Build An LED Propeller Clock
|My "Propeller Clock" is a mechanically scanned LED clock with seven light emitting diodes that spin, giving the illusion of numbers floating in the air. This is the first clock I ever built. I've built a few LED signs, but they get boring because I already know the message.|
This clock utilizes only a few relatively inexpensive electronic components and a recycled motor from a VCR or floppy drive.
|The Propeller Clock (Bundle) Parts List|
C1, C2 - 33pF ceramic capacitors
C3, C6 - 0.1µF ceramic capacitors
C4 - 47µF electrolytic capacitors
C5 - 47,000µF supercap (memory cap)
D1-D7 - light emitting diodes
D8-16 - 1N4001 general purpose 1 amp rectifiers
R1 - 120Ω DIP array or seven 120 ohm resistors
R2-R6 - 10kΩ resistors
J1 - Straight pin male header
SW1-SW3 - normally open pushbutton switches
U1 - 16F84 programmed with mclock code
XTAL1 - 4MHz crystal
MOTOR - Use or recycle any DC motor, preferably meant for 12 volts so the speed will not be too great when operated at approximately 6.2 volts.
How this clock works:A motor spins the "propeller", and a small microprocessor keeps track of time and changes the pattern on seven LEDs with exact timing to simulate a 7 x 30 array of LEDs. It is an illusion, but it works nicely.
If you want to build this clock, you will need a few things:
The clock is on a spinning piece of perfboard, but it must get power. I thought of many ways to do this, including using two motors (motor one has its shaft fixed to a base, and motor two spins the body of motor one, generating electricity), making arotary transformer, or using slip rings. Eventually, I decided to do it another way, taking power from the spinning armature of a plain DC motor. In order to run the wires
out of the motor, I removed the bearing from one end of the motor, leaving a big hole.
There are three terminals inside most small DC motors, and it acts a lot like three-phase alternating current, so it must be rectified back to DC. A nice side effect of this is that the position of the motor can be detected by taking one of the phases straight into the microprocessor.
Step One: Mangle a MotorFind a VCR, perhaps a Sharp or a Samsung, with a flat reel motor. The motor I have is marked JPA1B01, but Sharp knows it by the number RMOTV1007GEZZ (author's note: Sharp motor is obsolete. Use any DC motor, preferably meant for 12 volts so the speed will not be too great when operated at approximately 6.2 volts). Take it apart without mangling the brushes (there are little holes to slip a paperclip into to move the brushes out of the way), and notice that it has one ball bearing and one sleeve bearing.
Knock the sleeve bearing out of the case and glue or solder it to the other end of the motor, as an extension of the ball bearing. The shaft of the motor will have to be repositioned slightly to get the right height, press it in a vise with a hollow spacer on one end. Take a Berg connector with three wires and solder them to the three terminals on the motor's armature. Glue a short threaded spacer to the shaft at the end that will stick out the hole, and reassemble the motor (be careful with the brushes). You can glue the motor to a VCR head as a weighted base.
Step Two: Build the CircuitI used perfboard (Vectorboard) and hand-wired the circuit together. Use an 18-pin socket for the 16F84 because it needs to be programmed before putting it in the circuit. For the 7 current-limit resistors I used a DIP resistor array because it made it easy to experiment with LED brightness. I settled on 120Ω. You can use seven regular resistors, because 120 ohms works fine, though it puts the peak current right at the limit for the 16C84. Think about balance while you build this circuit, and reference my pictures, so you don't have to add a lot of balancing weight later. Substitute for any part values you like. Note that I used a47000µF supercap, it is to keep the clock running after turning it off so you can set the time. The LEDs get power separate from this. Don't substitute a ceramic resonator for the 4MHz crystal, this is a clock and should be accurate.
Step Three: Program the PIC16C84AYou'll need a programmer that will program a PIC16C84A. If you found this file/web page, you can find plans to build a 16C84 programmer. Program it using the hex file accompanying this document. I have included the source code (.asm) just for your amusement. When programming the chip, set the chip options to: watchdog timer (WDT) ON and oscillator to normal XTcrystal.
Step Four: Throw It Together and Keep TimeScrew the circuit board to the motor, and plug the three wire connector in. Apply power to the motor. The preferred voltage is 6.2 volts, but it will run from 5 volts to about 7.5 volts. Note that 5 volts gets to the circuit when 6.2 volts is applied to the motor, because of diode 252BNAV losses. The clock may be working at this point, displaying 12:00. If it isn't, there was probably some voltage on the supercap (memory cap) when you plugged in the chip.
Turn off the power and momentarily short pins 5 and 4 together (ground and /mclr) to reset the chip. Now when you apply power the clock should work, and you can set it by turning off the power and pushing the buttons (hours, 10 minutes, minutes) the right number of times. If the numbers appear backwards, reverse the polarity to the motor to make it spin the other way. You might experiment with balancing the clock, and the use of foam under the base to reduce vibrtion.
Step Five: ModificationsIf you look closely at the source code, you'll see that the "dot rate" is adjusted to the speed of the motor to make the display a consistent width regardless of the motor's speed. The motor I used has brushes set 90 degrees apart, and gives two indexes each revolution. The clock displays on two sides, 180 degrees apart. If you use a motor with the brushes 180 apart, the clock will only display on one side, and the numbers will be too wide. You'll want to modify the program, in the section marked D_lookup_3. The value in the W register when Delay gets called effects the width of the digits. You might try sending half of the period_calc value to Delay; perhaps by rotating period_calc right into W (remember to clear the carry flag first).
The source code in Microchip MPASM format.
;-------- ; mclock8.asm ; "The Propeller" mechanically scanned LED clock ; some changes since last version - ; modified table etc for compatiblility with 8th LED ; watchdog timer used to ensure startup ; Bob Blick February 12, 1997 ; Licensed under the terms of the GNU General Public License, www.gnu.org ; No warranties expredded or implied ; Bob Blick February 18, 2002 ;-------- list p=16C84 radix hex include "p16c84.inc" ;-------- ; remember to set blast-time options: OSC=regular xtal, WDT=ON ; timings all based on 4 MHz crystal ;-------- ; are these equates already in the include file? someday I'll look. ;-------- w equ 0 f equ 1 ;-------- ; Start of available RAM. ;-------- cblock 0x0C safe_w ;not really temp, used by interrupt svc safe_s ;not really temp, used by interrupt svc period_count ;incremented each interrupt period_dup ;copy of period_count safe from interrupt period_calc ;stable period after hysteresis calc. flags ;b2=int b1=minute b4=edge dot_index ;which column is being displayed digit_index ;which digit is being displayed hours ;in display format, not hex(01-12) minutes ;00 to 59 bigtick_dbl ;incremented each interrupt bigtick_hi bigtick_lo keys ;key value scratch ;scratch value tick ;used by delay endc ;-------- ; Start of ROM ;-------- org 0x00 ;Start of code space goto Start ;-------- ; INTERRUPT SERVICE ROUTINE ;-------- org 0x04 ;interrupt vector Intsvc movwf safe_w ;save w swapf STATUS,w ;swap status, w movwf safe_s ;save status(nibble swap, remember) ;-------- ; done saving, now start working ;-------- ; clear watchdog timer to ensure startup clrwdt ; ; increment period count incf period_count,f btfsc STATUS,Z ;zero set means overflow decf period_count,f ; 234375 interrupts every minute. Increment the bigtick each time. incf bigtick_lo,f btfsc STATUS,Z incf bigtick_hi,f btfsc STATUS,Z incfsz bigtick_dbl,f goto Bigtick_out ;-------- ; here? bigtick has rolled over to zero and one minute has passed. ; reload bigtick and set a flag for the main counter ;-------- movlw 0xFC ;234375 = 0x039387 movwf bigtick_dbl ;0 - 0x039387 = 0xFC6C79 movlw 0x6C movwf bigtick_hi movlw 0x79 movwf bigtick_lo bsf flags,1 ;notify Keep_time Bigtick_out ;-------- ; done working, start restoring ;-------- swapf safe_s,w ;fetch status, reswap nibbles movwf STATUS ;restore status swapf safe_w,f ;swap nibbles in preparation swapf safe_w,w ;for the swap restoration of w bcf INTCON,2 ;clear interrupt flag before return retfie ;return from interrupt ;-------- ; CHARACTER LOOKUP TABLE ; ignore high bit. set=LED off, clear=LED on, bit0=bottom LED, bit6=top LED ;-------- Char_tbl addwf PCL,f dt 0xC1,0xBE,0xBE,0xBE,0xC1 ;"O" dt 0xFF,0xDE,0x80,0xFE,0xFF ;"1" dt 0xDE,0xBC,0xBA,0xB6,0xCE ;"2" dt 0xBD,0xBE,0xAE,0x96,0xB9 ;"3" dt 0xF3,0xEB,0xDB,0x80,0xFB ;"4" dt 0x8D,0xAE,0xAE,0xAE,0xB1 ;"5" dt 0xE1,0xD6,0xB6,0xB6,0xF9 ;"6" dt 0xBF,0xB8,0xB7,0xAF,0x9F ;"7" dt 0xC9,0xB6,0xB6,0xB6,0xC9 ;"8" dt 0xCF,0xB6,0xB6,0xB5,0xC3 ;"9" dt 0xFF,0xC9,0xC9,0xFF,0xFF ;":" Char_tbl_end ;-------- ; SUBROUTINES STARTING HERE ;-------- ; clear important bits of ram ;-------- Ram_init movlw 0x07 movwf keys movlw 0x12 ;why do clocks always start movwf hours ;at 12:00 ? clrf minutes clrf dot_index clrf digit_index movlw 0xFC movwf bigtick_dbl retlw 0 ;-------- ; unused pins I am setting to be outputs ;-------- Port_init movlw 0x00 ;all output, b7=unused tris PORTB ;on port b attached to LEDs movlw b'00010111' ;port a has 5 pins. I need 4 inputs ;b0=minutes, b1=10mins, b2=hours ;b3=unused, b4=rotation index tris PORTA ;on port a retlw 0 ;-------- ; get timer-based interrupts going ;-------- Timer_init bcf INTCON,2 ;clear TMR0 int flag bsf INTCON,7 ;enable global interrupts bsf INTCON,5 ;enable TMR0 int clrf TMR0 ;clear timer clrwdt ;why is this needed? just do it.. movlw b'11011000' ;set up timer. prescaler(bit3)bypassed option ;send w to option. generate warning. clrf TMR0 ;start timer retlw 0 ;-------- ; test for index in rotation and store period in period_dup ;-------- Check_index movf PORTA,w ;get the state of port a xorwf flags,w ;compare with saved state andlw b'00010000' ;only interested in bit 4 btfsc STATUS,Z ;test for edge retlw 0 ;not an edge, same as last xorwf flags,f ;save for next time btfsc flags,4 ;test for falling edge retlw 0 ;must have been a rising edge movf period_count,w ;make a working copy movwf period_dup ;called period dup clrf period_count ;a fresh start for next rotation clrf digit_index ;set to first digit clrf dot_index ;first column ; calculate a period that does not dither or jitter ; period will not be changed unless new period is really different movf period_calc,w subwf period_dup,w ;find difference btfss STATUS,C ;carry flag set means no borrow goto Calc_period_neg ;must be other way sublw 2 ;allowable deviation = 3 btfss STATUS,C ;borrow won't skip incf period_calc ;new value much larger than calc retlw 0 Calc_period_neg addlw 2 ;allowable deviation = 3 btfss STATUS,C ;carry will skip decf period_calc ;no carry means it must be changed retlw 0 ;-------- ; change LED pattern based on state of digit_index and dot_index ;-------- Display_now movlw 0x05 xorwf dot_index,w ;test for end of digit movlw 0xFF ;pattern for blank column btfsc STATUS,Z goto D_lookup_3 ;it needs a blank bcf STATUS,C ;clear carry before a rotate rlf digit_index,w ;double the index because each addwf PCL,f ;takes two instructions D_10hr swapf hours,w goto D_lookup ;what a great rush of power D_1hr movf hours,w ;I feel when modifying goto D_lookup ;the program counter D_colon movlw 0x0A goto D_lookup D_10min swapf minutes,w goto D_lookup D_1min movf minutes,w goto D_lookup D_nothing retlw 0 D_lookup andlw b'00001111' ;strip off hi bits movwf scratch ;multiply this by 5 for lookup addwf scratch,f ;table base position addwf scratch,f ;is this cheating? addwf scratch,f ;I think not. addwf scratch,f ;I think it is conserving energy! btfss STATUS,Z ;test for zero goto D_lookup_2 ;not a zero movf digit_index,f ;this is just to test/set flag movlw 0xFF ;this makes a blank LED pattern btfsc STATUS,Z ;test if it is 10 hrs digit goto D_lookup_3 ;it's a leading zero D_lookup_2 movf dot_index,w ;get column addwf scratch,w ;add it to digit base call Char_tbl ;get the dot pattern for this column D_lookup_3 movwf PORTB ;send it to the LEDs movlw 0x0C ;overhead value sub from period subwf period_calc,w ;compensate for overhead and set call Delay ;width of digits with this delay incf dot_index,f ;increment to the next column movlw 0x06 ;6 columns is a digit plus space xorwf dot_index,w ;next digit test btfss STATUS,Z retlw 0 ;not a new digit clrf dot_index ;new digit time incf digit_index,f retlw 0 ;Display_now done. ;-------- ; a short delay routine ;-------- Delay movwf tick Delay_loop decfsz tick,f goto Delay_loop ;w is not damaged, so Delay can return ;be recalled without reloading ;-------- ; test for keypress and call time adjust if needed ;-------- Check_keys movf PORTA,w ;get port "a" xorwf keys,w ;compare with previous andlw b'00000111' ;only care about button pins btfsc STATUS,Z ;zero set=no buttons retlw 0 ;return xorwf keys,f ;store key value movlw 0x64 ;a fairly long delay will movwf scratch ;prevent key bounces Key_delay movlw 0xFF call Delay decfsz scratch goto Key_delay btfss keys,2 ;test "minutes" button goto Inc_mins btfss keys,1 ;test "tens" button goto Inc_tens btfss keys,0 ;test "hours" button goto Inc_hours retlw 0 ;must be a glitch. yeah, right! ;-------- ; increment ten minutes ;-------- Inc_tens movlw 0x0A movwf scratch ;scratch has ten Inc_tens_loop call Inc_mins decfsz scratch goto Inc_tens_loop ;another minute added retlw 0 ;-------- ; increment one hour ;-------- Inc_hours movlw 0x12 xorwf hours,w btfsc STATUS,Z goto Inc_hours_12 movlw 0x07 ;this part gets a little sloppy addwf hours,w movlw 0x07 btfss STATUS,DC movlw 1 addwf hours,f retlw 0 Inc_hours_12 movlw 0x01 movwf hours retlw 0 ;-------- ; increment the time based on flags,1 as sent by interrupt routine ; Inc_mins loop also used by time-setting routine ;-------- Keep_time btfss flags,1 ;the minutes flag retlw 0 ;not this time bcf flags,1 ;clear the minutes flag Inc_mins movlw 0x07 ;start incrementing time addwf minutes,w ;add 7 minutes into w btfsc STATUS,DC ;did adding 7 cause digit carry? goto Sixty_mins ;then test for an hour change incf minutes ;otherwise add 1 for real retlw 0 ;and go back Sixty_mins movwf minutes ;save the minutes movlw 0x60 ;test for 60 xorwf minutes,w ;are minutes at 60? btfss STATUS,Z retlw 0 ;no? go back clrf minutes ;otherwise zero minutes goto Inc_hours ;and increment hours ;-------- ; End of subroutines ; Program starts here ;-------- Start call Ram_init ;set variables to nice values call Port_init ;set port directions call Timer_init ;start timer based interrupt ;-------- ; Done initializing, start the endless loop. ;-------- ; Circle ;begin the big loop ; ;-------- ; detect falling edge on PORTA,4 to determine rotary index ; calculate rotation period and store in period_dup ; compare with working period(period_calc) and adjust if way different ;-------- call Check_index ;-------- ; check display state and change if needed ;-------- call Display_now ;-------- ; check keyboard and adjust time ;-------- call Check_keys ;-------- ; check minute flag and increment time if a minute has passed ;-------- call Keep_time ;-------- ; gentlemen, that's a clock, keep it rolling ;-------- goto Circle ;you heard the man, get going! end ;-------- ; end of file ;--------
The hex code ready to load into a PIC16C84A or 16F84 chip.
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