I've finally figured out what was wrong with the sleep mask charger and USB circuits: the pins on the connector were reversed. So, hilariously, every time I plugged it in, i was connecting V+ and GND backwards, leading to some considerable heating in the charger IC. Remarkably, the whole thing worked flawlessly once I flipped the connector.
Since I worked that out, I've designed version 2 of the sleep mask and helmet boards. Additionally, I designed boards for a few other projects, including an instrumented glove, and MARLOK key reader and a pulse oximeter. I've begun to populate the boards, but I'm out of some things, so I'm waiting for another Mouser order. Unfortunately, the component names ended up on the silkscreen, making it thoroughly messy.
Sleep Mask V2
After figuring out what I'd done wrong with the USB connector (as well as playing around with the REM detector), I moved forward with redesigning the sleep mask controller board. Most importantly, I significantly shrunk the board (the old version was very... clunky). I used smaller versions of the microcontroller, FET, headphone jack and opamp. Additionally, I added the option for a lowpass between the microcontroller DACs and the headphone amplifier, in the hopes that I can reduce power consumption.
I also wired up a new mask (the old one was... clunky. Also gaudy... very gaudy).
Helmet V2
The new version of the helmet implemented the analog-power-off changes, in addition to adding a charger circuit. However, it ends up being about the same size of the old board, owing to the use of smaller FET, opamp and microcontroller.
Instrumented Glove
I've long been interested in the idea of a joint-angle-sensing glove for computer interface. Additionally, I overheard someone around the lab implying that they would like to take such joint data over a whole day of normal hand-use. So, I thought that I could use some of the spare board-space on a circuit which would read at least 22 channels of joint angle data, and record them to an SD card. The flex sensors will be home-made, and will change their resistance with flexion (like in this article).
I decided to go for a controlled-current topology for resistor-sensing (rather than a divider) to get a linear read on the resistance. The resistor sensors are connected to the header at the top of the board; they connect to V+ on one side, and to the constant-current sink on the other side, through a matrix of FET switches; 5 banks of 5 sensors each give me 25 potential sensor channels for a mere 10 digital outputs. This circuit also includes a battery charger.
MARLOK key reader
I've long hated the MARLOK key; it seems like a perfect storm of high-cost and low-convenience and I don't understand why you would use it instead of an iButton system or RFID. In any event, I have a MARLOK key and I was curious about how the information (and clock) were encoded in it. There isn't much information online about the format; all I was able to find was that the information is encoded in the sequence of holes drilled in the shaft of the key.
I designed a pair of board upon which I could mount IR emitters and IR phototransistors to read all three tracks of the key; I added a few spare holes to weld the two sides together using wire scraps.
Pulse Oximeter Sensor
Finally, I wanted to try out reading pulse (and possibly blood oxygenation) non-invasively. I created a sensor board based on "A wireless reflectance pulse oximeter with digital baseline control for unfiltered photoplethysmograms" by Kejia Li and Steve Warren. The sensor is reflectance-mode, which means that you only need access to the surface of the body; in opposition to the transmission mode, where the emitter is opposite a protruding bit of anatomy (like a finger) from the detector. The emitters and detectors are in the upcoming order, so it's just the board and cable for now.
Since I worked that out, I've designed version 2 of the sleep mask and helmet boards. Additionally, I designed boards for a few other projects, including an instrumented glove, and MARLOK key reader and a pulse oximeter. I've begun to populate the boards, but I'm out of some things, so I'm waiting for another Mouser order. Unfortunately, the component names ended up on the silkscreen, making it thoroughly messy.
Sleep Mask V2
After figuring out what I'd done wrong with the USB connector (as well as playing around with the REM detector), I moved forward with redesigning the sleep mask controller board. Most importantly, I significantly shrunk the board (the old version was very... clunky). I used smaller versions of the microcontroller, FET, headphone jack and opamp. Additionally, I added the option for a lowpass between the microcontroller DACs and the headphone amplifier, in the hopes that I can reduce power consumption.
Helmet V2
The new version of the helmet implemented the analog-power-off changes, in addition to adding a charger circuit. However, it ends up being about the same size of the old board, owing to the use of smaller FET, opamp and microcontroller.
Instrumented Glove
I've long been interested in the idea of a joint-angle-sensing glove for computer interface. Additionally, I overheard someone around the lab implying that they would like to take such joint data over a whole day of normal hand-use. So, I thought that I could use some of the spare board-space on a circuit which would read at least 22 channels of joint angle data, and record them to an SD card. The flex sensors will be home-made, and will change their resistance with flexion (like in this article).
I decided to go for a controlled-current topology for resistor-sensing (rather than a divider) to get a linear read on the resistance. The resistor sensors are connected to the header at the top of the board; they connect to V+ on one side, and to the constant-current sink on the other side, through a matrix of FET switches; 5 banks of 5 sensors each give me 25 potential sensor channels for a mere 10 digital outputs. This circuit also includes a battery charger.
MARLOK key reader
I've long hated the MARLOK key; it seems like a perfect storm of high-cost and low-convenience and I don't understand why you would use it instead of an iButton system or RFID. In any event, I have a MARLOK key and I was curious about how the information (and clock) were encoded in it. There isn't much information online about the format; all I was able to find was that the information is encoded in the sequence of holes drilled in the shaft of the key.
I designed a pair of board upon which I could mount IR emitters and IR phototransistors to read all three tracks of the key; I added a few spare holes to weld the two sides together using wire scraps.
Pulse Oximeter Sensor
Finally, I wanted to try out reading pulse (and possibly blood oxygenation) non-invasively. I created a sensor board based on "A wireless reflectance pulse oximeter with digital baseline control for unfiltered photoplethysmograms" by Kejia Li and Steve Warren. The sensor is reflectance-mode, which means that you only need access to the surface of the body; in opposition to the transmission mode, where the emitter is opposite a protruding bit of anatomy (like a finger) from the detector. The emitters and detectors are in the upcoming order, so it's just the board and cable for now.
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