Critikon Dinamap Plus Vital Signs Monitor tear-down

Hello, it’s been a while since my last post.

I’ve decided to add here some things I initially posted on Eevblog
The original link is here and it includes some useful comments from EEVBlog users:
EEVBlog original post

A little history:
I’ve got this device as an impulse buy from e-bay, when I was playing with fpgas and displays and for some reason i really wanted a plasma / electro-luminescent display. The device was listed as “not working” but from the photos, the display looked undamaged ( no cracks, etc ).
The whole thing cost me ~15$ + more than 30$ for shipping …
It arrived properly packaged, pretty clean and exactly as described – a big chunk of the case was cracked – just the outer case as I saw after tearing it down.

As I received it the first step was to take it to bits – quite easily, as the entire case and lay-out is well engineered. The device was almost spotless – just some fine dust, 1 or 2 dust bunnies near the fan an a huge dead wasp.
After taking it to pieces and taking a quick look at the boards I decided to stick all board back together and try to power it up, to see if there is some magic smoke left inside.
Surprisingly, it started on the first go, and after putting the board in the proper place it worked perfectly – no actual electrodes, but touching the pins of the input connector showed signals on the display.
Even the blood pressure monitoring pump worked and tried to stabilize a pressure cuff.

It’s quite an interesting design, with a lot of hardware and software safety features – electrical protection for the patient and software safety so it either works 100% or not at all.
The user and service manuals are available online: Manual

The main board

This board contains all the control logic, display signal generator and uart interface.
The interesting chips are:
MC68302 Mcu , datasheet: MC68302UM
– MC68000 core
– secondary communication controller ( RISC cpu )
– DRAM controller and a ton on peripherals ( ISDN voice or data terminal )
it seems to be clocked at 16Mhz

4x TC551001 – 128kB, 85nS static RAM made by Toshiba
– 2 of them are used by the MCU
– the other 2 are used by the video controller

HD63484CP98 video controller, HD63484Y98
– advanced CRT controller, 9.8MHz pixel clock – the display needs a 12MHz pixel clock so i don’t know how it’s working
– a lot of acceleration features like drawing, sprites, character generator, etc
– up to 2MB of video memory
– connected to the plasma display via 4 lines: HSync, VSync, Data, PixelClock

HN27C4096 256K*16bit UV erasable EPROM, HN27C4096
– holds the code
– ceramic PLCC case, i don’t recognise the manufacturer’s logo

ML2009 – micro linear logarithmic gain / attenuator block ML2009
– 20 pin PLCC case

ML2036 – serial input sine wave generator with gain control ML2036
– it’s near ML2009 and some op-amps, also next to the speaker connector
– they generate the audio output – this thing is loud – very loud and got a lot of acoustic signals

DS1284QN – RTC and watchdog DS1284QN
– got a crystal next to it
– watchdog timer
– 50 bytes of user ram
– 0.5uA current draw from the battery input
– parallel interface
– 28 pin PLCC case

MAX172 – 12bit ADC and voltage reference MAX172
– parallel interface
– 10uS conversion time

MAX358 analog multiplexer MAX358
– dual supply
– some on-chip protection features: over voltage detection, etc
– it measures the power supplies and some other system voltages

MAX695 microprocessor supervisor
– voltage monitor
– power on reset generator
– watchdog timer
– battery back-up power switching

the white labelled chip might be a CPLD / FPGA glue logic – it’s serial number is unreadable.
a nice Tadiran 3.7V primary cell, that is still in spec. 3.66V

The board seems to be 4 layer, only the top side is populated
there is an interesting logo etched on the bottom side, under the battery : an ‘atom’ symbol with ‘FCC02″ inside, like this one:

The second board measures blood pressure and O2 concentration

It’s almost all analog with some DAC’s and interface stuff
The pressure sensor is a MPX2050 temperature compensated and calibrated sensor with differential output. MPX2050
Next to it there is a DG211 quad analog switch and a N5532 op-amp
The DAC is a MX7226, 8 bits with 4 channels, with parallel interface: MX7226
Also, there is a REF02C 5V refference: REF02C

Other that that there are some DG508 8 channel analog switches.

The SpO2 side is isolated with some opto-couplers and the 3 transformers. The 2 one that are close together seem to be for analog signals.
The one on the side of the board forms an isolated power supply. There is a big isolation gap in the ground plane around this sections and a thick metal shield on the back
This board is connected to a pneumatic control board that’s got another pressure sensor used as a safety over-pressure sensor and disconnect switch.
The pump is “Made in Germany”, membrane type, an adjustable balancing counter-weight, and a big motor with replaceable brushes.

The ECG board is designed as a stand alone unit

It’s powered by a Burr-Brown PWR1726 power block – 1.5W, unregulated, +/-15V dual output PWR1726
The data link is made via 2 HP branded otocouplers that isolate a simple serial port
The board got it’s own CPU – a Hitachi HD63B03Y 8 bit CMOS Mcu with an external EPROM.
Next to it is the main ADC – ADC1251 12 bit + sign ( 13 bits ), self calibrating, in a ceramic DIP case: DS011024

Some other intersting parts:
MAX664: programable voltage regulator MAX664
LP2951: voltage regulator LP2951
AD631: instrumentation amplifier AD6311
MAX333: precision quad analog switch MAX333
MAX358: fault protected analog multiplexer MAX358
TLE2021: precision operational amplifiers TLE2021
a Takamisawa relay, some 1k, 0.05% Vishay resistors and a ton of Wima film caps.

The input section is protected by the 2 neon bulbs, big carbon resistors and a lot of diodes.
This board has a complete metal shield.
Sniffing the serial port should be interesting – the unit can run by itself as an ECG front end.

The display section

The display is made by LOHA corp and it’s also got a Planar label. It’s a el panel display with a 320×256 resolution. It lights bright orange with a long after glow. The pixels are big – the display area is 95x75mm and the outer dimensions are 130x110mm.
It’s build with 2 stacked boards.
The lower one is the power supply board – it provides ~ 90V for the actual display.
There are some parts whose function i don’t understand: SNJ5407 open collector hex. buffers and a AM27S19A 128 bits PROM.
Both of them are in ceramic dip cases.

The second board contains the row and column drivers on the bottom and the el glass on top.


The power supply board

The power supply is built in 2 stages: 1 section gets from 220 to 14 ( if i remember properly ) and the second one makes all internal voltages.
The 14V output is used to charge an external lead-acid battery.
Both sections are built with isolated converters -> there is a dual isolation layer from mains to the internal voltages and a 3-rd one on each board that is electrically connected to the patient.



The following pictures show how this thing is put together, and the default operation screen


Tearing down this unit and looking at how it’s build was a good exercise. The designers took care in making it as safe as possible. The CPU monitors almost everything – voltages, pressures, proper operation, board presence, etc.
Also, the CPU itself is monitored by 2 hardware watchdogs ( there is also an internal watchdog but I don’t know if it’s used). The external watchdogs work also as power supply monitors – so the CPU can’t go crazy if the power supply is unstable.

Having the system operational was great for reverse engineering the display protocol. It uses 12V for the HV supply and 5V for the logic side.
The data interface has HSYNC / VSYNC / CLK and DATA. The CLK is 12MHz. The data line is serial, 1 bit for pixel. The timing is the classic VGA interface, with changed parameters : the back porch is very long, the front porch is short – 2 clocks if i remember. The display needs precise timing – 1 extra / less clock will make it go crazy and draw huge current pulses. Also, the clock signal is critical – it can stand at most +/- 500kHz deviation.

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