|
Insert the diode. Take the 1N4004 diode and bend it's leads into a 'U' shape. Making sure the stripe on the diode and the stripe on the board line up, insert the diode. The diode protects the board in case you insert an AC or center negative power supply. |
|
Bend the leads out. Hold the diode in place with your finger, and use the other hand to bend the leads out slightly. This will keep the diode in place while you solder it. |
|
Solder the leads. Solder the leads. |
|
Clip the leads. Use your side-clippers to cut the leads flush with the top of the solder joint or board. |
Installing resistors: we'll go through the resistors by function. You can either insert, bend, solder, and cut the resistors at each step, or you can insert and bend them, then save the soldering and trimming until you've done all the resistors. It's up to you.
Resistors are not polarized and can be inserted in either direction. Personally we like to keep all the tolerance bands on one side (down and right), but it doesn't matter.
There are only two values of resistors, 10K (brown-black-orange-gold) and 1K (brown-black-red-gold). Usually they'll be connected together in groups according to their resistance.
The board locations are marked with “1K” or “10K” to help you place the resistors. You could use these markings to insert all the resistors and skip this section, if you like. |
|
10K reset pull-up resistor. This resistor pulls-up (holds high) the reset signal, so the board is only reset when you push the reset switch or open the serial port (by uploading a sketch). Insert a 10K resistor in it's place above the reset switch. |
|
10K voltage divider resistors. These two resistors divide down the Vin/9V voltage so the opamp can sense the presence of an external power adapter. Install both 10K resistors. |
|
1K LED current limiting resistors. These limit the current through the pin 13 (L), power, RX, and TX LEDs so the LEDs don't burn out. Insert all four 1K LEDs. |
|
1K serial isolating resistors. These resistors isolate (mildly) the FT232's serial lines from digital pin 1 and 0. This fixed a mild bug in the bootloader. Install both 1K resistors. |
If you haven't been doing it as you go, solder the resistors in place. |
|
Install the MOSFET. The MOSFET works like a digital switch to connect or disconnect the board from USB power when you disconnect or connect the external supply. It's “switched” on and off by the opamp. There are two TO220 devices in the kit, the MOSFET has a plasticized tab and is labeled “FQPF” then “7P06”, consult the parts list for a picture. Insert the MOSFET's leads into the three holes, then bend the MOSFET flat to the board. Make sure the flat back of the MOSFET is against the board and not the “stepped” front side. The text on the body should be up when you've bent it back. Solder and clip it's leads.
|
|
Install the 7805. The 7805 converts the DC input voltage from the power adapter (usually 7-12v) into stable 5 volt power for the board. It works by burning off the excess voltage as heat, it can get pretty warm if you're drawing alot of current or have a high power supply voltage. Install the 7805 exactly like the MOSFET. |
|
Install the crystal. The crystal is actually a metal can with leads, but it does have an actual crystal inside. It helps the microcontroller run at a constant speed, so instructions always take the same amount of time. Install the crystal by inserting it's leads (in either direction) then bending them out. Solder the leads and cut them flush. |
|
100nF reset capacitor. This capacitor works with the 10K resistor we installed earlier to generate a reset pulse when you open the serial port. It works by creating “AC coupling” between the USB controller and the ATmega's reset line. The kit contains lots of capacitors, the 100nF or 0.1uF capacitors are the 9 similar ones. They're usually smaller than the other two and are generally labeled with “104” on one side. Install the capacitor by selecting one and inserting it into the two holes, bend out it's leads. Flip the board over, solder, and trim the leads. |
|
Bend the opamp leads. From the factory, ICs have slightly bent leads. To insert them into the board, the need to have straight leads. Take the op-amp (it has 8 legs) and bend the leads straight by gently pressing it against your work-surface. |
|
The opamp. The opamp “decides” between USB power and the DC connector by switching to external power (regulated by the 7805) whenever it senses external power through the two voltage dividing 10K resistors. It then turns on or off the MOSFET to disconnect or connect the USB power. Notice that the opamp has a notch in one end and notice that the board's silkscreen legend has a notch in one end. Orient the chip so the notches align (toward the bottom of the board) and then insert the chip. Slightly bend out some of the leads to keep the chip in place, then solder it. You don't need to clip the leads unless you really want to. |
|
The microcontroller socket. Because the ATmega chip is more sensitive, we install a socket for it to plug into. This way we can replace the chip if we ever need to and the chip isn't heated during soldering. Line up the notch in the socket with the notch in the board and insert it into the holes. Bend out some leads (or hold it) then solder. You don't need to clip the leads. |
|
100nF decoupling/filtering capacitors These capacitors store up small amounts of energy and then release it when a device near them uses more energy than normal. Install these 8 capacitors just like the reset capacitor, you can solder and trim them all at once after they're all in. Make sure not to install any in the two locations marked as “18pF” (and not highlighted). |
|
18pF crystal biasing caps. The crystal requires a small amount of capacitive coupling to ground in order to work. (The exact value is in the crystal's data sheet.) There's a capacitor for each side of the crystal. Install them just like the others, in the two spaces marked '18pF' (and highlighted). |
|
Status LEDs. These two LEDs indicate when the board is on and the status of digital pin 13. LEDs are polarized and must be inserted correctly to work. The positive side is denoted by a longer leg/lead than the negative side. Look closely at the board and you'll notice there's a tiny '+' sign beside one hole, insert the positive lead into this hole. The positive lead should be away from the top-edge of the board. Solder and trim the leads. |
|
RX/TX LEDs. These two LEDs indicate when the onboard USB chip is sending or receiving data. Install these two LEDs with their positive down, close to the LM358 chip. (on v2009.3 boards, the + sign is in the wrong place, ignore it.) Solder and trim the leads. |
|
Electrolytic bulk capacitors. These help to stabilize the V+/Vin/9v and 5v levels. Electrolytic capacitors are polarized and need to be installed correctly to function. The positive lead is again denoted by a longer lead. The negative lead is denoted by a black band/stripe on the body of the capacitor. The positive hole on the board is shown with a small '+' sign, the negative hole is closest to the edge of the board. Install both capacitors by inserting their leads, soldering, then trimming. |
|
Headers. The headers allow you to connect wires or a shield to the board. There are two 6 pin and two 8 pin headers. Install the headers by inserting them through the board, holding them in place, and soldering one pin. Then flip the board over and solder the rest of the pins. Do your best to install the headers at a 90° angle to the board and in a straight line. |
|
Reset switch. This switch resets the board. The switch has four leads in a rectangular pattern. It will fit into the board in two different orientations, either one is OK. The leads will hold it into the board while you solder. |
|
Power connector. The connector can only be installed one way, insert and solder. Make sure to use lots of solder here since these are mechanical joints too, you may need to spend more time that usual heating each joint. |
|
USB connector. Again, it can only be installed in one direction, insert and solder. Make sure to solder the 4 signal pins and then really solder the two lugs since they're mechanical. |
|
Bend the ATmega leads. From the factory, ICs have slightly bent leads. To insert them into the socket, they need to have straight leads. Take the ATmega chip and bend the leads straight by gently pressing it against your work-surface. |
|
Make sure the notch in the socket lines up with the notch in the board, if it's doesn't don't worry, just remember that. Align the notch in the ATmega chip with the board and gently press it into it's socket. |