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Need to know if this can be done... kinda sorta urgent

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New Member
First off, I'm extremely new at this... but I aint no fool

I need a chip/curcuit (maybe single chip??) to read in 3 different wires and for each wire output two others (ie: 3 in | 6 out), but they all need to be different resistances... so for example:

Wire1 is sending a 5V signal at 4.5ohm... this goes into the chip, and then the chip sends out two wires, one at 4.5ohm and the other at 9ohm... (ohm numbers are just for example)

What chips have instruction sets to do this ?? Do any exist ? Cheap easy programming is a serious plus. (Does a 28F020 have logic sets like this ?)

Can analog or digital ICs read in and output resistances ???


New Member
To clear this up, I'm getting input from switches where each switch sends a 5V signal at a different resistance to a processor that reads that resistance then performs an action...

My problem is I'm changing processors to a similar design but with a 'failsafe' system that requires all the signals coming in to be redundant but I can not change the swithes (its not a life critical application, designers

(ie: the original switch sends 1 signal wire and 1 ground wire to a chip... I changed chips but not switches (cant), so now I have a processor looking for 2 signal wires and 1 ground but switches that only send 1 signal wire....)

I'm a software programmer, and have only hit the surface of hardware. So... I'm kinda at a loss on where to start this.

I sort-of get the idea about measuring current to determine resistance, but i know all signals in the system will be 5V... Not sure about the wattage or amps.

This is getting more and more urgent everyday so I'm about to start stressing.

Anyhow... (This might be important) It seems that this 'failsafe' system is kind of a joke... The original system takes in a X resistance into the processor, while the new system is waiting for X and 2X (that is double the resistance of the first signal)... The problem is still that I have a 6 or 7 resistor system and i know it could be pretty complex trying to do this on a hardware only route. Which is why I posted about the chip at first.

AHH!!! I just thought of somthing!

Here is what I'm thinking now...

Voltage = Current * Resistance right ? (v=ir)

So then my system doesnt really care what the resistance is... It cares what the voltage is after hitting the resistor. (This is a revelation for me) So all i need is a chip with 1 input and 2 outputs... then inside the chip if I see 4.5V coming in (where i know i should be getting 5V) I know that a resistor of whatever has been hit (switch pressed) and i need the chip to output a 4.5V and a 2.25V signal to make the new processor think everthing is working smoothly.

Does this seem correct or am I totally mangaling electronic theory...


Active Member
Sounds like you're trying to do a A/D conversion to me.

Every switch will change the voltage on the output by activating another resistor.

do a search on A/D converters for this


New Member
sort of.

I need to take a 2 wire system and make a 3 wire system... some simple logic involded.

I need one signal to stay the same and proceed to the processor as it normally would, but i need a new signal created that also goes to the processor (its voltage depends on what the first signal was)

It would be a lot easier if i just needed to convert the one signal

I'm just a little hazzy on where to begin


New Member
wow... I am not so sure I am following that much..... Here is what I got correct me if I am wrong.

You used to have in the system two wires. 1-Ground, the other one change resistance according to what switch was pressed..... right? The old chip used to get this signal and do somestuff accordingly.
Now you have 3 wires. 1-Ground, 1- Signal (that changes resistance as before) and 1- I will call reference......

It seems like Exo mention that the chip is doing a ADC convertion. What this does is checks what voltage you have at certain pin and it assigns a digital value to that voltage according to the resolution of the ADC. So a 8-bit ADC can only generate 255 numbers for voltage change.

The switches as I can understand are connecting or disconnectig resistances to change this voltage.... by what is call a Voltage divider. I am not sure if you are familiar with potenciometers, but they work sort of that way.

Analog to Digital Convertors need 3 wires most of the time. 1- Would be your ground, 1- a signal (analog voltage-changing voltage), 1 you reference voltage. That sound awfully close to what you have now. Some processors have and ADC built it.... and they use their voltage supply as a reference, therefoe you don't need an external reference pin. But some can be configure as to have different voltages as a reference in case you want something different from your chip voltage supply.

I am guessing that if you connect the one voltage that goes to the switches to this new pin that will set the reference voltage as before. And just have the signal pin fed into the signal pin and the fround to ground.

I am assuming a whole bunch of stuff.... if you have schematic of the switch arrangement and chips, that might clarify a whole bunch.

Good Luck



New Member
Not a reference... its another signal... follow me here,

This new system is retarded. It has a failsafe setup in it where anytime any switch is pressed, its not good enough to have a signal (yes that hits a resistor) and a ground... no it needs a ground and 2 signal wires... that is 2 wires that hit different resistors but in the processor they end up meaning the same thing...

|oldprocessor| |


Its very very stupid. I'm just going to make a PIC chip to do this since they have builtin A/D and I can use C to program one.

I have some other things this same PIC can be doing so that works out well...

I dont really know which PIC to get tho.... needs built-in A/D and easy to program


New Member
I guess that is one of those things that you must see to figure out.... because I can't picture it :oops:

Well a PIC that could help you is the 16F877 rather simple to use and if you have a C compiler for it... heck why not?
You can really choose any with a ADC go to this **broken link removed** to find the one that best suits you.

Sorry I can't be of more help.

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