Probe

The PomeLabs Probe Module (PML-PR-01) puts precision measurement directly into the signal path. Two calibrated $1\,\mathrm{\Omega}$ shunt resistors sit in-line on the S+ and S− channels simultaneously — measure the voltage drop across either shunt and you have the current; measure either terminal to ground and you have the node voltage. One module, two channels, non-intrusive, always live.

Revision: v1.0 | Part Number: PML-PR-01 | Series: PomeLabs Core Kit

Pinout

Probe Pinout

Schematic

Probe Schematic

Digital Twin

In the PomeLabs App, the PML-PR-01 is mirrored as a digital twin in both the Playground and inside any Connect Activity. The twin streams live voltage readings from both shunt channels simultaneously — plot current waveforms, log differential measurements, or trigger on threshold crossings in real time without touching the circuit.

Controls — parameters you can set from the App

UART TX — Left port · pin TX_L-1 · serial data source

Drives USART1 transmit line through D1 ESD protection to the Left node connector.

UART TX — Right port · pin TX_R-2 · serial data source

Drives USART2 transmit line through D2 ESD protection to the Right node connector.

Monitors — values streamed back from the module

S+ channel voltage · pins S+_In / S+_Out · voltage trace

Live voltage at the input and output terminals of R1. Differential reading gives current: $I = \Delta V / 1\,\mathrm{\Omega}$ .

S− channel voltage · pins S-_In / S-_Out · voltage trace

Live voltage at the input and output terminals of R2. Differential reading gives current: $I = \Delta V / 1\,\mathrm{\Omega}$ .

UART RX — Left / Right ports · pins RX_L-1, RX_R-2 · serial data traces

Inbound data from downstream nodes through D1/D2 ESD protection back to the Backend MCU.

Datasheet

1. Overview

The PML-PR-01 inserts two precision $1\,\mathrm{\Omega}$ thick-film shunt resistors (R1 and R2, ERJ-1TRQF1R0U) in series with the S+ and S− signal paths respectively. The resistors are placed inside the FE Function block between Pogo-connector measurement points (S+_In / S+_Out and S-_In / S-_Out), allowing a Backend MCU or external instrument to measure the differential voltage across each shunt and derive the instantaneous current with a simple Ohm's law calculation.

At $1\,\mathrm{\Omega}$ and $1\,\mathrm{W}$ continuous power rating, each shunt can carry up to $1\,\mathrm{A}$ continuously ( $P = I^2 R$ ) before reaching its thermal limit, making it suitable for measuring signal-level and low-power load currents across the full PomeLabs Core Kit range. The $\pm 1\%$ resistor tolerance and $\pm 100\,\mathrm{ppm/{}^\circ C}$ temperature coefficient ensure measurement accuracy is dominated by the ADC resolution of the Backend MCU rather than the shunt itself across the full $-40\,\mathrm{{}^\circ C}$ to $+125\,\mathrm{{}^\circ C}$ operating range.

Two USBLC6-2P6 ESD protection devices (D1, D2) protect both UART communication ports.

2. BOM Components

Ref.	Type	Value / Part	Role on this module
R1	Thick-film shunt resistor	ERJ-1TRQF1R0U (Panasonic)	$1\,\mathrm{\Omega}$ , $1\,\mathrm{W}$ , $\pm 1\%$ , $\pm 100\,\mathrm{ppm/{}^\circ C}$ . Inserted in series on the S+ signal path inside the FE Function block. Voltage drop across R1 = current in S+ channel $\times\ 1\,\mathrm{\Omega}$ . 2512 SMD package.
R2	Thick-film shunt resistor	ERJ-1TRQF1R0U (Panasonic)	$1\,\mathrm{\Omega}$ , $1\,\mathrm{W}$ , $\pm 1\%$ , $\pm 100\,\mathrm{ppm/{}^\circ C}$ . Inserted in series on the S− signal path inside the FE Function block. Identical to R1.
D1	ESD protection IC	USBLC6-2P6 (ST)	IEC 61000-4-2 Level 4 ESD clamp on Left UART port. $3.5\,\mathrm{pF}$ max. SOT-666.
D2	ESD protection IC	USBLC6-2P6 (ST)	IEC 61000-4-2 Level 4 ESD clamp on Right UART port. Identical to D1.
Vcc	Connector	RH-5019	5V_Module power input connector. Supplies the module Vcc rail.
GND1, GND2	Connector	RH-5019	Left and Right ground reference connectors inside the FE Function block.
S+_In, S+_Out	Connector	RH-5019	Input and output measurement points on the S+ channel, flanking R1.
S-_In, S-_Out	Connector	RH-5019	Input and output measurement points on the S− channel, flanking R2.
p1, p2	Connector	Node headers	Left and Right node connectors exposing +5V, GND, S+, S−, RX/TX, TX/RX to downstream modules.

3. Electrical Specifications

Shunt specifications from Panasonic ERJ-1TRQF1R0U datasheet. ESD specifications from ST DS4260 Rev. 7 (USBLC6-2P6, Dec 2021).

3.1 Shunt Resistors (ERJ-1TRQF1R0U)

3.1.1 Absolute Maximum Ratings

Exceeding these values may permanently damage the shunt. Stress ratings only.

Parameter	Max Value	Unit
Continuous power dissipation ( $P$ )	$1$	W
Continuous current at $25\,\mathrm{{}^\circ C}$ ( $I_{max}$ @ $P$ = $1\,\mathrm{W}$ , $R$ = $1\,\mathrm{\Omega}$ )	$1.0$	A
Operating temperature	$-55$ to $+155$	°C
Storage temperature	$-55$ to $+155$	°C
Short-time overload ( $5\,\mathrm{s}$ pulse, $5 \times P_{rated}$ )	$5$	W

3.1.2 Recommended Operating Conditions

Parameter	Recommended Range	Unit
Continuous current	$0$ to $1.0$	A
Ambient operating temperature	$-40$ to $+125$	°C
Differential measurement voltage	$\pm 1.0$	V
Recommended ADC resolution	$\geq 12$	bits

3.2 Probe Connector — RH-5019

3.2.1 Absolute Maximum Ratings

Parameter	Value	Unit
Maximum voltage	TBD	V
Maximum current per pin	TBD	A
Operating temperature	TBD	°C

3.2.2 Recommended Operating Conditions

Parameter	Recommended Value	Unit
Recommended insertion cycles	TBD	cycles
Contact resistance	TBD	$\mathrm{m\Omega}$
Recommended operating voltage	$5$	V

4. Pin Descriptions

All signal pins are referenced to GND.

Pin / Net Name	Direction	Description
S+_L	Input	S+ signal input from the Left node connector. Enters the FE Function block and feeds S+_In / R1.
S+_R	Output	S+ signal output to the Right node connector. Exits the FE Function block from S+_Out / R1.
S-_L	Input	S− signal input from the Left node connector. Enters the FE Function block and feeds S-_In / R2.
S-_R	Output	S− signal output to the Right node connector. Exits the FE Function block from S-_Out / R2.
S+_In	Measurement point	Upstream terminal of R1. Connect ADC input here for differential current measurement on S+ channel.
S+_Out	Measurement point	Downstream terminal of R1. Connect second ADC input here for differential measurement.
S-_In	Measurement point	Upstream terminal of R2. Connect ADC input here for differential current measurement on S− channel.
S-_Out	Measurement point	Downstream terminal of R2. Connect second ADC input here for differential measurement.
5V_Module	Power In	$5\,\mathrm{V}$ supply input. Powers module Vcc rail via RH-5019 connector.
GND1, GND2	Ground	Left and Right ground references inside the FE Function block. Both connect to the common GND bus.
TX_L-1 / RX_L-1	Input / Output	UART transmit and receive — Left port, through D1 ESD protection.
TX_R-2 / RX_R-2	Input / Output	UART transmit and receive — Right port, through D2 ESD protection.

6. Connection Guide & Common Errors

Correct connection sequence:

Connect GND to the common ground bus shared across all modules.
Connect 5V_Module to a regulated $5\,\mathrm{V}$ source.
Insert the Probe Module in series with the signal path — S+_L / S-_L to the source, S+_R / S-_R to the load.
Connect Backend MCU ADC inputs to the measurement point pairs: S+_In and S+_Out for S+ current, S-_In and S-_Out for S− current.
Use differential ADC mode or subtract two single-ended readings to obtain $\Delta V$ .
Apply $I = \Delta V / 1\,\mathrm{\Omega}$ to convert voltage to current.

Common wiring errors and consequences:

Mistake	Symptom	Correction
Current through shunt exceeds $1\,\mathrm{A}$ continuously	Shunt self-heats beyond rated power ( $1\,\mathrm{W}$ ); resistance drifts then device fails	Keep continuous current $\leq 1\,\mathrm{A}$ . For higher currents, use an external lower-value shunt.
Measuring single-ended voltage at S+_Out only	Reading includes both shunt drop and source voltage — current calculation incorrect	Always measure differential: $V_{S+\_In} - V_{S+\_Out}$ . Use a differential ADC or instrumentation amplifier.
GND reference not shared with measurement instrument	Common-mode voltage causes ADC input to exceed rail, corrupts reading or damages ADC	Ensure ADC GND and module GND are on the same bus.
Probe inserted in wrong direction (input and output swapped)	Differential voltage reads negative — negative current result	Verify S+_L connects to signal source and S+_R connects to load.
USBLC6-2P6 VBUS unconnected on D1 or D2	ESD clamp has no rail reference; protection ineffective	Connect VBUS of D1 and D2 to 5V_Module supply rail.
High-impedance signal source loaded by $1\,\mathrm{\Omega}$ shunt	Signal voltage droops under load	$1\,\mathrm{\Omega}$ is appropriate for low-impedance sources only. Do not use on high-impedance voltage sources.