Tiny Wireless Capsule Camera

A capsule endoscope, also known as a capsule camera, is a tiny camera that can be safely swallowed and passed through the digestive tract. The device uses one or more camera sensors to capture images of the gastrointestinal tract and is useful in diagnosing or evaluating a myriad of diseases or dysfunctions of the digestive system. Many configurations are possible, but the core functions boil down to (1) capture images, (2) process and either store/transmit the image, and (3) operate continuously for 24-48 hours.

This kind of device is especially convenient for evaluating hard-to-reach places (such as the distal small intestine). It is also useful in situations where the patient cannot (or refuses to) tolerate more conventional approaches such as colonoscopy or esophagogastroduodenoscopy (EGD a.k.a. upper GI endoscopy). Though capsule cameras have not supplanted these conventional, "Gold-Standard" methods, they nevertheless have become an invaluable medical tool.

Why do this project?

Short version: I think it would be fun to build one.

Long version: Around the hospital, I have occasionally had the privilege of seeing these devices in action. The branded, FDA-approved versions used in real human patients are incredibly sophisticated systems with years of research and safety testing behind them. Like most things in medicine, they are also incredibly expensive and, understandably, highly proprietary. Devices like these take millions of dollars to develop and years (even decades) of research and development before they even see human trials, let alone actual sales. Overall, it's pretty inaccessible technology.

Still, the proliferation of tiny, versatile cameras in phones, tablets, and elsewhere made me wonder if it would be possible to develop a capsule camera with off-the-shelf parts and open software, and build it with materials, manufacturing, and resources readily available to the amateur hacker.

Crazy? A mini 2MP camera module in a 8mm x 8mm package can be bought on eBay for <$5. Incredibly powerful 32-bit micros have become completely accessible to total novices. A 4-layer board with 5mil pitch can be had for $10 per square inch (of note, I estimate the total board area needed for this project to be barely 1 sq inch. Even relatively cheap 3D printers may be able to make a suitable enclosure. This is hardly crazy (ok, maybe a little).

Application Example:

Full disclosure: I do not at this time have plans to ultimately test this device on living (human or otherwise) subjects. That particular ethical and legal minefield is not something to shoot for at this time.

Top-Level requirements

The system I want to build must meet a handful of high-level requirements.

Single camera VGA or better resolution (2MP goal) imaging captured at least every 10 seconds
On-board storage of at least 15 minutes of images
Wireless transmission of image data to external storage device
24-hour battery life
15mm diameter x 30mm length maximum (smaller better)

System Design

Overall System

The capsule hardware consists of three separate boards/modules:

Camera: contains the image sensor, LED flash, and supplemental power regulation required by the image sensor.

Battery: contains the battery holder, magnetic reed switch for power on/off, and the main boost regulator.

Control: contains the processor, storage memory, and radio transceiver.

Camera

The camera board contains the OV2640 camera module, a (up to) 2.0 megapixel image sensor with parallel RGB outputs. The image sensor requires a 2.8V rail for digital and logic, and a 1.3V rail for analog power (provided by a small LDO regulator). Since the typical application lacks ambient light, there are 4 white LEDs to provide a 'flash'.

The OV2640 accepts a minimum pixel clock of 6MHz (nominal 24MHz), provided by the system processor. The camera data electrical interface is 8-bit parallel, configurable as YUV, RGB, or RAW. The datasheet also mentions JPEG compression as an option, though this does not seem well-documented....

Image capture
Ryan Bailey • 02/07/2017 at 22:43 • 0 comments

One of the bigger challenges recently has been devising a way to capture output from the camera efficiently without relying on the DCMI interface available in other STM32 devices. One of my goals from the beginning was to avoid resorting to BGA or extremely fine-pitch parts. The idea was to keep board design and manufacturing relatively simple and cheap. Unfortunately, I have not found a DCMI-capable part with a sub-10mm diameter in a non-BGA package.
It is tempting to switch to something like the F407 or F429 (as found in the OpenMV). For now, I plan to forge ahead with the following strategy:
Much credit is due to the following article (link) that outlines how to capture data using DMA triggered by a timer in input capture mode. ST also has a decent app note (AN4666) discussing general-purpose synchronous parallel data transfer that proved fairly helpful.
Full image capture should be available soon - there are still some kinks to work out with camera configuration.
State of the Project: Part 2
Ryan Bailey • 10/10/2016 at 03:39 • 0 comments

It's been a good while since I've posted updates here. Several posts made earlier are more or less back-logs from the last three months, most of which I've been traveling to meet requirements for the rest of my education. Things are moving ahead and I have prepared a small video overview below:
Updates by specific system:
1. Camera: Progressing. Further tests needed once updated proto boards are assembled.
2. Power: Finished
3. Main Board: Updating Layout
4. Communications: RPi receiver implemented, command interface and display of received images in progress
5. Enclosure: Test enclosures working. Likely re-design pending new dimensions of board layout updates (see above).
6. Code: Test board and programmer working. Further coding efforts pending.
Camera footprint correction
Ryan Bailey • 10/10/2016 at 03:20 • 0 comments

I usually do my best to check (and re-check) footprints before things go out to fab. Unfortunately, there was an error in the camera module footprint that shorted one of the power supply pins to ground. I think I had visually transposed a few things from the (minimal) datasheet on this device. Luckily, the fix was relatively easy and some replacement prototyping boards were sent to fab.
The replacement camera modules arrived just after I had left for two months on the road. I intend to find some time in the coming weeks to assemble them - especially now that I have a viable strategy for keeping the module housings from melting during reflow
Stay tuned.
Layout Update
Ryan Bailey • 10/10/2016 at 02:51 • 0 comments

I spent some time during my travels going over the original layout. I've decided to take another crack at slimming everything down further - this means a main board width of 10mm or less. It's also a good opportunity, based on some previous dummy board assembly, to get the board-to-board approach right. I'm particularly interested in how far I can push down the size of castellations.
Obviously, still a work in progress. The goal is still to get everything on the same board using 0402 passives and OSHPark 4-layer spec DRCs. You can see why a lot of commercial units use flex circuits extensively.
Receiver Setup
Ryan Bailey • 10/10/2016 at 02:38 • 0 comments

Radio update: configuration and sensor data will be received by an external device, in this case a Raspberry pi with a nrf24L01+ module attached.
Right now I'm simulating 16-byte image packets sent from the capsule camera to the RPi.
Next steps include implementing full back-and-forth communication and displaying received image data on the RPi.
Microcontroller board update
Ryan Bailey • 07/15/2016 at 03:26 • 1 comment

Update: Initial programming was a modest success. There is still some temperamental behavior to work out with the programmer - some searching suggests that termination/reflection issues on the data line sometime cause programming to fail. Still, I was able to load and run a simple LED blink program:
It's been a busy couple weeks but I finally found the time (and the correct parts) to finish assembling a couple of the microcontroller testing boards that I cooked up last month.
Also pictured: complete mess-of-wires version of the final system. The main voltage rail is 2.8V, regulated from 4-5V input, as required by the camera.
Also notable is the quick proto board I threw together for the 256Mbit flash device. It's a slightly weird-looking package so I wanted to try a standalone board before 100% committing it to the final design.
No magic smoke so far. Programming tests coming soon.
A quick update
Ryan Bailey • 07/01/2016 at 15:56 • 0 comments

It's been a busy couple weeks with the school year ending. Subsystem software prototyping is almost finished. Most of what I've accomplished so far has been under the mbed environment, but sometime in the coming week or so I'll be ready to start transitioning over to writing specifically for the STM32F411 micro. Speaking of the F411, the proto boards are back and assembly will start sometime today:
Also of note, I had a handful of dummy enclosures 3D printed through the Dirty SLA service over at dangerousprototypes (http://dangerousprototypes.com/store/print3d) just to get my head around the case size and any issues with the board fit (so far so good!).
Microcontroller board
Ryan Bailey • 06/09/2016 at 00:15 • 1 comment

Just shipped a new board design off to fab. This time it's a small prototyping board for the STM32F411 microcontroller used in the camera capsule. I already have a Nucleo board for the purpose of prototyping, this board is to prove to myself that I can build up a functional system from scratch using this particular microcontroller. It integrates a 2.8V regulator and the option to forego an external crystal - both of which are requirements for the final system.
I expect the board back in a few weeks.
A Modestly Powerful Update
Ryan Bailey • 06/07/2016 at 03:53 • 0 comments

The battery + boost converter board seems to be working. After a blown out board due to ordering the wrong inductor (note to self: triple-check BOM), things seemed to work pretty well. The boost converter accepts as little as 0.9V from the battery and outputs ~2.8V, the supply voltage required by the imager and therefore the common supply I'll use for all other components.
The proof is in the molten lead pudding:
Fully assembled (with the right inductor this time).
Running at minimum voltage
~2.8-ish volts. Maybe 1% resistors next time.
Boards!
Ryan Bailey • 05/16/2016 at 02:31 • 0 comments

I received a few dummy copies of the initial board design today. These are certainly not final but I wanted to get an initial look at how they fit together and identify any gotchas in the mechanical design. I'll solder one of them together in the next night or so.
update 5/21/16:
Rough mechanical check with the board-board connections soldered together:
Camera prototyping board: