An LDR allows you to set the level of darkness required - before this repeating timer will start to run.

COMMENTS SUGGESTIONS	Repeating Timer No.4 - Testing Your Circuit	MORE TIMER CIRCUITS

Timer No.4 Schematic	The Rest of Ron's Circuits	Write To Ron	More Free-to-Use Circuits	Circuit Exchange International

Repeat Timer No.4 - Support Material

Do not use the "on-board" relay to switch mains voltage. The board's layout does not offer sufficient isolation between the relay contacts and the low-voltage components. If you want to switch mains voltage - mount a suitably rated relay somewhere safe - Away From The Board.

Introduction

The prototype of the Repeating Timer No.4 was built using only the Stripboard Layout as a guide. So - if you have faithfully reproduced that layout - you will have a working circuit.

Once you're satisfied that your layout is correct - and you have made a careful and thorough check of the underside of the board - it's time to power-up the circuit and test its operation. This is always an anxious moment. If you construct a lot of circuits - you might consider building the Current Limiting Power Supply - or alternatively - you could add the Simple Current Limiter to your existing PSU. Both will let you set an upper limit on the amount of current supplied to your circuit - and so protect it from any serious damage.

Setup

Click Here For A Photograph Of The Prototype

Details of How to Prepare The
Repeating Timer No.4 - For Testing

A resistor and a couple of LEDs are all that's needed to demonstrate that the relay is working properly. 

Connect a 2k2 resistor between the  Pole and the Positive terminals. 

Connect two LEDs from the N/O and N/C terminals to the Negative terminal. 

I used a red and a green LED in the diagram - so that I can distinguish between them.

But you can use whatever colour LEDs you have available. 

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Next - connect the 12-volts DC to the input terminals. 

Pay particular attention to the polarity of the supply. 

Note that the positive connection goes to the top terminal. 

Before you switch on the power - turn R2, R3 & R7 all the way to the left.

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When you switch on the power - the relay may or may not energize immediately.

It all depends on the switching characteristics of the actual gates you are using.

That is - it depends on whether your 4011 powers up with pin 3 high or low.

If the relay doesn't energize immediately - wait 30 to 60 seconds.

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When the relay energizes - the green LED should switch off - and the red LED should light.

It should remain lit for about 30 to 60 seconds.

Then the relay should de-energize - the red LED should turn off - and the green LED should light.

It should remain lit for about 30 to 60 seconds.

Then the relay should energize again - and the red LED should light.

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The circuit should continue switching back and forward - between the red and green LEDs - at 30 to 60 second intervals.

It's likely that the two intervals will be different lengths.

This is not a fault. It's caused by the switching points of the actual gates you're using.

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Allow the switching to continue - until you're satisfied that your circuit is working reliably.

Then turn (R3) a little to the right - see the photo of the prototype.

The relay should continue to energize for 30 to 60 seconds - as before.

But now - it should remain de-energized for a longer period - say about 3 to 5-minutes.

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When you're satisfied your circuit is wotking as described - turn R3 all the way back to the left.

Then turn R2 a little way to the right.

Now - the relay should remain energized for - about 3 to 5-minutes.

And remain de-energized for 30 to 60 seconds

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When you're satisfied your circuit is working as described - turn R2 all the way back to the left.

This should restore the shorter on/off cycle.

Let it run for a few cycles - then turn R7 all the way to the right.

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This should stop the timer.

If the relay is de-energized - it should remain de-energized.

If the relay is energized - it should stay that way for the balance of its 30 to 60 second time period.

Then it should de-energize - and remain de-energized.

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Do this next bit in a subdued light.

It doesn't need to be too dark.

We're trying to simulate dusk or dawn.

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When you're satisfied that the timer has stopped completely - place your hand over the LDR - so as to shade it from what little light is available.

It doesn't need to be in complete darkness.

It just needs to be significantly darker than the surroundings.

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Next - turn R7 slowly to the left.

Do this in a series of small discrete steps.

You're looking for the point where the relay just begins to operate again.

With your hand still in place - let the timer run for a few cycles - to confirm that it's operating correctly.

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Then remove the shadow of your hand from the LDR.

If you've adjusted R7 correctly - the timer should stop.

And when you restore the shadow - the timer should start up again.

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Remember - if the relay is energized when you remove the shadow - it will not drop-out immediately.

You have to wait for what remains of the relay's 30 to 60 second time period to expire. 

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The same is true when you apply the shadow.

You may have to wait for the remainder of the 30 to 60 second "off" time period to expire - before the relay will energize.

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Using the shadow of your hand, continue to stop and start your timer - until you're satisfied it's working reliably.

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If You Find a Problem

If - in the course of the test - you find that something is not working properly - then a careful inspection of the relevant area of the circuit board should turn up the cause of the problem. Where you've cut the board to size - look for small loose strands of copper left behind by the saw. Check the board for short-circuits caused by component leads touching each other. If an LED is not lighting - check that it's connected the right way round. It can also happen that the stripboard itself is faulty. I have seen cases where the copper tracks have not been completely severed from one another during manufacture.

If you've built your circuit using the specified components - and you've followed the step-by-step construction guide described on the Repeating Timer No.4 - Support Page - then the chances are that any bug will be caused by something minor - a component connected the wrong way round - a missing or unwanted solder bridge - an incomplete cut in the track etc.

If you can't see anything obvious then adopt a systematic approach to faultfinding. Begin by double-checking that all of the cuts in the tracks have been made, that they are all - In The Right Place - and that they sever the track completely. Use a magnifying glass. It only takes the smallest strand of copper to cause a problem. If you backlight the board during the examination - it makes them easier to spot.

When you're satisfied that the tracks have been severed in all the right places, check that you have made - and correctly placed - all of the solder bridges. Mark each bridge with a felt-tip pen - or something similar - so that it can be easily identified later.

Next - carefully examine the full length of each track. Look for unwanted solder bridges. Your felt-tip markings will tell you which ones should be there - and help you identify any that shouldn't be there. Again, if you backlight the board during the examination - it makes potential problem areas easier to spot.

If all else fails and you still haven't found the cause of the problem - work your way through the assembly instructions on the Support Page. Check each individual component and link - to make sure that it's present and correctly positioned.

Print out the drawings and mark off the components as you go. Pay particular attention to the orientation of the diodes, the transistor and electrolytic capacitors. Take your time and examine each individual component carefully.

Repeating Timer No.4 - Support Material

Repeating Timer No.4 Schematic	The Rest of Ron's Circuits	Write To Ron	More Free-to-Use Circuits	Circuit Exchange International

Repeating Timer No.4 - Testing Your Circuit

Introduction

Setup

If You Find a Problem