nodusdesign

Joined Oct 19, 2021
1
Hello all,
I'm here to ask for advice on a circuit I'm redesigning from my original, that used an Arduino, to a more elegant (and less power hungry) logic circuit.

It is what I would have called simple before playing with it but have run into some problems.

The circuit is checking for continuity and shorts on a part. There are 6 pins (1, 2, 3, 4, 5, and 6) and the goal is to make sure there is a short between 1&2, 3&4, and 5&6 while at the same time ensuring there is NOT a short between 1 and 3-4-5-6, between 2 and 3-4-5-6, between 3 and 1-2-5-6, between 4 and 1-2-5-6, between 5 and 1-2-3-4, between 6 and 1-2-3-4.

On my circuit that I tried, it seems that in pulling up one pin to test for continuity with its pair I unintentionally short it with the pins I'm testing for shorts for through the power rail.

I've considered somehow using opto-couplers, but have never used them before and unsure of how to proceed.

To sumerize in a different way, this is what I need to check for all simultaneously:
Pin 1 connected to 2 but not 3, 4, 5, 6
Pin 2 connected to 1 but not 3, 4, 5, 6
Pin 3 connected to 4 but not 1, 2, 5, 6
Pin 4 connected to 3 but not 1, 2, 5, 6
Pin 5 connected to 6 but not 1, 2, 3, 4
Pin 6 connected to 5 but not 1, 2, 3, 4

To give a bigger picture, this will be in a handheld box, it will be powered from a 9V battery (this is flexible), it will have a green LED showing good if it passes all checks, and it will have a red LED and a buzzer if it fails one or more of the [30] checks.

ericgibbs

Joined Jan 29, 2010
14,130
The circuit is checking for continuity and shorts on a part. There are 6 pins (1, 2, 3, 4, 5, and 6) and the goal is to make sure there is a short between 1&2, 3&4, and 5&6 while at the same time ensuring there is NOT a short between 1 and 3-4-5-6, between 2 and 3-4-5-6, between 3 and
hi nodu
I would suggest you do not use the word short for a circuit you are testing for Continuity

Pin 1 continuity to 2 but not 3, 4, 5, 6

What IC's do you have available for the project.?
E

AnalogKid

Joined Aug 1, 2013
9,479
You are correct in that you need some form of isolation among the connections. What you are missing are diodes.

There is no static circuit that will do what you want, but a continuous scanner will. Are the connections inside the "part" purely resistive, as in wire or PCB trace, or are there other active or passive electronic components in there?

AND - if all you are after are reductions in SWAP (Size, Weight, and Power), then a PIC can do this for less than 100 uA (plus the LED current).

ak

mtedaldi

Joined May 10, 2021
2
You are correct in that you need some form of isolation among the connections. What you are missing are diodes.

There is no static circuit that will do what you want, but a continuous scanner will. Are the connections inside the "part" purely resistive, as in wire or PCB trace, or are there other active or passive electronic components in there?

AND - if all you are after are reductions in SWAP (Size, Weight, and Power), then a PIC can do this for less than 100 uA (plus the LED current).

ak
I think it should be possible with as a static design with the help of some resistors and some window comparators...

Just put a resistor between 2 and 3 as well as 4 and 5. Connect V+ to 1 and 6 to VCC and check the voltages at 2 and 4.

best regards, Marco

Wolframore

Joined Jan 21, 2019
2,386
I also recommend going to an ATTINY or similar, you will make you 9V battery last much longer. However, I would also advise to figure out a better power source, 9V batteries are very low capacity and have a high cost. Generally logic chips are less efficient and more so if you need multiples to get the job done.