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# A/D Converter problem...

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#### Rescue1

##### Member
Hello everybody.What I am trying to accomplish is use 6 switches that have a different resistor for each switch,and of coarse give a different voltage with each down a single wire.This part of the project is fixed and I cant change it.Also, the switches do not switch a positive,they switch a negative.This is all on a 12v system.What I want to do is get a seperate output by using a lm3914 a/d-led driver chip.The problem is the negative switching from the switches,as the lm3914 requires a positive.How can I go about converting the different negatives to a positive.When my meter is connected to the switches,positive to 12v,and the negative lead on my single wire,the voltage will change anywhere from 8v to 11.5v depending on which switch is pressed.Please help.Thank you for the time... :?

Can you draw a diagram or at least clarify what switching a negative means?

Connect the LM3914 between ground and -12 volts, ground being positive, then the switch signals will be positive relative to the LM3914 negative termenal.

crust said:
Can you draw a diagram or at least clarify what switching a negative means?

I agree with crust, it is not clear whether (by negative) you mean 0 Volt or a negative voltage. A diagram would assist us

Len

I am sorry for the confusion,as I was tired when I wrote the post,and I was a little confused myself.. ..Anyway,let me re-explain things.I have 6 normally open ,momentary resistor multiplexed switches.Now from what I know they are sent a 5v reference signal on one circuit,and another circuit senses the status of all the switches by reading the voltage drop.The computer then reads the voltage drop and sends a message down a databus(which is a whole other can of worms... :roll: ).What I am concerned with is tapping into the switches so I can use them to control other things.I believe I was wrong in picking the lm3914 as the basis for my circuit.I hope someone can steer mr in the right direction.When I was probing wires I noticed an increase in voltage when I had my "negative" multimeter lead attached to it,so I believe that there is another wire I need to find.Please help,and thank you very much for the replys....
P.S.-If it helps I have the resistance of each switches resistor...

It is impossible to comment without seeing the circuit. The description is not adequate.

Len

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