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Clock Circuit

Picaxe 18M2 Programmed with Logicator Flow Chart

Use the same coil as both a voltage pickup to sense the oncoming magnet, and as an electro-magnet to drive the pendulum. Separation between the pendulum magnet and the coil is about 1 mm.

Magnet: neodymium, chrome plated; cylindrical, ¾”dia. x ½” height with ¼” dia. through hole; centered on pendulum rod below the rating nut.

Pickup/Drive coil: the form is a plastic sewing machine bobbin, fully wound with 1480 turns of 34 AWG wire gauge; wire resistance 58.9 Ω; wire length 222 feet.

Read the pickup/drive coil on pin C.1 (actual leg 18) with internal analog/digital converter (ADC). The threshold is set pretty low. If the voltage at C.1 is 5/255 x 5V».1V, then drive the coil; if not, keep checking the input until it is.

This program drives the pendulum at equilibrium each half-period.

Power to drive the bob is adjusted by varying the time during which the output pin C.1 is high, using the “Wait” command.

In lieu of a schematic, the circuit layout is shown. Power to the circuit is provided by +12 V dc with an on-board +5 V dc regulator (as shown in the diagram, the link must be removed in order to use the regulator; refer to the PicAxe-18 Project board datasheet for details regarding the power connections). The +5 V is for the 18M2 microprocessor and Darlington transistor chip; the +12 V is used for the solenoid.

The electronics of a small quartz clock movement have been removed so that the going-train of gears, which moves the hands, can be driven by the PicAxe 18M2. These typical quartz movement gear trains require a 1 Hz signal, so the output pins B.5 and B.7 simulate that signal: on one half-cycle, pin B.5 is low and B.7 is high, and on the next half-cycle, the pins’ outputs are reversed.

Output B.4 is connected to the Darlington transistor chip. The output of the Darlington transistor will operate at a higher voltage than the microprocessor and will provide more current than the PicAxe output, and is used to drive a dc solenoid. B.4 is programmed to provide a pulse each second. This solenoid may be used to drive a mechanical movement.

B.3 output displays the time via an OLED (organic light emitting diode) display. Power connections to the OLED are not shown.

Momentary contact buttons (set, select Hour/Minute/Second/Return, increment, decrement) are used to control the time display and the power to drive the pendulum.

The following graph is the pick-up coil voltage as a function of time as the magnet swings overhead. For this data, the coil is disconnected from the PicAxe microprocessor and therefore the pendulum is not driven. In this graph, zero voltage between pulses occurs when the bob is at maximum amplitude. Notice that as the magnet approaches the coil, the voltage is positive-going. The magnet is at equilibrium, that is, directly over the coil, at the zero crossing between peaks. The coil is connected so that the positive-going voltage occurs first. The microprocessor may be damage or destroyed if the input voltage is negative. The microprocessor is programmed so that as the magnet approaches and is recognized, the pin turns into an output, and a pulse is sent to the coil. This pulse width is variable, but the pin is kept as an output long enough to mask any negative-going voltage at the pin due to the moving magnet.

This next graph is a measure of the magnetic field strength of the neodymium magnet. The coil is removed and a Hall sensor is placed under the equilibrium position of the pendulum. The magnet is too strong for the Phillips-Harris Blue-Box magnetic field sensor, so the field is measured – not at the coil location – but about 1.5 cm below the magnet (Recall that the top of the coil is to be placed about 1 mm below the bottom of the magnet.). The magnet is placed under the rating nut such that the South pole is up; therefore, the North pole of the magnet is in closest proximity to the coil, so the orientation of the magnetic field vector is down through the coil.

With a magnetic field perpendicular to the plane of the coil windings, and for a uniformly wound N-turn coil of cross-sectional area A, Faraday’s law gives us the voltage, V, induced in the coil as

The voltage in the coil is proportional to the negative of the rate-of-change of the magnetic field strength through the coil. An inspection of the B vs. t graph below will show that the slope is indeed indicative of the Pick-up Coil Voltage vs. t graph above. The two graphs were made during different experimental runs, of course, so the peak in magnetic field will not necessarily occur at the same time as the zero crossing of the coil voltage.

Schematic diagram for the four momentary contact switches.

The 10 kΩ resistor in series and the capacitor to ground are the de-bounce circuit for the switch. The other 10 kΩ resistor is on the 18M2 project board. The voltage at the pin is either +5V (contact) or 0V (open).

Code for reading the switches in Working Pendulum Drive and Clock Program in Basic, given below, has been derived from D. Lincoln’s book “Programming and Customizing the PICAXE Microcontroller”, 2^nd edition, Tab Books, 2011. An excellent treatise on PicAxe programming, highly recommended.

Pendulum Drive Logic

This simple scheme is the basis of the pendulum drive. Upon detection (at pin C.1 via the pick-up coil) of the approaching permanent magnet – attached to the pendulum below the rating nut – the microprocessor converts that input to an output and sends a pulse of variable length to the same coil. The magnetic field produced by this pulse in the coil exerts a force on the permanent magnet, thus driving the pendulum. The pause command determines the length of the pulse delivered to the pendulum. This sample program drives the pendulum every half-cycle but does not drive a clock.

Pick-up/Drive coil voltage

These next two graphs show voltage induced in the coil as the magnet swings nearby. In this case, the coil is attached to the PicAxe microprocessor.

The amplitude of the drive pulse is less than the five-volt output of the PicAxe microprocessor. The maximum current output of the microprocessor is 20 mA, but the coil dc resistance is about 50 Ω. The coil would draw about 100 mA if it were available, but it isn’t, thus the pin voltage is supressed. With 1.75 V, or so, at the pin, the current through the coil is about 35 mA.

The amplitude of the pendulum swing is inversely proportional to the pulse width.

The basic block just after the start command contains the lines:

#picaxe 18M2

pause 500

serout B.3,N2400,(254,1)

pause 30

This program illustrates the simulated one Hertz output on pins B.5 and B.7. The variable B indexes the alternate swings of the pendulum. This scheme of hacking a quartz movement and driving it with a simulated 1 Hz is derived from Rod Elliot, http://sound.westhost.com/clocks/index.html

In order to be able to find an average period over 100 half-swings of the pendulum, the variable U is an index to count 100 input pulses in the pick-up coil; the program then sends a pulse out on pin B.6 (the output pulse actually occurs at count 3 and again at count 103). This version of the program does not include any code to read the momentary push-button switches used to set the time or drive pulse delay time.

'BASIC converted from flowchart:

'PicAxe\EOS Laboratory Pendulum\Elliott clock circuit 18M2 version

{ ;Symbols

symbol varA = b0

symbol varB = b1

symbol varC = b2

symbol varD = b3

symbol varE = b4

symbol varF = b5

symbol varG = b6

symbol varH = b7

symbol varI = b8

symbol varJ = b9

symbol varK = b10

symbol varL = b11

symbol varM = b12

symbol varN = b13

symbol varO = b14

symbol varP = b15

symbol varQ = b16

symbol varR = b17

symbol varS = b18

symbol varT = b19

symbol varU = b20

symbol varV = b21

symbol varTEMPBYTE1 = b22

symbol varTEMPBYTE2 = b23

symbol varTEMPBYTE3 = b24

symbol varTEMPBYTE4 = b25

symbol varTEMPBYTE5 = b26

symbol varTEMPBYTE6 = b27

symbol varTEMPWORD1 = w11

symbol varTEMPWORD2 = w12

symbol varTEMPWORD3 = w13

}

main:

let dirsB = 0

let dirsC = 8

#picaxe 18M2

pause 500

serout B.3,N2400,(254,1)

pause 30

let varD = 51

let varH = 10

let varC = 0

let varB = 0

low B.0, B.1, B.2, B.3, B.4, B.5, B.6, B.7

Cell_7_5:

readadc C.1, varTEMPBYTE1

if varTEMPBYTE1 >= 0 and varTEMPBYTE1 <= 5 then

goto Cell_7_5

end if

if varB = 1 then

goto Cell_7_8

end if

high B.5, C.1

pause 350

low B.5, C.1

pause 100

let varB = 1

Cell_13_15:

if varC = 59 then

goto Cell_16_15

end if

let varC = varC + 1

Cell_13_8:

serout B.3, N2400, (254,128," Time ")

bintoascii varC, b11, b12, b13

bintoascii varD,b14,b15,b16

bintoascii varH, b17,b18,b19

if varH > 9 then goto line200

serout B.3, N2400, (254,192, " ",b19,":",b15,b16,":",b12,b13," ")

goto line400

line200:

serout B.3, N2400, (254,192, " 1",b19,":",b15,b16,":",b12,b13," ")

line400:

if varU = 3 then

goto Cell_16_7

end if

Cell_13_5:

inc varU

if varU = 103 then

goto Cell_16_4

end if

goto Cell_7_5

Cell_16_4:

let varTEMPWORD1 = 10

pulsout B.6, varTEMPWORD1

let varU = 0

goto Cell_7_5

Cell_16_7:

let varTEMPWORD1 = 10

pulsout B.6, varTEMPWORD1

goto Cell_13_5

Cell_16_15:

let varC = 0

let varD = varD + 1

if varD = 60 then

goto Cell_16_12

end if

goto Cell_13_8

Cell_16_12:

let varD = 0

let varH = varH + 1

if varH > 12 then

goto Cell_16_9

end if

goto Cell_13_8

Cell_16_9:

let varH = 1

goto Cell_13_8

Cell_7_8:

high B.7, C.1

pause 350

low B.7, C.1

pause 100

let varB = 0

goto Cell_13_15

#no_data 'reduce download time

//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

This is the program currently in use:

Working Pendulum Drive and Clock Program in Basic

'BASIC converted from flowchart:

#picaxe 18M2

{ ;Symbols

symbol varA = b0

symbol varB = b1 'path index, 1 or 2; needed only for hacked quartz movement

symbol varC = b2 'counter; up to 100

symbol delay = b3 'delay after driving pendulum

symbol varE = b4 'char1 for hour

symbol varF = b5 'char2 for hour

symbol varG = b6 'char3 for hour

symbol H = b7 'hour

symbol varI = b8

symbol varJ = b9 'char1 for min

symbol varK = b10 'char2 for min

symbol varL = b11 'char3 for min

symbol M = b12 'minute

symbol bcdnum = b13 'bcdnum (varN)

symbol bcdmin = b14 'bcdmin (varO)

symbol bcdmax = b15 'bcdmax (varP)

symbol varQ = b16

symbol varR = b17

symbol S = b18 'seconds

symbol varT = b19 'char1 seconds

symbol varU = b20 'char2 seconds

symbol varV = b21 'char3 seconds

symbol coil = b22 'coil

symbol varTEMPBYTE2 = b23 'char1 amplitude

symbol varTEMPBYTE3 = b24 'char2 amplitude

symbol varTEMPBYTE4 = b25 'char3 amplitude

symbol varTEMPBYTE5 = b26

symbol varTEMPBYTE6 = b27

symbol varTEMPWORD1 = w11

symbol varTEMPWORD2 = w12

symbol amplitude = w13 'amplitude = length of pulse to drive pendulum = pause length for pulse; 100ms to 500ms

}

main:

let dirsB = 0

let dirsC = 8

symbol down = 1

symbol up = 0

symbol setampbutton = pinC.7

symbol settimebutton = pinC.2

symbol incbutton = pinC.5

symbol decbutton = pinC.6

pause 500

serout B.3,N2400,(254,1)

pause 30

let amplitude = 350

let delay = 100

let M = 59

let H = 12

let S = 0

let varB = 0 'index for path, either 0 or 1

let varC = 0 'index counter for 100 seconds (50 complete swings)

'main loop

gosub drivependulum

setint %10000000,%10000000 'activate interrupt when pin7 goes high

'first number = high(or low), second number = pin7 (only)

'disables itself after use, so it must be put in loop

loop

interrupt:

gosub setamplitude

gosub settime

return

'subroutines

drivependulum:

Cell_7_5:

readadc C.1, coil 'C.1 is the coil

if coil >= 0 and coil <= 5 then

goto Cell_7_5

end if

if varB = 1 then

goto Cell_7_8

end if

high B.5, C.1, B.4

pause amplitude

low B.5, C.1, B.4

pause delay

let varB = 1

Cell_13_20:

If S = 59 then

goto Cell_16_20

end if

let S = S + 1

Cell_13_11:

serout B.3, N2400, (254,128," Time ")

bintoascii S, b19, b20, b21

bintoascii M,b9,b10,b11

bintoascii H, b4,b5,b6

if H > 9 then goto line200

serout B.3, N2400, (254,192, " ",b6,":",b10,b11,":",b20,b21," ")

goto line250

line200:

serout B.3, N2400, (254,192, " 1",b6,":",b10,b11,":",b20,b21," ")

line250:

'count from 3 (start) to 103 (100 pulses later) and send pulses (output B.6) to 28X2 chip;

'100 half-swings between pulses; should be 100 seconds

If varC = 3 then

goto line168

end if

line136:

inc varC

if varC = 103 then

goto line164

end if

goto line600

line164:

pulsout B.6, 1000

let varC = 0

goto line600

line168:

pulsout B.6, 1000

goto line136

Cell_16_20:

let S = 0

let M = M + 1

If M = 60 then

goto Cell_19_16

end if

goto Cell_13_11

Cell_19_16:

let M = 0

let H = H + 1

if H > 12 then

goto Cell_19_12

end if

goto Cell_13_11

Cell_19_12:

let H = 1

goto Cell_13_11

Cell_7_8:

high B.7, C.1, B.4

pause amplitude

low B.7, C.1, B.4

pause delay

let varB = 0

goto Cell_13_20

line600:

return

setamplitude:

do while setampbutton = down loop

bcdmax = $32 : bcdmin = $0A 'limits 50 max, 10 min; arbitrary scale 100 to 500

serout B.3, N2400, (254,128," Set Amplitude ")

bintoascii amplitude, b23, b24, b25

serout B.3, N2400, (254, 192, " ",b23,b24,b25," ")

if incbutton = down then

bcdnum = amplitude/10

gosub bcdinc

amplitude = bcdnum*10

bintoascii amplitude, b23, b24, b25

serout B.3, N2400, (254, 192, " ",b23,b24,b25," ")

do while incbutton = down loop

endif

if decbutton = down then

bcdnum = amplitude/10

gosub bcddec

amplitude = bcdnum*10

bintoascii amplitude, b23, b24, b25

serout B.3, N2400, (254, 192, " ",b23,b24,b25," ")

do while decbutton = down loop

endif

if setampbutton = down then goto line300

loop

line300:

return

settime:

do while settimebutton = down loop

serout B.3, N2400, (254,128,"Set Time: Hour")

serout B.3, N2400, (254,192, " ",b5,b6,":",b10,b11,":",b20,b21," ")

bcdmax = $0C : bcdmin = $01

bcdnum = H

if incbutton = down then

do while settimebutton = down loop

gosub bcdinc

H = bcdnum

bintoascii H, b4,b5,b6

serout B.3, N2400, (254,192, " ",b5,b6,":",b10,b11,":",b20,b21," ")

do while incbutton = down loop

endif

if decbutton = down then

do while settimebutton = down loop

gosub bcddec

H = bcdnum

Bintoascii H, b4,b5,b6

serout B.3, N2400, (254,192, " ",b5,b6,":",b10,b11,":",b20,b21," ")

do while decbutton = down loop

endif

if settimebutton = down then goto line500

loop

line500:

do while settimebutton = down loop

serout B.3, N2400, (254,128,"Set Time: Minute")

bcdmax = $3B : bcdmin = $01

bcdnum = M

if incbutton = down then

do while settimebutton = down loop

gosub bcdinc

M = bcdnum

bintoascii M, b9,b10,b11

serout B.3, N2400, (254,192, " ",b5,b6,":",b10,b11,":",b20,b21," ")

do while incbutton = down loop

endif

if decbutton = down then

do while settimebutton = down loop

gosub bcddec

M = bcdnum

bintoascii M, b9,b10,b11

serout B.3, N2400, (254,192, " ",b5,b6,":",b10,b11,":",b20,b21," ")

do while bdecbutton = down loop

endif

if settimebutton = down then goto line700

loop

line700:

do while settimebutton = down loop

serout B.3, N2400, (254,128,"Set Time: Second")

bcdmax = $3B : bcdmin = $01

bcdnum = S

if incbutton = down then

do while settimebutton = down loop

gosub bcdinc

S = bcdnum

bintoascii S, b19,b20,b21

serout B.3, N2400, (254,192, " ",b5,b6,":",b10,b11,":",b20,b21," ")

do while incbutton = down loop

endif

if decbutton = down then

do while settimebutton = down loop

gosub bcddec

S = bcdnum

bintoascii S, b19,b20,b21

serout B.3, N2400, (254,192, " ",b5,b6,":",b10,b11,":",b20,b21," ")

do while decbutton = down loop

endif

if settimebutton = down then goto line900

loop

line900:

return

bcdinc:

bcdnum = bcdnum + 1

if bcdnum > bcdmax then

bcdnum = bcdmin

endif

return

bcddec:

if bcdnum = bcdmin then

bcdnum = bcdmax

else

bcdnum = bcdnum - 1

endif

return

#no_data 'reduce download time

Slightly more complex version of a clock counter.

This version incorporates the clock counter with the drive code.

finito

Clock Counter Logic

A scheme for a clock counter using Picaxe 18M2 for a two second period pendulum, which counts every half-period.

In this example, A represents seconds, B represents minutes, and C represents hours. Entering initial values is the only way to set the clock in this test version of the counter.

First, set the analog sensor range. The Analog command reads the voltage at the pin connected to the pickup coil; this command is also a logic test. Here, the range is set between about 2/255 x 5V = 40mV and 500mV. The voltage becomes within this range as the magnet approaches equilibrium; the counter advances by one.

The LCD (liquid crystal display) command displays the time via pin B.7 (actual leg 13); in this instance, the default setting displays three digits without suppressing the zeros before a number. To suppress the zeros, the code must be modified by hand in Basic language.