Elastic Sheep

Because elasticdog was already taken

Elastic Sheep header image 2

Physical design, first iteration

December 15th, 2009 · No Comments · Project Wiggum

Choosing an enclosure

My main requirement for choosing an enclosure was to find the smallest unit able to contain the GPS module and the user interface. Something barely bigger than the internal parts gathered together.

After searching the internet, I found very few choices that pleased me. A model I found interesting was the 1593K plastic model from Hammond Mfg. I ordered two of them, one black, one translucent blue (1593K datasheet).

Waiting for my order with a few evenings to kill, I began to model the important parts of my system to see how they would fit using measurements from the datasheet:

Hammond 1593K with GPS - Sketchup model

Not so bad. I could fit the GPS and a mini USB connector on the back. The front panel would receive the leds indicating the selected speed limit. And the two switches could be placed just behind the leds.

Now I could see that the PCB screw holes will cause some trouble. One hole would be under the GPS and the two front ones would be very close to the switches position. If I want to have enough space between my switches, I will have to exclude front holes and avoid using through-hole parts too close to the underside standoffs.

To access the switches from the top panel, I will need some kind of raiser glued on them.

Sourcing components

I choosed at the start of my project to try to work mainly with SMD components. According to forum opinions, 0803 components would not be too hard too solder by hand so I searched for them on Ebay and quickly found some providers of 0803 resistors and capacitors in typical value selection packs.

Here are the components I choosed to use:

Component Origin Package/Quantity
ATMEGA328P Sparkfun TQPF32
Resistors Ebay 0803, 5000-pieces kit
Capacitors Ebay 0803, 5000-pieces kit
Transistor Ebay SOT-23, 100-pieces cut from a reel
Diodes Ebay LL4148, 100-pieces kit
Crystal Ebay 16MHz, standard HC49US
Switches Ebay SMD tactile push button switch, B3F-like, 20-pieces kit
EM-406A SMD connector Sparkfun  

After some days for some and some weeks for the others, here are the bags of components:

SMD components (switches, crystal, resistor, capacitor, transistor, diodes)

And for an idea of the SMD components size along a centimeters ruler:

SMD transistor, diode and 0803 resistor close to a ruler

Cardbox prototyping

Here are some photos of the enclosures. The top and bottom parts are maintained with two long screws. Two models of front/rear panels are provided, one flat, one curved. No screws are provided to use with the stand-offs.

Hammond 1593K enclosures

To have an overview of the PCB estate, I quickly cut a piece of carboard to fit inside. Here is the result with the GPS and some components. Not far from my initial digital model.

Cardbox PCB template in Hammong 1593K enclosure with EM-406A GPS

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