Problem with PWM

[phoenixcomm]

I have a flight instrument with several + 0 - meters with no inputs they are read 0. But they can be made to move by using the diode test on my Fluke.
I know I can use PWM to drive in only one direction at a time. so some times the wires need to be connected:
for + 1 pwm 2 ground
for - 2 pwm 1 ground.
I was thinking of an h-bridge but that would destroy the movements.
any ideas, please
~~Cris

 

[ronsimpson]

Connect one meter wire to the pwm at 50% and the other end to 1/2 supply.

 

[rjenkinsgb]

Add a series resistor to limit the deflection to no more than full scale at whatever supply voltage you are using, and add a capacitor across the meter to damp the movement.

A limiting resistor is pretty essential no matter what type of drive circuit you use, to avoid excess current and damage.

You can always reduce it as appropriate later on if the circuit you end up with does not give sufficient meter deflection.

ps. If you are trying to drive or use the resolver section, you most likely need a 400Hz sine wave at around 10V, plus either phase shifted versions of that for drive or measure the output phases if it's a sensor.

 

[phoenixcomm]

Thanks for in the info about the cap.
It looks like I need 2 PWM outputs one for the positive and one for the negative.
I think I can use a 74HCT4044 Quad Analog Switch, and build an H-bridge. with out the power
I'm not much good with analog stuff, but digital is another story,

 

[Pommie]

If you're using a micro, use two pwm pins and set one to either +ve or gnd and pwm the other. Instant low power h bridge.

Mike.
Edit, or as many pins as you need.

 

[phoenixcomm]

Mike I think you are right since I am using an Arduino I know I can use digitalWrite( pin, HIGH|LOW but I have to try it on the bench to make sure that it will sink the current. as the Arduino has no way to set an arbitrary pin to hard ground.
~~Cris

 

[phoenixcomm]

MIKE, from the Arduino forum: "once you command digitalWrite(pinX, LOW), it will sink all the current you let it, and if more than 40mA will burn up doing so."

Thank you for the help!
~~Cris