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Page history last edited by MrTundraMan 7 years, 3 months ago

Screwduino - An Arduino compatible with Screw Terminals


I find most of the approaches to Arduino breadboarding annoying. They work OK if you don't know what you want to make and you just want to mess around, but they are painful when you are ready to really make something useful.


I have spent countless hours soldering simple interconnect wires on prototype shields.They give me exactly what I need/want but why do I have to spend time soldering in yet another connector that doesn't do much more than pinout another connector?


Sensor shields are a pretty decent solution since they pin out everything with a power and ground for each signal, but they can get pretty pricey when you add in the cost of the shield and cabling. Plus they get pretty tall till you have a Processor, Sensor Shield and then the vertical wiring above all that.


Then, I saw a screw shield and it looked like the ideal solution for loose wires and builder frustrations. Easy to connect with just a small screwdriver. No connectors to install for simple wiring but no accommodation for I2C connections. The stackup height has less of the same height problems as a sensor shield.  The screw shields got 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?


Here is the result which I call the Screwduino:



"In character, in manner, in style, in all things, the supreme excellence is simplicity.” — Henry Wadsworth


Screwduino Details



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.


Method Material Costs Labor Tasks Power/Ground pins Wires secure? Mounting I2C Support
Processor UNO - $30 Strip wires and solder to parts 3 GND
Wires don't stay in holes with any stress. Poor No connector
Breadboards Uno - $30 +
Breadboard $10
Strip wires or use breadboard wires 120 each PWR/GND for 700 point breadboard Moderately secure since the holes are usually “tight” Poor No connector
ProtoShields Uno - $30 +
Shields - $15
Lot of time- consuming soldering of custom wiring Vary but usually enough although maybe not connectorized in the best use Wires typically soldered so secure Poor No connector
Sensor Shields Uno - $30 +
Shields - $15
Use custom wires Excellent at 1 per Arduino Digital/Analog pin Connectors are secure Poor Yes
Screw Wings Uno - $30 + Wing Shield - $15 Strip wires and solder to parts Varies depending upon shield Connections very secure Poor No connector
Screwduino $25 (est) Strip wires and solder to parts 5 – Ground
4 – Power
Additional on other connectors
Connections very secure Excellent Yes



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.
  • Costs approximately the same as an Arduino UNO


Rev X3 PL


0.1uF 7 C1 C3 C5 C6 C7 C8 C9
10uF 2 C2 C4
1N4001 1 D1
CONN_6 1 JP1
CONN_3 1 JP2
CONN_3X2 1 JP3
CONN_8 4 JP4 JP5 JP6 JP7
CONN_4 1 JP8
JACK-3.5MM 1 K1
10K 3 R1 R2 R3
AP1117 1 U2
ATMEGA328-P 1 U1
16MHz 1 X1


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