Finally solved using some pretty tight soldering, insulation tape, jumper wires and several clamps.
Powering the Nexus Sensors
My last post now makes me laugh quite a bit with some of the solutions i was offering! After a little more research into potential difference (PD) i tried a few things.
Firstly i tried an op amp to try and invert 0v to 5v to give a -5v to 0 output. This doesn't work of course because you have to power the op amp with a PD enough thats high enough to swing between -5v and 5 volts which is of course 10V. I tried to do this using a few batteries. I then found out that i am not using a common earth by using two different voltage supplies. So i needed to use the Arduino to power everything. Luckily i later found out that the microcontroller has the facility to use an external power source. Using this knowledge i managed to provide a 0V, 5V, and a 14V supply from the device. Using a potential divider and i can pull the 14V level to 10V which give me a 10V PD. I then will use 5V as a virtual earth, 0V then translates to -5V, and 10V to 5V. This gives me the power and reference levels i need to power the Nexus sensors whilst providing a common earth.
However, when i get return signals from the BVP device (in particular because it requires calibration) it will be in respect to 5V as a virtual ground. As the Arduino only samples analog inputs from 0 to 5V at a resolution of 1023, i will have to again have to employ another signal conditioning stage to work within these levels. Of course with small voltage work it is important to try to avoid as many potential noise producing phases as possible. Hopefully though, if i am only using potential dividers the only real noise problems (providing good component placement and decent interconnect) will be thermal noise from resistors.
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