 capacitors.
  8. Next, solder the 16MHz resonator.
  9. Before soldering the crystal for RTC (32,768 Hz), bend its terminals, with pliers, to 90 degrees, about 2 mm from their base. This allows the crystal to stay parallel and close to the board.

  10. Break the 40-pin female header into 4 pieces: two 8-pin headers and two 6-pin headers. This is done by removing one pin, then cutting with a wire-cutter along the empty place.
  11. Position the headers in their locations, then turn over the board and let it stand on the headers, making sure that they are perpendicular to the board. Now solder all four headers.

  12. Solder the transistor, placing it to match its shape in silkscreen.
  13. Optionally (if you want to use the XBee adapter), insert the 10-pin female header on the other side (not the parts side) of the PCB and solder its pins on the parts side.

  14. Insert the chips (ATmega328, 24LC256, DS1307) into their respective sockets, paying attention to their orientation, by matching the notches on the chip with the notches in the socket(s).
  15. Carefully insert the cell battery into its holder. Place the cell under the two plastic stoppers, then gently push the cell down against the lateral contact (it helps if that contact is lifted up a tad, from the hook, with a small screwdriver).
The assembled board should look similar to the one below.

A few clarifications and explanations about the Wiseduino board:
  • the FTDI header does not have the 5V power pin connected; therefore 5V needs to be supplied from the 2-pin power connector, usually 4 AA rechargeable batteries;
  • the power slide switch turns the power on when its position is up (towards the top of the board);
  • the board does not have standoff mounts because of the XBee adapter that can be placed on the back; in Wise Clock, the board is standing on its edge, with the LED matrix shield plugged in; should the board need to be mounted (without the Xbee, obviously) to a case or some other surface, I recommend using velcro (with sticky tape on one side);
  • the row of headers parallel to D0-D13 headers is designed to be used with .1" prototype board, similar to Seeeduino (Arduino clone from seeedstudio);
  • 3V3 is provided by the XBee adaptor, only if that is plugged in;
  • the INT pin (from RTC), can be connected to digital pin 2 or digital pin 3, to generate interrupts;
  • an FTDI cable or an FTDI breakout are required for uploading (and communicating) with Wiseduino;
  • there is no reset button, since there is always a shield (with reset button) above the Wiseduino board;
  • to conserve battery in sleep mode, the power indicator LED was dropped (that would have added 10-20 mA).
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