# Pls Help for build cable tester

#### sathikul

Joined Apr 14, 2014
8
I would like to create a circuit for testing the cable (with 3 point connector). My requirement is 3 LED (for show the each cable point is OK) and a buzzer for all the 3 point OK. Please help me with some ideas (sathikul @hotmail .com ) is my email. Thank you very much.

Joined Jul 18, 2013
23,339
Continuity or insulation?
Both?
Max.

#### sathikul

Joined Apr 14, 2014
8
Continuity . Using the DC.

#### sathikul

Joined Apr 14, 2014
8
I worked out some simple way to test the cable, but i need help to combine the both circuits. Thanks.

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#### ErnieM

Joined Apr 24, 2011
8,167
I worked out some simple way to test the cable, but i need help to combine the both circuits. Thanks.
Where is the cable? I see batteries buttons and LEDs.

#### sathikul

Joined Apr 14, 2014
8
Please assume the button as wire (cable for testing). I thinking if anybody could help me using the 4073 AND gate....

Joined Jul 18, 2013
23,339
You could use an opto in series with each LED, parallel the output emitters of the opto and feed the base of a transistor suitable to supply the buzzer.
Max.

#### shteii01

Joined Feb 19, 2010
4,644
Or feed the led to the AND gate instead of ground. Connect the output of the AND gate to the buzzer. When all three LED are ON, the inputs to the AND gate are ON, then the output of the AND gate is ON.

#### djsfantasi

Joined Apr 11, 2010
7,749
Max - I'd like to see a schematic. Paralleling the optos outputs doesn't make sense to me.

Shteii01 - Same request. I don't understand how the input of the 4073 can sink current to light the LEDs? And when there is a cable break, won't the input float?

#### shteii01

Joined Feb 19, 2010
4,644
Shteii01 - Same request. I don't understand how the input of the 4073 can sink current to light the LEDs? And when there is a cable break, won't the input float?
Good points.

I looked at TI 3 input AND gate ic. If I am reading datasheet right, the inputs of the AND gate can sink uA. So typical 15-20 mA coming out of LED is too much. Use buffer between led and AND gate?

As far as float condition. Use pull down resistors on the AND gate inputs.

But that brings another question. Can AND gate output source necessary current to get the buzzer buzzing? Off hand I think not. So probably use transistor as a switch.

Joined Jul 18, 2013
23,339
Max - I'd like to see a schematic. Paralleling the optos outputs doesn't make sense to me.
Open collectors are commonly paralleled for a OR function, parallel the emitters and it is a NOR function.
Max.

#### djsfantasi

Joined Apr 11, 2010
7,749
Open collectors are commonly paralleled for a OR function, parallel the emitters and it is a NOR function.
Max.
Thanks. Let me chew on that.

#### sathikul

Joined Apr 14, 2014
8
I try this circuit using simulator, but please comment.

Please assume the switch as the cable connector (If the cable is broken then it open & If the cable is OK then it closed).

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#### djsfantasi

Joined Apr 11, 2010
7,749
Sathikul - what happened in the simulator?

Max - I tried to draw a schematic and write a truth table for the circuit as I see it described by you. I only included two pair, as it can easily be generalized to 3 or more pairs. As hopefully you can see too, I don't think that the NOR function is what is required here. Please explain where I am going wrong.

A basic drawing of the circuit follows:

The output of the paralleled optos is negated (~b1) by the transistor driving the buzzer.

For the truth table for this circuit, I get:

This sounds when all cable pairs are bad. It sounds the buzzer when all pairs are good OR if some of them are bad. I believe the OP wanted to buzzer to sound if only all pairs are good.

I am an intermediate hobbyist, so please explain where I might be wrong.

Thanks, Max.

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Last edited:

Joined Jul 18, 2013
23,339
How is this?
Max.

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#### inwo

Joined Nov 7, 2013
2,419
Or this?..............................

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#### shteii01

Joined Feb 19, 2010
4,644

#### sathikul

Joined Apr 14, 2014
8
Thanks guys,

I like the inwo idea, but its seem give different output, I'm attached the simulation output...

The LED only works if the all the cable is OK.

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#### shteii01

Joined Feb 19, 2010
4,644
Thanks guys,

I like the inwo idea, but its seem give different output, I'm attached the simulation output...

The LED only works if the all the cable is OK.
Back to the AND gate then.