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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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Motorola Cordless DECT Phone Teardown

Motorola DECT Phone
Motorola DECT Phone

Another random teardown from the junk box time!
Here’s an old Motorola DECT landline phone, no use to me as I’ve not used a landline for many years.

Battery Compartment
Battery Compartment

Not much on the back, other than the battery compartment for a pair of AAA rechargables. The base unit contains the charger.

Main PCB
Main PCB

Here’s the main PCB removed from it’s casing. There’s not really much going on, one of the main ICs, which is probably a microcontroller, is a COB device, so no part numbers from there. There’s a row of pads for programming the device at the factory. The RF section is on a dedicated IC, a DE19RF19ZCNC from DSP Group. I couldn’t find much on this part, but it’s one of a range of DECT/VoIP DSP devices.

 

Base Unit PCB
Base Unit PCB

Inside the base unit is a similar board, just without the keypad. Main microcontroller is again a COB device, the RF IC is under the shield.

Main Chipset
Main Chipset

Removing the shield reveals the same IC as in the handset, only this PCB has a pair of antennas.

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ETI Thermamite Catering Thermometer

Catering Thermometer
Catering Thermometer

Here’s another bit of commercial gear, a catering thermometer. These are used to check the internal temperature of foods such as meat, to ensure they’re cooked through.

This was given to me with some damage, the battery cover is missing & the plastic casing itself is cracked.

Battery Compartment
Battery Compartment

Power is provided by 3 AAA cells, for 4.5v

Main PCB
Main PCB

There’s not much to these units, the large LCD at the top is driven by the IC in the centre. A programming header is also present on the board near the edge.

Microcontroller
Microcontroller

The core logic is taken care of with a Texas Instruments M430F4250 MSP430 Mixed-Signal Microcontroller. This MCU has onboard 16-bit Sigma-Delta A/D converter, 16-bit D/A converter & LCD driver. Clock is provided by a 32.768kHz crystal.
The probe itself is just a simple thermistor bonded into a stainless steel rod.