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

Item	Value
USB	USB-C receptacle (Molex 2171790001), USB 2.0 only, 5.1 kΩ CC pulldowns
USB-UART bridge	Silicon Labs CP2102N-A02-GQFN24 (QFN-24)
Regulator	TLV75733, 3.3 V out from USB 5 V
Programming pins	6 pogo pins on a 2x3 array at 1.27 mm pitch (Mill-Max 855-22-006-30-001101)
Auto reset	MBT3904DW1T1G dual NPN plus two 10 kΩ resistors, driven by DTR and RTS
Buttons	RESET (SW1) and BOOT (SW2), C&K PTS526 SM15 SMTR2 LFS
LEDs	PWR (blue), TX (yellow), RX (green)
Board	42.75 x 19.00 mm, 2 layers, 1.51 mm FR-4 core, 1 oz copper, about 1.6 mm total
Mounting	2 x M2 holes plus the 3D printed clamp
Clamp parts	clamp_upper.step, clamp_lower.step, pin.step

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:

U1 pin	Name	Net
3, 4	D+, D-	USB data from J1
8	VBUS	+5V
5, 6, 7	VIO, VDD, VREGIN	+3.3V
9	~RST	R5 1 kΩ pull-up to +3.3V
20, 21	RXD, TXD	pogo TX (pad 5), pogo RX (pad 6)
19, 23	~RTS, ~DTR	auto-reset transistors (U2)
13, 14	~TXT, ~RXT	RX and TX LED cathodes
2, 25	GND	GND

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.

Silk	Pad	Net	Probe side	Target side
GND	1	GND	ground	ground
RST/EN	2	/RESET	auto-reset transistor, SW1	EN (reset)
VCC	3	+3.3V	3.3 V from the LDO	3V3
BOOT	4	/BOOT	auto-reset transistor, SW2	IO0 (boot select)
TX	5	/RXD	CP2102N RXD (input)	target TXD0
RX	6	/TXD	CP2102N TXD (output)	target RXD0

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).

File	What it is
firmware/.project, firmware/.settings/	Simplicity Studio project metadata, so the folder opens straight in the IDE
firmware/squidgrip.document	the device configuration document
firmware/squidgrip.configuration	the saved configuration: FilterVidPid 10C4:EA60 plus the config byte array

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/:

File	Part	Qty
squidgrip - clamp_upper.step	upper jaw (SQUIDGRIP embossed on it)	1
squidgrip - clamp_lower.step	lower jaw	1
squidgrip - pin.step	pins that connect the PCB to the print	2

Hardware:

Part	McMaster-Carr	Qty
M3 x 16 mm socket head cap screw	91292A115	1
M3 nyloc nut	93625A100	1
Spring (in the handle)	9271K577	2

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/):

Ref	Value / Part	Package	LCSC
U1	CP2102N-A02-GQFN24R	QFN-24 4x4	C969151
U2	MBT3904DW1T1G	SOT-363	C110150
U3	TLV75733PDRVR	WSON-6 2x2	C2868428
C1	4.7 µF	0805	C1779
C2, C3	0.1 µF	0805	C1711
R1, R8	10 kΩ	0805	C17414
R5	1 kΩ	0805	C17513
R6, R7	5.1 kΩ	0805	C27834
R9, R10, R11	2.2 kΩ	0805	C17520

Everything else is hand soldered:

Ref	Part	Notes
J1	Molex 2171790001	USB-C receptacle
SG1	Mill-Max 855-22-006-30-001101	6-position pogo pin header
SW1, SW2	C&K PTS526 SM15 SMTR2 LFS	RESET and BOOT switches
D1, D2, D3	0805 LEDs, yellow / green / blue	TX, RX, PWR
-	2 x M2 screws	PCB to clamp
-	pivot pin or screw for the hinge	see hardware/clamp_design/

Manufacturing

File	Description
hardware/squidgrip.kicad_pro	KiCad project (design rules and netclass)
hardware/squidgrip.kicad_sch	schematic (title block: Squidgrip ESP32 Interface, rev 1.4, Midnight CAD)
hardware/squidgrip.kicad_pcb	PCB layout
hardware/manufacturing/squidgrip-v1.4-gerbers.zip	gerber and drill package, ready to upload
hardware/manufacturing/gerbers/	the same files unpacked (F and B Cu, mask, paste, silk, Edge_Cuts, PTH and NPTH drills, job)
hardware/manufacturing/squidgrip_v1.4_BOM.csv	BOM with LCSC part numbers, in the JLCPCB assembly format
hardware/manufacturing/squidgrip.step	3D model of the assembled board
hardware/clamp_design/	clamp STEP files
hardware/squidgrip_pogo_2x03_P1.27mm.kicad_mod	the 6-pin pogo footprint on its own, for your own boards
docs/	photos, layer renders and the CAD image used here

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/
    │   ├── squidgrip - clamp_upper.step
    │   ├── squidgrip - clamp_lower.step
    │   └── squidgrip - pin.step
    └── manufacturing/
        ├── squidgrip-v1.4-gerbers.zip
        ├── squidgrip.step
        ├── squidgrip_v1.4_BOM.csv
        └── gerbers/             # unpacked gerbers and drill files

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