The prototypes of the 24-Hour Timers were both built using only the Stripboard Layouts as a guide. So - if you have faithfully reproduced one of those layouts - 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.

Circuit No.1 - Setup

Click Here For A Photograph Of The Prototype

Connect a temporary Range link to Pin 4 of the IC. Connect two lengths of wire to the Reset terminals. Strip the ends of the two wires - but keep them separate from one another. 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 Blue LED in the diagram - to distinguish them from each other - and from the LEDs already on the board. But you can use whatever colour LEDs you have available. ========= Finally, connect the 12-volts DC to the input terminals. Pay particular attention to the polarity of the supply. Note that the negative connection goes to the bottom terminal. Before you switch on the power - turn R4 all the way to the left. ========= Turn On The Power The Blue LED should light and remain lit. This indicates that the relay's normally-closed contact is working properly. The Green LED should turn on and off at roughly 2-second intervals. This indicates that the oscillator is working properly. ========= When the Green LED switches Off for the Eight Time - the Yellow LED should light. This indicates that the binary counter is working properly. Allow the timer to continue to run. When the Yellow LED switches Off for the Second Time - the relay should energize. As it does so - the Blue LED should turn off - and both the Red and Green LEDs should light and remain lit. All of this indicates that the timer has performed its task correctly. ========= Repeat the test by briefly touching together the ends of the two wires connected to the Reset terminals. The relay should de-energize. The Red LED should turn off. The Blue LED should light. And the Green LED should once again begin to turn on and off at about 2-second intervals. All of this means that the Reset is working properly. Repeat the test as often as you like - until you're satisfied that your timer is working reliably. ========= Next - switch off the power for a few seconds. Turn R4 about one-third of the way to the right. And measure the time it takes from the moment power is applied - to the moment the Yellow LED lights for the first time. The further to the right you turn R4 - the longer it will take to light. Repeat this procedure as often as necessary - adjusting R4 each time - until the time taken for the Yellow LED to light is 45 seconds. ========= When you're satisfied with the setting - touch the two Reset wires together briefly - to restart the timer. The relay should energize three minutes after the Reset wires have been separated. This shows that the timer adjustment is working properly. ========= Your circuit is now ready to use. Remove the temporary Range link. Choose the Range you want to use - and adjust R4 to give the time period you require. =========

Circuit No.2 - Setup

Click Here For A Photograph Of The Prototype

Connect a temporary Range link to Pin 4 of the IC. Connect two lengths of wire to the Reset terminals. Strip the ends of the two wires - but keep them separate from one another. 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 Blue LED in the diagram - to distinguish them from each other - and from the LEDs already on the board. But you can use whatever colour LEDs you have available. ========= Finally, connect the 12-volts DC to the input terminals. Pay particular attention to the polarity of the supply. Note that the negative connection goes to the bottom terminal. Before you switch on the power - turn R4 all the way to the left. ========= Turn On The Power The relay should energize and the Red LED should light and remain lit. This indicates that the relay's normally-open contact is working properly. The Green LED should turn on and off at roughly 2-second intervals. This indicates that the oscillator is working properly. ========= When the Green LED switches Off for the Eight Time - the Yellow LED should light. This indicates that the binary counter is working properly. Allow the timer to continue to run. When the Yellow LED switches Off for the Second Time - the relay should de-energize. As it does so - the red LED should turn off - and both the Blue and Green LEDs should light and remain lit. All of this indicates that the timer has performed its task correctly. ========= Repeat the test by briefly touching together the ends of the two wires connected to the Reset terminals. The relay should energize. The Blue LED should turn off. The Red LED should light. And the Green LED should once again begin to turn on and off at about 2-second intervals. All of this means that the Reset is working properly. Repeat the test as often as you like - until you're satisfied that your timer is working reliably. ========= Next - switch off the power for a few seconds. Turn R4 about one-third of the way to the right. And measure the time it takes from the moment power is applied - to the moment the Yellow LED lights for the first time. The further to the right you turn R4 - the longer it will take to light. Repeat this procedure as often as necessary - adjusting R4 each time - until the time taken for the Yellow LED to light is 45 seconds. ========= When you're satisfied with the setting - touch the two Reset wires together briefly - to restart the timer. The relay should de-energize three minutes after the Reset wires have been separated. This shows that the timer adjustment is working properly. ========= Your circuit is now ready to use. Remove the temporary Range link. Choose the Range you want to use - and adjust R4 to give the time period you require. =========

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.

If you've built your circuit using the specified components - and you've followed the step-by-step construction guide described on the 24-Hour Timer - 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.

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. If you've used a transistor other than the one specified - check its pin configuration. Just because it looks the same as the specified transistor - don't assume that the pin configuration is also the same.

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 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 - and backlight the board. It only takes the smallest strand of copper to cause a problem.

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 or other connections between the tracks. Your felt-tip markings will tell you which ones should be there - and help you identify any that shouldn't be there. If you backlight the board during the search - it'll make them 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 and the transistor. If the oscillator is not running perhaps C3 is leaking. Take your time and examine each individual component carefully.