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Rheostat for SMA (MEC143E)

This circuit described here is based on my book Robotics, Mechatronics and Artificial Intelligence (sold out) published in the United States. It can be used to control SMA (Shaoe Memory Alloy) in robotics and mechatronics projects. The SMA requires a specific minimum amount of current to be heated to its transition temperature. You can determine this current using the circuit shown in Figure 1.


This circuit can be connected to any power supply or batteries from 3 to 12 V and can produce currents up to 3 A with the recommended transistor. The transistor can be installed on a heat sink. For currents up to 2 A, the transistor can be replaced with a TIP31, and for currents up to 1 A with a BD135.


Figure 1 – Rheostat for SMA
Figure 1 – Rheostat for SMA


You can also invert the polarity of the power supply and use PNP transistors.