Circuit Description

The Cmos 4060 is a 14 bit binary counter.

It can count up to 16 384 - that's two raised to the power fourteen.

Because it's a counter - it must have something to count.

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The IC comes with two built-in inverters - at pins 9, 10 and 11. 

And they - together with the four green components - are wired to form an oscillator.

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The output from the oscillator - at pin 9 - is switching constantly from high to low - and vice-versa. 

It's rather like the swing of a pendulum - or the ticking of a clock. 

Pin 9 is connected internally - to the input of the binary counter.

And the counter counts the ticks.

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As the count progresses - its state is reflected by the output pins. 

For example - after 8 oscillations - Q4 at pin 7 will go high.

After 16 oscillations - Q5 at pin 5 will go high.

After 32 oscillations - Q6 at pin 4 will go high.

And so on - until after 8192 oscillations - Q14 at pin 3 will go high. 

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Although the 4060 is a 14-bit counter - only 10 of those bits are available as outputs. 

Bits number 1, 2, 3 & 11 do exist within the counter.

But they're not connected to output pins.

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The speed at which the count increases depends on the frequency of the oscillator.

The higher the frequency - the faster the count will progress.

The lower the frequency - the more slowly the count will progress.

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R4 controls the speed of the oscillator.

Therefore - you can use R4 to set the length of time it will take - for any given output pin to go high.

And you can use that output pin to control the relay.

In other words - you can use R4 to set the length of the delay - before the relay energizes.

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The speed of the oscillator depends on the values of R3, R4 & C3.

While the oscillator is running - pins 9 & 10 take turns at charging and discharging C3 - through the two resistors.

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The oscillator runs because the polarity of the charge on C3 is constantly reversing. 

As a result - the junction of C3 & R4 is constantly changing from high to low - and vice versa.

So the junction of C3 & R4 is constantly changing the state of pin 11 - through R5.

And since pin 11 is constantly changing state - the polarity of the charge on C3 is constantly reversing. 

It's a sort of controlled feedback - where the frequency generated is determined by the values of R3, R4 & C3.

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The main purpose of R3 is to set an upper limit on the frequency. 

Its value was chosen to provide a minimum period of about 30 seconds at pin 7 (Q4). 

The value of R4 was chosen to provide a maximum period in excess of 24-hours at pin 3 (Q14). 

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In other words - depending on your choice of output pin - you can set the timer to re-trigger at intervals ranging from about one minute - up to at least 24-hours.

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Since the charge on C3 is constantly reversing in polarity - ideally the capacitor should be non-polarized. 

However - modern electrolytic capacitors generally have a very low leakage current - even in the reverse direction. 

So you can usually get away with using a regular polarized electrolytic capacitor.
 
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Because the minimum value of R3 + R4 is 150k - very little current will flow through the resistors. 

So - even if C3 does leak rather badly - it won't do any harm.

The worst that can happen is that the oscillator won't run. 

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It's easy to tell if the oscillator is running. 

Set R4 at about mid-point. 

And if the green LED is turning on and off at about 3-second intervals - 

The oscillator is working properly.

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When power is applied to the circuit - C2 & R9 perform an automatic reset.

So the count always starts at zero.

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To begin with - C2 is discharged. 

In its discharged state - it acts like a wire link connecting pin 12 to the positive rail.

In other words - it takes pin 12 high.

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Pin 12 is the Reset pin.

When pin 12 is taken high - all of the output pins - including your chosen range pin - will go low.

When the range pin goes low - it's connected internally to the negative line.

And it connects the negative plate of C2 to ground - through R9 & D3.

This quickly charges C2 - takes pin 12 low - and starts the count.
 
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The count proceeds at the preset speed - until your chosen range pin goes high.

When the range pin goes high - it's connected internally to the positive line.

And it does three jobs.
 
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Firstly - it takes pin 11 high - through D1.

This prevents pin 11 from changing state.

If pin 11 can't change state - the oscillator can't run.

And if the oscillator can't run - the count can't continue.

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In other words - when the range pin goes high - it will stay high - 

Because it prevents the count from proceeding any further.

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The range pin's second job is to energize the relay.

It does this by supplying base current to Q1 - through R6.

The base current switches the transistor on.

The transistor connects the negative side of the relay coil to ground.

And the relay energizes.

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At power-up - the low range pin charged C2 rapidly - through R9 & D3..

It quickly removed the positive charge - from the capacitors negative plate.

This takes the reset pin low .

 And the count begins immediately.

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The range pin's third job is to discharge C2 again - slowly.

It does this by returning the positive charge - to the capacitor's negative plate.

D2 prevents the charge from returning rapidly - through R9.

Instead - it returns slowly - through R8.

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How long the relay remains energized - depends on the value of C2 - 

And on the setting of R8.

With the values shown in the diagram - up to about six minutes is available.

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Eventually - the charge delivered by R8 - takes pin 12 high.

Then all of the output pins - including your chosen range pin - go low.

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The low range pin is once more connected internally to the negative line.

It can no longer supply base current to Q1.

So the transistor switches off - and the relay drops out.

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Since the low range pin can no longer hold pin 11 high - through D1 -

The oscillator is free to run once more.
 
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And when the low range pin takes pin 12 low - through R9 & D3 - 

The count begins again zero.

And the timer's sequence repeats.

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In other words - every time your chosen range pin goes high - the relay energizes.

It remains energized until C2 discharges through R8.

Then the relay de-energizes - and the count starts again from zero.

When the count takes your chosen range pin high once more 

The relay will re-energize

And the sequence will repeat.

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The Reset button is optional.

It discharges C2 through R10 - and takes pin 12 high.

When the button is released R9 & D3 take pin 12 low again

And the count restarts at zero.

R10 limits the peak discharge current to about 20mA.

So any small momentary-action push-to-make switch will do.

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Relay coils can produce high reverse voltage spikes that will destroy Cmos ICs.

D2 short-circuits those spikes at source - before they can do any damage.

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The remaining diodes create one-way paths.

D1 allows a high range pin to take pin 11 high - 

But it prevents a low range pin from holding pin 11 low.

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D3 allows a low range pin to charge C2 rapidly - through R9.

But it forces a high range pin to discharge C2 slowly - through R8.

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At power-up - the automatic reset guarantees that the count will always begin at zero.

For the reset to work - C2 must always begin in a discharged state.

So the moment the power is switched off - D4 connects R11 across C2.

And C2 discharges rapidly - through the resistor and the diode. 

But while the power is on - D4 blocks the connection between pin 12 and ground.

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The LEDs are there to help set up the timer.

They are not necessary to the operation of the circuit.

And you can leave them out if you wish.

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You can remove R1 and the yellow LED at any time.

But R2 and the green LED have a small effect on the speed of the oscillator.

So - if you're going to leave them out of your finished timer

Remove them before you make your final adjustment to R4.

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The purpose of R7 is to make the transistor a bit more difficult to switch on.

It connects the base of Q1 to ground - 

And it keeps the transistor switched firmly off - 

Until the count takes your chosen range pin high.

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R7 is only important at power-up.

It's there to counteract the effect of the range pin's internal resistance (impedance).

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While the range pin is low - it's connected internally to the negative line.

But there is the equivalent of (typically) about 200 ohms resistance - 

Between the external pin - and the internal ground connection.

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At power-up - and while C2 is charging - this internal resistance forms a brief potential divider with R9.

As a consequence - and for a fraction of a second - 

The voltage on the range pin rises to one or two volts.

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Even though the voltage rise is small - 

It will still supply some base current to the transistor - through R6.

And depending on the value of C2 and the gain of your transistor - 

That small base current may be sufficient to switch the transistor on - 

And so energize the relay briefly.

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The relay will only energize for a fraction of a second - 

Just long enough for C2 to charge through R9 & D3.

For lower values of C2 - it may not last long enough to be noticeable.

But adding R7 - will  prevent it from happening.

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The components used in the circuit should be widely available. However, none of them are critical. So - if you can't find the specified parts - You're certain to find something that will do just as well.

Stripboard or Veroboard is a board drilled with a matrix of 1mm holes spaced approximately 2.5 mm apart and joined in rows by copper strips. The piece used for the prototype has 18 rows with 30 holes in each - and measures about 7.5 cm by 5 cm (3" by 2"). The drawing shows the board with PCB mounting terminal blocks. But to save money and/or space - you can use veropins instead. Or you could simply solder the wires directly to the board itself.

Parts List

Click Here For A Photograph Of The Prototype.

How To Choose The Right Parts	RS Components	Rapid Electronics	Farnell Electronics

Construction Notes

Click here if you're new to constructing stripboard projects.

The terminals are a good set of reference points. To fit them, you may need to enlarge the holes slightly. Then turn the board over and use a felt-tip pen to mark the 25 places where the tracks are to be cut. Use the "actual size" drawing to Check That The Pattern is Correctly Marked .

Actual Size

When you're satisfied that the pattern is right - cut the tracks. Make sure that the copper is cut all the way through. Sometimes a small strand of copper remains at the side of the cut and this will cause malfunction. Use a magnifying glass - and backlight the board. It only takes the smallest strand of copper to cause a problem. If you don't have the proper track-cutting tool - a 6 to 8mm drill-bit will do. Just use the drill-bit as a hand tool - there's no need for a drilling machine.

Pattern for Cutting
The Tracks on the
Underside of the Board

Next - make and fit the Five Wire Links. For the links - I used bare copper wire on the component side of the board. Telephone cable is suitable - the single stranded variety used indoors to wire telephone sockets. Stretching the core slightly will straighten it - and also allow the insulation to slip off.

Next fit the nine fixed resistors - and the 2 presets. To fit the presets you may need to enlarge the holes slightly. All the fixed resistors are drawn lying flat on the board. However, those connected between close or adjacent tracks are mounted standing upright. See the Photo Of The Prototype.

The next stage is to fit the diodes - the transistor and the LEDs. Pay particular attention to the orientation of each and every component. Note that two of the 1N4148 diodes are facing up - and the other two are facing down.

Fit the remaining components - the four capacitors - the IC socket - and the relay. Pay particular attention to the orientation of the electrolytic capacitors. They generally have a stripe down the side next to the Negative terminal. Note that the two 22uF capacitors are mounted with their positive terminals facing in opposite directions. See the Photo Of The Prototype.

Turn the board over and examine the underside carefully - to make sure that there are no unwanted solder bridges or other connections between the tracks. If you backlight the board during the examination - it makes potential problem areas easier to spot. When you're satisfied that everything is in order - add the six (blue) solder bridges. These are just small blobs of solder - used to connect adjacent copper tracks.

Finish off by inserting the Cmos 4060 into the socket. Pin 1 of the IC should be in the top left-hand corner. Check that all 16 pins have entered the socket. Sometimes - instead of entering the socket - a pin will curl up under the IC.

You Are Now Ready To Test Your Circuit

Repeating Timer No.8 - Support Material

Circuit Description

Parts List

Construction Notes

Actual Size