Hi,
I am working on a simple air-core coil and a magnet pendulum project. A hal effect sensor detects the incoming magnet and MSP430 gives a small pulse as needed and pushes the pendulum away.
One end of coil is directly connected to one of the GPIOs and the other end of coil is connected to GND. The coil uses very fine magnet wire and has low current thus does not need a transistor. When circuit is in deep sleep, it waits for magnet and the coil GPIO is low. The problem is when i use heavy magnet, the Faraday effect causes the pendulum to slow down and eventually stop. For example, if I just take coil, take it out of circuit and connect its both ends together, it will still slow down the pendulum because the induced voltage flows through coil and fight with the pendulum. The only way to fix it to completely disconnect both ends of coil and magnet can fly over freely and induced voltage doesn't go anywhere.
In short, my question is what GPIO configuration should i choose for one end of coil so that there is no GND supplied? Hi-impedance input? Is there a GPIO configuration in MSP430 so that pin will act as a totally disconnected state, neither GND, not VCC and not even floating state etc.? I really want the GPIO to be entirely disconnected from circuit? Is it even possible, similar to using a relay physical disconnection, where there is not connection at all? Of course I cannot use relay, MOSFET etc. because this is low current application as every micro ampere counts. I am thinking of a low current load switch but it might be an overkill if some GPIO state can take care of it.
Thanks!
