patweadock
Joined: 13 Feb 2009
Posts: 35
Helped: 3
Location: Near Burlington, VT
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 05 Mar 2009 19:59 l297 cheap |
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You don't really need to program a "stop", where you apply 0V, in fact, applying 0 V may allow inertia to move it a couple more steps, where if you just stop pulsing it to effect a stop, the last phase power will still be applied, which will tend to hold it in place. Then maybe a very small delay to dissipate inertia, then change the direction bit and start stepping again. I doubt you need the delay though.
R7 is used with R6 to make an adjustable voltage devider for Vref. This is compared internaly to Vsense. When Vsense is greater than Vref, phase power is turned off. Then it waits for Vsense to go to 0V before turning power on again. This is what limits the current in the coils from deystroying itself thru heat. It allows you to apply a greater voltage than what the motor is rated for. When you apply voltage to an inductor (a coil), the current is not instantaneous, it has to wait for the magnetic field to expand, conversly, when voltage is removed, it takes a while for current to stop - until the mag field collapses completly. This time is the L/R time constant. This confiquration for powering stepper motors is called "chopper drive".
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