USB Hub

This is a 7-port USB hub with 4 USB3 ports and 3 USB2 ports by Zoweetek, ZW-H355.  It essentially is consisted of two ICs, GL3523 by Genesys Logic is a 4-port USB3.1 compliant hub controller and HS8836 which appears to be a 4-port USB hub controller but very little information is available online.   It appears that one of the USB2 signals goes from  GL3523 to HS8836 and HS8836 has 4 pairs of USB2.0 signals going to 3 USB2 ports and one of the USB3 ports.  The PC board is not well cleaned especially around through-hole connections, perhaps the switches and connectors are hand soldered.  It is not clear if the high-speed traces are matched.  There is a footprint for input USB3 connector, but here the wires are directly soldered to the board.

RaspberryPi Zero W

I came across a RaspberryPi Zero W, the older generation RPi Zero with WiFi.  For $10, it is a great little board.  Although it can run the desktop environment, it cannot really be expected to run the memory intensive applications such as internet browser because of limited memory.  But 512MB is a huge amount of memory for embedded systems.  To run the camera, it needs to allocate 128MB to the GPU (perhaps 64MB if only still picture).

It is straightforward to wiring up a display module.  And with the python module luma.oled, the display is up and running quickly.

Starter Motor

I recently had to replace a starter motor, so I got a chance to look the interior of the starter motor assembly.    The starter motor assembly is consisted of a DC brushed motor, a solenoid and gears.   

The DC motor has series field winding: the input positive battery coming through the solenoid switch first goes into the field winding, then to a pair of copper brushes.  The negative terminal is the chassis connecting to the other brushes.  

The solenoid serves two functions: switching the battery power to the motor and pushing the gear to engage the engine flywheel.  Because of the large starting current (hundreds of amperes),  heavy gauge wires and large copper contact are used.   The solenoid has two coils: push-in coil that is connected to the motor positive terminal (the output of the switch) and the holding coil connected to the chassis.   This is a clever design: before the motor power switch is closed, the push-in coil is energized through the motor windings.  Once the motor power switch is closed; the push-in coil becomes inactive and a lower power holding coil keeps the solenoid in place.

The motor shaft is geared to the output the starter.  The solenoid has a spring loaded pin that pushes the gear to engage the flywheel.  There is also a clutch that prevents the flywheel to backdrive the motor once the engine has started.