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OLED Pulse Oximeter Teardown

OLED Pulse Oximeter
OLED Pulse Oximeter

Here’s a piece of medical equipment that in recent years has become extremely cheap, – a Pulse Oximeter, used to determine the oxygen saturation in the blood. These can be had on eBay for less than £15.

Powered On
Powered On

This one has a dual colour OLED display, a single button for powering on & adjusting a few settings. These cheap Oximeters do have a bit of a cheap plastic feel to them, but they do seem to work pretty well.

Pulse Oximeter
Pulse Oximeter

After a few seconds of being applied to a finger, the unit gives readings that apparently confirm that I’m alive at least. 😉 The device takes a few seconds to get a baseline reading & calibrate the sensor levels.

Main PCB Top
Main PCB Top

The plastic casing is held together with a few very small screws, but comes apart easily. here is the top of the main board with the OLED display panel. There appears to be a programming header & a serial port on the board as well. I’ll have to poke at these pads with a scope to see if any useful data is on the pins.

Main PCB Bottom
Main PCB Bottom

The bottom of the board has all the main components of the system. The microcontroller is a STM32F03C8T6, these are very common in Chinese gear these days. There’s a small piezo beeper & the main photodiode detector is in the centre.
There is an unpopulated IC space on the board with room for support components. I suspect this would be for a Bluetooth radio, as there’s a space at the bottom left of the PCB with no copper planes – this looks like an antenna mounting point. (The serial port on the pads is probably routed here, for remote monitoring).
At the top left are a pair of SGM3005 Dual SPDT analogue switches. These will be used to alternate the red & IR LEDs on the other side of the shell.
A 4-core FFC goes off to the other side of the shell, bringing power from the battery & supplying the sensing LEDs.

Battery Compartment
Battery Compartment

Power is supplied by a pair of AAA cells in the other shell.

Dual LED
Dual LED

The sensor LEDs are tucked in between the cells, this dual-diode package has a 660nm red LED & a 940nm IR LED.

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PSi 150 Power Inverter

Front
Front

This is a small 120W power inverter, intended for small loads such as lights, fans, small TVs & laptop computers.

End Cover
End Cover

End cover of the unit, 12v DC input cord at the top, power switch & indicator LEDs at the bottom.

Mains Output
Mains Output

Opposite end of the unit, with the standard 240v AC 50Hz Mains output socket.

Cover Removed
Cover Removed

Cover removed from the top of the unit. Main power transformer is visible in the centre here, MOSFET bank is under the steel clamp on the left, the aluminium case forms the heatsink.

PWM Controllers
PWM Controllers

On the right is a KA3525 switchmode PWM controller & on the left is a LM324N quad Op-Amp IC. The buzzer on the far left is for the low battery warning.

PCB Removed
PCB Removed

PCB removed from the casing, with the MOSFET bank on the right hand side. Two potentiometers in the centre of the board tweak the frequency of the switcher & the output voltage.

 

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Vivicam 5190

Front
Front

A 5 megapixel digital camera from Vivitar. Visible here is the lens, viewfinder & flash.

Back
Back

Rear of the unit showing the LCD & user control buttons.

Cover Removed
Cover Removed

Front frame removed showing some of the internals. Shutter assembly & lens in centre, battery compartment at left.

Rear Cover Removed
Rear Cover Removed

Rear frame removede, showing the LCD module & tactile switches.

LCD
LCD

LCD module removed from the PCB

Flash PCB
Flash PCB

Flash PCB removed. Transformer is fed with the 4.5v from the 3 AA cells & steps it up to ~300v DC for the flash capacitor. A pulse transformer energizes an electrode next to the Xenon flash tube with ~5kV to ionize the gas.

Main PCB
Main PCB

Main PCB removed. Internal flash ROM & RAM IC visible above the SD card socket. USB connector is at the top right, next to the piezo buzzer.

CPU
CPU

Main processor on reverse side of the PCB.

Image Sensor
Image Sensor

Closeup of the CMOS image sensor with the lens assembly removed.