Driving a Bipolar Stepper Motor with Arduino and ULN2803AG

  
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While I`m getting ready to rip open some 10+ broken DVD-RW drives coming to me from an eBay seller, I though it would be great to have a testbed for the bipolar stepper motors I will harvest from those. I have a bunch of ULN2803AG Eight Darlington Transistor Arrays with Common Emitters left from past projects and these can sink (but unfortunately
Driving a Bipolar Stepper Motor with Arduino and ULN2803AG - schematic

not source) peak loads of 600mA (500mA continuous) and are well suited for power application like driving small motors. However, there is a problem with 4-wire bipolar stepper motors: they don`t have the common points of windings wired to the outside which would be needed for providing the motors with power. See the ULN2003 datasheet for more information about the IC: ULN2801, 2802, 2803, 2804 and 2805 Darlington Array datasheet Still, it looked to me that it would still be possible to make a small bipolar stepper work by floating the voltage using some 22 Ohm resistors to the motor supply voltage (motor you see on the video has 18 Ohm windings, so this was the closest resistor value). At first I attempted to use for the motor voltage the same +5V supplied by Arduino but because of the floating middle point the max voltage across each winding was only 1. 7V and that was not enough to move the rotor. When the motor supply voltage was increased to +9V (the 9V battery on the picture), things started working. There is still only 4V across each winding at any time it`s energized but it looks enough to make the linear slide move with some force which I hope will be enough for carrying the laser diode housing. Here is the schematic of the whole setup and below is the Arduino sketch. Please note that the resistors needed to be at least 1/4W rated but I did not have the 22 Ohm needed for the project and used 1/8W ones. They did get...



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