Hi, I have a bootloader issue (I think so). One of my two Arduino Pro Mini 3.3V 8MHz refuses to upload sketchs. I MUST press reset button to make it upload. So I have reflashed the bootloader. That solved the problem. But at subsequent uploads, I have the same error. In fact, after burning the …

"can only upload once" usually indicates a problem with the auto-reset circuit. Are you using the same USB to TTL serial adapter (AKA "FTDI") on both the working and non-working Pro Mini? Do you connect it exactly the same on both Pro Minis?

pert: Are you using the same USB to TTL serial adapter (AKA "FTDI") on both the working and non-working Pro Mini? Do you connect it exactly the same on both Pro Minis? Yes, I have 3 same adapters. It's the same with the three. One arduino works always, and one is uploadable only once after bur…

Try this to determine whether the problem is with the auto-reset circuit on the bad Pro Mini: If you don't have a working auto-reset circuit, you'll need to manually reset your Arduino during the upload. When you don't have that auto-reset, and are resetting manually, you need to get the timing rig…

OK! So we now know this is a problem with the auto-reset circuit, since the upload problem is solved by a manual reset. The reason you are able to upload once without a manual reset after burning the bootloader is because when you burn the bootloader the sketch is erased from your Pro Mini and when …

You're welcome. I'm glad if I was able to be of assistance. Enjoy! Per

Good news! I have checked with a scope what's happening on DTR and RESET pin. When DTR goes down, there's no pulse on the RESET pin. On the "good" module, I can see this pulse. So I have replaced C2 (0.1

Great work on identifying and fixing the hardware problem nbenm. Assuming it was a new board that hadn't been mistreated, I do think Adafruit would have replaced the board for you, but likely it would have been just as much work dealing with customer service as it was to just fix the problem. It ma…

Can upload sketch to Arduino pro mini only once

Development Tools Uploading

nbenm August 23, 2019, 7:21pm 5

Pressing the reset button at compile time always makes the sketch be uploaded.

Topic		Replies	Views
3.3v pro mini can only load sketch once Programming	6	1185	January 12, 2018
Custom Arduino Pro Mini stuck on uploading Uploading	43	1027	August 19, 2025
Arduino pro mini 8MHz 3.3V sudden inability to upload code Uploading	7	204	October 7, 2025
Problems uploading a program into Pro Mini the 2nd time Uploading	11	1587	March 16, 2022
[Pro Mini clone] Can only upload once IDE 1.x	5	2390	August 24, 2015

Can upload sketch to Arduino pro mini only once

Related topics