Bolt-on Electrical Stimulation Drive

Low-Cost Add-On for Converting a Microscope into a Fully Automated Electrical Stimulation Screening Platform

e-stim device

About

This open-source “bolt-on” electrical stimulation device is designed to electrically excite cells in multiwell plates, allowing a standard motorized inverted microscope to be upgraded to a fully automated electrical stimulation screening platform. The design is based on previous work by the GENIE Project Team at HHMI Janelia Research Campus, where it was used to screen hundreds of variants of genetically encoded fluorescent protein sensors such as jGCaMP8, Voltron2 and iGABASnFR2.

The stimulation hardware comprises an electrode drive and an interface board. The electrode drive lowers platinum electrodes into the wells of a 96-well plate. The interface board contains the electronics to power the electrode drive and can be controlled manually using buttons or via external TTL signals.

The cost to manufacture the drive itself is less than \$500. The platinum electrodes used here (1 mm diameter) are the most expensive part of the design (>\$1,000).

Features

  • Quick mounting on the condenser holder on virtually any inverted microscope
  • Adjustable height and travel range of drive to accommodate different screening plates
  • Manual (push-button) or digital control of electrode movement
  • Digital confirmation of electrode position

Electrode drive

Drive image

Materials

Off-the-shelf

QuantityItemDescriptionLinkAdditional notes
1Linear actuatorActuator for moving the electrode into the wellPQ12-100-6-S (Digikey) 
2Limit switchSets upper and lower travel limits of the linear actuatorPM-F25 (Digikey)The limit switches are mounted in a groove on the actuator mounting bracket. Their relative position can be adjusted to modify the travel range of the electrode
1Carriage railHolds the electrode carriage8381K39 (McMaster) 
1Tension springSpring for keeping tension on the carriage, returning it back to upper travel limit5108N002 (McMaster)One end of the spring is wound around a
1Limit switch contactTag on the electrode carriage that activates the limit switches1267 (Digikey)The small tag opposite of the hole was cut off
2Electrode wire (Platinum)Platinum rod; diameter 1 mm, length 300 mmPT-M-02-R (American Elements)Contact American Elements to get a quote
3O-ringFor securing the electrodes to the outside of the housing9262K252 (McMaster) 
1Condenser mounting bracketConnects to condenser mount to hold the rest of the assemblyMS-KIT-Z-1 (Newport) 
1Vertical adjusterLinear stage for setting the vertical position of the electrode (13 mm travel range)MS-500-X (Newport) 
1Vertical adjustment screwAdjustment screw for the vertical adjusterAdjustment Screw, Tiny Knob, 28.7 mm Travel, Ball Tip, 6-80 (Newport)The vertical adjuster comes with an adjustment screw which can be used, but it is too short to be used conveniently; therefore, this is a replacement for that screw
1Spring mount postPost on the actuator mounting bracket that holds one end of the tension springH9004-01 (Digikey)Press fit into the actuator mounting bracket
218-8 Stainless Steel Socket Head Screw, Thread Size: 2-56, Length: 3/16”Connect mounting bracket to vertical adjuster92196A076 (McMaster) 
218-8 Stainless Steel Socket Head Screw, Thread Size: M4 x 0.7 mm, Length: 10 mmConnect retention bracket to mounting bracket91292A019 (McMaster) 
418-8 Stainless Steel Socket Head Screw, Thread Size: 0-80, Length: 3/8”Connect vertical adjuster to condenser mounting bracket92196A057 (McMaster) 
2Button Head Hex Drive Screw, Thread Size: 10-32, Length: 1/2”Connect electrode carriage to carriage rail92095A452 (McMaster) 
5Alloy Steel Socket Head Screw, Thread Size: 6-32, Length: 3/8”For mounting the carriage rail on the actuator mounting bracket; mounting the tension spring on the carriage91290A022 (McMaster) 
318-8 Stainless Steel Cup-Point Set Screw, Thread Size: 1/4”-20, Length: 1/4”For connecting electrode housing cap to electrode carriage92015A205 (McMaster) 
318-8 Stainless Steel Socket Head Screw, Thread Size: 4-40, Length: 1/2”For connecting the condenser mount to the condenser mounting bracket92196A049 (McMaster) 
218-8 Stainless Steel Socket Head Screw, Thread Size: M2.5 x 0.45 mm, Length: 8 mmFor mounting the limit switches on the actuator mounting bracket91292A016 (McMaster) 
2Black-Oxide Steel Hex Nut, Thread Size: M2.5For mounting the limit switches on the actuator mounting bracket90593A025 (McMaster) 

3D printed

QuantityItemDescriptionLink
1Condenser mountSlides into the condenser slot on the microscope. Note: this piece will need to be custom-made for different microscopes. It was tested with an Olympus IX-83.STL
1Actuator mounting bracketHolds the actuator, rail, and limit switchesSTL
1Electrode carriageCarriage that slides on the rail and holds the housingSTL
1Electrode housingHolds the electrode wiresSTL
1Actuator retention bracketHolds the actuatorSTL

Assembly

The entire drive design is available for download as a STEP file to simplify assembly.

Drive assembly Drive carriage zoomed in



Interface board

The interface board is a PCB that controls the linear actuator and receives signals from buttons, external control logic, and limit switches.

Electrical design

Interface board schematic

The general principle of operation of the circuit is as follows: when neither the top or bottom limit switches are activated, the linear actuator (M1 on the schematic) receives inputs from the two relays UP_RLY1 and DWN_RLY1. These relays send +5V or 0V on either the + or - side of the actuator, enabling it to change direction. When either limit switch is tripped, indicating that the actuator is at the top or bottom of its’ travel range, the transistor Q1 switches off. The limit switches are only active when the actuator is moved in the corresponding direction, e.g. UP_LIM1 only gets powered (+5V on +V) when the command to move up is given (either with the manual switch SW_UPDWN1 or the BNC input DAQ_IN_UP1). When either limit switch is tripped or the movement command is stopped, the transistors Q1 and Q2 driving the relays turn off and the corresponding actuator input line goes to 0V.

Printed Circuit Board (PCB)

The 2-layer PCB for the schematic shown above can be downloaded as a Gerber zip file or as a KiCAD PCB file. I used OSHPARK to manufacture the PCB. For a 2-layer 4.00 x 3.00 inch (101.6 x 76.2mm) board, it will cost ~$60. Other PCB manufacturers can also be used.

The full bill of materials (BOM) is here as an Excel file.

PCB enclosure

The PCB enclosure can be 3D printed as two separate pieces (enclosure body and lid). The front of the enclosure has BNC inputs and outputs for driving the actuator and sensing the position. The lid has spaces for two rocker switches.

QuantityItemDescriptionLinkAdditional notes
1Enclosure bodyMain body of the PCB enclosureSTLShould be printed the way it is shown in the image (standing upright). Ensure that supports are enabled to properly reproduce the connector cutouts
1Enclosure lidLid for PCB enclosureSTLShould be printed the way it is shown in the image (labels facing up) to ensure that the labels are properly printed

Enclosure inputs and outputs

Enclosure body: front

Input/OutputDescriptionAdditional notes
OutputBottom limit switch signal BNC (5V) Active LOW; this line goes LOW when the bottom limit switch is activated. This line can be monitored using a DAQ or microcontroller to confirm that the drive has reached the bottom position. 
InputMove down command signal BNC (3.3-5V)To move actuator down, set this line HIGH and the “Move up” line low
OutputTop limit switch signal BNC (5V)Active LOW; this line goes LOW when the top limit switch is activated. This line can be monitored using a DAQ or microcontroller to confirm that the drive has fully retracted from the well.
InputMove up command signal BNC (3.3-5V)To move actuator up, set this line HIGH and the “Move down” line low

Enclosure body: back

Input/OutputDescriptionAdditional notes
InputBarrel jack (power input) 
OutputLED ON indicator 
InputTop limit switch connectorWiring: pin 1 (left): +V (brown); 2: 0V (blue); 3: Out2 (white, but does not need to be connected); 4: Out1 (black). See datasheet for details
OutputLinear actuator powerThe pins should connect to pins 2 (black) and 3 (red) on the extension cable that goes to the PQ12 actuator. The other pins in the cable can remain unconnected. Note: the polarity may need to be flipped to make sure the actuator goes up and down when the corresponding buttons are pushed. See datasheet for details.
InputBottom actuator connectorWiring: pin 1 (left): +V (brown); 2: 0V (blue); 3: Out2 (white, but does not need to be connected); 4: Out1 (black). See datasheet for details

Enclosure Lid

DescriptionLink
Input mode rocker switch (DAQ/SW)GRS-4022-0001, Mouser
Manual drive control rocker switch (UP/DOWN)GRS-4023C-1300, Mouser

Input Mode Rocker Switch (DAQ/SW) Wiring Information

Pin on the switchPin on SW_DAQ_OR_MAN_1
Pin 1 (common1)2
Pin 2 (common2)5
Pin 1a3
Pin 1b1
Pin 2a6
Pin 2b4

Manual Drive Control Rocker Switch (UP/DOWN) Wiring Information

PinPin on SW_UPDWN1
Pin 1 (common)2
Pin 1a1
Pin 1b3

Ensure proper orientation of the switch in the lid cutout for label consistency.

Additional hardware/software requirements

  • To automatically trigger the drive, use two digital output pins on an Arduino or an NI DAQ. Two more digital inputs can be used to confirm the electrode position.
  • The electrodes need to be connected to an electrical stimulator such as a A385 (WPI) or Model 4100 (A-M systems).
  • Data acquisition software such as ACQ4 (Python-based, free), Wavesurfer (MATLAB-based), or NI LabVIEW can be used to synchronize camera frames with the stimulation.

Known issues, planned improvements

  • Cannot use condenser (i.e. transmitted-light imaging such as phase contrast) during operation