Hi,
I was wondering what happens when a stepper finds an overload such as, for instance, if you try to stop it with your hand.
I guess the intensity going through the coils increases.
Can that be detected with the ADC converters, using eg a 1 ohm resistor, and then the engine stopped ?
I would use that to drive a mechanism to its initial, known, position.
I'm playing with an unipolar stepper and using a L293D chip to drive it, but for the real application it would be a bipolar and probably the same chip.
What do you think ?
Use a shunt resistor and measure the voltage across it to determine the current flow. (current = voltage/resistance)
When it jumps up, stop driving.
Thanks !
A couple of questions:
Will 1 Ohm be ok ? Intensity in normal conditions seems to be about 120-160 mA, will this range of 120-160 mV be above the noise level of the AD conveters ?
Arduino can only measure analog tensions respecto to its ground, right ?
Is this a standard solution known to work ? I fear that the pulse of intensity may be too short to be detected by the converter or.. who knows what else can go wrong?
The A/Ds have a lower limit of 4.8mV per step change, so 120-160 should give reading of 25-33, assuming you have the resistor above ground. In the stalled condition that can jump up quite a bit, to an amp or more, so a reading 200+ could be seen.
Yes, the A/Ds work on 0 to 5V.
If you are monitorng the current, it will not go down until you tell it to, correct? So you drive it to the end position, and either stop driving when you see the current go up, or you add a stop switch & stop driving when you see the switch change state.
Thanks !!
This is more or less what I have been thinking about all the day, the current will be there until I switch off the coils or I step back the engine.
I can't try as I don't have the hardware here, I will see it on monday 
All this stuff is very exciting for me, it is my first experience with steppers !!
Correct me if I'm wrong but isn't the current in a stepper motor independent of the load on the shaft. After all, all you are doing is providing a rotating magnetic field which is being followed by a permanent magnet. The strength of the field and the magnet is what determines the output torque and all you are effectively doing is switching field coils on or off to produce a fixed field "rotational effect"
Edit : I suppose at high speed (pulse rate) there is some back emf induced into the coils by the rotor which will tend to reduce the coil current but at low rotation speeds or when simply jogging this effect must be minimal so coil resistance (or rather reactance) will determine current irrespective of whether the rotor is free to rotate or jammed. There may however be some "signal" induced into the coil (perturbation on the pulse shape) as the rotor moves which might be "seen" by by an intelligent monitoring system.
jack