Mice Whisker Stimulator for Research Purposes

This project is meant to be used during neuroelectrophysiological experimental procedures involving anesthetized animals.

This whisker stimulator was created to mechanically displace animal vibrissae with high spatial and temporal precision in the rostral-caudal axis. Many such stimulators are available from laboratory equipment companies, but while working on my bachelor thesis I required cheaper and more universal alternative. This stimulator utilizes galvanometers dedicated to reflecting laser beams, most commonly applied to laser projectors or high-precision laser targeting mechanisms.

Briefly, galvanometers are directly driven through a low-impedance circuit with a dedicated driver unit supplied in the set. Thus, it is crucial to maintain as little resistance past the driver unit as possible to avoid any interference. At the same time, we would like to minimize EM interference during the experimental procedure, preferably keeping as many components as far as possible from the specimen. To achieve this, the stimulator was designed and divided into three separate units:

1. Main unit: power supply, input ports, switches, outputting compact signal, and supplying power to galvanometers.
2. Driver unit: directly driving galvanometers with the incoming signal provided by the main unit
3. Mounting: simple galvo mounting, installed at stereotaxic apparatus directly displacing specimen vibrissae.

Note: This project requires basic knowledge of electronics and 3D printing. If any of these instructions are unclear, contact me directly.

Tools

This project requires access to basic electronic workshop tools and devices e.g. digital multimeter, and soldering machine. Apart from them, more specialized equipment is needed:

1. 3D printer with printing space of at least 200x140x50 mm
2. Universal glue e.g. acrylic glue
3. (Most probably) Crimping tool able to fasten flat connectors

Components

A list of required and optional components is attached below. Note, that optional parts are listed as my suggestions and can be swapped with preferred substitutes. Some parts, such as the driver heatsink, were made from scraps and unfortunately, I cannot provide you a website from which you can acquire them - please try to improvise and tweak the provided CAD designs before printing.

Printed components

As noted above, a major part of this project is cases meant to be 3D printed. CAD designs and suggested printing settings are attached below. These cases were designed to house listed components, nevertheless, there is a possibility that you will have to edit them for your specific purpose, such as other driver unit heatsink.

In this project, I am including .f3d files so you can redesign the parts according to your needs. Before printing, make sure to change the designs, especially Inside_unit (heatsink holder) and stereotax_mounting (inner wall diameter).

As noted above, you need a 3D printer with printing space of at least 200x14x50mm. All parts were designed to be printed with PLA. Designs include dimensional tolerances chosen for best results while using well-calibrated Prusa mk.3 (screw holes, latches, etc.).

Recommended printer and slicing settings (used in every print, unless stated otherwise):

1. Nozzle: 0.4mm
2. Layer height: 0.3mm (0.1mm for sweep_mount parts)
3. Infill: 10%, Grid (90% for sweep_mount parts)
4. No autogenerated supports (include support enforcers in inside_case and Enclosure-compact, see photos)
5. Printing speed: Default

1. Glue two M4 nuts and four M3 nuts inside the main unit case.
2. Prepare:
3. Glass fuse
4. Fuse socket with soldered wires.
5. Line socket with switch
6. Line filter
7. Two M4x11 screws, two M4 washers
8. Wires connecting all these components (flat connectors)
9. Install fuse socket and line socket. No glue should be needed.
10. Connect the fuse socket, and line socket according to the schematic Power switch (Ignore line filter).
11. Install fan with M3x20 screws. Connect power supply through DC/DC step-down converter according to schematic Fan power supply. Important: there should be an arrow pointing in the direction of airflow on the fan case - the arrow should point inward.
12. If installed properly, the back of the case should look like this.
13. Swap power supply screws for longer ones (M3x11) and install the supply inside the case. Connect line filter to supply AC input.
14. Install BNC connectors at the front of the case. Remember to connect both BNC connector washers together, creating a shared ground wire (white wire in the picture). Pin outcoming wires to some kind of connector (XH connector on the picture, you can use any type you prefer).
15. Solder wires to toggle switch, according to schematic Signal switch. It will either provide a signal from BNC connectors or output 0VDC to both galvos.
16. Solder D-Sub socket to input wires, according to schematic Main unit output D-Sub connector. Two connectors will be provided: one for supplying +- 15VDC and one for transmitting driving signals from BNC inputs.
17. Install both the toggle switch and D-Sub socket on the front panel of the case. D-Sub connector should be glued to the case. Connect the power supply to one of the connectors and signal from the toggle switch to the second connector.
18. Install rubber feet at the bottom of the case with M4x11 screws.
19. At the end, put on the case lid. Screw both parts of the case together using M3x20 screws with washers. The finished main unit should look like the one in picture no.0.

1. Prepare:
2. Driver unit printed case and lid.
3. D-Sub connector, with outcoming wires according to schematic Driver unit input D-Sub connector.
4. Driver circuit with attached heatsink.
5. Driver-to-galvo cables are provided in the set.
6. M3x10 screws.
7. Install and glue the D-Sub connector. Note that angled connector pins are pointing upward, for better wire management.
8. Install the heatsink. Depending on the heatsink you have chosen, this step can vary. In my case, a heatsink is slid into place with no glue required. Connect the two cables leading from driver to galvos, which should be included in galvo set ordered online.
9. At the end, put on the case lid and screw it in using M3x11. The finished driver unit should look like the one in picture no.0.

1. Prepare:
2. Printed mountings
3. M3x20 and M4x10 screws with M3 nuts
4. Threaded rod (optionally non-threaded, change galvo mounting rod hole diameter according to rod diameter)
5. Thick, coarse material - I used pieces of rubber-like pad.
6. Swivel joint, commonly found on soldering helping hand (change stereotaxic mounting swivel hole according to swivel dimensions)
7. Glue M3 nuts onto the main mounting. Glue rubber padding inside stereotaxic mounting.
8. Install a swivel joint and screw it in place with M4 screw. Connect both clamps of stereotaxic mounting.
9. Prepare:
10. Galvanometer - if your galvanometer has mirrors glued to the shaft, remove the mirrors
11. Printed sweep mounting parts
12. Toothpick
13. Injection needle
14. Nail polish
15. Acrylic glue
16. Glue both pieces of sweep mounting. You can do it however you want and adjust the sweep position using a swivel, clamp, and rod.
17. Cut 1/3 of the toothpick and stick it onto the needle. Glue them together. Cut the bottom part of the needle using a wire cutter.
18. Prepare all mounting parts.
19. Glue sweep mounting onto galvo shaft using nail polish.
20. Assemble all the parts according to picture no.0. Mount the sweep after installing galvo!

Assembly:

1. Connect the power supply cable at the back of the main unit.
2. Connect the main unit with the driver unit using a D-Sub male-male cable.
3. Clamp galvo mountings onto your stereotaxic rods.
4. Connect driver unit cables to galvos.

Important note: As you may have noticed, this stimulator has little to no protection features, thus it is crucial to operate it following this instruction.

First activation: Ensure everything is wired correctly, according to the provided schematics. I recommend activating electrical components sequentially by unplugging further components starting from the power supply, for example: disconnecting output wires from the power supply and making sure that the power supply alone is working properly. Then proceed by connecting the power supply to the D-Sub port, disconnecting the galvos from the driver unit, etc. Verify if correct voltages occur on appropriate wires. Driver unit should be supplied with +15VDC, -15VDC and GND. Check if the fan is running properly.

Signal input: Signal input should range from -5VDC to +5VDC. In this version, there is no protection feature from overvoltage.

For stimulator steering, I highly recommend utilizing your primary data acquisition device's DAC outputs. This way ensures that data acquisition and stimuli times are synchronously registered using the same software. My stimulator was driven with Data Acquisition Interface Power1401-3A by DAC outputs, using Spike2 software.

Calibration and fastening the sweep to the whiskers: When activated, the toggle switch in the off position should drive galvos in the default, middle position. In this state, galvos should resist any external rotation. First, using many degrees of freedom in the mounting, place the galvos in your desired position. During the surgical procedure fasten the sweep to the whiskers using easily removable adhesive e.g. nail polish.

Performance: As galvanometers used for reflecting laser beams have exceptionally high temporal precision and spatial repeatability in rotation, full displacement stimulation occurs approximately instantly. Moreover, there should be little delay in relaying the driving signal to the driver unit, as there are no intermediate components between signal BNC ports and the driver unit. Nonetheless, the magnitude of this delay should be established in order to accurately measure any electrophysiological response latency.

At last, no significant EM interference during data acquisition should occur, as the driver unit has virtually no varying currents, apart from the driving signal.

I tried my best to describe the process of creating and assembling this stimulator. Many steps rely on your knowledge and common sense - if you feel like assembling one might is overwhelming, try reaching out to me or people with more experience. I am aware that many solutions incorporated here are not great, but I was learning and creating this stimulator at the same time. Feel free to contact me regarding any feedback and better solutions you know of.

Supplies for this project were financed by the Nencki Institute of Experimental Biology.

I extend my gratitude to prof. Ewa Kublik for trusting me in my ability to complete this project and mentorship.