Home » 16 Analog 4–20 mA Outputs for Raspberry Pi I/O Back Panel
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16 Analog 4–20 mA Outputs for Raspberry Pi I/O Back Panel on panel
16 Analog 4–20 mA Outputs for Raspberry Pi I/O Back Panel with case
16 Analog 4–20 mA Outputs for Raspberry Pi I/O Back Panel on DIN-Rail
16 Analog 4–20 mA Outputs for Raspberry Pi I/O Back Panel top
16 Analog 4–20 mA Outputs for Raspberry Pi I/O Back Panel bottom
16 Analog 4–20 mA Outputs for Raspberry Pi I/O Back Panel - side
16 Analog 4–20 mA Outputs for Raspberry Pi I/O Back Panel on panel
16 Analog 4–20 mA Outputs for Raspberry Pi I/O Back Panel with case
16 Analog 4–20 mA Outputs for Raspberry Pi I/O Back Panel on DIN-Rail
16 Analog 4–20 mA Outputs for Raspberry Pi I/O Back Panel top
16 Analog 4–20 mA Outputs for Raspberry Pi I/O Back Panel bottom
SKU: SM-P-140

16 Analog 4–20 mA Outputs for Raspberry Pi I/O Back Panel

16 analog 4–20 mA outputs with load detection for Raspberry Pi I/O Back Panel. Industrial current-loop control with RS485 MODBUS, OpenPLC, and CODESYS support.

Coming soon
$95.00

Overview

High-density 4–20mA analog output expansion for the Raspberry Pi I/O Back Panel. The card provides 16 independently controlled current loop outputs routed directly to the Back Panel's terminal blocks, making it ideal for process control applications that require a large number of analog output channels in a compact, DIN-rail mounted enclosure.

  • Sixteen 14-bit 4–20mA analog outputs
  • Outputs routed to Back Panel terminal blocks for clean field wiring
  • Open Drain MOSFET drivers with common ground — external 24VDC supply required
  • Native RS485 / MODBUS RTU interface for PLC and SCADA integration
  • Compatible with Command Line, Python, OpenPLC, and CODESYS
  • Mounts directly on the Raspberry Pi I/O Back Panel

INTERFACES AND I/O

I/O's Communication Software Integration
• 16 Analog 4-20mA Outputs (source) • I2C Port to Raspberry Pi • Command Line

• RS485/MODBUS Port • Python Library

• CAN Port • Node-RED nodes

• CODESYS Driver

• OpenPLC Module

• Home Assistant

• Arduino
OTHER FEATURES
• Mounts directly on the Raspberry Pi I/O Back Panel — no additional wiring or hardware needed between card and panel
• RS485 / MODBUS RTU port for PLC, SCADA, and HMI integration without a Raspberry Pi
• CAN / CANopen interface for reliable communication in industrial networks
• 16 status LEDs provide immediate visual feedback on output state
• OLED display for real-time monitoring of output values and system status
• PANIC input — when enabled via firmware command, an opto-isolated signal from the Back Panel triggers the local processor to set all outputs to user-defined default levels, moving connected devices to a known safe state independently of the control software
• Stack up to 8 HOP cards of each type on the same Back Panel for high channel count applications
• ECCN classification EAR99 — no export restrictions under U.S. regulations

DESCRIPTION

The 16 Analog 4–20mA Outputs Card is part of the HOP (Hardware on Panel) family developed by Sequent Microsystems — a range of industrial I/O expansion cards designed to mount directly on the Raspberry Pi I/O Back Panel.

Sixteen independently controlled 4–20mA outputs are routed directly to the Back Panel's terminal blocks for clean, reliable field wiring. All outputs are source-type driven by Open Drain MOSFETs with a common ground — an external 24VDC supply is required. Each output includes automatic load interruption detection, which flags an open circuit condition if the connected receiver is disconnected or fails.

The card includes an opto-isolated PANIC input connected to the Back Panel's PANIC line. When enabled via firmware command, the PANIC function sets all outputs to user-defined default levels upon receiving the PANIC signal — ensuring connected devices move to a known safe state regardless of what the control software is doing.

An RS485 port supports MODBUS RTU communication, allowing any PLC, SCADA system, or HMI to read status and control outputs directly without a Raspberry Pi. A CAN / CANopen interface provides an additional communication path for industrial networks.

Eighteen LEDs provide complete visual feedback: the power LED blinks when the local processor is running, the error LED activates when the PANIC line is triggered, and sixteen output LEDs show the real-time state and configured mode of each channel. An onboard OLED display shows output values and system status at a glance.

Up to 4 or 8 cards — depending on Back Panel version — can run on a single panel alongside one Raspberry Pi or Compute Module. Panels can be chained horizontally up to a maximum of 64 HOP cards per system, all controlled by a single Raspberry Pi running CODESYS, Node-RED, Python, or any other supported software environment.

TECHNICAL DETAILS

Board Layout
16 Analog 4–20 mA Outputs for Raspberry Pi I/O Back Panel Layout
Mechanical Dimensions
16 Analog 4–20 mA Outputs for Raspberry Pi I/O Back Panel mechanical dimensions

POWER REQUIREMENTS

The card is powered via the Back Panel power connector.

  • Outputs are power from the 24V supply and can draw up to 200mA

  • The local processor is powered from the 5V rail through a 3.3V LDO regulator and consumes 10 mA.

ERROR PROCESSING

One pin on the spring-loaded terminal block of the Back Panel is reserved for signaling an error condition. The user can connect this pin to an external contact of their choice. When the error signal is activated, the 16 Analog 4–20 mA Outputs Card automatically resets all outputs to a predefined default state.

WATCHDOG: If the watchdog is enabled and the Raspberry Pi fails to access the 8-Channel 4–20 mA Output Card within the preset time, the card signals the Back Panel, which performs a hard reset of the Raspberry Pi by turning the power off for 10 seconds.

STACK LEVEL: The stack level is automatically determined by the slot into which the card is inserted on the Back Panel. It is shown on the OLED display after power up. Up to eight cards of the same type can be connected to a single Back Panel installation. Different cards can be mixed and matched up to eight types of each card.

INTERRUPT: Any HOP card can be programmed to interrupt the Raspberry Pi. The interrupt handler running on Raspberry Pi needs to monitor pin 37 on the GPIO interface.

BACK PANEL TERMINAL BLOCK PINOUT
Each slot on the Back Panel has alocated three 6-pin spring-loaded terminal blocks for IO wiring. The pinout is shown in the following picture:
Raspberry Pi Backpanel Terminal Block IO

16 Analog 4–20 mA Outputs: Odd-numbered inputs are routed to the high side, and even-numbered inputs to the low side.

IO01-IO02: Output #1
IO03-IO04: Output #2
IO05-IO06: Output #3
IO07-IO08: Output #4
IO09-IO10: Output #5
IO11-IO12: Output #6
IO13-IO14: Output  #7
IO15-IO16: Output #8
IO17: ERROR
IO18: PANIC

IO17 is an open drain output triggered by a predefined error condition on an out of bounds input. It can be used to activate an external alarm, or can be routed back to IO18 to reset the outputs to a predefined state.

IO18 is a dry contact to ground input and can be activated by an external contact wired to the Back Panel terminal block. When triggered, it resets all outputs to a predefined state. 

DOT MATRIX DISPLAY
16x4-20mA outputs for Raspberry Pi Back Panel OLED display

The 16 Analog 4-20mA Analog Outputs card includes a 128 × 32 dot-matrix display driven by the on-board processor. It can show status information, self-test results, and error messages. At power up it displays the card name and the I2C address.

DOWNLOADS

3D STEP Model

3D Printable Enclosure


SOFTWARE

Command Line Drivers

Python Libraries

CODESYS Driver

OpenPLC Module


QUICK START

  1. Plug the 16 Analog 4–20 mA Outputs Card on the Back Panel for Raspberry Pi and power up the system.
  2. Enable I2C communication on Raspberry Pi using raspi-config.
  3. Install the software from github.com:
  • git clone https://github.com/SequentMicrosystems/sequent-cli.git
  • cd /home/pi/sequent-cli
  • sudo make install
  • sequent-cli 4-20ma-out -h
The program will respond with a list of available commands.

FAQ

What Back Panel do I need to use this card?

This card is designed to plug directly into the Sequent Microsystems Raspberry Pi I/O Back Panel, available in 4-slot and 8-slot versions. The Back Panel provides power, field wiring terminal blocks, CAN, RS485, and the 2×20 HOP connector that all cards in the family use.

Can I mix different HOP card types on the same Back Panel?

Yes. Any combination of HOP cards can be installed on the same Back Panel. You can mix analog output cards, analog input cards, digital I/O cards, and any other cards in the HOP family in any slot order.

How many Raspberry Pi units do I need?

Only one Raspberry Pi or Compute Module is needed for the entire system, regardless of how many Back Panels are chained together. The Raspberry Pi sits in the dedicated slot on one panel and communicates with all HOP cards across all linked panels via CAN and RS485.

What is the maximum number of HOP cards in a system?

Up to 64 HOP I/O cards can be installed in a single system. The 4-slot Back Panel supports up to 16 panels chained horizontally (16 × 4 = 64 cards). The 8-slot Back Panel supports up to 8 panels chained horizontally (8 × 8 = 64 cards).

Can the cards operate without a Raspberry Pi?

Yes. Each HOP card has an onboard processor that implements the MODBUS RTU protocol over RS485. Any MODBUS master — PLC, SCADA system, or HMI — can read all inputs and control all outputs directly without a Raspberry Pi.

What software can I use to control the cards?

HOP cards are supported by Command Line, Python, Node-RED, CODESYS, and OpenPLC. MODBUS RTU over RS485 and CANopen provide integration with third-party industrial software and controllers.

What is the PANIC function?

The PANIC function is a safety feature available on all HOP output cards. It must first be enabled using a firmware command, and the user defines the default output levels to apply when PANIC is triggered. When the PANIC signal is received through the opto-isolated input on the Back Panel connector, the local processor immediately sets all outputs to those predefined levels — moving connected devices to a known safe state independently of the control software.

What external power supply does this card require?

The 4–20mA outputs require an external 24VDC power supply. The supply connects to the Back Panel's power terminal block and is shared across all output channels.

What is load interruption detection?

Each output continuously monitors the connected load. If the receiver is disconnected or fails, the card automatically detects the open circuit condition and flags it — allowing your software to respond to wiring faults or device failures in real time.

Are HOP cards compatible with all Raspberry Pi versions?

Yes. HOP cards are compatible with all Raspberry Pi versions from Zero to 5, as well as Compute Modules.

Are there any export restrictions on these cards?

No. All HOP cards are classified EAR99 under U.S. Export Administration Regulations and can be exported freely without a license to most destinations.

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