Input Voltage Selection on Digital I/O Board
TinkersALot
Posts: 535
Somebody talk me down, please·
Since, 'fixed features' are something I avoid (this is why I like things to be programmable after all). I was wondering:
On the new digital I/O board from parallax, they have some resistors that are part of the input circuits that are selected for a specific voltage range (15-30 Volts if memory serves), and a formula that should be used to select different resistance values for other ranges.
I was wondering about utilizing a PCB-mounted potentiometer instead of a fixed resistor so that I can retain a higher amount of flexibility for use of the input side.
Are there any reasons why I should definitely NOT do this?
As always, thanks in advance for all who care to reply.
TinkersALot
Since, 'fixed features' are something I avoid (this is why I like things to be programmable after all). I was wondering:
On the new digital I/O board from parallax, they have some resistors that are part of the input circuits that are selected for a specific voltage range (15-30 Volts if memory serves), and a formula that should be used to select different resistance values for other ranges.
I was wondering about utilizing a PCB-mounted potentiometer instead of a fixed resistor so that I can retain a higher amount of flexibility for use of the input side.
Are there any reasons why I should definitely NOT do this?
As always, thanks in advance for all who care to reply.
TinkersALot
Comments
There's no reason you couldn't use a potentiometer as long as you observed its maximum ratings. Remember, potentiometers generally handle much less power than a standard resistor. So if you replace the resistor, just be sure you're within the safe operating range of the pot. Also remember that, the pot may appear to work great at its maximum resistance, but as you reduce the resistance the current increases given the same voltage through the circuit. There will be a lower range on a potentiometer which will always be too low without a standard resistor in series. One other option is a rheostat if it gets to that point.
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Chris Savage
Parallax Engineering
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Given your feedback, I am thinking more about this. I am thinking now of a small daughterboard for each input port that has a PCB mounted DIP switch with one side used as a common, and the other side of the switch having a set of resistors so that I can switch in the range that I'd like, something like:
····|--- R1 --- SW1 --|
IN >|--- R2 --- SW2 --|-- >
··· |--- R3 --- SW3 --|
sorry about the "bad art" ... With well selected values, and accounting for some "valid parallel resistances" this arrangement should provide the flexibility I am looking for and also avoid some of the issues you pointed out.