MicroRint Service Manual
Contents
1. 9 s r 7 1 WOSMET SH AQ OMEN WS TODIO AA 110 135945 00Z 1dv g a a ST 10 090 VOS sequin yry dng T F 3110 6TA anto DEE 4 70 WOSSSWT QIONATOS L 1 106 AAA TOS a ei INOI sa 4 EA 4 TG SAYHL E 23 T msa En T VJEZLETIN GT END MOL a 2 8 pat A oo 1 su FIN sisva 80 wee T OWL ho A MOLF ba LI9 LNWAl AN TAL v v IDA IDA 9 1914 1 tai IDA D A Es LILIANA 1 SUL MI 279 DIL oza w DA A9LVH 1 TAL ILVE N LILLWWA pu 4 KOM 7 _ 1089 4 su E T DAWI SE INIOd 1591 INIOd 1881 TAL ial vnairerxvw TIA 7 wav WI taNISOOXAs any el a lu STA ore 7 IDA JADE TAL ka ajo S ODA MEE 9 Ino LTA sa a lo 8 gt id 100 a ed 39A T SWIEGZNI ta D2. Pressure transducer pressure __ Rotary esa iF solenoid transducer flow Battery pack The Interrupter Transducer is now ready for fault finding Reassembling Interrupter Transducer 1 2 3 Push the two mouldings together ensuring that no tubing or wires are caught between the two mouldings Replace the three screws into the moulding and secure The unit will now require calibration Refer to operating manual Circuit Description Interrupter Transducer Refer to Drawing 060 01 Overview During measurement the interrupt transducer monitors tidal flow and provides for a means of momentary airways occlusion during which time the pressure at the mouth is measured The flow is measured by monitoring the pressure across a resistive element using a high frequency silicon solid state sensor Occlusion is provided by a fast acting rotary solenoid attached to a shutter During occlusion a second sensor is used to monitor the pressure developed at the mouth Power supply 9 volt power is supplied to the transducer from the microcomputer unit at pin 2 of connector J1 The 9 volt power is regulated down to 5 volts VCC by the linear voltage regulator U4 that provides power for
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5. Revision No 15 Designation Part No R27 82K resistor 1 0805 package R28 OOK resistor 1 0805 package R29 39K resistor 1 0805 package R30 13K resistor 1 0805 package R31 100K resistor 1 0805 package R32 337 729 F 82 ohm 1 watt resistor axial package R33 100K resistor 1 0805 package R34 100K resistor 1 0805 package R35 10K resistor 1 0805 package R36 10K resistor 1 0805 package R37 1K resistor 1 0805 package R38 1K resistor 1 0805 package RN1 107 048 F 6 pin 5 commoned 100K SIL network R1 18 S I S B S T 20 Piher 20K linear potentiometer C1 2pF Philips or AVX ceramic 0805 package C2 47pF Philips or AVX ceramic 0805 package 1nF Philips or AVX ceramic 0805 package C4 1nF Philips or AVX ceramic 0805 package C5 100nF Philips or AVX ceramic X7R dielectric 0805 package C6 100nF Philips or AVX ceramic X7R dielectric 0805 package C7 100nF Philips or AVX ceramic X7R dielectric 0805 package C8 100nF Philips or AVX ceramic X7R dielectric 0805 package c9 100nF Philips or AVX ceramic X7R dielectric 0805 package C10 197 324 F 47uF 16v Surface mount Tantalum C11 100nF Philips or AVX ceramic X7R dielectric 0805 package C12 100nF Philips or AVX ceramic X7R dielectric 0805 package C13 100nF Philips or AVX ceramic X7R dielectric 0805 package C14 100nF Philips or AVX ceramic X7R dielectric 0805 package C15 100nF Philips or AVX ceramic X7R dielectric 0805 package C16 100nF Philips or AVX ceramic X7R
6. 8 bit CMOS static RAM SOL32 525 package Rohm individual CMOS gate SOT23 5 package Hitachi H8S 2318 microcontroller TAFP100 package Maxim power monitor SOT23 5 package CMOS Dual D Type flip flop SO 14 package CMOS Quad NAND Schmitt input gate 50 14 package Linear Technology DC DC convertor SOT23 5 package Linear Technology DC DC convertor SOT23 5 package Quad 2 input OR gate Display driver Linear Technology DC DC convertor SOT23 5 package Quad surface mount op amp Gold Star 32K X 8 bit CMOS static RAM 28 pin SOP package Dallas semiconductor digital thermometer TO 92B package resistor 1 0805 package resistor 1 0805 package resistor 1 0805 package 100K resistor 1 0805 package 10M resistor 5 0805 package 100K resistor 1 0805 package 100K resistor 1 0805 package 220K resistor 1 0805 package 100K resistor 1 0805 package 10K resistor 1 0805 package resistor 1 0805 package 10K resistor 1 0805 package 10K resistor 1 0805 package 10K resistor 1 0805 package 100K resistor 1 0805 package 100K resistor 1 0805 package 10K resistor 1 0805 package 10K resistor 1 0805 package 100K resistor 1 0805 package 100K resistor 1 0805 package 10 ohm resistor 1 0805 package 1K resistor 1 0805 package 150K resistor 1 0805 package 68K resistor 1 0805 package 91K resistor 1 0805 package 100 ohm resistor 1 0805 package Parts List For MicroLoop MK6 Drawing No 067 00 Pate 42 07 02
7. socket from JST Murata piezo ceramic sounder 32 768 KHz crystal WATCH package OMHz crystal HC49 4H package 10 crystal Sanyo NI CAD battery pack M1 7 X 3mm screw M1 7 plain washer 14 way ribbon cable for keypad PCB Iss 1 Parts List Interrupter Transducer Designation U1 U2 U3 U4 US U6 U7 U8 TR1 TR2 TR3 TR4 TRS TR6 TR7 R1 R2 R3 R4 R5 R6 R7 R8 RQ R10 R11 R12 R13 R14 R15 R16 R17 R18 R19 R20 R21 R22 R23 R24 R25 R26 R27 R28 R29 C1 C2 C3 Description AD623ARM INSTRUMENTATION AMPLIFIER AD623ARM INSTRUMENTATION AMPLIFIER MAX1247BCEE SERIAL 12 BIT A D CONVERTER LM2931M 5 0 LOW DROP OUT 5 VOLT REGULATOR SDXL005D4 5 DIFFERENTIAL PRESSURE TRANSDUCER SDXL005D4 5 DIFFERENTIAL PRESSURE TRANSDUCER MAX4241EUA OP AMP LM555CM TIMER FMMT717 PNP TRANSISTOR FMMT617 NPN TRANSISTOR FMMT717 PNP TRANSISTOR FMMT617 NPN TRANSISTOR FMMT617 NPN TRANSISTOR DMMBT2369LT1 HIGH SPEED SWITCHING NPN TRANSISTOR BCV62C MATCHED PNP TRANSISTOR PAIR 390 OHM SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 0805 820 OHM SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 0805 100K SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 0805 33K SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 0805 39 OHM SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 0805 390 OHM SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 0805 100K SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 0805 10K SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 0805 120K SURFACE MOUNT
8. 081 F 067 09 067 15 067 13 10pF Philips or AVX ceramic 0805 package 10pF Philips or AVX ceramic 0805 package 100nF Philips or AVX ceramic 0805 package 1uF Philips or AVX ceramic X7R dielectric 0805 package 1uF Philips or AVX ceramic X7R dielectric 0805 package 1uF Philips or AVX ceramic X7R dielectric 0805 package 1uF Philips or AVX ceramic X7R dielectric 0805 package 1uF Philips or AVX ceramic X7R dielectric 0805 package 1uF Philips or AVX ceramic X7R dielectric 0805 package Rohm PNP digital transistor SOT 23 package Rohm NPN digital transistor SOT 23 package Rohm NPN digital transistor SOT 23 package Rohm NPN digital transistor SOT 23 package P channel MOSFET SOT23 6 package P channel MOSFET SOT23 6 package etex NPN Transistor SOT 23 package etex Schottky diode SOT 23 package etex Schottky diode SOT 23 package etex Schottky diode SOT 23 package etex Schottky diode SOT 23 package etex Schottky diode SOT 23 package oshiba 1A diode etex Schottky diode SOT 23 package 3 3UH inductor 1210 package 3 3UH inductor 1210 package 2uH inductor 1210 package 2uH inductor 1210 package 2uH inductor 1210 package 2uH inductor 1210 package yco 700mA Polyswitch Nan Ya 240 X 160 graphic display Molex 6 way data socket 18 way 1mm pitch cable connector from JST 4 way mini DIN socket 14 way 1mm pitch cable connector from JST way 0 1 pitch pin header 5mm DC power socket from G English 3 way 0 1 pitch pin header way PCB
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10. CI1 is used in asynchronous mode for RS232 Real Time Clock U3 is a Xicor X1243 real time clock with 2Kbyte of EEPROM It operates at 32 768 Khz and is powered by the lithium battery The device requires a very small amount of power during standby mode and as the unit will never drain the battery out this should be sufficient to keep the clock going for a long period of time before recharging The date and time can be changed from the system menu The interface to the clock is via an ZC bus The micro controller does not have a dedicated I C bus so two port lines P20 P21 are used under software to emulate the bus The EEPROM is used for storing the calibration value and other system data If the device is ever replaced the unit will have to be reconfigured and recalibrated Temperature Sensor U20 is a Dallas 0518520 temperature sensor operating on their one wire bus protocol It has an accuracy of 0 5 degree centigrade A port line P23 is used under software to emulate the one wire bus The ambient temperature reading is used for adjusting inspiratory flow at ambient temperature to respective flow at body temperature Transducer interface 067 05 An SPI bus consisting of serial data in SIN serial data out SOUT and clock signals SCLK is used to interface with the 12 bit analogue to digital converter in the Rint transducer The SEN signal activates the shutter Display 067 11 The display is a high resolution cust
11. LAYER CERAMIC CAPACITOR SIZE 0805 10nF MULTILAYER CERAMIC CAPACITOR SIZE 0805 LOW CURRENT YELLOW 3mm LED BAS19 GENERAL PURPOSE SMALL SIGNAL DIODE BAS19 GENERAL PURPOSE SMALL SIGNAL DIODE BAS19 GENERAL PURPOSE SMALL SIGNAL DIODE 5 x 1 3AA SIZE 110mA hr SANYO BATTERY PACK 6 WAY PIN HEADER GDAY 025 X20 B25 EMMESEM ROTARY SOLENOID 6 8V 7 DUTY 1 25 OHMS 65 DEG Fault Analysis The following analysis is only a guideline and should be carried out in a logical sequence If the fault is still apparent after the following suggestions then the unit should be fault found using the circuit descriptions and circuit diagrams provided When the unit is turned on there is no display present Rotate contrast thumb wheel anti clockwise to see if screen darkens Connect charger to see if screen darkens and charging light illuminates When the unit is turned on the display is dark purple Rotate contrast thumb wheel clockwise to see if screen colour becomes lighter and characters are displayed Connect charger to see if screen characters appear The recorded values are low Ensure that the unit is calibrated Refer to operating manual Ensure that the mouthpiece holder is fully inserted into the interrupter transducer unit Check that the resistive element is not damaged Check that there are no leaks in the patient circuit If a mouthpiece is used then check that there are no leaks around the patient s mouth and that a nose clip has b
12. MicroRint Service Manual 060 17 Revision 1 1 May 2003 Micro Medical Limited P O Box 6 Rochester Kent ME1 2AZ MicroRint Microcomputer System Overview Fig 1 The Micro Medical MicroRint is a data recording airways resistance meter consisting of the following items 1 MicroRint microcomputer unit with graphic display 2 Micro Medical interrupter transducer 3 2 off caps 4 Disposable filter 5 Universal mains adapter 6 Mouthpiece adapter 7 Facemask 8 Pressure calibration adapter 1 4 I 3 lt e 2 6 l 2 d Z NS l 27 TIT 4 _ A A je 7 3 L ed l us i Le e The MicroRint is powered by internal rechargeable Nickel Cadmium cells or by the mains adapter supplied The interrupter transducer is used to measure the subject s airways resistance in accordance with the operating manual Microcomputer Unit Refer to drawings 067 01 067 05 067 11 and 067 12 The microprocessor control circuit carries out the Rint test routines monitors the transducer signals and keypad and drives the display under the control of the program module The drawing 067 01 is a hierarchical block diagram showing the connections of the sub sections The rest of the drawings are su
13. RESISTOR 0 125 WATT 5 SIZE 0805 150 OHM SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 0805 3 9 OHM 1 WATT 5 RESISTOR 33K SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 0805 390 OHM SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 0805 10K SURFACE MOUNT RESISTOR 0 125 WATT 1 SIZE 0805 47 OHM SURFACE MOUNT RESISTOR 0 125 WATT 1 SIZE 0805 1M SURFACE MOUNT RESISTOR 0 125 WATT 1 SIZE 0805 470 OHM SURFACE MOUNT RESISTOR 0 125 WATT 1 SIZE 0805 15K SURFACE MOUNT RESISTOR 0 125 WATT 1 SIZE 0805 150K SURFACE MOUNT RESISTOR 0 125 WATT 1 SIZE 0805 1K SURFACE MOUNT RESISTOR 0 125 WATT 1 SIZE 0805 1K SURFACE MOUNT RESISTOR 0 125 WATT 1 SIZE 0805 1M SURFACE MOUNT RESISTOR 0 125 WATT 1 SIZE 0805 1 5K SURFACE MOUNT RESISTOR 0 125 WATT 1 SIZE 0805 1M SURFACE MOUNT RESISTOR 0 125 WATT 1 SIZE 0805 1M SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 0805 33 OHM SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 0805 33 OHM SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 0805 100 OHM SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 0805 1K SURFACE MOUNT RESISTOR 0 125 WATT 5 SIZE 0805 100nF MULTILAYER CERAMIC CAPACITOR SIZE 0805 100nF MULTILAYER CERAMIC CAPACITOR SIZE 0805 100nF MULTILAYER CERAMIC CAPACITOR SIZE 0805 C4 C5 C6 C7 C8 C9 C10 D1 D2 D3 D4 BAT J1 J2 47uF ELECTROLYTIC CAPACITOR SIZE UWX6 3 47uF ELECTROLYTIC CAPACITOR SIZE UWX6 3 10nF MULTILAYER CERAMIC CAPACITOR SIZE 0805 100nF MULTILAYER CERAMIC CAPACITOR SIZE 0805 100nF MULTILAYER CERAMIC CAPACITOR SIZE 0805 10nF MULTI
14. b sections and are described in detail below Micro controller 067 02 U9 is a Hitachi HD64F2318 16 bit microprocessor with 256K of flash memory and 8K of Ram The system clock is supplied by 20MHz crystal X2 There is also 512 Kbyte U7 of external Ram used for running a module and storing variable data The internal flash is used for the boot software kernel and the base module The kernel handles the low level interface to display keyboard etc and the base module runs on start up and gives a choice of which module needs to be executed The modules are stored in the external 8 Mbyte Flash PROM 05 The kernel also has a flash filing system which keeps track of all the files in the external Flash PROM The files can be an executable Rint module or other module data The filing system is similar to a PC Dos filing system U15 is used to control the access to the flash device The speaker J5 is directly connected to the Port pins and the pins are toggled at 1 KHz to generate the buzzing sound U9 is used for enabling the internal flash to be overwritten If a new kernel is downloaded the flash is enabled and data transferred U10 is the reset controller which holds the reset line low for 350 ms on power up This ensures that the supply has stabilised before the micro starts TR3 is used by the micro to hold the power supply ON whilst it is writing to the filing system This is to ensure that data is not corrupted when it is writi
15. dielectric 0805 package C17 33pF Philips or AVX ceramic X7R dielectric 0805 package C18 100nF Philips or AVX ceramic X7R dielectric 0805 package C19 33pF Philips or AVX ceramic X7R dielectric 0805 package C20 100nF Philips or AVX ceramic X7R dielectric 0805 package C21 100nF Philips or AVX ceramic X7R dielectric 0805 package C22 1uF Philips or AVX ceramic X7R dielectric 0805 package C23 197 324 F 47uF 16v Surface mount Tantalum C24 1uF Philips or AVX ceramic X7R dielectric 0805 package C25 100nF Philips or AVX ceramic 0805 package C26 301 8544 F 33uF 16v Surface mount Tantalum C27 301 8544 F 33uF 16v Surface mount Tantalum C28 301 8544 F 33uF 16v Surface mount Tantalum C29 100nF Philips or AVX ceramic 0805 package 100nF Philips or AVX ceramic 0805 package C31 301 7000 F 100uF 16v C32 100nF Philips or AVX ceramic 0805 package 301 8593 47uF 25v Surface mount Tantalum C34 301 8544 F 33uF 16v Surface mount Tantalum Parts List For MicroLoop MK6 Drawing No 067 00 Revision No 1 3 Part No C35 C36 C37 C38 C39 C40 C41 C42 C43 R1 R2 R3 R4 R5 R6 DTB113EK DTC114EK DTC114EK DTC114EK XM62P02E6 XM62P02E6 FMMT491 HCS1000 HCS1000 HCS1000 HCS1000 HCS1000 U1JC44 HCS1000 NLFC453232 3R3M NLFC453232 3R3M 853 1340 F 353 1340 F 853 1340 F 853 1340 F MICROSMDO35 2 LTA75R227J 95001 2661 18FMN BMTTN TF MDS4 14FMN BMTTN TF B2B PH K S PKM35 4A0 571 672 F 485
16. eans of the MC_OFF line which resets U11 U14 is a DC DC converter with an input range of 0 9V to 10V and an output of 3 3 volts to power the unit Since the range is up to 10V only care should be taken not to use any other external power supply as most of them are unregulated and could output 12V for a 9V unregulated supply U14 is another DC DC converter with an output of 9V This higher supply is used for powering the Rint transducer R28 and R31 divide the unregulated voltage to a third and are applied to the A D converter of the micro controller The micro controller continuously examines the reading and gives a battery low or battery dead warning message From the reading the micro controller can also deduce that the external supply is connected so it can turn itself off if the unit is left on for a long time Inductors L1 and L2 are placed for EMC filtering and D5 protects the unit from reverse polarity power supply Disassembling the Interrupter Transducer for Circuit Investigation 1 Disconnect the Interrupter Transducer from the MicroRint Computer 2 Remove the three case screws and put to one side Micro Medical Limited P O Box 6 Rochester Kent MET 2AZ England Case screws 3 Turn the transducer over and ease the moulding apart to reveal the circuitry 4
17. een used If a facemask is used then check that it is held firmly against the face The shutter does not activate Check that the battery low message is not displayed on the LCD display Ensure that the interrupter transducer is connected to the microcomputer unit Technical Support Great Britain and World Headquarters Micro Medical Ltd PO Box 6 Rochester Kent ME1 2AZ Telephone 44 0 1634 360044 Fax 44 0 1634 360055 Web Site http www micromedical com uk Email support micromedical com uk Contact Micro Medical Ltd for the local agent in your region or country for local service LI 8 9 t SWOJTG wed YPS I0 L90AWALEH JO Pous TONT AON 9 Ea 01 10190 Ed aas ynon doo TOA ap os amod Adding amod MET OS OVINA VIA IN PORIN SIOSUAS 8 L g T 580040 MES ZO LOA ald Jo ZOOTAON 9 01 20 190 sequin ans 10853001 doo Jo13tIW mL DEE anro anro anto 69 812 SID AOU ANLE
18. he microcomputer unit When the valve is de energised the shutter returns to the open position by the action of the internal spring on the solenoid The power for the solenoid is taken from the internal 6 volt ni cad rechargeable battery pack BAT1 When the trigger input is taken high TR4 is turned on and a pulse generated through the action of C1 and R8 is applied to the trigger input of a timer U8 The timer is set by R9 and C3 to supply a 10ms positive pulse at the output pin3 This pulse will turn on TR2 and TR3 and apply the full battery voltage to the solenoid to ensure rapid closure In normal operation the solenoid is energised for 100ms The holding current is supplied through TR1 and R11 and is supplied as long as the trigger input at pin 5 of J1 is high The trigger input is also fed to the jack socket J3 which is used when the transducer is connected to the external suction device used for the negative expiratory pressure test NEP Drawing No 067 00 Revision No 1 3 Page 1 OF 3 Part No K9F6408U0A TCBO MAX3221CAE K6T4008V1C BB70 BU4S11 HD64F2318VTE25 MAX824T EXK T IGM76C256CLLFW 55 T R 0518520 Rohm individual CMOS Schmitt invertor SOT23 5 package Rohm individual CMOS Schmitt invertor SOT23 5 package icor clock calander with 256 X 8 bit RAM SO 8 package Maxim SPDT analogue switch SOT23 6 package Samsung 8M X 8 bit FLASH memory TSOP44 40 package Maxim RS232 transceiver SSOP16 package Samsung 512k X
19. ing the potentiometer VR2 to give 1 24 volts at the output of U1 with no flow applied The output from U1 is filtered by R19 and C10 and applied to the analogue input CHO of the A D The microcomputer unit communicates with the A D converter using the DIN and DOUT lines synchronously with the serial clock SCLK DOUT from the A D converter is inverted by TR6 to obtain the correct polarity Pressure measurement The pressure transducer U6 measures the pressure at the mouth U6 contains a piezo resistive bridge whose differential output is amplified by the instrumentation amplifier U2 The reference for U2 pin 5 is 1 24 volts derived from the 5 volt supply by R7 and R12 and buffered by U7 The output of U2 will thus be centred on 1 24 volts This voltage is also applied to REFADJ pin of the A D converter U3 and gives the A D converter a full scale input voltage of 2 48 volts The offset of U6 is nulled using the potentiometer VR1 to give 1 24 volts at the output of U2 with no flow applied The output from U2 is filtered by R18 and C9 and applied to the analogue input CH1 of the A D The microcomputer unit communicates with the A D converter using the DIN and DOUT lines synchronously with the serial clock SCLK DOUT from the A D converter is inverted by TR6 to obtain the correct polarity Shutter Operation The shutter is closed when the shutter solenoid is energised This happens when the trigger input at pin 5 of J1 is taken high by t
20. ng and the power is turned off TR4 allows the micro to turn off the power and switch off the unit This is normally done when the unit is left on for a long period of time To preserve the battery it turns it off Memory Map 0x000000 0 040000 256K Internal Flash 0x400000 0 480000 512K External Ram for modules 0x800000 Flash Prom Single address used 0xC00000 Display Controller OxFFDCOO OxFFFBFF 8K Internal Ram stack Keypad interface 067 03 The 26 keypad switches are arranged in a 5 X 5 matrix and a separate On Off key When the keypad is being read by the processor the 5 columns are sequentially driven low by the port lines PEO PE4 The state of the 5 rows is read by the port P40 P44 The diodes in the keypad PCB isolate the outputs from the Port to ensure that a high current will not flow from an output set high to one set low if two keys are pressed simultaneously The ON OFF key is connected to the power control circuitry described in the Power Supply section Resistor RN1 ensures that the keys which are not pressed are read as high Serial interface 067 04 The micro controller communicates with the PC or the printer via an RS232 serial interface at 38 4 Kbits per sec baud rate with 8 bits data 1 stop bit and no parity U6 converts the RS232 signal to a logic signal of 3 3V The micro controller has two inbuilt serial controllers SCIO and SCI1 SCIO is used for synchronous data transfer whilst S
21. om graphic 240 by 120 dot LCD It is controlled by an Epson SED1335 display controller U16 which directly interfaces to the micro controller The display controller timing is generated by a 10 MHz crystal X3 U19 is a 32K byte RAM to hold the display data The LCD display is based on four planes each requiring different plane voltage It is biased by 22 V generated by DC DC controller U17 VR1 varies this voltage which in turn changes the contrast At dark level the bias voltage is typically 22 6V and the plane voltages are 20 9V 19 2V 3 5V and 1 7V Of course they would be slightly different for different contrast level The plane voltages are generated by resistor ratio dividers R12 R13 R25 R14 R17 and buffered by quad Op amps U18 J2 is a connector to the display Power Supply 067 12 The power to the system is either supplied by the 3 9V lithium battery or from an external 9V DC regulated power supply If the external supply is connected then is switched off and the battery is not used R32 ensures that the battery is trickle charged at all times The on off key is conditioned via U12 and applied to set reset D type flip flop U11 On every key press the flip flop toggles between the on and off state In the On state TR7 is switched on switching on TR6 The on state can be held by MC_ON line from the micro controller whilst it is saving data in the Flash PROM The micro controller can also switch the power off by m
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23. the logic and sensor circuits A rechargeable 6 volt Ni cad battery pack supplies the power to the rotary solenoid The battery pack is trickle charged from the 9V supply by the constant current generated by the current mirror formed by R26 R27 R5 and TR7 Battery monitor With the transducer connected to the microcomputer unit TR5 is saturated as current will pass into its base connection through R16 which is connected to the incoming 9 volt supply TR5 connects the resistor divider formed by R3 and R4 The output of the divider is connected to channels 2 and 3 of the 12 bit A D converter U3 and is read by the microcomputer unit to monitor the battery voltage TRS turning off when the incoming 9 volt supply is not present ensures that the battery is not discharged when the transducer is not in use Flow measurement The flow through the transducer is measured by monitoring the pressure drop across the internal resistive element consisting of a stainless steel mesh in a plastic holder The pressure transducer U5 contains a piezo resistive bridge whose differential output is amplified by the instrumentation amplifier U1 The reference for U1 pin 5 is 1 24 volts derived from the 5 volt supply by R7 and R12 and buffered by U7 The output of U1 will thus be centred on 1 24 volts This voltage is also applied to REFADJ pin of the A D converter U3 and gives the A D converter a full scale input voltage of 2 48 volts The offset of U5 is nulled us
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