Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: madsci1016 on January 08, 2011, 04:04:28 PM
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Hi guys,
I need to control (with a MCU) a pressure regulator that takes 0-10V as an analog control signal.
On my MCU board, I'll have 24V and 5V supplies.
My two thoughts are:
Digital Potentiometer as a resistor in a voltage divider from the 24V source. Cheap, but not sure how to apply the terminal voltage ratings. Obviously it will be the resistor closer to GND. I'm assuming it must tolerate 10V across the pot, or should it be 24V?
DAC with separate supplies, though they are expensive an I can't find many (if any) that will handle that high voltage.
Any Chip suggestions from the experienced?
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My first thought is a DAC followed by an Op-amp with enough gain and rail voltage to produce 0-10V output.
You could do the same with a digital pot followed by an Op-amp.
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I found a digital POT (http://www.analog.com/static/imported-files/data_sheets/AD5290.pdf) that's rated for 30V single supply, so I think it might be a winner. Though I really wish they had a through-hole package.
DAC followed by an OpAmp makes sense too, but it's more parts.
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PWM --> Transistor (push - pull) --> RC filter --> wanted voltage??? :-p
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PWM --> Transistor (push - pull) --> RC filter --> wanted voltage??? :-p
Though of that, too complicated, would likely need a feedback loop to maintain a set voltage, risk sending more then 10V if PWM signal goes above 50% duty cycle, and more parts (aka, space required) on a PCB leading to bigger price to fab.
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For what currents are you talking about... Since you're thinking of using a digital pot... I don't really think we're talking for more than some mA...
What I'm talking about costs nothing to buying a digital pot or DAC... two JFET, one cap, some resistors... And... ZENERS!!!
Zeners can also work as a comparator if you need to know you closing to the cap. limit...
And even if you need some extra current... You can always build a buffer... No need for a nasty op amp... A common-collector BJT will do...
Anyhow... A digital pot probably costs 1 to 2 dollars a piece probably more, what I'm proposing costs only some cents, since you can find any component in the .05 to .08 price range...
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What I'm talking about costs nothing to buying a digital pot or DAC... two JFET, one cap, some resistors... And... ZENERS!!!
Zeners can also work as a comparator if you need to know you closing to the cap. limit...
That's great, but I'm talking about the cost to make the room for the parts on the PCB:
and more parts (aka, space required) on a PCB leading to bigger price to fab.
not the cost of the parts themselves.
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Dunno about these things....
I guess no SMD thoughts....