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Help with alarm clock / comparator circuit

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ericgibbs

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Agreed. But if the diode as shown isn't for spike suppression what is it for? It seems redundant.
Further, the comparator shown in the sketch is wired with the wrong polarity; its output goes high when the alarm input goes above 3V.

hi,
I also think the circuit is rubbish, but all the OP asked for, was to name the components.:rolleyes:
 

sick_kent

New Member
Hi,
if the circuit is rubbish,
do you know where i could find an alarm clock circuit that is good in theory and explain it?

Any help much appreciated
 

ericgibbs

Well-Known Member
Most Helpful Member
Hi,
if the circuit is rubbish,
do you know where i could find an alarm clock circuit that is good in theory and explain it?

ny help much appreciated
hi,
When you say alarm clock, do you mean a Timer that sounds an alarm/buzzer after a preset time.??

Or do you mean a 'real time clock' that shows the time of day and has a settable alarm.?
 

ericgibbs

Well-Known Member
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sick_kent

New Member
sorry, the circuit in post 7 will have to do as we are doing an assignment on simple circuits, would you be able to explain how the circut works though?
 

ericgibbs

Well-Known Member
Most Helpful Member
sorry, the circuit in post 7 will have to do as we are doing an assignment on simple circuits, would you be able to explain how the circut works though?

hi,
For a homework assignment, you should post an explanation on how you think the circuit works and we can check it for you.:)
 

sick_kent

New Member
Well,
i know that 12V flows out of the battery and into R1 with 3V flowing into the operational amplifier, alsosome current flows into the operational amplifier which has not been through a resistor and enters the amplifier from the side which i am unsure what this means. Now some current flows into the relay contacts but the contacts don't make contact as there has to be current through the coil for them to make contact. The horn is sounded when the relay contacts make contact.

So basically I am unsure about what the operational amplifier does and the operation of the thing that says ALARM.
 

ericgibbs

Well-Known Member
Most Helpful Member
hi,
I will give a quick explanation.
Resistors R1 and R2 divide the 12V, so that there is a 3Volt DC level at the junction of the resistors. This 3V reference is connected to a comparator input [-Vsignal input].

When the input voltage at +Vsignal pin of the comparator, from the 'alarm' [ which could be almost any type of sensor, ie: thermistor, photo diode] is LESS than the Vref on the -Input the OUTPUT of the comparator will be 0V.
This means the relay coil will not be powered [ energised] so the realy contacts will be open. As the contacts are open the Horn gets no voltage and will not sound.

When the 'alarm' input voltage becomes greater than the 3 V ref, the output of the comparator will switch to a high voltage,, say about 10V, so the relay coil will be energised, the contacts will close and the horn will sound.

So the triangle is a COMPARATOR, it compares the Vref and Alarm voltage and controls the relay
 
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alec_t

Well-Known Member
Most Helpful Member
@sick_kent
I think from your post #28 that it would be helpful for you to go back to basics and get a thorough understanding of the difference between voltage and current before you try analysing this circuit. Then google for a tutorial on op-amps.
 

sick_kent

New Member
ok that's starting to make sense,

however i looked up a tutorial of an op amp and am starting to understand, found a helpful diagram which is also below,

but if the diagram below is right how can current flow from both directions, as i thought that it only flowed from positive to negative as is indicated by the arrow I added.
 

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ericgibbs

Well-Known Member
Most Helpful Member
ok that's starting to make sense,

however i looked up a tutorial of an op amp and am starting to understand, found a helpful diagram which is also below,

but if the diagram below is right how can current flow from both directions, as i thought that it only flowed from positive to negative as is indicated by the arrow I added.

Hi,
Conventional current flow is from positive to negative.

Dont confuse the symbols on the OPA terminals with current flow.
These symbols only indicate whether the input voltage to the OPA output will be inverted or not.
All that means is that a positive voltage in the OPA -inv input will make the output voltage go negative, ie : LESS than 1V.
A negative input in -inv input would make the output go more positive.
That is the signals on the -inv will appear on the output in the opposite voltage direction, INVERTING the signals

For the +input , often marked +inp, input voltages are not inverted, so if you input a negative voltage the output will go more negative, for a positive input voltage the output will go more positive. ie: NON inverting the signals.
Do you follow.?
 
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