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UM25C USB Power Meter

UM25C USB Power Meter
UM25C USB Power Meter

Here’s a nice little feature-packed USB power meter, the UM25C. This unit has USB-C along with the usual USB type A connectors, along with a bluetooth radio for remote monitoring of stats via a Windows or Android app. Construction is nice, it’s a stack of two PCBs, and polycarbonate cover plates, secured together with brass posts & screws.

Back Cover
Back Cover

The back cover has the legend for all the side connectors, along with the logo.

USB Micro Input
USB Micro Input

Down the sides are the user interface buttons, and here the Micro-B input connector. The 4-pin header is visible here that takes serial data down to the bluetooth section.

USB-C Connectors
USB-C Connectors

The other side has the remaining pair of buttons, and the USB-C I/O. I don’t yet own anything USB-C based, but this is good future proofing.

LCD Display
LCD Display

Removing the top plastic cover plate reveals the small 1″ TFT LCD module. This will be hot-bar soldered underneath the screen. There’s an unused footprint next to the USB input connector, judging by the pin layout it’s probably for a I²C EEPROM.

Main Board Components
Main Board Components

The underside of the top PCB has all the main components. The brains of the operation is a ST STM8S005C6T6 microcontroller. It’s at the basic end of the STM range, with a 16MHz clock, 32K flash, EEPROM, 10-bit ADC, SPI, UART & I²C. The main 0.010Ω current shunt is placed at the top left of the board in the negative rail. A couple of SOT-23 components in the centre of the board, I haven’t been able to identify properly, but I think they may be MOSFETs. The large electrolytic filter capacitor has a slot routed into the PCB to allow it to be laid flat. Providing the main power rail is a SOT-89 M5333B 3.3v LDO regulator.

Bluetooth Radio
Bluetooth Radio

The bottom board contains the bluetooth radio module, this is a BK3231 Bluetooth HID SoC. The only profile advertised by this unit is a serial port. There’s a local 3.3v LDO regulator & support components, along with an indicator LED.

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Dell SE197FPf Monitor 12v Conversion

My other monitors are a different model, and have a slightly different main PCB inside, but the process is mostly the same for converting these to 12v supply.

Main PCB
Main PCB

In this monitor type, there is only a single board, with all the PSU & logic, instead of separate boards for each function.

PSU Closeup
PSU Closeup

This monitor is slightly different in it’s power supply layout. The mains supply provides only a single 12v rail, which is then stepped down by a switching converter to 5v, then by smaller linear regulators to 3.3v & 1.8v for the logic. This makes my life easier since I don’t have to worry about any power conversion at all.

PCB Reverse
PCB Reverse

Here’s the backside of the PCB, the mains PSU section is in the centre.

Attachment Points
Attachment Points

Here’s the pair of 12v supply wires soldered onto the main board, onto the common GND connection on the left, and the main +12v rail on the right. I’ve not bothered with colour coding the wiring here, just used whatever I had to hand that was heavy enough to cope with a couple amps.

12v Socket
12v Socket

A small mod later with a cone drill & the 12v input socket is mounted in the LCD frame.

Casing Mod
Casing Mod

Some light removal of plastic & the back cover fits back on. Current draw at 13.8v is ~2A.

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Rigol DS1054Z DC Power Supply – Linear Post Regulation

Finally, here’s the last part of the Rigol 12v DC Power Supply project, the linear post regulation section to remove some of the ripple.

I have made a couple of layout adjustments since the last post about this part of the project – a little more filtering on the DC outputs. As usual the Eagle project files are at the bottom of the post for those who might find them useful.

Updated PCB
Updated PCB
Updated Schematic
Updated Schematic

 

Completed PCB
Completed PCB

Here’s the completed PCB, partially installed in the back of the scope. The missing regulator is the 5v one, since I already have a source of clean 5v from my original attempt at the supply, it’s not a problem not using a linear after the switcher. The filtering is the same on all channels, input from the switchers is on the right, outputs to the scope on the left.

PCB Bottom
PCB Bottom

Here’s the bottom of the PCB, with the common mode input chokes. The design of this board has allowed me to remove a couple of the switching modules as well, as I can use a single bipolar supply to run both sets of bipolar regulators on this board. This should help remove some of the noise also.

The ripple level has now dropped to lower than it was originally on the mains supply! Current draw at 13.8v DC is about 1.75A.

Scope Ripple
Scope Ripple

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