For many embedded or custom ESP-based projects (like this one), a dedicated USB to TTL chip on the main PCB isn't always necessary—especially if firmware uploads are rare.

In these cases, an external USB-to-serial programmer comes in handy.

However, uploading firmware to ESP chips isn't always straightforward.

As you may know, ESP chips require specific pin states (typically toggling EN and IO0) to enter boot mode. Without automation, you're left using awkward workarounds like holding down buttons, shorting pads with tweezers, or improvising other unreliable methods.

That's where this CH340K programmer with auto-reset comes in. Inspired by development boards, it uses two NPN transistors to control the reset and boot pins automatically during firmware upload—no more manual intervention.

This version features:

• compact design using the CH340K USB-to-serial chip
• USB-C connector for modern compatibility
• built-in auto-reset circuit for ESP chips (using the DTR and RTS signals)
• simple 1x6 header connection to your ESP board (don't forget to swap RX and TX pins)

Just connect the programmer to your ESP’s serial header and hit upload. The rest is handled for you.

💡 Make sure the CH340 driver is installed on your computer.

🔩 Want to keep the header stable during programming? You can 3D print a clip or holder.

• STL files: Modular Programming Clip