The circuit of the HTC original sensor is out there. You can also buy those sensors from the US. We decided to build our own sensor anyways. As it turned out, our sensor has a pretty cool property. More on that later...

The HTC sensor works by measuring the envelope signal of modulated light pulses. Luis sensor is based on cascaded amplification stages and signal conditioning filters.

After some breadboard prototyping, Luis tweaked the different amplification levels.

We etched the circuit and build a more compact prototype. 

On the picture above you can see the cool feature of our sensor. The photodiode can be placed up to 1 meter away from the amplification circuit using coax cable. We are planning on building a full body morph suit.

Then we miniaturized the sensor further. Check out the design here.

We ordered the pcbs in china and assembled them in makerspace. The result is a 16x12mm sensor. We moved from de0-nano to de10-nano-soc. The sensor data is retrieved from the fpga via altera master/slave interface and sent to the host via ROS message.