Thursday, August 25, 2011

Calunium: Construction

Prepare the strip board
Marking the stripboard
Click on the image for an annotated version.
Mark the locations of the cuts to be made. I found this easiest by printing just the strip board layer from Fritzing onto transparency (use the correct type for your printer). I highlighted the cuts and turned the transparency upside down to give me the view of the copper side of the strip board. I then overlaid the transparency onto the strip board and marked the board. There are 70 cuts to make with a spot-face cutter and 4 with a scalpel. Make sure you cut through all of the track, but avoid damaging the copper of the adjacent tracks. Use a multimeter to check that all of the cuts have been made properly; it is much easier to test and debug an empty board than a populated one. I thought I was careful but found two cuts which had not been made completely.

Add the link wires
Insert the link wires

Begin populating the board with the link wires. Most of the link wires can be safely made with uninsulated wire if you are careful and keep the wire taught and straight. Wires which run closer than 0.1" spacing should be insulated - see the photographs on Flickr. Don't fit any wires to the underside of the board at this time. I colour-coded the wires in the Fritzing layout:

Red+Vcc (digital and analogue)
GreenGround (0V)
BlueMiscellaneous, can be uninsulated
WhiteConnect on underside (or under IC socket if possible)
BrownInsulate due to length

Add the remaining components
Add the remaining components, except for 1N4001 diode, starting with the lowest ones first. Some of the decoupling capacitors are fitted inside the IC socket; keep the leads short so that they do not stop the microprocessor from being inserted. Align the IC socket so that the notch indicates pin 1 end. Ensure that the metal can of the crystal does not touch any of the surrounding wires. Add the ISP header and solder the wires to the underside of the board.

Finally add the headers. Remember that the D8-D13 header is an offset header. I found it easiest to use an ethernet shield to hold the headers at the correct spacing.

Test the board
Before inserting the microprocessor test all of the connections. Then add the FTDI cable/breakout board and power the board from USB. The red LED should light indicating that power is applied. Then check that +5V power is applied to the correct locations of the IC (pins 10 and 30). Check that the GND connections are good (pins 11 and 31). Now add the reverse protection diode; if the polarity of the power supply is reversed the diode will conduct and trip out the polyfuse.

Insert the microprocessor, taking care to get the correct orientation. There's several possible options, see this feature comparison to select the most appropriate one. If you are intending to upload sketches via USB you will need to add a bootloader to the microprocessor. (To be covered in a later post).

Use the blink sketch to test the board. If everything is ok it should just work (it did for me).

Further photos are available on Flickr. The Fritzing files are on GitHub.

Bill of materials
QuantityItemOrder code
1ATmega164P, ATmega324P, ATmega644P or ATmega1284P
1MCP1702 LDO 3V regulator
12N7000 FET
1red LED (3 or 5mm)
1green LED (3 or 5mm)
11N4001 diode
1RXEF025 500mA polyfuseOnecall 1175860
Sparkfun COM-08357
116MHz crystal, 18pF load capacitance, HC49 case
222pF ceramic capacitor
6100nF ceramic capacitor
1100µF electrolytic capacitor, 16V
21kΩ resistor, 0.25W
110kΩ resistor, 0.25W
1SPST switchOnecall 1813689
Sparkfun COM-00097
140 pin 0.6" IC socketOnecall 4285669
Sparkfun PRT-07944
14 pin stackable headerProtopic PP4PSHF
16 pin stackable headerSparkfun PRT-09280
38 pin stackable headerSparkfun PRT-09279
18 pin offset stackable headerSparkfun PRT-09374
23 pin 0.1" header (male)
12×3 pin 0.1" header (male)
1Break-away headers, straightSparkfun PRT-00116
1Break-away headers, longSparkfun PRT-10158
1Break-away headers, right-angleSparkfun PRT-00553
42 pin jumperSparkfun PRT-09044
1stripboard, 38 strips, 30 holes long
wire, 22AWG
Most of the components I bought from Onecall (CPC/Farnell); some I already had. The Sparkfun components I bought from Proto-pic.

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