Squidgrip

Squidgrip

Squidgrip is a clamp-on USB-UART probe for programming ESP32 boards. It is a CP2102N on a small USB-C board with a 6-pin pogo pin array on a thin tongue, plus a 3D printed clamp that presses that tongue onto the programming pads of a target board.

It carries the ESP32 auto-reset circuit, so esptool, the ExpressLRS Configurator, PlatformIO, Arduino IDE, etc can drop a target into the bootloader and flash it without you touching anything. There are RESET and BOOT buttons for doing it by hand, power/TX/RX LEDs, and a 3.3 V LDO so the probe can power the board it is flashing.

squidgrip in the clamp (3D render)


Copper and silkscreen: front and rear


Assembled: front, side and rear


Bare PCB front and rear, and the CAD assembly

Contents

• Features
• Specs
• How it works
• Pinout
• Configuring the CP2102N
• Using it
• The clamp
• Bill of materials
• Manufacturing
• Repo layout
• License

Features

• CP2102N USB-UART bridge on USB-C. It shows up as a normal serial port, no drivers needed on Windows 10 or newer, macOS and Linux.
• The one-time CP2102N configuration is in firmware/, so a clone comes up with a proper name instead of as a generic bridge.
• ESP32 auto-reset circuit (a dual transistor driven by DTR and RTS), so flashing tools can put the target into the bootloader on their own.
• RESET and BOOT buttons for manual control.
• Power, TX and RX LEDs.
• 6-pin pogo array on a thin tongue, 2x3 at 1.27 mm pitch, so you can reach a small pad array on a crowded board. Or get a 90 degree header for even tighter access.
• 3.3 V LDO on board: the probe can power the target while flashing, no second supply needed.
• 3D printed clamp (upper jaw, lower jaw, pivot pin) that holds the pogo pins on the target pads.
• 42.75 x 19.00 mm, 2 layers, 1.6 mm FR-4.

Specs

How it works

   USB-C ─────▶ +5V ─────▶ TLV75733 ─────▶ +3.3V ─────▶ pogo VCC (powers the target)
     │                        (3.3 V LDO)
     │ D+ / D-
     ▼
  CP2102N ── TXD ──▶ pogo RX   (target RXD0)
     │    ── RXD ◀── pogo TX   (target TXD0)
     │
     │ DTR / RTS
     ▼
  MBT3904 (dual NPN) ──▶ pogo RST/EN (target EN) and pogo BOOT (target IO0)

  SW1 = RESET, SW2 = BOOT, D1/D2/D3 = PWR/TX/RX LEDs

The auto-reset part is the standard ESP32 arrangement: DTR and RTS from the CP2102N drive two transistors through 10 kΩ resistors, which pull EN low and hold IO0 low in the right order. That is the same trick an ESP32 dev board uses, so esptool and friends can reset the target into the bootloader by themselves. The buttons do the same job by hand if you need them.

The CP2102N runs off the 3.3 V rail (VREGIN, VDD and VIO are all tied to +3.3 V), senses USB VBUS on +5 V, and has a 1 kΩ pull-up on its reset pin.

Main connections on U1:

Pinout

Six pins, 2x3 array at 1.27 mm pitch. One column is GND / RST-EN / VCC and the other is RX / TX / BOOT, and the silkscreen labels match the layout. TX and RX are named from the target's point of view, so the pin marked RX is the one the probe drives and the pin marked TX is the one the probe reads.

To put it on your own board: 6 pads, 1 mm diameter, 0.54 mm holes, 1.27 mm pitch, in a 2x3 block with that pinout. It is in this repo as hardware/squidgrip_pogo_2x03_P1.27mm.kicad_mod, and the SquidTX Nano TX board carries it as SG1, so the two work together out of the box.

Configuring the CP2102N

The CP2102N leaves the factory with a generic identity, so it needs a one-time configuration before the probe behaves like a squidgrip. That configuration is in firmware/, and Silicon Labs' own tool programs it.

Tool: Simplicity Studio with the Xpress Configurator. The firmware/ folder is a Simplicity Studio project, and its settings file pins the exact part (ffd.usbxpress.cp2102n.cp2102n_a02_gqfn24).

Steps:

1. Install Simplicity Studio, then plug the squidgrip into USB-C.
2. Open the firmware/ project, or make a new Xpress Configurator project and open its document file.
3. Use Import From Device to read the chip's current configuration, then set the fields you want. The one that matters is the Product String, because that is the name your OS shows for the port (set it to squidgrip). The manufacturer string and serial number are also there.
4. Click Program to Device.
5. Unplug and replug the probe. It comes up under the new name.

The configuration keeps Silicon Labs' VID/PID (10C4:EA60) instead of a custom one, and that is deliberate: the stock VCP driver matches it, so there are no .inf edits and no driver install. If you change the VID/PID you are on your own for driver matching.

Two notes from Silicon Labs' documentation. If Simplicity Studio does not pick up the new name after programming, clear its device cache: delete the device's .info file from SimplicityStudio/<workspace>/.metadata/.plugins/com.silabs.ss.platform.device.core/device and replug. And if the product string in squidgrip.configuration is still Silicon Labs' default (CP2102N USB to UART Bridge Controller), then that is the field to change in step 3.

Using it

1. Plug the squidgrip into USB. The blue PWR LED lights up and a serial port appears. The CP2102N needs no drivers on Windows 10 or newer, macOS and Linux.

2. Line the tongue up with the pad array on the target board and close the clamp. The pogo pins point down from the underside of the tongue, so the target sits below it.

3. Flash. The auto-reset circuit does the reset and boot pin dance for you, so anything that talks to a serial port works: the ExpressLRS Configurator (pick the target, set the upload method to UART, choose the COM port, Build & Flash), PlatformIO, the Arduino IDE, or plain esptool, for example:

   esptool.py --chip esp32 --port COM5 --baud 921600 write_flash 0x0 firmware.bin

The TX and RX LEDs blink with traffic, so you can see whether the target is answering. If a tool cannot get the target into the bootloader, do it by hand: hold BOOT, tap RESET, release BOOT.

Two things worth knowing:

• The probe feeds 3.3 V to the target through the VCC pin, so a bare board can be flashed with nothing else connected. If the target already has its own supply, be aware the two will be tied together.
• The 3.3 V rail comes from the TLV75733 and USB VBUS, so what you can pull depends on the USB port you are plugged into. It is plenty for an ESP32 (and an RF module while flashing).

The clamp

It works like an alligator clip. Three printed parts in hardware/clamp_design/:

Hardware:

The two printed pins hold the PCB to the clamp, the M3 screw and nyloc nut are the pivot, and the two springs sit in the handle so the jaws spring back open. The target board goes between the jaws, under the tongue. The one in the photos is FDM printed, so print settings are up to you. squidgrip.step in hardware/manufacturing/ is the finished assembly if you want to check clearances before printing.

Bill of materials

Parts that LCSC can assemble (this is the CSV in hardware/manufacturing/):

Everything else is hand soldered:

Manufacturing

Fab options that match the layout:

• 2 layers, 1.6 mm FR-4, 1 oz copper (1.51 mm core plus 2 x 0.035 mm copper).
• 0.1524 mm minimum track and clearance, 0.2 mm netclass tracks with 0.16 mm clearance, 0.6 mm vias with a 0.3 mm drill, 0.5 mm copper to the board edge. Those are the values in the project file.
• ENIG is worth the extra if you want the pogo pads and the USB-C shell to hold up.
• The USB-C receptacle, pogo header, switches and LEDs are hand soldered, so order those yourself along with the LCSC parts.

Repo layout

.
├── README.md
├── LICENSE                      # CERN-OHL-S-2.0
├── docs/
│   ├── squidgrip.gif                    # 3D render of the assembly
│   ├── squidgrip_assembled_front.jpg    # photo, assembled front
│   ├── squidgrip_assembled_side.jpg     # photo, side view in the clamp
│   ├── squidgrip_assembled_rear.jpg     # photo, assembled rear
│   ├── squidgrip_pcb_front.jpg          # photo, bare PCB front
│   ├── squidgrip_pcb_rear.jpg           # photo, bare PCB rear
│   ├── squidgrip_assembly_cad.png       # CAD view of the assembly
│   ├── squidgrip_copper_front.png       # KiCad render, front copper and silk
│   └── squidgrip_copper_rear.png        # KiCad render, rear copper and silk
├── firmware/
│   ├── squidgrip.configuration          # CP2102N configuration
│   ├── squidgrip.document               # Xpress Configurator device document
│   ├── .project                         # Simplicity Studio project
│   └── .settings/                       # Simplicity Studio tool settings
└── hardware/
    ├── squidgrip.kicad_pro      # KiCad project
    ├── squidgrip.kicad_sch      # schematic
    ├── squidgrip.kicad_pcb      # PCB layout
    ├── squidgrip_pogo_2x03_P1.27mm.kicad_mod   # the 6-pin pogo footprint
    ├── clamp_design/

License

squidgrip is licensed under the CERN Open Hardware Licence Version 2 - Strongly Reciprocal (CERN-OHL-S-2.0). The full licence text is in LICENSE.

Copyright (C) 2026 Midnight CAD / SquidTX

This source describes Open Hardware and is licensed under the CERN-OHL-S v2.

You may redistribute and modify this source and make products using it under
the terms of the CERN-OHL-S v2 (https://ohwr.org/cern_ohl_s_v2.txt).

This source is distributed WITHOUT ANY EXPRESS OR IMPLIED WARRANTY, INCLUDING
OF MERCHANTABILITY, SATISFACTORY QUALITY AND FITNESS FOR A PARTICULAR PURPOSE.
Please see the CERN-OHL-S v2 for applicable conditions.

Source location: https://github.com/unixvoid/squidgrip