I am trying to drive an Air-Core movement (taken from a car speedo) with my Arduiono. I would like to drive this to as near as 360deg as I can.
I have worked out the maths for the voltages required to be delivered at each coil to drive it through the four quadrants being:
Vs = Vmax sin(rad) and Vc = Vmax cos(rad)
where Vs is the voltage applied to the sine coil, Vc is the voltage applied to the cosine coil, and Vmax is 5V.
Since V is proportional to PWM, I will replace the letter V in the above by PWM, and use PWMmax=255.
This should give me all four quadrants correctly, provided I can get the hardware to deliver a negative voltage.
I want to use the PWM outputs of my arduino and have wired these up to a HBridge (L293D) to handle the 60ma+ that the coils pull.
The problem I have is that what I discovered earlier doing the maths is that for some quadrants I need to reverse the coils. As the two coils have a common ground I have decided to use two suply voltages (+5 & -5).
i.e there will be four combinations of voltages driving the coil: +5 --- 0 ---- +5 +5 --- 0 ---- -5 -5 --- 0 ---- +5 -5 --- 0 ---- -5
1) does anyone have a nice circuit to produce -5V from a +5v regulated supply. I have read about using a MAX232cpe as it has an inbuit charge pump, but I have not been able to get this to work. Any help on this or other sugestions?
2) given I want two output voltages now delivered to the coil do I need a second HBridge? i.e. do I need to use one for +5V output and one for -5V output?
3) has anyone driven one of these air-core movement?
I am in the learn as you go categopry so please don't assume a lot of prior knowledge here :-)