I dont know what is wrong.

[jeyes56]

hi, im new here, and i don't know where to post my question, please correct me where to post this...

I'm making a simple project.
i want to trigger the relay when my cellphone rings or vibrate.

what i did was, i remove the vibrator from the cellphone and solder 2 wires from where the vibrator is attached.

i connect the to wires to an non inverting OP AMPS (LM741).

My problem is:
when the cellphone rings (and supposed to vibrate) i get an output voltage of around 8v (or greater than 6v) from the op amp.
i also get the same voltage when the cellphone is not ringing, w/c is supposed to be lower than 6v. (based from different simulators i used).

the voltage output from the vibrator of the cellphone is 0V (not ringing) and 1.5V (ringing).

what is wrong with my circuit?

i will provide the circuit diagram.

**broken link removed**

 

[ericgibbs]

hi,
Try connecting a 47K resistor from the +vin [non inverting] of the 741 and 0v.

 

[jeyes56]

oh, i already disconnected the + input and is not connected anywhere, the output is the same, 8v.
i connect 10k resistor between the input and the ground, but still the same output.

does it really need an negative input to the negative terminal

 

[ericgibbs]

oh, i already disconnected the + input and is not connected anywhere, the output is the same, 8v.
i connect 10k resistor between the input and the ground, but still the same output.

does it really need an negative input to the negative terminal

hi,
What is the output when you connect +vin [NI] directly to 0V.??? let me know

 

[jeyes56]

hi,
What is the output when you connect +vin [NI] directly to 0V.??? let me know

the output is the same.

do i really need to put a +9v to the + source for op amp and -9v for negative source? this means having two different sources.

does my ic is damage? how to determine that?

 

[ericgibbs]

the output is the same.

do i really need to put a +9v to the + source for op amp and -9v for negative source? this means having two different sources.

does my ic is damage? how to determine that?

hi,
IF the circuit is connected as you have shown, when you connect NI of the OPA to 0V, you should get about +1V or so on the output.!

What was the output of the 741 connected too.???

 

[jeyes56]

the output is not connected anywhere.
i intended to connect it in an 6v relay, but before connecting, this problem occurs,
(relay is not yet connected).


P.S. I'm having slow loading connecting in this website, i don't know why, but my computer loads fast in other website.

 

[crutschow]

An 741 will not work to ground with only one power supply. You need both a plus and minus supply, or get an op amp designed for rail-to-rail operation.

Also all op amp inputs need a DC path to ground for the input bias current. You can not connect the input through a diode without adding a resistor to ground.

 

[jeyes56]

An 741 will not work to ground with only one power supply. You need both a plus and minus supply, or get an op amp designed for rail-to-rail operation.

Also all op amp inputs need a DC path to ground for the input bias current. You can not connect the input through a diode without adding a resistor to ground.

thank you for your reply.
how can i have both positive and a negative voltage having a only one source?
i think there's an IC for that but I'm not really sure.

 

[Nigel Goodwin]

Presumably this is a more sensible post than your other completely vague one?.

Also, presumably, you are simply wanting to switch a relay?.

You don't need an opamp (and one would be a really bad choice), just a simple NPN switching transistor, check my tutorial hardware extras, the fifth diagram:

 

[jeyes56]

ok, how can i switch a 6v relay from a 1.5v?
im thinking of amplifying the 1.5v to a 6v or higher.

i'm also thinking how to amplify that using a transistor.
https://www.electro-tech-online.com/threads/amplifying-1-5v-to-7v.117595/

can you suggest how to switch a relay with 1.5v?

 

[audioguru]

The lousy old 741 opamp is 43 years old and was designed to use a plus 15V and minus 15V supply.
Its inputs don't work if they are within 3V from the positive supply or the negative supply and since your circuit doesn't have a negative supply then the inputs don't work.

Use an MC34071 opamp that works when the supply is 3V to 44V. Its inputs work all the way down to ground in your circuit if the (+) input has a 100k resistor to ground.

Opamps have a fairly low output current so select a relay that uses low coil current.

 

[jeyes56]

Presumably this is a more sensible post than your other completely vague one?.

Also, presumably, you are simply wanting to switch a relay?.

You don't need an opamp (and one would be a really bad choice), just a simple NPN switching transistor, check my tutorial hardware extras, the fifth diagram:

can you please suggest what type of transistor is to be used? im not familiar with the types, you may also want to specify the value of resistors to be used.

 

[Nigel Goodwin]

ok, how can i switch a 6v relay from a 1.5v?
im thinking of amplifying the 1.5v to a 6v or higher.

i'm also thinking how to amplify that using a transistor.
https://www.electro-tech-online.com/threads/amplifying-1-5v-to-7v.117595/

can you suggest how to switch a relay with 1.5v?

I've just shown you - it couldn't be much simpler.

 

[Nigel Goodwin]

can you please suggest what type of transistor is to be used? im not familiar with the types, you may also want to specify the value of resistors to be used.

The resistor is shown as 1K, which should be fine, the transistor depends on the relay - but something like a BC107 (general purpose NPN) should be OK for most small relays.