Screwduino
"In character, in manner, in style, in all things, the supreme excellence is simplicity.” — Henry Wadsworth
Screwduino Details
Design Concept
I find most of the Arduino breadboards annoying. They work fine if you don't know what you want, but are painful when you are ready to really make something. Then, I saw a screw shield and it looked like the ideal solution for loose wires and breadboard frustrations..
The shield me thinking. It's a great idea, but why add the shield? Why not just take an Arduino design and replace the headers/pins with screw terminals?
Design Advantages
- Gets away from all of the painful wire jumpers and pins that constantly come loose.
- Makes the step from prototype to final design much easier.
- I thought that I invented the name, but someone beat me to it.
- Since there was little information on the site and the seller didn't list shipping to the US, etc. I decided to make my own design.
- Besides, I know that nobody will make it exactly like I want it.
Design Goals
- No USB connector/chip.
- I can use a FTDI download cable to set this unit up and another development Arduino can also do downloading.
- The Hobbydino card put pin 1 on the wrong end and people who expected to plug the black wire on the FTDI cable into the square pin of the board ended up plugged in backwards. I also added marking to the reverse of the card.
- Keep the ICSP header for download and skip having the USB interface as part of the base card.
- Use a 4-pin I2C connector for easy attachment of an I2C LCD display and other I2C sensors (like temperature sensors).
- Looked around and there's no standard pinout for I2C so I went with the sensor shield pinout.
- Added 10K ohm pullup resistors (R3 and R4) from the I2C SDA/SCL to +5V.
- Only use through hole parts so that it is easier to assemble.
- The sole exception is the three (really four) pin regulator which is pretty easy to solder onto the board.
- Make the board half the size of an ExpressPCB mini-board.
- ExpressPCB boards are quick and relatively cheap.
- They make 3 (doubled to 6) boards with soldermask and top side silkcreen for $85 plus shipping (around $90).
- That's about $15 a board which is pricey but would come down in volume.
- Use 5mm pitch screw terminal blocks.
- There are smaller pitch parts which would match the ATMega part better (it has a.1" pitch) but they are not as convenient to use since the screws are too small).
- One of the real downfalls of all of the Arduino boards that I have seen is that they are very poorly designed for mounting into a real chassis.
- They have part pads on critical parts very close to their very small mounting holes.
- They are even inconvenient if you just want to put rubber feel on the corners since there are parts at the corners.
- What's the point of a microcontroller if you can't actually mechanically use it in your application?
- This board will forever be consigned to the "toy" pile if it can't really be used for real-world controls.
- I wanted four good mounting holes that could take 4-40 screws and have more than enough clearance for screw heads, standoffs and/or nuts.
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