Minimum Mass Wireless Coupled Scanning Voltmeter by Dick Cappel
A 10 bit scanning voltmeter with a Minimum Mass Wireless Coupler, based on the ATMega8.Range to the Minimum Mass Base Unit is 10 to 15 cm. If the voltmeter is battery operated, it can be floated from ground.
The basic Minimum Mass Wireless Coupler technology is described and links to other projects on this site that use the Minimum Mass Wireless Coupler are located on the web page, Minimum Mass Wireless Coupler: http://cappels.org/dproj/minmassrf/Min_Mas...ss_Coupler.html
This project is very simple physically, intended to demonstrate how easily the Minimum Mass RF Link can be added to a project. The circuit shown does not have a lot if the nice things that I would usually include in an instrument, such as the ability to handle out-of-range input signals without the circuit suffering damage. Therefore, I suggest that if you build this as a stand-alone instrument, that you add protection crcuitry to the inputs.
The power suuply is the reference voltage in this case, and the binary-to-decimal conversion assumes that the refernce voltage is +5 volts, so I sugges that an adjustable regulator be used to obtain a precise +5 volts. You could use three alkaline cells (for example) in series, but the calibration would be way off.
The A/D converter setup and binary-to-decmial conversion routines were taken from the Low Cost Telemetry Device project on this site. The firmware was created by taking the Low Cost Telemetry Device firmware, removing the un-needed code, and adding calls to the Minimum Mass Wireless Coupler drivers instead of to the USART routines.
Link to Site: http://cappels.org/dproj/minmassrfM8/minmassrf8.html
A 10 bit scanning voltmeter with a Minimum Mass Wireless Coupler, based on the ATMega8.Range to the Minimum Mass Base Unit is 10 to 15 cm. If the voltmeter is battery operated, it can be floated from ground.
The basic Minimum Mass Wireless Coupler technology is described and links to other projects on this site that use the Minimum Mass Wireless Coupler are located on the web page, Minimum Mass Wireless Coupler: http://cappels.org/dproj/minmassrf/Min_Mas...ss_Coupler.html
This project is very simple physically, intended to demonstrate how easily the Minimum Mass RF Link can be added to a project. The circuit shown does not have a lot if the nice things that I would usually include in an instrument, such as the ability to handle out-of-range input signals without the circuit suffering damage. Therefore, I suggest that if you build this as a stand-alone instrument, that you add protection crcuitry to the inputs.
The power suuply is the reference voltage in this case, and the binary-to-decimal conversion assumes that the refernce voltage is +5 volts, so I sugges that an adjustable regulator be used to obtain a precise +5 volts. You could use three alkaline cells (for example) in series, but the calibration would be way off.
The A/D converter setup and binary-to-decmial conversion routines were taken from the Low Cost Telemetry Device project on this site. The firmware was created by taking the Low Cost Telemetry Device firmware, removing the un-needed code, and adding calls to the Minimum Mass Wireless Coupler drivers instead of to the USART routines.
Link to Site: http://cappels.org/dproj/minmassrfM8/minmassrf8.html
| CODE |
;File name: vlfcwm8.inc ;Copyright 2004 Richard Cappels, projects@cappels.org www.project.cappels.org ;Instructions for use and initialization code are afer the firs .exit statement. ;Reload and prescale values .equ XmtTimerReload = $CC ;Timer 0 reload value for T 1 1200 baud value .equ RcvTimerReload = $F3;Timer 0 reload value for T/4 1200 baud value .equ RecThresh = 10 ;Minimum number of counts to detect carrier. .equ RecHighThres = 65 ;1+ maximum counts for valid carrier .equ Timer0Prescale = $03;Timer 0 prescaler selector -clock/64. .equ delaytime = 20;Waiting time after transmit mode before receiving. .equ rcvmultiplier = 7;Number of delaytimes to wait bafter receiving before transmitting. ;//////////////BEGIN BASIC RF COUPLER ROUTINES\\\\\\\\\\\\\\\ .macro pushall push r2; push r18 ; push r17 ; push r19; .endmacro .macro popall pop r19; ;Temporaty storage of status register pop r17 ;General purpose scratch register pop r18 ;General purpose scratch register. pop r2;;Comparitor interrupt counters .endmacro PostXmitDelay: push r18 push r17 ldi r18,delaytime rcall delay pop r17 pop r18 ret PostRCVDelay: push r18 push r17 ldi r18, rcvmultiplier * delaytime rcall delay pop r17 pop r18 ret delay: ;Delay - load 00 into r18 for max delay, 01 for minimum delay. ;r18 and r17 destroyed. lptrf1: clr r17 lptrf12:dec r17 brne lptrf12 dec r18 brne lptrf1 ret ReceiveRFByte: ;Receive a byte by RF and put into RFChar ;Returs with carry set if data received, otherwise cleared. pushall ;Save working registers on stack ldi r18,Timer0Prescale;Initaize prescaler. out TCCR0, r18 ldi r18, RcvTimerReload;Initialize counter. out TCNT0,r18 in r18,TIMSK ;Enable interrupts TIMSK. ori r18,0b00000001 out TIMSK,r18 clr r2 ;Zero comparitor interrupt counter. ldi r17,0b00001011 ;Comparitor setup: enable interrupt on positive edge. out ACSR,r17 clr r17 ;Clear start bit test counter. wfsbrf1: ;Wait for start bit. rcall QCDrf1 ;Sample for 1/4 bit time. dec r17 ;See if too many consecutive unsuccessful samples. breq bailrf1 mov r18,r2 cpi r18,RecThresh ;Check number of carrier cycles against threshold. brmi wfsbrf1 cpi r18,RecHighThres;Check to see if too many received. brpl wfsbrf1 rcall QCDrf1 ;Wait T/4. rcall QCDrf1 ;Wait T/4. ldi r17,8 ;Set number of bits: 8 data. nbrf1: sbi LEDOutPort,LEDOutPin rcall QCDrf1 ;Wait T/4. rcall QCDrf1 ;Wait T/4. rcall QCDrf1 ;Wait T/4. clr r2 rcall QCDrf1 ;Sample for 1/4 bit time <== use this sample mov r18,r2 cpi r18,RecThresh ;Set carry true if threshold exceeded. brpl oirf1 clc rjmp zeinrf1 oirf1: sec zeinrf1: ror RFChar ;Get carry into lsb of RFChar. dec r17 brne nbrf1 sec ;Data received - set carry flag rcxtrf1: ldi r18,0 out TCCR0,r18 ;Turn off timer0 interrupt out ACSR,r18 ;Turn off Comparitor interrupt cbi LEDOutPort,LEDOutPin popall ret bailrf1:clc ;No data received - clear carry and return rjmp rcxtrf1 SendRFByte: ;Shift byte in RFChar out through RF channel. ;RFChar changed by routine. pushall ;Save all working registers except RFChar. sbi LEDOutPort,LEDOutPin;For indication purposes ldi r18,Timer0Prescale;Initaize prescaler out TCCR0, r18 ldi r18, XmtTimerReload;Initialize counter out TCNT0,r18 in r18,TIMSK ;Enable interrupts TIMSK. ori r18,1 out TIMSK,r18 ldi r17,11 ;Set number of bits:1 start, 8 data, 2 stop sec ;Start bit nxbtrf1: brcs bitsonerf1 rcall szerorf1 rjmp iwzrf1 bitsonerf1: sbi RFSigDDR,RFSigPin ;Set signal output pin to output. rcall SendOnerf1 cbi RFSigDDR,RFSigPin ;Set signal output pin to input. iwzrf1: lsr RFChar ;Shift next bit into carry. dec r17 ;Decrement bit counter. brne nxbtrf1 ;If not all done, then continue. out TCCR0,RFChar ;(RFChar was cleared by shifting.) cbi RFSigPort,RFSigPin ;Set signal output low (no pullup). cbi LEDOutPort,LEDOutPin popall ;Restore all working registes except RFChar. ret szerorf1: ;Send no carrier for for one bit time. ldi r18, XmtTimerReload;Initialize counter out TCNT0,r18 WaitNotSend: rjmp WaitNotSend ;Do nothing but wait for interrupt to yank out of loop. SendOnerf1: ;Send carrier for T us ldi r18, XmtTimerReload;Initialize counter out TCNT0,r18 ;Send carrier until next interruput MakeRF1: ;Make 181.8181 Mhz sbi RFSigPort,RFSigPin;Output High sbi and cbi are 2 clock instructions. sbi RFSigPort,RFSigPin sbi RFSigPort,RFSigPin sbi RFSigPort,RFSigPin sbi RFSigPort,RFSigPin nop ;(need this nop for timing) cbi RFSigPort,RFSigPin;Output Low cbi RFSigPort,RFSigPin cbi RFSigPort,RFSigPin cbi RFSigPort,RFSigPin nop rjmp MakeRF1 ;Interrupt will yank out of loop. QCDrf1: ;Send no carrier for T/4 us ldi r18, RcvTimerReload;Initialize counter out TCNT0,r18 WaitHere1: rjmp WaitHere1 ;Send no carrier until next interruput timer0service: ;Return to routine that called interrupted routine. The processor ;must be in a subroutine when this interrupt occurs! Disable ;the timer the rest of the time. pop r18 pop r18 reti ;Return from interrupt.to routine before interrupt comparitorservice: ;Increment r18 upon comparitor interrupt. in r19,sreg ;Save status register. inc r2 ;Increment SigCount. out sreg,r19 ;Restore status register. reti ;Return from interrupt. Total of 7 cycles including the return. ;//////////////END BASIC RF COUPLER ROUTINES\\\\\\\\\\\\\\\ .exit ;*************** Following are instructions for use and starter code for the calling .inc file*************** ;Inlcude the code below in the calling file. It may be customized. ;Copy the code from "START OF INITIALIZATION CODE" TO "END OF INITIALIZATION CODE", ;below into the assembler source document, then modify as needed. ;REFERENCE CIRCUIT: ;AT<ega8 microcontroller with 4 MHz clock. Timer 0 (8 bit) and the comparitor interrupt are used. ;if this code moved to another controller, the include file code relating to these peripherals will ;most likely have to be modified. ;A resonant loop antennat tuned to 182 kHz is connected across the comparitor intputs. ;The comparitor is used to receive data, The bit configured as the RFSigPort (Port D, pin 6, ;the + input of the comparitor inputs) is used to send data. ;One example resonant circuit is 14 turns of #30 emammeled wire on 5.5 cm in diameter, air core, ;brought into resonance with a .033 uf capacitor in parallel with it. ;The - (non-inverting) input of the comparitor is also connected to the tap on a 2:1 resistive voltage devider, ;which serves to bias the resonant circuit at half the supply voltage. Both resistors in the devider are ;of the same vlaue and may range from about 220 Ohms to 2 k Ohms each. The value of these resistors determines ;the maximum possible transmitter power. ;The voltage devider may be power from the microcontroller's positive power supply, or optionally, ;powered from one of its output pins The constants realted to BridgePowerPort designate this pin. ;Powering from an output pin allows power reduction during sleep. The example initialization code sets ;this pin high. Additoinal code would be needed to set this pin low. ;The LEDOutPort pin is intended to drive an activity indicator LED. It goes high briefly while transmitting ;and receiving data over the RF link. The example initialization code sets this pin as an output. ;If this pin is needed for some other function, code that controls the pin will have to be removed ;from the initialization and the include file. ;CALLABLE SUBROUTINES: ;Four callable routines are available. Each of these routines saves all working registers on the ;stack and restores thme before returning to the calling routines. The sole exception is, ;RFChar, which is used to transfer the data between the RF routines and calling routines. ;RFchar needs to be assigned to a high register (r16..r31),but CANNOT be r17, r18. or r19. ;RFChar is only modified by the RF routines while one of the four callable routines is being executed, and ;may be used freely in other parts of the program. ;Here is a list of the callable routines: ;SendRFByte (subroutine) Sends contents of RFChar ;Sends contents of RFChar via RF. Modifies RFChar. ;Example ; ldi RFChar,$2A ;Send astersik via RF link. ; rcall SendRFByte ; ;ReceiveRFByte (subroutine) Receive RF singal into RFChar, carry set if successful. ;Waits for start bit on RF channel for 63.75 bit times. Returns with carry set and ;data in RFChar if character received. Returns with carry clear if no byte received within ;that time. ;Example ;getchar: ; rcall ReceiveRFByte ;Wait for character to be received ; brcc getchar ; ;PostXmitDelay (subroutine);Wait for antenna to stop ringing from transmit operation. ;Use this delay after transmitting if listening is to follow. The delay allows ;ringing in the antenna to die down so that the received does not mistake ringing as data. ;This is meant to be used when between sending mode and receiving modes, not to be ;used on a character-by-character basis, as this would needlessly reduce the data ;rate. ;See example below "PostRCVDelay". ;PostRCVDelay (subroutine);Wait for far end receiver to recover. ;Use this after receiving data, before sending to give the receiver associated ;with the transmitter that just sent data time to recover. This is meant to be used ;when switching between receiving mode and sending modes, not to be used on a ;character-by-character basis, as this might result in the loss of garbling ;of characters within a stream. ; ;Example ;Receive a character via RF and echo it back via RF. ; ;wait: rcall ReceiveRFByte ;Wait for a character to be received ; brcc wait ; rcall PostRCVDelay ;Wait for rining in far end transmitter to stop. ; rcall SendRFByte ;Echo character to far end. ; rcall PostXmitDelay ;Wait for rining in local antenna to die down. ; rjmp wait ;Go back to top and get another character. ;////////////////// START OF INITIALIZATION CODE \\\\\\\\\\\\\\\\\\\\\\\\\ ;Copyright 2004 Richard Cappels, projects@cappels.org ;vlfcw initialization code. .include "m8def.inc" ;Include file in same directory as project. ;How to connect this chip: ;Pin 7 to + 5 V ;Pins 8 and 22 to ground. ;Pin 21 connected to +5V through a decoupling network. For example a 33 uh choke \ ; from +5V to pin 21 and a 0.22 uf monolithinc capacitor from pin 21 to ground. ;Pin 6 connects to one end of a 22 uh loop antenna in parallel with a .033 uf capacitor. ;Pin 7 the other end of the loop antenna and capcaitor connect to pin 7, Pin 7 is also ; connected to the center tap of a pair of 220 t 1,000 Ohm resistors connected in series ; between +5V to ground. ; ;The four A/D inputs have an input range of 0 to 5 Volts. ;Pin 23 Analog input A ;Pin 24 Analog input B ;Pin 25 Analog input C ;Pin 26 Analog input D ; ;The output is on-off keyed 182.818181 kHz RF, keyed by serial ASCII ;(1200 baud, 1 start bit, 2 stop bits, no parity, lsb first) ; .include "m8def.inc" ;Include file in same directory as project. ;definition of I/O ;B0 (not assigned - configure as INPUT with weak pullup) ;B1 (not assigned - configure as INPUT with weak pullup) ;B2 (not assigned - configure as INPUT with weak pullup) ;B3 (not assigned - configure as INPUT with weak pullup) ;B4 (not assigned - configure as INPUT with weak pullup) ;B5 (not assigned - configure as INPUT with weak pullup) ;B6 (not assigned - configure as INPUT with weak pullup) ;B7 (not assigned - configure as INPUT with weak pullup) .equ PORTBdata =0b11111111;Initial data .equ DDRBdata =0b00000000;Initial data ;C0 A/D A configure as INPUT ;C1 A/D B configure as INPUT ;C2 A/D C configure as INPUT ;C3 A/D D configure as INPUT ;C4 (not assigned - configure as INPUT with weak pullup) ;C5 (not assigned - configure as INPUT with weak pullup) ;C6 (not assigned - configure as INPUT with weak pullup) ;C7 (not assigned - configure as INPUT with weak pullup) .equ PORTCdata =0b11110000;Initial data .equ DDRCdata =0b000000O0;Initial data ;D0 (not assigned - configure as INPUT with weak pullup) ;D1 (not assigned - configure as INPUT with weak pullup) ;D2 (not assigned - configure as INPUT with weak pullup) ;D3 (not assigned - configure as INPUT with weak pullup) ;D4 (not assigned - configure as INPUT with weak pullup) ;D5 (not assigned - configure as INPUT with weak pullup) ;D6 AN0 ;D7 AN1 .equ PORTDdata =0b00000000;Initial data .equ DDRDdata =0b00000000;Initial data ;The statements below establish I/O pins needed for RF operation. .equ RFSigPort = PORTD;Port output signal is to appear on. .equ RFSigDDR = DDRD;Data Direction Register for signal output .equ RFSigPin = 6;Pin output signal is to appear on. .equ LEDOutPort = PORTD;Indicator LED .equ LEDOutDDR = DDRD .equ LEDOutPin = 2 .equ CompPlusPort = PORTB;Comparitor noninverting input (input 0) .equ CompPlusDDR = DDRB .equ CompPlusPin = 6 .equ BridgePowerPort = PORTB;Power for voltage devider (bridging resistors) .equ BridgePowerDDR = DDRB .equ BridgePowerPin = 3 .def RFChar = r16;RF character I/O buffer (must be a high register) .def temp = r17;General purpose scratch register. .cseg .ORG $0000 ;Initializaton code rjmp start .org $0009 rjmp timer0service .org $0010 rjmp comparitorservice .include "vlfcwm8.inc" ;Include file to be in same directory as this file. start: ;Entry point after reset -initialize everything ldi temp,high(ramend) ;Initialize 16 bit Stack Pointer out sph,temp ldi temp,low(ramend) out spl,temp ldi temp,DDRBdata ;Set PORTB. out DDRB,temp ldi temp,PORTBdata out PORTB,temp ldi temp,DDRCdata ;Set PORTC out DDRC,temp ldi temp,PORTcdata out PORTc,temp ldi temp,DDRDdata ;Set PORTD. out DDRD,temp ldi temp,PORTDdata out PORTD,temp sei ;Enable interrupts. ;////////////////// END OF INITIALIZATION CODE \\\\\\\\\\\\\\\\\\\\\\\\\ .exit |