detecting a bipolar signal with Arduino

hello everyone,

I have a question about a bipolar signal issue i have with one of my machine at work. Been rattling my brain for awhile on this.

The Machine i am working is a customers machine and i am not allowed to even open the machine taking this in consideration before i start.

The Signal is comming out of a 15db pin connector with a -16v from each pin. the port does not have a postive pin or a gnd pin, just the -16v used for presence. the chasis is the postive signal. i do realize i need a +16v to complete the cirsuit, but i dont have cuase i am not allowed to tap into the machine powersupply. sounds complicated but i am stuck on this part.

i am trying to connect the arduino to every pin to keep a log and count of everytime the there is signal (presence) when a part is detected.

Can anyone here give me some kind of advice? It would be nice if i do get positive repsonds.

would really appreciate and many thanks in advance.

Gromero

opamp inverting amp circuit is the way to go.

MarkT Tried the inverting opamp. Thing is i dont have a constanat straight -16v signal from the machine only what is comming out of the 15Pin Serial port. and the signal changes according to the presences signal.

i tried using lm741 and lm358, is what i had on hand. i did a unipolar to bipolar conversion with the 5 volts from the arduino, so i get a -5v +5v. so and best i get is -1.478v

Thing is i dont have a constanat straight -16v signal from the machine only what is comming out of the 15Pin Serial port.

What do you actually have? Describe the signal so that we can understand what you are talking about.

A graph showing signal voltages versus time would be useful.

If the connector does not have a + pin or ground pin. How in the world do you get a measurement of -16? There must be some other connection for the second lead of your meter!

Paul

Paul_KD7HB:
If the connector does not have a + pin or ground pin. How in the world do you get a measurement of -16? There must be some other connection for the second lead of your meter!

Paul

I took this:

gbetromero:
the chasis is the postive signal.

... to mean that the other probe goes on the chassis and the pins go 16V below the chassis.

But then I'm wondering how the thing the db connects to in normal use, manages to detect a change on the pin if there's no "other side" in the connector?

Perhaps the body of the db, and a shield on the connector cable connected via a clamp in the connector? Didn't they work that way back in the day?

sorry guys for the late reply.

The Machine i have is a pressure mearuing tool. and all i need is the presence signals to send to a microcontroller that each fixure detected a product. and all i need a positive signal comming from the machine to an arduino to indicate presence. Keep in mind that machine belongs to my customer and i am not allowed to open it up or modify anything and all i have is the 15pin serial port to go by.

The Serial port is a 15pins. there are 12 signals out of the 15 pin from the port. there is no Ground , POsitive or +16vsignal. when I measure the Signal of each 12 pins from the 15 pin serial port with my Red wire(positive) with my meter and my black wire being (negative) to the chasis (Becuase there is no ground pins other then the chasis). i get -16v. If i measure the Pins with my Black wire( Negtaive from the meter) and Red wire to chasis (postive from the meter) i get a +16v.

i hope that is clear enough to understand.

Now i tried doing a Bipolar to Unipolar converation and followed every step from this website , which i think its a pretty good site to learn for this issue.

https://masteringelectronicsdesign.com/summing-amplifier-calculator-java/

KEEP IN MIND THE SERIAL PORT DOES NOT HAVE A POSTIVE, GROUND OR A +16v. AND I AM NOT ALLOWED TO OPEN OR MODIFY THE MACHINE

According to the Bipolar to Unipolar convertor i must need +16v and a -16v for the conversation.

Unless i am doing somthing wrong.

PLease help on this and many thanks ahead of time. really really appreciate anyhelp.

The Arduino can measure any voltages that your meter can.

Use whatever connection gives you +16V, and (for example) a 4:1 voltage divider as input to an analog input. A 33K and 10K resistor should work. But an optocoupler, with a 5-10K resistor on the LED side, would be much safer and give electrical isolation, as well as a digital readout.

Note that all electrical signals require a ground reference, so your claim that there is no ground is mistaken.

I don't see where you EVER told us what was originally connected to that connector. You keep referring to it as a serial port, which it obviously is NOT! What was the port for?

Paul

It could be an idle serial port.

jremington:
It could be an idle serial port.

Or it could be something broken inside the machine. Have you ever seen a "ground" wire melted because a fuse was incorrect value?

Paul

You know what1? If the OP's customer won't let him open the machine to diagnose the problem, then my red light goes on. I suspect the "customer" has opened the machine and broken something and now expects the OP to fix it. Has happened before!

Paul

My usual response to "you're not allowed to open this box" is to ask for the manual. If there is no manual clearly describing the communication protocol then you are SOL.

You do know the RS232 standard don't you? It uses negative voltages as signals. It is a very old standard from before "HIGH" and "LOW" were standardized.

You say there is no ground. Well you must have had the second probe from your multimeter touching something to measure -16V. Use that as your reference. Sometimes the metal shell of the DB connector is the best reference. I buy 9-pin D-sub connectors with solder lugs on the shell for exactly that.

Paul I think the same as you, If the customer doent let me touch the machine then he must of did somthing for his own use.

I want to add a picture so i can show you guys what i have and working with. Its just a 15pin port thats it. i just have the pins to work and the chasis which iuse as second point to measure from.

Arduino doesnt pick up negtaive signals which i tried on both Analog and digital pics with the bipolar to unipolar opamp convertor. Arduino will pick up signal from anything above 0 up to 5 volts. anything from above 5 volts i use opto couplers.

I hope i am not wasting your guys time. but i am in a pickle on this one

i am not a novice in electronics and full knowledgable of how industrial devices function. But i had never came across something like this.

Earlier you wrote: "The Machine i have is a pressure mearuing tool. and all i need is the presence signals to send to a microcontroller that each fixure detected a product. and all i need a positive signal comming from the machine to an arduino to indicate presence.".

What happens to the signal when a pressure is measured?

Paul

gbetromero:
Arduino doesnt pick up negtaive signals which i tried on both Analog and digital pics with the bipolar to unipolar opamp convertor. Arduino will pick up signal from anything above 0 up to 5 volts. anything from above 5 volts i use opto couplers.

Assuming you can make a complete circuit, would not an optocoupler suffice?

Hey Paul,

The machine measures the PSI of tubes, once the tube pass/fail the pressure test or reaches the proper PSI it indicates pass or fail.

there are 4 Presences sensors which are the pins from 9 - 12. which is what i want to read keep count with an arduino.

there are 4 pass which are the pins from 1,3,5,7
there are 4 fail which are the pins from 2,4,6,8
pins 13, 14, 15 have no connectons

chasis is Positive
every pin from the 15pin serial port is -16v not including 13,14,15

Other that the machine is working fine

see the pic i just create, what you see on the drawing is all i got to work with.

Thank you so much Paul for being patient, i really appreciate your help.

gbetromero:
Hey Paul,

The machine measures the PSI of tubes, once the tube pass/fail the pressure test or reaches the proper PSI it indicates pass or fail.

there are 4 Presences sensors which are the pins from 9 - 12. which is what i want to read keep count with an arduino.

there are 4 pass which are the pins from 1,3,5,7
there are 4 fail which are the pins from 2,4,6,8
pins 13, 14, 15 have no connectons

chasis is Positive
every pin from the 15pin serial port is -16v not including 13,14,15

Other that the machine is working fine

see the pic i just create, what you see on the drawing is all i got to work with.

Thank you so much Paul for being patient, i really appreciate your help.

Well, since nothing happens to those voltages when the machine is working, the whole thread is pointless and should never have gotten beyond the first 2-3 posts.

Paul

Optocoupler. Something like this https://www.mouser.com/ProductDetail/Vishay-Semiconductors/ILQ620?qs=sGAEpiMZZMteimceiIVCBwfsK9X9U0O6WdK%2FXVVOvcE%3D