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Saturday, May 7th, 2011

Slot Car Speed Controller

Categories: [ DIY/Arduino ]

I just tested the first prototype of the speed controller for the Tyco slot cars. Currently, the Arduino reads the potentiometer with analogRead() and applies PWM (with analogWrite()) on the base of a BC547 transistor. The transistor acts as a driver for a FQP70N10 MOSFET which controls the motor. The MOSFET doesn't seem to heat at all (I selected this model for exactly that reason) and speed control works (i.e., I can drive the car on a simple ring circuit, down to quite low speed).

My initial idea was to drive the MOSFET directly with the Arduino, but I noticed after buying a pair of those that they it's not a logic-level MOSFET. Driving it with 5 V would theoretically work (I need about 1 A, which is well within the capabilities of the device), but the internal resistance would be much higher that the value touted on the datasheet, and thus dissipate more heat (exact figures for the resistance at 5 V are not available from the datasheet).

This was a proof of concept, and the concept is therefore proven, I can start working on measuring, with the Arduino, the current delivered to the motor.

[ Posted on May 7th, 2011 at 22:21 | no comment | ]

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