DAC life expectancy

T Chap

For a product that needs to last 10 years plus, would the RC DAC on the Prop be a reliable option? I mean, how many times can you hit the cap before it fails? The goal is to control the reference voltage to a mosfet driver, such that after some elapsed time(X seconds), the current regulation to the stepper can change to keep the motor/mosfets cool when not is use, yet maintain some level of holding torque. Then, when motion is required, first raise the DAC back to the max REF for the current rating on the motor.

Something like:

If no steps after X time
     DAC = .5 volts DC

'plus the reverse

If StepPin = 1 then
    DAC = 1.5 volts

Is this workable and reliable, or should a real IC be used for additional relaiability?

Thanks

OzStamp

Hi Originator 99

I recommend a simple 2 stage control with pots.. running torque and standstill holding torque.
Most industrial stepper motor drivers employ these sort of settings within themselves ..
Depending on what type software controllable ..
So use 2 digital outputs or 1 with some resistors/ pots ..voltage divider type setup as a reference into a comparator ...
Maybe the chip your using has all this build in ??

Your doing a great job.
Ronald Nollet
Parallax Australia distributor

Gavin

Are you trying to set the chopper current via the ref voltage.
How about a serial digital pot? SPI or I2C, get a 4 pot version for 4 motors.

Trim pots would be easier just have pcb test pin so you can connect a multimeter to it.
It only needs to be set once to match the motor and less code to write[noparse]:)[/noparse]
Use a second pot for holding current and switch between them.

I would be too scared of getting the code wrong and cooking the motor, mind you pots are know to fail.

Gavin

T Chap

Yes it is a ref pin to a built in comp on the driver, so it sets the chopping threshold. OzStamp that is a much better idea than mine, two pins, two pots, bussed to the 3 or 4 drivers. Minimal code involved, Thanks!