The Screwduino Story
A Screwduino is an Arduino UNO compatible with Screw Terminals.
We 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.
We have spent countless hours soldering simple interconnect wires on prototype shields. They give us exactly what we need/want but why do we 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, we 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 we call the Screwduino:
In character, in manner, in style, in all things, the supreme excellence is simplicity. - Henry Wadsworth
- Arduino UNO compatible
- Arduino UNO bootloader
- Select UNO in Arduino IDE to download card
- No USB connector/chip.
- ICSP header for download
- 4-pin I2C connector for easy attachment of an I2C LCD display and other I2C sensors (like temperature sensors).
- Beware there are many different I2C pinouts.
- Added 10K ohm pullup resistors (R3 and R4) from the I2C SDA/SCL to +5V
- If the user doesn't want the resistors, they can snip them out of the circuit
- Uses through hole parts so that it is easier to assemble.
- The sole exception is the voltage regulator which is surface mount for heat transfer
- 5mm pitch screw terminal blocks.
- Reset switch.
- 7-12V DC on standard 2.1mm DC power connector
- Power selection jumper (FTDI, Regulator, Screw Terminals)
- Four (4) good mounting holes that take 4-40 screws and have more than enough clearance for screw heads, standoffs and/or nuts.
- 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.
|Method||Material Costs||Labor Tasks||Power/Ground pins||Wires secure?||Mounting||I2C Support|
|Processor||UNO - $30||Strip wires and solder to parts||3 GND1 PWR||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||$30 (est)||Strip wires and solder to parts||5 – Ground 4 – PowerAdditional on other connectors||Connections very secure||Excellent||Yes|
Measured 15 mA with 9V external power input (no loads but running program).
Card Power Source - VSEL Jumper
- This jumper selects the power source for the card
- Install jumper across the USB pins to power the card from the FTDI interface.
- Install jumper across the EXT pins to power the card from the DC jack.
- Leave the jumper off when powering the card from the ISP connector.
Rev X3 PL
|0.1uF||7||C1 C3 C5 C6 C7 C8 C9|
|6-pin rt angle header||1||JP1|
|8-pin Terminal blocks||4||JP4 JP5 JP6 JP7|
|10K, 1/4W||3||R1 R2 R3|
Factory Test Procedure
- Remove power select jumper JP2 (install with 1 side of jumper on pin 1 and other side of jumper to air)
- Disconnect USB cable from ISP programmer to power programmer off
- Connect ISP cable to JP3 being careful to observe location of pin 1 (red power lead is at pin 2)
- Program the Screwduino with UNO bootloader - verify it programs without error
- Move power select jumper JP2 to USB pins
- Attach FTDI to USB being careful to observe proper polarity of connector
- Upload Screwduino Test Code
- Attach LED with series resistor
- Ground to GND connection in bottom right screw terminal
- Move LED + side to terminal pins D3-D13 and A0-A5. LED should blink shortly at each position
- Disconnect USB at FTDI
- Install power select jumper JP2 on EXT pins
- Apply 9V power to DC power jack using current limited power supply
- Verify power is 5.0V +/- 0.1V at terminal block pins +5V and Ground
- Verify LED lights briefly on terminal pins D3-D13 and A0-A5. LED should blink shortly at each position
- Disconnect DC power jack
- Move power select jumper JP2 to USB pins
- Download Arduino minimal sketch via FTDI USB connector (not via programmer)
- Part should program (this checks the D0 and D1 connections to the FTD))
- Remove power select jumper JP2 (install with 1 side of jumper on pin 1 and other pin to air)
Board ships with the power select jumper in the open position (for ISP programming) or USB (for FTDI)
Rev X6 (vs X5)
- From kiCompNL.py
First netlist: Screwduino X5\screwduino.net Number of Nets: 33 Second netlist: screwduino.net (Rev X6) Number of Nets: 33 Mismatch in net (1): +5V diff ['JP8-3'] Mismatch in net (1): /SDA diff ['JP8-2'] Mismatch in net (1): /SCK diff ['JP8-1'] Mismatch in net: +5V diff ['JP8-2'] Mismatch in net: /SDA diff ['JP8-3'] Mismatch in net: /SCK diff ['JP8-4']
Rev X5 (vs X4)
- From kiCompNL.py
First netlist: C:\Users\doug_000\Documents\GitHub\lb-boards\Screwduino\ScrewduinoX4\screwduino.net Number of Nets: 33 Second netlist: C:\Users\doug_000\Documents\GitHub\lb-boards\Screwduino\Screwduino X5\screwduino.net Number of Nets: 33 Mismatch in net (1): 5V diff ['C8-1', 'C7-1'] Mismatch in net (1): SDA diff ['R3-2'] Mismatch in net (1): SCK diff ['R2-2'] Mismatch in net (1): RST* diff ['C1-1', 'R1-2'] Mismatch in net (1): VIN diff ['C2-1', 'C3-1'] Mismatch in net (1): DTR* diff ['C1-2'] Mismatch in net: 5V diff ['C1-1', 'C2-1'] Mismatch in net: SDA diff ['R2-2'] Mismatch in net: SCK diff ['R1-2'] Mismatch in net: RST* diff ['C3-1', 'R3-2'] Mismatch in net: VIN diff ['C8-1', 'C7-1'] Mismatch in net: DTR* diff ['C3-2']
Rev X4 (vs X3)
- No netlist changes
Rev X3 (vs X2)
- From kiCompNL.py
net is in 1 but not 2 ['+5V', 'JP6-7', 'JP7-2', 'JP3-2', 'D1-2', 'R1-1', 'JP4-3', 'JP2-2', 'JP4-4', 'U1-7', 'U1-20', 'C8-1', 'C9-1', 'C7-1', 'C4-1', 'JP8-3', 'C5-1', 'R3-1', 'R2-1', 'C6-1'] net is in 1 but not 2 ['/D12', 'U1-18', 'JP3-1', 'JP6-2'] net is in 1 but not 2 ['/AREF', 'U1-21', 'JP5-8'] net is in 1 but not 2 ['/D5', 'U1-11', 'JP7-3'] net is in 1 but not 2 ['/D4', 'U1-6', 'JP7-4'] net is in 1 but not 2 ['/D0', 'JP1-4', 'JP7-8', 'U1-2'] net is in 1 but not 2 ['/D6', 'U1-12', 'JP4-8'] net is in 1 but not 2 ['/D7', 'U1-13', 'JP4-7'] net is in 1 but not 2 ['/D8', 'JP4-6', 'U1-14'] net is in 1 but not 2 ['/SDA', 'JP8-2', 'R3-2', 'U1-27', 'JP5-2'] net is in 1 but not 2 ['/VROUT', 'U2-2', 'U2-4', 'JP2-1'] net is in 1 but not 2 ['/VUSB', 'JP1-3', 'JP2-3'] net is in 1 but not 2 ['/SCK', 'R2-2', 'U1-28', 'JP8-1', 'JP5-1'] net is in 1 but not 2 ['/AD3', 'U1-26', 'JP5-3'] net is in 1 but not 2 ['/AD2', 'U1-25', 'JP5-4'] net is in 1 but not 2 ['/AD1', 'JP5-5', 'U1-24'] net is in 1 but not 2 ['/AD0', 'JP5-6', 'U1-23'] net is in 1 but not 2 ['/RST*', 'SW1-1', 'U1-1', 'JP4-5', 'SW1-2', 'D1-1', 'R1-2', 'JP3-5', 'C1-1'] net is in 1 but not 2 ['/D11', 'U1-17', 'JP3-4', 'JP6-3'] net is in 1 but not 2 ['/D13', 'JP3-3', 'JP6-1', 'U1-19'] net is in 1 but not 2 ['/D2', 'U1-4', 'JP7-6'] net is in 1 but not 2 ['/VIN', 'C2-1', 'C3-1', 'U2-3', 'K1-1', 'JP6-6'] net is in 1 but not 2 ['/D9', 'JP6-5', 'U1-15'] net is in 1 but not 2 ['/D10', 'U1-16', 'JP6-4'] net is in 1 but not 2 ['/D1', 'JP1-5', 'U1-3', 'JP7-7'] net is in 1 but not 2 ['/D3', 'JP7-5', 'U1-5'] net is in 1 but not 2 ['""', 'MTG4-1'] net is in 1 but not 2 ['""', 'MTG3-1'] net is in 1 but not 2 ['/CX1', 'X1-1', 'U1-10'] net is in 1 but not 2 ['/CX2', 'U1-9', 'X1-3'] net is in 1 but not 2 ['/DTR*', 'JP1-6', 'C1-2'] net is in 1 but not 2 ['""', 'MTG1-1'] net is in 1 but not 2 ['""', 'MTG2-1']