Gate Valve Drive Electronics

[TerryJC]

Attached to this post is the latest version of the Gate Valve Circuit and Assembly Drawing. Changes that I have made since the last prototype:

1. Redesigned the Veroboard to make the connections more logical; eg power terminals on the left adjacent to the DC/DC Converter Module and Actuator Motor connectors in the middle, closer to the Motor Drive Board.
2. For consistency, the Veroboard is the same width as the one used for the B-Model Interfacing. However, it is only 11 holes deep instead of 16, because there are no ICs to carry and we need the space for the Motor Drive Board.
3. Minor circuit changes - again for consistency with the B-Model Interfacing.
4. Adjusted the wire lengths to suit the new layout.
5. Removed the 10 k protection resistors from the three GPIO pins because they aren't really needed and they add labour to assembly.

I will now use this det of drawings to build another Gate valve assembly in the new box that has been 3D printed. Once any errors have been identified, we should be pretty close to using these drawings for production of the remaining dozen or so Gate Valves.

[TerryJC]

The recent problems with over-current in the Actuator Motor, related in the Status topic viewtopic.php?f=13&t=31 has triggered a discussion about the need for over-current protection. A number of options have been proposed, which are summarised here:

1. Over-current protection implemented wholly in hardware, eg limit the current drawn from the +12V into the motor drive circuit in hardware. No detailed design for this has yet been proposed.
2. Measure the current drawn by the motor via a sense resistor and feed that back to the RPi for action:
   1. Add a sense resistor to the Veroboard and include a comparator to generate a logic signal that the Pi would monitor.
   2. Hack the Motor Drive Board to add the sense resistor in the return of the current for each motor as described in the L298N Data Sheet. This would generate a voltage that could be measured by a channel of the A/D Converter to shut the motor down by removing the drive voltages of the enable (which is currently unused.

The best solution for a technical standpoint is almost certainly 2.b but this involves cutting tracks and soldering components to the underside of the Motor Drive Board.

More thought and discussion is needed.