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diff --git a/hardware/README.md b/hardware/README.md new file mode 100644 index 0000000..52b9854 --- /dev/null +++ b/hardware/README.md @@ -0,0 +1,66 @@ +## Hardware assembly ## +Depending on your specific needs, you may want to introduce some variations. +In most cases it's possible to assemble a device with partial functionality (e.g. only for audio latency) on a solderless breadboard. + +### List of suggested parts ### + + * USB OTG cable like + [this](http://www.amazon.com/Generic-Micro-Cable-Cellphone-Tablet/dp/B00AYPEL56) + (or a USB Type-C to A adapter) + for connecting WALT to your phone or tablet + * Microcontroller board - [Teensy LC](https://www.pjrc.com/teensy/teensyLC.html) + * Photodiodes - [BPW34](http://www.digikey.com/product-detail/en/osram-opto-semiconductors-inc/BPW34/475-1070-ND/607274) (3 units) + * Laser - any laser pointer will do, ~1 mW is just fine (5 mW is ok, but avoid stronger ones) + * Accelerometer board [Adafruit ADXL335](https://www.adafruit.com/product/163) **with filter capacitors removed**. + It's very important to remove the filter capacitors, otherwise they smooth out the abrupt shock we are looking for. + Alternatively use the ADXL335 chip directly without the breakout board, but it's rather difficult to solder manually. + * Some resistors and capacitors - see schematics + * TRRS connector or wire for audio measurements + * Clipboard, like [this one](https://upload.wikimedia.org/wikipedia/commons/c/c0/Wood-clipboard.jpg) + +### Schematic ### +The current hardware version we use (r0.7) can be found as KiCAD project in this directory. + * [PDF](WALT_schematic.pdf) + * Blank PCBs can be ordered directly via [this shared project on OSH Park](https://oshpark.com/shared_projects/M5Z8fYCX) + * List of parts for version r0.7 - [BOM as a tsv file](WALT_bom_r07.tsv) + +  + + +### Microcontroller code ### + +Important pin numbers from the code listed below, defined in [walt.ino](../arduino/walt/walt.ino) + + * PD_LASER_PIN 14 - Photodiode that looks at the laser + * G_PIN 15 // Same as A1 - Accelerometer for detecting when touch probe hits the screen + * PD_SCREEN_PIN 20 // Same as A6 - Photodiode that looks at the screen + * AUDIO_PIN 22 // Same as A8 - Detects audio signal from headphones output + * MIC_PIN 23 // Same as A9 - uses PWM to generate a tone for measuring microphone latency. + +### Schematic - older version ### +An older version can be found +[here on Upverter](https://upverter.com/kamrik/8af1f3b04e47ab78/WALT_w_audio/) + + + + +### More electronics notes ### + + * If using Teensy 3.1 instead of LC, it won’t be able to directly read + the screen photodiodes - a buffer opamp will be needed. The screen photodiodes + are bundled as a couple to produce more current, a single photodiode with 1.5M + resistor should provide the same result, but might be at the limit of what the + teensy can measure (input impedance), and again, an opamp will be needed. + * BPW34 photodiode has a small protrusion on the cathode pin (cathode marker). + Anode has a white dot near it. + * Note the different setup of the laser and screen photodiode. The laser one + uses internal pullup resistor (about 20k), enabled by pinMode(PD_LASER_PIN, + INPUT_PULLUP); + +## Mechanical ## + +Enclosure must be made from a non conductive and non transparent material. + +* The enclosure used for r0.7 production run is available in this repo as [STL](enclosure/WALT_recessed_enclosure.stl) and [STEP](enclosure/WALT_recessed_enclosure.step) files. It also used four M3x6 screws (McMaster-Carr PN 92000A116) and M3 hex nuts (McMaster-Carr PN 91828A211) +* A slightly simpler enclosure suitable for printing on a desktop 3D printer is available as a [public OnShape project](https://cad.onshape.com/documents/6410a1ac7964cb29c4a5ba41/v/32bc78539f48ab7f514eeb31/e/fa513fcc84a825e97020c8b3) and [STL](enclosure/WALT_3DP_enclosure_v7.stl) file +* A minimal enclosure suitable for 2D cutting from any 5 to 8 mm thick substrate is available as a [public OnShape project](https://cad.onshape.com/documents/5d7f21c8877ea8961bc499ef/v/84a66f3baf5f4a8f41be3bd7/e/e2a23559efbeb63be3916123) |