Arduino scratch programs can be uploaded via RX/TX pins rather than USB.
This experiment was done using a USB UART/USART (Universal Synchrnous/Asynchronous Receiver/Transmitter) cable. Other names such as TTL or USB to Serial are similar. This specific cable has four wires at the and with individual female connectors. The cable exposes itself in my PC’s operating system as a COM port. The cable can be used with both Raspberry Pi and Arduino.
The Arduino Uno hookup is pretty simple.
- Green to RX (Receive, Pin 0)
- The white wire goes to TX (Transfer, Pin 1)
- Black goes to GND (Ground)
- The Arduino Uno has 3 pins labeled GND. It doesn’t matter which one is used.
- Red goes to 5v (5 volt power supply)
- Red is not needed if your board is already powered. I was already powering my board with a 9v battery.
Uploading the scratch programs to the chips is a bit tricky. The chip needs to be manually reset to prepare for a new sketch. This is done by pressing the reset button just after the code is compiled, and just before it is about to upload.
The preferences in the scratch editor can be changed to show verbose output during the upload. The output may help diagnose when to click the button, and if you were successful. The upload makes 10 attempts. Attempt to reset the board on each failed attempt.
The instructions for building a MintDuino it left off with getting it to run. There weren’t any steps to program with it, and there was a notice about using a USB to serial connection,with a recommendation to use an FTDI Friend, or any FTDI cable. Suffice to say, the breadboard sat dormant for many years, and an Arduino Uno was purchased that permitted programming via USB much easier.
None of the MintDuino pins on the integrated circuit are labeled, but the last step in the instructions shows you the pin layout.
- Green to RX: Pin 2
- White to TX: Pin 3
- Black to GND: Can be either pin 8 or 22
- Red to VCC: Pin 7 (if the chip doesn’t already have power)
The MintDuino isn’t listed as a board that the Arduino scratch program editor recognizes. The default blink program has been changed, but now the green light only lights up briefly when power is first applied. I believe I may have a MintBrick.