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Contec CMS-50F Pulse Oximeter Teardown

Rear Case
Rear Case

The rear has the specifications, laser-marked into the plastic. The serial numbers are just sticky labels though, and will come off easily with use.

Contec CMS-50F
Contec CMS-50F

This is the Contec CMS-50F wrist-mounted pulse oximeter unit, which has the capability to record data continuously to onboard memory, to be read out at a later time via a USB-Serial link. There is software supplied with the unit for this purpose, although it suffers from the usual Chinese quality problems. The hardware of this unit is rather well made, the firmware has some niggles but is otherwise fully functional, however the PC software looks completely rushed, is of low quality & just has enough functionality to kind-of pass as usable.

Top Cover Removed
Top Cover Removed

A total of 4 screws hold the casing together, once these are removed the top comes off. The large colour OLED display covers nearly all of the board here. The single button below is the user interface. The connection to the probe is made via the Lemo-style connector on the lower right.

Lithium Cell
Lithium Cell

Power is provided by a relatively large lithium-ion cell, rated at 1.78Wh.

Main Processor
Main Processor

All the heavy lifting work of the LCD, serial comms, etc are handled by this large Texas Instruments microcontroller, a MSP430F247. The clock crystal is just to the left, with the programming pins. I’m not sure of the purpose of the small IC in the top left corner, I couldn’t find any reference to the markings.

Aux Processor
Aux Processor

The actual pulse oximetry sensor readings seem to be dealth with by a secondary microcontroller, a Texas Instruments M430F1232 Mixed-Signal micro. This has it’s own clock crystal just underneath. The connections to the probe socket are to the right of this µC, while the programming bus is broken out to vias just above. The final devices on this side of the board are 3 linear regulators, supplying the rails to run all the logic in this device.

Main PCB Rear
Main PCB Rear

The rear of the PCB has the SiLabs CL2102 USB-Serial interface IC, the large Winbond 25X40CLNIG 512KByte SPI flash for recording oximetry data, and some of the power support components. The RTC crystal is also located here at the top of the board. Up in the top left corner is a Texas Instruments TPS61041 Boost converter, with it’s associated components. This is probably supplying the main voltage for the OLED display module.

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New Scope!

Alas, my old trusty Hameg HM303 30MHz oscilloscope has finally died. I’ve had this scope for many years, an eBay buy when I noticed they were going cheap.

It’s been replaced with a brand new Rigol DS1054Z, a 4-channel 50MHz DSO.

Scope
Scope

This is a big jump from the old analogue CRT scope I was using, it’s certainly going to be a steep learning curve!

System Info
System Info

I chose this scope through the help of the EEVBlog & it’s associated forums. Through this I discovered that I could upgrade the scope with a key to enable some extra features! In the above screenshot, the key has been applied, and the model number now shown is the DS1104Z.

This is the next scope up in the model chain, with many more triggering options, serial decoders, higher memory depth, recording & 100MHz bandwidth. While I rarely need to measure anything higher than in the kHz range, these options will definitely come in useful! The list of installed options is below:

Installed Options
Installed Options

And now for some sample waveforms, the scope has the option to save screenshots to USB flash disks, so when I make posts with waveforms in the future, the need to photo the screen of the scope is gone!

DS1Z_QuickPrint1 DS1Z_QuickPrint2 DS1Z_QuickPrint3 DS1Z_QuickPrint6 DS1Z_QuickPrint7 DS1Z_QuickPrint8 DS1Z_QuickPrint9

 

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Recording QSO’s From My Shack

Since my new Wouxun has audio output jacks, I figured it would be useful to have the ability to record what my rig hears, if anything interesting comes on the air.

Under Linux, I use an application called, (creatively enough), Audio Recorder.

Recorder Screenshot
Recorder Screenshot

Using a simple connection to the mic input on a USB soundcard, I can capture everything the radio hears. Unfortunately this doesn’t work for outgoing audio, so it’s not much good at capture of my personal QSOs. For this I will have to set up another radio to act as the main receiver.

At some point in the future I will implement this with a Raspberry Pi as the audio capture server.