Many micro-controller circuits are powered from the USB port. Supply voltage is usually less than USB five volts. Supply circuit has adjustable output voltage with few jumpers. Some circuits require two supply voltages, one for digital part and second for analog part. Jumpers and resistors are selected such that when no jumper is inserted, the output voltage will be at minimum level. This prevents electronic circuit from damage when jumpers are forgotten. It’s shown in schematic:
Second part of the circuit is USB data connection with hot plug switch control. It is simply one transistor opertating as switch between D+ and power supply. When host detects high level at D+ it recognizes it as active connection and starts enumeration. The host includes 15 kΩ pull-down resistors on each data line. When no device is connected, this pulls both data lines low into the so-called “single-ended zero” state (SE0 in the USB documentation), and indicates a reset or disconnected connection. A USB device pulls one of the data lines high with a 1.5 kΩ resistor. This overpowers one of the pull-down resistors in the host and leaves the data lines in an idle state called “J”. For USB 1.x, the choice of data line indicates a device’s bandwidth support; full-bandwidth devices pull D+ high, while low-bandwidth devices pull D− high.
Schematic of USB part:
Additional single-in-line connector is added, as shown in Complete USB power supply and hot plug schematics.
All components are placed on a single sided module. It can be reproduced with toner transfer method of PCB production. Mirrored artwork in 1:1 scale is here.
Output connector pinout is shown here: