Sync errors when uploading to Pro Mini

Hi,

I just got my new SparkFun Arduino Pro Mini 3.3V and SparkFun CH340 FTDI in the mail. I want to try out the example Blink program. Unfortunately, every time I try to upload to the microcontroller I get the same behavior:

  1. Select the upload button in Arduino IDE.

  2. Program compiles.

  3. Upload phase begins.

  4. Several minutes pass before a timeout occurs.

  5. Many error messages appear about STK500 syncing problems. The hex values change each time.

In terms of troubleshooting steps, I have completed the FTDI Tx → FTDI Rx loopback jumper trick, confirming that the FTDI is basically functional. Each time I try to upload, I can see the FTDI Tx LED flashing at the beginning of the upload.

The two microcontroller lights appear to be working well. The red power light is on and stable. It wasn’t easy to connect the microcontroller to the FTDI without soldering. Neither the Elegoo jumper cables nor the SparkFun straight headers are long enough to reliably wire up the microcontroller with the FTDI on a breadboard. Fortunately, I have some right angle headers from a handy JST kit. The right angle headers are able to securely grip the microcontroller onto the breadboard, or even directly to the FTDI.

The green microcontroller light briefly turns on at the right times. When I hold down the reset button. When I trigger a fresh upload attempt. I gather from online troubleshooting material that the stock bootloader is present.

I installed all the SparkFun boards, but could not find an applicable one. In Arduino IDE, I am targeting the Arduino “Pro or Mini” board. At 3.3V, 8MHz.

My host is Windows 10, Microsoft Surface Pro 7.

A unreliable connection will cause the issues you’re seeing. You need to solder the right angle headers onto the Pro Mini so that there’s a reliable electrical connection between the Pro Mini and your FTDI board.