USB_Power Supply Introduction


This stage is quite simple, sort of an "icebreaker" for the builder. It provides the interface to the computer via a USB cable and provides the +5V dc power via the USB cable to power the digital "side" of the MOBO with 5 vdc and a ground isolated from the analog "side".

It is always a good idea to double check the bill of materials in this set of documentation with the official BOM on the Mobo site. Discrepancies may be introduced inadvertently, as the changes are sometimes not communicated or discovered, making timely update of this site a problem.

Theory of Operation

The MOBO is divided into two "sides", the digital and the analog sides. These two sides are galvanically isolated from one another by two separate ground planes and 5 V voltage sources on the board. The digital side is powered by a USB-provided 5 volt source labeled "+5Vd" against a ground plane labeled "DGND".

The analog side has 12 V power (from the mated Softrock RXTX V6.3) and a regulated 5 volt source derived from that voltage. Voltages and grounds are indicated by the customary labels ("+12V, +5V, GND"). Interaction between the digital and analog "sides" is via an ADUM1251 which bridges the I2C signals across the two sides.

(go directly to build notes)

USB_Power Supply Schematic

(Click for Full Schematic)
USB_Power Supplyschematic


(go directly to build notes)

USB_Power Supply Bill of Materials

Stage Bill of Materials

(resistor images and color codes courtesy of WIlfried, DL5SWB's R-Color Code program)

1header, 14-pinHeader
1header, 2-pin Header
1header, 4-pin RA Header
1header, 5-pin RA Header
1USB-B pcb jack (rt-angle) Jack-RA
222 ohm 1%SMT 0805 1/8W
110 k ohm pot SMT 0805 POT
110 ohm 5%SMT 1206 1/4W
2bi-directional 5V SMT diode Socket

USB_Power Supply Summary Build Notes

USB_Power Supply Detailed Build Notes

Bottom of the Board

USB_Power Supply Bottom View

Install Bottomside Resistors and Diodes

D03bi-directional 5V SMT diode Socketbi-directional diodes (no orientation issues)
R5610 ohm 5%SMT 1206 1/4W
D04bi-directional 5V SMT diode Socketbi-directional diodes (no orientation issues)
R4522 ohm 1%SMT 0805 1/8W
R4622 ohm 1%SMT 0805 1/8W

Top of the Board

USB_Power Supply Top View

Mount USB Jack

J01USB-B pcb jack (rt-angle) Jack-RA

Install Digital Headers

Graeme ZL2APV advises that, In this step, you should install RV1 first as it is really hard to get the iron tip down to that pot with the plug in place - don't ask :-) Also may note that LCD1 incorporates P36 to bring the total pin count, at the LCD end, up to 16 pins.

All of these headers are installed with the short ends in the solder holes and the long ends protruding out feom the board topside.

A later change to the BOM replaced P34 and P24 straight headers with right-angled headers. This change came AFTER the photos of the completed (BETA) board below. Don't let that confuse you. Right-angled is correct for these headers.

VR110 k ohm pot SMT 0805 POT
Install BEFORE installing P36 and LCD01 header strips
LCD1header, 14-pinHeader
P36header, 2-pin Header
LCD background LED light
This will mate with Pin 15-16 of SIL LCD connector. Current from USB port
P24header, 4-pin RA Header
I2C connector
For attaching external uC, such as SDR-Widget board
P34header, 5-pin RA Header
Rotary Encoder

USB_Power Supply Completed Stage

Top of the Board

View of Completed Top

Bottom of the Board

View of Completed Bottom

USB_Power Supply Testing

Test for Digital Isolation

Test Setup

Connect the board's USB jack via a USB cable to a PC's USB connector

measure voltage at the testpoints shown on the graphic

Test for Digital Isolation

Test Measurements

TestpointUnitsNominal ValueAuthor'sYours
Point 1 with respect to point 2V dc+5tbd_______
Point 3 with respect to point 4V dc+5tbd_______
point 5 with respect to point 6V dc+5tbd_______
Point 7 with respect to point 8V dc+5tbd_______