Assembly
We have worked hard to make Miniscope assembly as easy and error-proof as possible. If you use a connectorized coaxial cable with a Hirose U.FL connector, no soldering at all is needed. Assembly consists of 1) visual inspection of all parts (especially the Miniscope housing), 2) press fitting lenses into the housing, 3) sliding optical filters into slots, 4) screwing housing parts together, 5) attaching the rigid-flex PCB, and 6) testing the system. Below is a detailed guide of this process along with a video tutorial.
TODO: Add assembly video tutorial
A soldering guide for the U.FL coax cable connector is at the bottom of this page.
- Keep lenses, filters, and imaging sensor as clean as possible. Use lint free filter paper or Kimwipes for cleaning if needed. Optical surfaces closer to the image and object planes are the most critical to keep clean.
- Try not to kink the flexibly portions of the Rigid-Flex PCB. All bends should be smooth and gentle.
- The coated side of filters and dichroics should always face towards incoming light.
- The less curved side of a lens should face toward the side of light with the steeper angle. For the V4 Minsicope, this means the flatter side of the lenses in the Objective Module should face toward the brain and the tube lens inside the Emission Module should face toward the imaging sensor.
- We suggest using self-threading M1 screws for assembling the body. Make sure to not over tighten these screws and risk stripping the threading.
- Avoid using most types of Cyanoacrylates (super glue) as these can off-gas and coat the optics in a hazy white film. Also, some Cyanoacrylates can cause Delrin to become brittle. We have found that some Cyanoacrylates designed for PCBs work well but you need to leave the Miniscope in the open air for a few days for the glue to completely off-gas. See MCU Programming.
The steps below will walk you through the entire process of assembling a V4 Miniscope.
Make sure the on-board microcontroller has been programmed with the more recent MCU firmware (located in this repository). If you get a pre-assembled and tested Rigid-Flex PCB the MCU should already be programmed and ready to go.
Inspect the Miniscope body parts and clean out any pieces of plastic/resin.
Step 2: Press-fit of the 4mm diameter achromatic tube lens into the Emission Module. There is an inner lip in the emission module that will act as a hard stop from the 4mm diameter lens. You should be able to see that the back side of the lens is sitting against this inner lip through the dichroic slot.
The less curved side of this lens should be facing up toward the opening for the imaging sensor.
If this lens is flipped around you will still be able to image but you will have noticeably more distortion in your image.
Make sure the coated side of the dichroic is facing towards the incoming light. This means it should be facing down toward the Objective Module. The orientation of the filters and lenses are indicated in the figure above. Note the arrows on the side of the filters.
Step 4: Placement of the 4mm x 4mm x 1mm excitation filter into the pocket in the Excitation Module.
The coated side of this filter should be facing the hole for the LED (The arrow on the side of the lens will point toward the LED). The face of the filter will be flush with the face of the excitation Module. It is important to not scratch or chip this filter... a bit of dirt isn't an issue though.
Step 5: Placement of the 3mm diameter half-ball lens into the half dome pocket on the side of the Emission Module.
This lens has the tendency to fall out during 'Step 6' so be careful. If when imaging after assembly you see a very bright small square in your image instead of uniform illumination, the half-ball lens is likely missing.
You will likely need a Torx-2 torx wrench.
The less curved side of these lenses should both face down towards where the brain will end up being. We usually set each lens on filter paper on a table and then press the Objective Module onto the lens. Do this twice and you will have both lenses pressed into the Objective Module with the bottom lens flush with the bottom of the Objective.
If the fit of these lenses seems too tight, you may damage a lens when pressing it into the housing. In this case you can slightly open up the hole with a 3mm diameter reamer or contact the supplier of your V4 Miniscope.
By mix and matching the focal lengths of these lenses, you are able to choose a range of working distances and field-of-view sizes. More information on this can be found on the Lens Configurations page.
Step 8: Screw the excitation LED portion of the Rigid-Flex PCB onto the Excitation Module using two M1 screws.
This will act as a rigid mount for the Rigid-Flex PCB, making the remaining steps a bit easier.
Step 9: Place the 4mm x 4mm x 1mm emission filter into the pocket at the top of the Emission Module.
The coated surface should be facing away from where the image sensor will go. In other words, it should face down towards the rest of the optics you have mounted in the Miniscope. It is important to keep both surfaces of this filter clean as any dust or debris will should up reasonably clearly when imaging.
Step 10: Glue/Epoxy the CMOS imaging sensor part of the Rigid-Flex PCB to the top of the Emission Module.
Clean the surfaces of the Miniscope housing and PCB with a little bit of alcohol to remove any dirt or oils that would inhibit bonding.
Make sure the emission filter does not fall out during this process. Make sure to remove the protective plastic film on the CMOS imaging sensor before doing this. It is very important to keep the glass of the imaging sensor very clean here as any dirt or debris will show up clearly when imaging.
We suggest before gluing, to turn on the Miniscope and image your surroundings to check to make sure the emission filter and imaging sensor are free of dirt. In this configuration, the Miniscope should be able to image objects (remember it is only seeing the filtered wavelengths the emission filter is passing) far away from it so just hold it up to room lights, or a computer monitor for testing.
If you need to clean the surface of the imaging sensor please look up proper imaging sensor cleaning techniques so that you do not leave any residue on the glass.
TODO: Add link to sensor cleaning tutorial.
Our glue of choice for this step is Norland 68 as it bonds well to plastic and PCBs and is UV curable in seconds. You can also use PCB potting compound if you have more patience. We have also had success with 2-part epoxies and even Loctite 444 plus its compatible accelerator. It is key to use a pretty viscous glue here as you do not want any seeping onto the imaging sensor.
This is the most difficult step so take your time. It is helpful to slightly screw in the 3 M1 screws into the Objective Module before beginning this step.
Step 11a: Place the electrowetting lens flex cable portion of the Rigid-Flex PCB in the top cutout of the Objection Module.
Step 11b: Place the electrowetting lens on top of the flex cable in the top pocket of the Objection Module.
Step 11c: Sandwich the electrowetting lens in between the 2 circles of the Rigid-Flex PCB and screw the Objective Module onto the Emission Module.
Step: 12: Glue/Epoxy the MCU/BNO and Serializer/Power postions of the Rigid-Flex PCB to the Miniscope housing
We are just about there! All that is left is to bend down the remaining floating sides of the Rigid-Flex and secure them to the Miniscope body. The MCU/BNO should be attached especially securely as it hold the head orientation sensor and we don't want that wiggling around when the animal moves. The Serializer/Power portion of the Rigid-Flex PCB can get pretty warm and some glues will not maintain a hold at these temperatures.
TODO: Add pictures for all these steps.
**After assembly, consider following the Initial Testing of Assembled Miniscope tutorial to test the system before in vivo recording.
A more detailed guide is on its way but until then we have a short guide below.
You will need to solder the inner conductor of the coax cable to the small pin sticking out of the back of the U.FL connector. The braided shield of the coax cable can be soldered to any other part of the metal housing of the U.FL connector. **Make sure to check for shorts between the inner and outer conductors of the coax cable before plugging it in to a Miniscope DAQ**
The U.FL connector is not meant for many repeated connects and disconnects so we suggest treating this as a fixed connection that doesn't get disconnected unless the coax cable needs to be replaced. Along with avoiding many connects/disconnects you also want to try to avoid the connector rotating. We suggest adding a drop of flexible epoxy between the coax cable and PCB (avoiding getting epoxy inside the connector) once the cable is connected to the V4 Miniscope. This will secure the coax cable to the Miniscope but still allow for its removal if necessary.
