Driving an Air-Core movement.

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi all,

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

Two questions,

  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 :slight_smile:

Cheers everyone

Craig

2
  1. 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?

you'll need one H-bridge per coil, it can do the +5/-5V reversal. the common ground might be a problem, if 2 coils are on at the same time -> BRRZZZzz ! needs to be looked at closely.

there's chips with 2 H-briges in one package.

some tutorial with arduino code:

http://itp.nyu.edu/physcomp/Labs/DCMotorControl

3

so what happened with that

any videos?