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Iris-128S Quickstart Guide

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Open-Source 128-Channel Headstage for Neural Recording and Stimulation (Based on Jacobs et al., 2025 – “Iris 128x: Open-Source 128-Channel Headstages for Neural Stimulation and Recording”)

1. System Overview

The Iris-128S neural interface consists of a headstage and an adapter, and provides with 128-channel, selective bidirectional recording and stimulation capability using two RHD2164 and one RHS2116 Intan integrated amplifier and amplifier/stimulation chips. It interfaces with thin-film microelectrode arrays through a Samtec SEAF8 connector and communicates with an Intan RHD Controller and a RHS Controller via low-voltage differential signaling (LVDS) through Intan Omnetics cables. The headstage and adapter are connected with a 36-wire custom cable. A microcontroller (MCU) in the adapter can be programmed with a MCU-compatible programmer.

The architecture of Iris-128S neural interface is shown in the figure below.

graph LR
    c0("128-Ch
        Electrode
        Array")
    c1("`**Iris-128S
        Headstage**`")
    c2("`**Iris-128S
        Adapter**`")
    c3("Intan RHD
        Controller")
    c4("Intan RHS
        Controller")
    c5("Programmer")
    c6("Computer")
    c0 <--> c1
    c1 <-- 36-Wire
           Custom Cable --> c2
    c2 <-- 12-Pin
           Intan Cable --> c3
    c2 <-- 16-Pin
           Intan Cable --> c4
    c2 <-- 10-Pin
           Flat Cable --> c5
    c3 <--> c6
    c4 <--> c6
    c5 <--> c6

Figure 1. System Architecture of Iris-128S.


2. Hardware Components

List of required components:

  • Iris-128S Headstage
  • Iris-128S Adapter
  • 36-Wire Custom Cable
  • 160-pin Samtec SEAF8 connector
  • Electrode Array
  • Intan RHD Controller
  • Intan RHS Controller
  • 12-Pin Intan Cable
  • 16-Pin Intan Cable
  • 10-Pin Ribbon Cable
  • STLINK-V3 Programmer
  • Computer


2.1. Iris-128S Headstage

The figure below shows the different components of the headstage.

Figure 2. Photos of the Headstage top and bottom sides indicating its main components.


The table below shows the main components of the Iris-128S headstage. Note the component correspondance with the previous figure.

Component Description
RHD2164 64-ch neural recording amplifier chip, Intan.
RHS2116 16-ch neural recording/stimulation chip, Intan.
ADGS5414 Octal high-voltage analog switch, Analog Devices.
SEAM8-20 160-pin high-density connector, Samtec.
A79024-001 36-pin high-density connector, Omnetics.
R14 Unpopulated resistor which can be used to connect REF and GND.
REF Reference pin.
GND GND pin.
VDD1 +3.3 V Supply for RHD2164 chips, testpoint.
VDD2 +3.3 V Supply for RHS2116 chip, testpoint.
VDD3 +3 V Supply to ADGS5414 chip, testpoint.
VDD_SW +9 V Supply for ADGS5414 chip, testpoint.
VSS_SW -9 V Supply for ADGS5414 chip, testpoint.
VSTIMp +7 V Supply for RHS2116 chip, testpoint.
VSTIMm -7 V Supply for RHS2116 chip, testpoint.

2.2. Electrode Mapping

The figure below shows the mapping between the Electrode Array Connector, RHD2164 recording chips, and RHS2116 stim/record chip.

Figure 3. Electrode array connector mapping.


The figure below shows the daisy-chain SPI connection for the ADGS5414 analog switches.

graph LR

    subgraph ADGS5414-U8
        direction LR
        SDI8 --> SDO8
    end
    subgraph ADGS5414-U7
        direction LR
        SDI7 --> SDO7
    end
    subgraph ADGS5414-U1
        direction LR
        SDI1 --> SDO1
    end

    MOSI_SW --> SDI8
    SDO8 --> SDI7
    SDO7 -..-> SDI1
    SDO1 --> MISO_SW

Figure 4. Analog switches daisy-chain SPI connection.


Analog Switches State

Analog Switch SWX_EN Description
UX-Y 0
1		 Open
Closed

X,Y= {1,..,8}


Recording Electrodes

Electrode Array
Connector Pin		 RHD2164
Pin		 Electrode Array
Connector Pin		 RHD2164
Pin
R0 REC0IN1 R48 REC0IN4
R1 REC0IN54 R49 REC0IN6
R2 REC0IN62 R50 REC0IN26
R3 REC0IN60 R51 REC0IN31
R4 REC0IN58 R52 REC0IN33
R5 REC0IN56 R53 REC0IN22
R6 REC0IN3 R54 REC0IN13
R7 REC0IN29 R55 REC0IN15
R8 REC0IN46 R56 REC0IN14
R9 REC0IN48 R57 REC0IN18
R10 REC0IN52 R58 REC0IN20
R11 REC0IN50 R59 REC0IN24
R12 REC0IN5 R60 REC1IN46
R13 REC0IN27 R61 REC0IN12
R14 REC0IN59 R62 REC0IN17
R15 REC0IN63 R63 REC1IN17
R16 REC0IN45 R64 REC1IN0
R17 REC0IN47 R65 REC1IN16
R18 REC0IN7 R66 REC1IN63
R19 REC0IN25 R67 REC1IN8
R20 REC0IN51 R68 REC0IN21
R21 REC0IN55 R69 REC1IN2
R22 REC0IN43 R70 REC1IN18
R23 REC0IN61 R71 REC1IN4
R24 REC0IN9 R72 REC1IN61
R25 REC0IN23 R73 REC1IN26
R26 REC0IN40 R74 REC0IN19
R27 REC0IN35 R75 REC1IN20
R28 REC0IN57 R76 REC1IN6
R29 REC0IN41 R77 REC1IN22
R30 REC0IN11 R78 REC1IN45
R31 REC0IN16 R79 REC1IN43
R32 REC0IN30 R80 REC1IN53
R33 REC0IN32 R81 REC1IN37
R34 REC0IN53 R82 REC1IN24
R35 REC0IN39 R83 REC1IN10
R36 REC0IN0 R84 REC1IN47
R37 REC0IN10 R85 REC1IN55
R38 REC0IN36 R86 REC1IN41
R39 REC0IN38 R87 REC1IN42
R40 REC0IN49 R88 REC1IN12
R41 REC0IN37 R89 REC1IN28
R42 REC0IN2 R90 REC1IN59
R43 REC0IN8 R91 REC1IN57
R44 REC0IN28 R92 REC1IN51
R45 REC0IN34 R93 REC1IN49
R46 REC0IN42 R94 REC1IN39
R47 REC0IN44 R95 REC1IN44

Connections: REC0INX U9; REC1INX U10


Stimulating/Recording Electrodes

Connected to RHS2116

Electrode Array
Connector Pin		 RHS2116
Pin		 Switch FW Variable
RS0 STIM9 U8-2 sw8[1]
RS1 STIM9 U8-1 sw8[0]
RS2 STIM8 U8-3 sw8[2]
RS3 STIM8 U8-4 sw8[3]
RS4 STIM11 U8-5 sw8[4]
RS5 STIM11 U8-6 sw8[5]
RS6 STIM4 U8-8 sw8[7]
RS7 STIM4 U8-7 sw8[6]
RS8 STIM3 U7-2 sw7[1]
RS9 STIM3 U7-1 sw7[0]
RS10 STIM0 U7-3 sw7[2]
RS11 STIM0 U7-4 sw7[3]
RS12 STIM14 U7-7 sw7[6]
RS13 STIM12 U7-5 sw7[4]
RS14 STIM12 U7-6 sw7[5]
RS15 STIM14 U7-8 sw7[7]
RS16 STIM15 U2-1 sw2[0]
RS17 STIM15 U2-2 sw2[1]
RS18 STIM13 U2-4 sw2[3]
RS19 STIM13 U2-3 sw2[2]
RS20 STIM1 U2-6 sw2[5]
RS21 STIM1 U2-5 sw2[4]
RS22 STIM5 U2-7 sw2[6]
RS23 STIM5 U2-8 sw2[7]
RS24 STIM6 U1-1 sw1[0]
RS25 STIM6 U1-2 sw1[1]
RS26 STIM2 U1-4 sw1[3]
RS27 STIM2 U1-3 sw1[2]
RS28 STIM7 U1-6 sw1[5]
RS29 STIM7 U1-5 sw1[4]
RS30 STIM10 U1-7 sw1[6]
RS31 STIM10 U1-8 sw1[7]

Connections: STIMX U12


Connected to RHD2164

Electrode Array
Connector Pin		 RHD2164
Pin		 Switch FW Variable
RS0 REC1IN60 U5-7 sw5[6]
RS1 REC1IN62 U5-8 sw5[7]
RS2 REC1IN58 U5-6 sw5[5]
RS3 REC1IN56 U5-5 sw5[4]
RS4 REC1IN38 U5-4 sw5[3]
RS5 REC1IN36 U5-3 sw5[2]
RS6 REC1IN31 U5-1 sw5[0]
RS7 REC1IN34 U5-2 sw5[1]
RS8 REC1IN27 U6-7 sw6[6]
RS9 REC1IN29 U6-8 sw6[7]
RS10 REC1IN25 U6-6 sw6[5]
RS11 REC1IN23 U6-5 sw6[4]
RS12 REC1IN3 U6-2 sw6[1]
RS13 REC1IN7 U6-4 sw6[3]
RS14 REC1IN5 U6-3 sw6[2]
RS15 REC1IN1 U6-1 sw6[0]
RS16 REC1IN9 U3-8 sw3[7]
RS17 REC1IN11 U3-7 sw3[6]
RS18 REC1IN15 U3-5 sw3[4]
RS19 REC1IN13 U3-6 sw3[5]
RS20 REC1IN30 U3-3 sw3[2]
RS21 REC1IN14 U3-4 sw3[3]
RS22 REC1IN19 U3-2 sw3[1]
RS23 REC1IN21 U3-1 sw3[0]
RS24 REC1IN32 U4-8 sw4[7]
RS25 REC1IN33 U4-7 sw4[6]
RS26 REC1IN40 U4-5 sw4[4]
RS27 REC1IN35 U4-6 sw4[5]
RS28 REC1IN50 U4-3 sw4[2]
RS29 REC1IN48 U4-4 sw4[3]
RS30 REC1IN52 U4-2 sw4[1]
RS31 REC1IN54 U4-1 sw4[0]

Connections: REC1INX U10


2.3. 36-Wire Custom Cable

The 36-wire custom cable is made out of two 36-pos dual row cable assembly (A79029-001) connected in a 1-to-1 fashion. Each wire connection is soldered and protected with a heat-shrinking tube. Additional heat-shrinking tubes are placed near the connectors. A metal shielding mesh is wrapped around the cable.

Figure 5. 36-Wire Custom Cable.


2.4. Adapter

The figure below shows the different components of the adapter.

Figure 6. Rendering of the Adapter top and bottom sides indicating its main components.


The table below shows the main components of the Iris-128S adapter. Note the component correspondance with the previous figure.

Component Description
RHD +3.3V 64-ch neural recording amplifier chip, Intan.
RHS +3.3V 16-ch neural recording/stimulation chip, Intan.
J1-1 RHD +3.3V pin header.
J7-1 VDD3V pin header. This +3 V supply is generated by the PMU.
J2-1 VDD_SW pin header. This +9 V supply is generated by the PMU.
J3-1 VSS_SW pin header. This -9 V supply is generated by the PMU.
J1-2, J7-2
J2-2, J3-2		 GND pin headers.
A79623-001 12-pin high-density connector, Omnetics.
A79633-001 16-pin high-density connector, Omnetics.
A79024-001 36-pin high-density connector, Omnetics.
J4 SWD 10-pin 0.05' pitch Programming Port.
J6 Reset Button connected to the MCU.
J5 Expansion Port with MCU GPIOs.
STM32U0 STM32U083KCU6 Ultra-low-power Arm M0+, 32-bit MCU.
PMU Power management unit which generaters +3 V and ±9 V.
X1 ECX-1210B 32.768 kHz Crystal.

3. Programming the Adapter MCU

The adapter board has a STM32U083 ultra-low-power Arm M0+ 32-bit microcontroller (MCU) which is used to program the state of the switches in the headstage through SPI communication. You can use any tool you want to build the firmware and program the MCU; here we use the STM32Cube tools. You can download all the project documents from our GitHub repository.

Building & Programming the Project

1. Install software & hardware:

  • STM32CubeIDE
  • STM32CubeProgrammer
  • STLINK-V3 box with cable (for programming the STM32)

2. Download and import the project files:

  • From GitHub, locate the controller folder.
  • In STM32CubeIDE, go to File → Import → Existing Projects into Workspace.
  • Select the controller folder and finish the import.

3. Connect the hardware:

  • Connect the adapter board to the STLINK-V3 through the programming port.
  • Connect the Intan RHD Controller and RHS controller using the Intan Record and Stim cables.
  • Power on the RHD Controller (first) and RHS controller.

4. Open the project in STM32CubeIDE:

  • Open the controller.ioc file.

Figure 7. Screenshoot of the STM32CubeIDE showing the controller.ioc.


5. Open and edit code:

  • In the Project Explorer, open main.c.
  • Edit the switch states as described below (these control which electrodes connect to which chip).
    • Example: To switch electrode RS0 from RHD to RHS, set the corresponding value in the switch matrix to 1 - in the screenshots. Section 2.2 lists the switch positions.

Figure 8. Screenshoot of the STM32CubeIDE showing the main.ioc.


Switch=0
aTxBuffer[0] = 0b00000000; // sw1
aTxBuffer[1] = 0b00000000; // sw2
aTxBuffer[2] = 0b11111111; // sw3
aTxBuffer[3] = 0b11111111; // sw4
aTxBuffer[4] = 0b11111111; // sw5
aTxBuffer[5] = 0b11111111; // sw6
aTxBuffer[6] = 0b00000000; // sw7
aTxBuffer[7] = 0b00000000; // sw8
Switch=1
aTxBuffer[0] = 0b00000000; // sw1
aTxBuffer[1] = 0b00000000; // sw2
aTxBuffer[2] = 0b11111111; // sw3
aTxBuffer[3] = 0b11111111; // sw4
aTxBuffer[4] = 0b10111111; // sw5
aTxBuffer[5] = 0b11111111; // sw6
aTxBuffer[6] = 0b00000000; // sw7
aTxBuffer[7] = 0b00000001; // sw8

Figure 9. Changing the RS0 switch state from RHD to RHS.


6. Build and compile:

  • Click the 🔨 icon (“Build Project”) to compile.
  • Wait for “Build Finished” to appear in the console.

7. Locate the compiled output:

  • The compiled firmware file is saved in the project’s Debug folder:
    C:\Users\...\STM32CubeIDE\workspace_1.17.0\controller\Debug\controller.elf
  • This .elf file can be used directly with STM32CubeProgrammer.

8. Flash the controller using STM32CubeProgrammer:

  • Open STM32CubeProgrammer.
  • Connect to the board via STLINK-V3.
  • Click Open file and select controller.elf (or controller.bin if generated).
  • Click Start Programming.

Figure 10. Screenshoot of the STM32CubeProgrammer showing the main.ioc.


9. Verify the update:

  • Restart the Intan RHD and RHS software.
  • Check that the switches have updated correctly (e.g., this can be checked by running the impedance function in Intan RHS controller for that electrode. It should switch from the RHD controller to the RHS controller. Unconnected channels will have MOhm impedances.).


Quick Summary

Step Action Tool
1 Install CubeIDE and CubeProgrammer
2 Import project CubeIDE
3 Connect hardware
4 Open project and connect CubeIDE
5 Edit main.c CubeIDE
6 Build project CubeIDE
7 Locate controller.elf in Debug folder
8 (Optional) Generate controller.bin CubeIDE
9 Flash firmware CubeProgrammer
10 Verify in Intan software

Changing the State of the Switches

You can change the state of each of the switches in the eight octal ADGS5414 by updating the values of the constants shown below. Notice that the bit swX[Y] corresponds to the Y switch of component uX, where X,Y \(\in \{1,2,...8 \}\) . The value of 0 indicates the switch is open whereas the 1 indicates it is closed.

Function Actions
Recording OPEN the switch to the RHS2116 and CLOSE the one to the RHD2164.
Stimulation CLOSE the switch to the RHS2116 and OPEN the one to the RHD2164.

Example Code

/* Switches states: swX=[7..0] */
// Default values
aTxBuffer[0] = 0b00000000; // sw1
aTxBuffer[1] = 0b00000000; // sw2
aTxBuffer[2] = 0b11111111; // sw3
aTxBuffer[3] = 0b11111111; // sw4
aTxBuffer[4] = 0b11111111; // sw5
aTxBuffer[5] = 0b11111111; // sw6
aTxBuffer[6] = 0b00000000; // sw7
aTxBuffer[7] = 0b00000000; // sw8

Warning

When configuring a stimulation channel, make sure to OPEN the switch connected to the RHD2164. Failure to do so can cause damage to the RHD2164 due to the possibility of higher than expected voltages at its input.

Further Development

The current use of the MCU is to program the state of the switches in the headstage after the adapter board is powered on. You could further expand the functions of the MCU to adapt the Iris-128s neural interface to your project. For this purpose, the adapter board features a reset button, a 32 kHz crystal, and a expansion port with flexible GPIO for easy prototyping and development.

4. Hardware Setup

The figures below show the required hardware setup.

Figure 11. Hardware setup diagram.


Figure 12. Hardware setup picture.


Figure 13. Iris-128S performing measurements in PBS inside a Faraday cage.

Step 1 — Prepare for Surgery

  1. Secure the animal in a stereotaxic frame.
  2. Mount the 3D-printed headstage holder onto the stereotax.
  3. Seat the thin-film electrode connector into the holder.
  4. Plug the Iris-128S headstage into the thin-film connector.
  5. Fasten the headstage to the holder via mounting holes.

Step 2 — Connect to Adapter

  1. Connect the 36-pin custom cable between headstage and adapter.
  2. Route this cable outside the Faraday cage.
  3. Plug in the 1 RHD interface cable (blue Omnetics) and 1 RHS interface cable (red Omnetics):
    • S1 RHD Controller
    • S4 RHS Controller

Step 3 — Ground and Reference

  • Connect REF and GND pads using platinum wires soldered into the through-holes on the headstage.
  • Keep REF and GND unshorted during normal operation.
  • Optionally, these may be tied together or implemented on the thin-film array.
  • Ensure the entire setup (animal, cage, supplies) shares a common ground.

5. Software Setup

  1. Install Intan RHD Recording Controller Software into Computer 1 (see Intan User Guide).
  2. Install Intan RHS Recording Controller Software into Computer 2 (see Intan User Guide).
  3. Connect the RHD Controller to Computer 1 via USB.
  4. Connect the RHS Controller to Computer 2 via USB.
  5. Power on the Intan RHD Controller.
  6. Power on the Intan RHS Controller.
  7. Launch the software in both computers — channels should automatically appear.
  8. Adjust sampling rate and channel naming as needed.

Figure 14. Two computers running the (left) Intan Recording Controller software and (right) Stimulation/Recording Controller software.

6. Power-Up Sequence

  1. Confirm all mechanical and electrical connections.
  2. Turn on RHD Intan Controller.
  3. Turn on RHS Intan Controller.
  4. Verify communication in the Intan software.

7. Bench & Animal Setup Checklist

Stage Procedure
Bench Validation Connect planar 128-ch polyimide MEA verify impedance in PBS (~295 kΩ @ 1 kHz).
Grounding Attach platinum wires for REF and GND to headstage pads.
Recording Launch Intan software set sampling rate 30 kSa/s confirm signal.
In Vivo Setup Craniotomy insert MEA into cortex connect headstage.
Validation Observe LFPs (0.5–100 Hz) and single-unit spikes (~250–500 μVpp).

8. Performance Summary

Metric Iris 128S Comparison (Intan 32 ch)
Noise (Vrms) 3.33 μV 2.4 μV
Weight 4.47 g 1.4 g
Volume 720 mm3 576 mm3
Channels 32 stim / 128 record 32 stim / 32 record
Frequency Response 0.5 Hz – 5 kHz (flat midband gain) Similar
Impedance (1 kHz, Pt site) ~2.9 × 105 Ω 2.4 × 105 Ω
Supply ±7 V & 3.3 V 3.3 V (single)

9. Stimulation Parameters

  • Chip: Intan RHS2116 (D5716)
  • Current Range: 2.55 µA – 255 µA
  • Step Size: 10 nA – 10 µA
  • Supply Range: ±3.3 – 10.7 V (max combined 14 V)
  • Sampling Rates: 1 – 30 kS/s
  • Test Waveform: Biphasic cathodic-first 4 µA, 500 µs pulses, 100 Hz (0.1 mC/cm² charge density)

10. Additional Notes

  • The 36-wire custom cable was built on-premise; contact manuel@openic.org for any questions.
  • The design files, schematics, BOMs, and firware are open-source on GitHub (OpenIC / U Oregon).
  • The Iris 128B and 128S share identical PCB stack-up and fabrication parameters:
    • 8-layer (3 mil trace / space, ENIG finish, 1 oz Cu).
  • Designed in KiCad, STM32CubeIDE, verified by micro-CT imaging and in vivo rat recordings.
  • For portable or wireless operation, future iterations aim to reduce weight < 3 g.

11. Reference Setup Recipe

  1. Connect all GNDs in the system.
  2. Connect electrode array headstage adapter Intan Controllers.
  3. Verify REF/GND connections (platinum wire, bone screw, headstage ground, system ground).
  4. Power on Intan RHS Controller and RHD Controller and confrim communication with headstage.
  5. Update MCU firmware if needed.
  6. Begin recording and stimulation tests.