I drew up the circuit schematic using the free open-source KiCad EDA tool, for a single board containing all the electronics including finger attachments. As I mentioned in my previous log entry, I decided that for this first wearable prototype, I would just build 1 finger attachment and make it part of the single board.

I designed the circuit to allow 2 finger attachments, but I'll start off only building 1 finger attachment and just ignore the part of the circuit diagram for the 2nd finger attachment.

Here are the parts I came up with for building the initial working prototype based on parts I already had at home (cheap parts I purchased either from AliExpress in China or Element14 / Farnell in Australia when on sale):

• 1 x USB LiPo Charger (USD$0.27 in 1 pcs)
• 1 x 3.7V 240mAh LiPo battery (USD$0.76 in 5 pcs)
• 1 x On/Off switch (USD$0.05 in 30 pcs)
• 1 x Arduino Pro Mini 328 3.3V (USD$1.71 in 1 pcs)
• 1 x 0.1uF SMD capacitor (USD$0.01 in 1 pcs)
• 1 x 30pF SMD capacitor (USD$0.01 in 1 pcs)
• 1 x OFL-3102 IR LED (USD$0.16 in 1 pcs)
• 2 x 18 Ohm SMD resistors (USD$0.02 in 2 pcs)
• 1 x TEFT4300 IR Receiver (USD$0.47 in 1 pcs)
• 1 x 75K Ohm SMD resistor (USD$0.01 in 1 pcs)
• 1 x Schottky SMD diode (USD$0.23 in 1 pcs)
• 2 x Logic-level N-ch MOSFETs (USD$0.89 in 2 pcs)
• 1 x Vibration motor (USD$0.66 in 1 pcs)

TOTAL COST FOR PARTS: USD$5.25

(for a single working prototype for a single finger, ignoring the tiny amounts of hookup wire, solder and PCB stripboard used for the prototype).

Note: The links given above are mostly for items that come with free postage worldwide from China, so that price includes shipping! But the OFL-3102 IR LED isn't available on AliExpress for free shipping, it only comes with free shipping from Element14 on orders atleast USD$30.

The circuit can be downloaded as a KiCAD project on GitHub at https://github.com/shervinemami/DepthIR/tree/master/DepthIR_SingleBoard, or as a PDF at https://github.com/shervinemami/DepthIR/blob/master/DepthIR_SingleBoard/DepthIR_SingleBoard.pdf

The circuit is simply made up of a Power section, a Microcontroller section, and a Finger Attachment section (duplicated for each finger).