Hello to all,
In the time from last post I have designed an realized the board for step motor driving.
Three step motors need to be driver by the controller in order to act as focuser. For step motor adapting an L298 bridge is chosen. From the market is possible found chip board with this component and radiator.
Every board need 5 digital output for driving: Enable, IN1 (A phase +), IN2 (A phase -), IN3 (B phase +), IN4 (B phase -). It is not mandatory have the possibility to move all focus at the same time so phase signal can be common for all motor having maintaining one enable signal for each motor. In this way 3 enable signal plus 4 phase signal are needed.
No more digital output are available directly on raspberry board so the solution for increase its number is the use of a little board with the component PCF8574. It is a remote 8-Bit I/O Expander for I2C Bus
Because of step motor power signal can generate noise in the low power CPU
signal is a good solution make outputs optoisolated.
This is the board schematic available also as external file
