Guide/Miniscope V4 Assembly
Overview
This guide covers bench assembly of the Miniscope V4 from a parts kit. Assembly takes approximately 1 to 2 hours per scope for a first-time builder; experienced builders average 30 to 45 minutes. Steps are sequential, so do not skip ahead, and in group sessions keep everyone at the same step.
The annotated exploded diagram below shows where each step occurs in the scope. Step numbers on the diagram correspond to the steps in this guide.
Each assembly step has a short video tutorial, embedded in the relevant section below. The videos are adapted from the UCLA Workshop slides (Federico N. Sangiuliano Jimka, Miniscope team) and are collected in the Miniscope V4 Assembly YouTube playlist.
General recommendations
Read these before starting. They prevent the most common and most expensive mistakes.
- Work on a clean surface and wear gloves. This is especially important while handling screws, lenses, and the imaging sensor. Optical surfaces closest to the image and object planes are the most critical to keep clean.
- Keep all optics clean. Use lint-free filter paper or Kimwipes if cleaning is needed. A small amount of dust on the excitation filter is not a problem, but dust on the emission filter or imaging sensor will show up clearly in the image.
- Check the orientation of every lens and filter before inserting it. Orientation mistakes are the leading cause of a scope that assembles cleanly but does not image. See Coated side and lens orientation below.
- Have all assembly tools within reach before you begin. Several steps are time-sensitive once a module is open.
- Do not kink the flexible portions of the rigid-flex PCB. All bends should be smooth and gentle.
- Do not over-tighten the M1 self-threading screws. They strip easily. Seat them firmly but stop as soon as they are snug.
- Avoid most cyanoacrylates (super glue). Many off-gas and leave a hazy white film on the optics, and some make Delrin brittle. Use the recommended UV epoxy or a two-part epoxy instead (see Step 11).
Coated side and lens orientation
Several steps depend on getting a filter, dichroic, or lens the right way around. Use these methods every time rather than trusting printed arrows.
Identifying the coated side of a filter or dichroic:
- Look at one face. If it appears metallic or highly reflective, that is the coated side.
- Flip it over. If you can see a colorful internal reflection (the room around you visible within the glass), that is the uncoated side.
- Printed arrows are not reliable. They may be absent on small filters, faded, or pointing the wrong way. On sub-module filters such as the ET470, forget the arrows entirely and use the reflective-surface method.
- General rule: the coated side always faces toward the incoming light.
Identifying the curved side of an achromat lens:
- Hold the lens by its edge and look at the profile. One side curves outward, one is flatter.
- Or set it flat on the bench. If it sits stably, the flat side is down. If it rocks, flip it.
- General rule: the flatter (less curved) side faces toward the side with the steeper light angle. For the V4 this means the flat side of the objective lenses faces toward the brain, and the flat side of the emission tube lens faces toward the imaging sensor.
Parts and Tools
Optics
| Qty | Part | Spec | Notes |
|---|---|---|---|
| 2 | Achromat lens | 3 mm Ø, 6 mm FL | Objective module; flat side down (curved side up). Mixing focal lengths sets working distance and field of view (see Lens Configurations) |
| 1 | Achromat lens | 4 mm Ø, 10 mm FL | Emission tube lens; flat side up (curved side down) |
| 1 | Half ball lens | 3 mm | Side of the emission module |
| 1 | Dichroic mirror | T495LpXR, 6 x 4 x 1 mm | Coated side toward the incoming light (down toward the objective) |
| 1 | Excitation filter | ET470, 4 x 4 x 1 mm | Excitation module; coated side toward the LED |
| 1 | Emission filter | ET525/50m, 4 x 4 x 1 mm | Top of emission module; coated side down |
| 1 | Electrowetting lens (EWL) | Sandwiched between the two gold rings of the rigid-flex PCB, between the objective and emission modules |
Hardware
| Qty | Part | Notes |
|---|---|---|
| As needed | M1 × 3 mm self-threading screws | McMaster-Carr only (outside the US these are not reliably available; order spares). Handle carefully, they get lost easily |
| 1 | Objective module | Machined body |
| 1 | Emission module | Machined body |
| 1 | Excitation module | Machined body, the detached side piece |
| 1 | Rigid-flex PCB assembly (LED/EWL, Python480, MCU/BNO, SER/POW) | Arrives with flex legs flat; legs are folded during assembly. If pre-assembled and tested, the MCU is already programmed |
| 1 | UV-cure epoxy | Norland 68 or equivalent. A two-part epoxy or Loctite 444 with accelerator also works |
| 1 | UV curing gun | |
| 1 | Coaxial cable with Hirose u.FL connector | A connectorized u.FL cable needs no soldering. See Coaxial cable assembly if you are soldering your own |
Tools
| Part | Notes |
|---|---|
| T2 Torx screwdriver | For the M1 thread-forming screws. About $15 each; order extras, one per person for a group session |
| Flat-tipped cotton swabs | Must be flat-tipped, not the ear-cleaning type. A wooden stick or toothpick works in a pinch and will not scratch lenses |
| Precision plastic tweezers | For handling filters and removing protective tape without scratching surfaces |
| Toothpicks | For UV epoxy application |
| 3 mm reamer | To gently open the objective lens holes if a lens is too tight |
| 4 mm reamer | To gently open the emission module hole if the 4 mm lens is too tight |
| Lens cleaning tissue | A protected hard surface for press-fitting lenses, and for cleaning optics |
| Compressed air can | For clearing debris from threaded holes |
| Gloves | Keep oils off the optics and PCB |
Assembly Steps
Step 1 to 3: Objective module, thread holes and insert 3 mm achromat lenses
Step 1: Thread all screw holes before any assembly.
Before putting anything together, thread all screw holes in the objective module, emission module, and excitation module by screwing a screw in and then backing it out. This pre-taps the holes and makes assembly significantly easier at every subsequent step.
Steps 2 and 3: Insert the two 3 mm achromat lenses into the objective module.
Open lens packets carefully, since lenses eject easily and tend to land on the floor.
Orientation: flat (less curved) side faces DOWN toward the brain. The curved side faces up toward the image sensor. Check the orientation before inserting (see Coated side and lens orientation).
To insert: set the lens flat side up on lens tissue over a hard surface, then press the objective module down onto the lens until it seats flush with the bottom of the objective. Do not drop it in, it must seat flat. Repeat for the second lens.
Step 4: Emission module, insert 4 mm achromat tube lens
The 4 mm achromat (4 mm Ø, 10 mm FL) goes into the emission module, not the objective module. There is an inner lip in the emission module that acts as a hard stop. You should be able to see the back of the lens sitting against this lip through the dichroic slot.
Orientation: flat side faces UP toward the imaging sensor opening. The curved side faces down. This is the opposite of the objective module lenses. If this lens is flipped you will still image, but with noticeably more distortion.
Insert using the flat end of a cotton swab. Push until seated. A small protrusion is acceptable, since this lens sits in infinity space and needs firm seating rather than precise axial positioning.
Step 5: Emission module, insert dichroic mirror (T495LpXR)
This step requires care. An incorrectly oriented dichroic means the scope will not work.
Identify the coated side with the reflective-surface method (see Coated side and lens orientation). Do not rely on the printed arrow.
Orientation: the dichroic sits in the diagonal slot of the emission module with the coated side facing the incoming light, which means it faces down toward the objective module and toward the half-ball lens hole. The excitation light enters from below, and the coated side must intercept it.
Before inserting the dichroic, check the orientation of the 4 mm lens one more time. If the lens is wrong it can be removed easily with a cotton swab from the top of the module.
Confirmation check: after placing the dichroic and closing the module, shine light from the top of the scope body. You should see blue reflected back, and looking through from the top should appear yellowish-green. If so, orientation is correct.
Step 6: Excitation module, insert ET470 excitation filter
The excitation module is the detached side piece. Thread its two screw holes before inserting the filter (same reason as Step 1; these holes are particularly small in some batches and benefit from threading).
Identify the coated side with the reflective-surface method. Smaller filters like the ET470 often have no printed arrow, so rely entirely on the coated-side visual check.
Orientation: coated side faces the LED PCB (toward the excitation light source). The face of the filter sits flush with the face of the excitation module. If the filter does not drop into the pocket, push it gently on the edges with a cotton swab. Do not scratch or chip it, although a little dust is not an issue here.
Step 7: Insert 3 mm half ball lens
The half ball lens is stored in a small protective container (often an Eppendorf tube). Handle by the edges only.
Insert it into the half-dome pocket on the side of the emission module. It has one correct orientation; the flat face and curved face are distinguishable by feel and by profile. It should seat without excessive force. Try to place it as flat as possible before joining the modules.
Step 8: Fold the rigid-flex PCB and EWL flex legs
The PCB ships with its flex legs lying flat. Before joining the modules, fold the electrowetting lens (EWL) flex legs so the two gold contact rings face each other; these rings will sandwich the EWL lens in the next step. Bring the contacts together gently. The legs will spring back partially, and a partial fold is sufficient. Do not crease all the way, and do not kink the flex.
Step 9: Sandwich the electrowetting lens and join the objective and emission modules
This is the most mechanically demanding step, so take your time. Loosely start the three M1 screws in the objective module before you begin; this holds position and lets you correct alignment later.
- Place the EWL flex cable in the top cutout of the objective module.
- Place the electrowetting lens on top of the flex cable, in the top pocket of the objective module, in the correct orientation.
- Sandwich the EWL lens between the two gold rings of the flex PCB, then bring the objective and emission modules together.
- Use the pre-threaded screws as guides. Seat one screw partially to hold position before tightening anything.
Do not tighten all screws simultaneously. Seat one screw first, check alignment, then seat the others. Once the objective, EWL, and emission are sandwiched, screw them together loosely first so you can correct the EWL cable alignment, then tighten.
Watch the flex loop: the loop of PCB flex should sit flush against the module body. If it disappears inside or kinks outward, re-thread it before tightening.
Lateral alignment: hold the PCB in position as the screw seats so it does not rotate sideways. Check visually that it sits straight before fully tightening.
Step 10: Attach the excitation module
Screw the excitation module onto the assembled body using two M1 screws, one on each side. Placing the screws in the excitation module beforehand makes this easier. This also screws the LED portion of the rigid-flex PCB down, giving the flex a rigid mount for the remaining steps.
Step 11: Place the emission filter and glue the imaging sensor PCB
- Place the emission filter (ET525/50m) in the pocket at the top of the emission module, coated side DOWN, facing down toward the rest of the optics (away from where the imaging sensor will go). Use the reflective-surface method to confirm orientation. Push it into the pocket with a cotton swab.
- Remove the protective tape from the emission filter only when you are ready to glue. Remove it with plastic tweezers, taking care not to scratch the surface, then clear any dust with lens tissue.
- Remove the protective plastic film from the CMOS imaging sensor on the PCB.
- Test before gluing. Power the Miniscope and image your surroundings (room lights or a monitor) to confirm the emission filter and sensor are free of dust. In this configuration the scope sees only the filtered wavelengths, so it can image distant objects. Any dust or debris on the emission filter or sensor will show up clearly.
- Clean the bonding surfaces of the housing and PCB with a little alcohol to remove oils.
- Glue the imaging sensor PCB to the top of the emission module. Apply a small amount of epoxy along the sides with a toothpick and glue one side at a time, curing each with the UV gun. Hold the assembly so the emission filter does not fall out.
Step 12: Final PCB bending and cable attachment
Bend the remaining floating sections of the rigid-flex PCB (MCU/BNO and SER/POW) down against the body and glue them in place. Attach the MCU/BNO section especially securely, since it holds the head-orientation sensor and must not wiggle when the animal moves. The SER/POW section can get warm, so use a glue that holds at elevated temperature.
Connect the coaxial cable. A connectorized u.FL cable plugs in with no soldering. If you are soldering your own connector, see Coaxial cable assembly below. Cable attachment is typically completed during the software setup session that follows assembly.
Coaxial cable assembly
A connectorized coaxial cable with a Hirose u.FL connector needs no soldering. The following is for builders soldering their own cable. A microscope with good illumination gives the best results.
Coax Step 1: Solder the coaxial cable to the SMA connector
Do not use cable strippers, they are not suitable for these coaxial cables. A scalpel gives the best results: gently press the scalpel into the jacket and roll the cable, then remove the cut jacket with tweezers.
Coax Step 2: Solder the coaxial cable to the u.FL connector
Solder the inner conductor of the coax cable to the small pin on the back of the u.FL connector. Solder the braided shield to any other part of the metal housing of the connector.
The u.FL connector is not meant for many connect and disconnect cycles, so treat it as a fixed connection unless the cable needs replacing. Avoid rotating the connector. Once connected, add a drop of flexible epoxy between the coax cable and PCB (without getting epoxy inside the connector) to secure the cable while still allowing removal if necessary.
Workshop Tips
These apply specifically to group assembly sessions (workshops with multiple builders).
| Tip | Reason |
|---|---|
| Keep everyone at the same step at all times | People who move ahead tend to make orientation errors that are difficult to diagnose later; the assembler running the session ends up troubleshooting while everyone else waits |
| One screwdriver per builder enforces pacing | Without this, some builders pre-assemble future steps, usually incorrectly |
| Thread all holes (Step 1) before distributing any other parts | Modules vary batch to batch and some holes are tight. Better to discover this before the module is partially assembled |
| Never leave screws loose on the bench | They roll, fall, and disappear. Return every screw to its hole immediately after threading |
| Announce lens-opening steps as a group | Lenses fly. Having everyone open their packet at the same time means one person's lost lens can be quickly located |
| Mark assembled scopes immediately | Assembled scopes are visually identical. Use nail polish, a scratch mark, or any other physical ID before leaving the bench |
Sourcing Notes
| Component | Primary source | Notes |
|---|---|---|
| M1 × 3 mm screws | McMaster-Carr | Only reliably available source outside the US; validated for this application |
| Achromat lenses | Edmund Optics | Japan-sourced; about $90 each for 3 mm achromats |
| Filters (ET470, ET525/50m, T495LpXR) | Chroma / AHF | Verify coated-side orientation regardless of batch |
| PCBs | Taiwan (fabricated) | Shipped through assembly house; not available separately through standard vendors |
| Module bodies | US (machined) | Shipped to assembly point; not available separately |