Need some help on this Project

[Carlos Nunes]

Hello everyone

I need some help because being new to electronics ando n a course we came to a final Project.

First I choose the battery-level-indicator at https://www.electronicspoint.com/ but then I’ve decided to go for the luggage-security-alarm-project-circuit on the same site but the first thing I have to do is draw the circuit with Multisim 14 and test it there before I go any further. I’ve done that but it seems to be everything ok but the relay does not act after the switch I’ve got to simulate the alarm ring.

I’m sending the Multisim file if that can help you see what I mean.

Another thing, what’s the use of the 0,1 uF capacitor rand the 2 resistors, one 1kohms and the 4,7Kohms.

I’ve got na lamp to simulate the buzer and the lamp does not go on, off course because the relay does not switch on the circuit.


Thank you so much for you precious help.


Regards

Carlos

 

[gunnadoo]

hi carlos , i am new too. i am probably wrong but the catch diode on the relay looks the wrong way around

 

[Carlos Nunes]

hi carlos , i am new too. i am probably wrong but the catch diode on the relay looks the wrong way around

Thank you Gunnadoo. I've done the change as you sugested on Multisim 14 and it did work but that depends on the use of that diode. I think it's for the transistor protection and according to the original circuit it is as it was.

 

[kellys_eye]

There is no purpose to the logic gates - logic 1 in, logic 1 out, they may as well be replaced by a wire!

The relay should be in the collector circuit and the diode polarity reversed.

 

[Carlos Nunes]

There is no purpose to the logic gates - logic 1 in, logic 1 out, they may as well be replaced by a wire!

The relay should be in the collector circuit and the diode polarity reversed.

Hi Kellys_eye
Thank you very much.
I've tried that on the Multisim and it did work.
Regards

 

[Carlos Nunes]

There is no purpose to the logic gates - logic 1 in, logic 1 out, they may as well be replaced by a wire!

The relay should be in the collector circuit and the diode polarity reversed.

What is the function of that Diode?

 

[Audioguru]

The circuit and maybe the website it comes from is full of errors so why is it going to be your "learning how to solder" final project?
1) The entire project is completely useless. The relay can be driven by the wire loop and a battery directly, without the IC, transistor, capacitor, resistors and diode.
2) The diode is shown backwards.
3) The transistor is wrongly shown as an emitter-follower instead of as a switch.

Here is why it does not work:
1) Maybe your sim program knows that a 5V relay needs at least 4V to work and that its coil current is about 70mA.
2) With an emitter current of 70mA the BC547 has a current gain of about 150 then its base current is about 0.5mA.
3) The schematic does not show a part number for the IC but the text in the project says it is a CD4011. With a 5V supply and a 0.5mA load, the output high of the IC is about 4.5V.
4) Then the 4.7k base resistor for the transistor should be removed then the relay coil gets the 4.5V minus the 0.7V base-emitter voltage which is 3.8V then the relay might work but probably will not work.

 

[Carlos Nunes]

The circuit and maybe the website it comes from is full of errors so why is it going to be your "learning how to solder" final project?
1) The entire project is completely useless. The relay can be driven by the wire loop and a battery directly, without the IC, transistor, capacitor, resistors and diode.
2) The diode is shown backwards.
3) The transistor is wrongly shown as an emitter-follower instead of as a switch.

Here is why it does not work:
1) Maybe your sim program knows that a 5V relay needs at least 4V to work and that its coil current is about 70mA.
2) With an emitter current of 70mA the BC547 has a current gain of about 150 then its base current is about 0.5mA.
3) The schematic does not show a part number for the IC but the text in the project says it is a CD4011. With a 5V supply and a 0.5mA load, the output high of the IC is about 4.5V.
4) Then the 4.7k base resistor for the transistor should be removed then the relay coil gets the 4.5V minus the 0.7V base-emitter voltage which is 3.8V then the relay might work but probably will not work.

Thank you so much for your help. It was a very detailed help.
Withe the test on the Multisim simulator I took out the relay coil, after all I've seen no use for it as well.
I've choosen this circuit because it was a simple one and we will have a litte time to finish it so I'm no so worried.
Can you please tell me what is the use of the Capacitor of 0.1uF and the 1k resistor? The 4,7k after the NAND gates was causing a drop of voltage but anyway I dont have the relay now.
Thank you Audioguru

 

[Audioguru]

The capacitor might prevent a nearby radio station transmitter from activating the relay when the wire loop is cut.
The 1k resistor causes the input of the useless logic circuit to be high when the wire loop is cut and prevents the wire loop from shorting the 5v power supply when the wire loop is intact.
The 4.7k resistor causes a voltage drop because it is not needed with an emitter-follower transistor.
The relay is needed if the alarm buzzer or light uses a high current or high voltage electricity.

Why don't you select a useful project from a website that has no circuit errors?
Show your teacher that you learned not to drip solder onto a soldered joint.

 

[Carlos Nunes]

The capacitor might prevent a nearby radio station transmitter from activating the relay when the wire loop is cut.
The 1k resistor causes the input of the useless logic circuit to be high when the wire loop is cut and prevents the wire loop from shorting the 5v power supply when the wire loop is intact.
The 4.7k resistor causes a voltage drop because it is not needed with an emitter-follower transistor.
The relay is needed if the alarm buzzer or light uses a high current or high voltage electricity.

Why don't you select a useful project from a website that has no circuit errors?
Show your teacher that you learned not to drip solder onto a soldered joint.

Thank you so much for you help.
I'll check arround for another project. The problem is the time I've got to do it. That's why I choose a simple one because I still have to do the circuit board.
With your experience can you sugest a site?
Once again, thank you very much

 

[Audioguru]

Sorry, I have never looked at sites with simple school projects until you posted that wrong and useless circuit. Look at www.555-timer-circuits.com where there are many simple circuits but most are missing an important supply bypass capacitor that is mentioned on the LM555 datasheet.

 

[Carlos Nunes]

Sorry, I have never looked at sites with simple school projects until you posted that wrong and useless circuit. Look at www.555-timer-circuits.com where there are many simple circuits but most are missing an important supply bypass capacitor that is mentioned on the LM555 datasheet.

LoooL
You right, useless circuit. When I finnish this course I'll check for better circuits and get a better cource as well.
Thank you very much for your help. It was great.
I'll check that site you've sent the link.
Regards