Manually adjust output voltage?

[sam_boytor]

I am looking to manually adjust an output voltage to a get specific voltage. For example: the output voltage needs to be 2.5 VDC and my output may be 2.3 VDC or 2.8 VDC. I am looking for a way to manually adjust the voltage using a potentiometer (and possibly some op-amps). Any suggestions?

 

[crutschow]

What is the load impedance/output current requirements.

 

[MrAl]

Hi there,


Are you saying that your output *now* runs from 2.3 to 2.8, and you want
it to be a constant 2.5v at all times intead?

 

[CCD]

Hii,
use the classic LM317 voltage regulator, u can adjust the o/p as u wish using a pot.

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www.dharmanitech.com

 

[sam_boytor]

crutschow - the output is going to a microcontroller so the current requirements are in the mA range.

MrAl - the output will be constant, but for each circuit I make the voltage may be above or below what I want it to be (2.5VDC).

CCD - the classic LM317 voltage regulator can bring my voltage down to what I want, but if my starting voltage is too low I need to increase it somehow.

 

[crutschow]

What you are trying to do doesn't make a lot of sense. Could you elaborate on where this output voltage is coming from?

 

[sam_boytor]

The output is coming from an accelerometer. The Accel is on a circuit board which is on a table. When the table is level, the Accel should output 2.5 VDC to the microcontroller. But circuit board doesn't sit level on the table, so I want to be able to adjust a Potentiometer to tell the microcontroller that the table is level.

 

[pc88]

The output is coming from an accelerometer. The Accel is on a circuit board which is on a table. When the table is level, the Accel should output 2.5 VDC to the microcontroller. But circuit board doesn't sit level on the table, so I want to be able to adjust a Potentiometer to tell the microcontroller that the table is level.

Can you modify the software? Just push a button that tells the uc that the current reading represents "level".

 

[pc88]

Here's an op amp circuit which should allow you to add an offset voltage to your signal.

 

[crutschow]

Here's an op amp circuit which should allow you to add an offset voltage to your signal.

sam_boytor needs both plus and minus offset adjustment. For that you would need to connect the bottom of the R3 pot to a minus voltage.

 

[pc88]

sam_boytor needs both plus and minus offset adjustment. For that you would need to connect the bottom of the R3 pot to a minus voltage.

You're right. Alternatively, you could connect the ground of the ground leg of R2 to Vcc/2 (buffered by a voltage follower).

I think the key issue is which op-amp to use. You'll definitely want a rail-to-rail op-amp that can work with your supply voltage (likely 5V). Add the requirement that you want a through-hole component, and that narrows down the field quite a bit. I'd check out what National has to offer (like the LM6142) as well as Microchip.