Pots and voltage

[andy_rb]

Hello All

Please excuse my ignorance, but what is the simplest and most elegant way to control a voltage range with a relatively small variable resistor?

Let me explain:

I'm using a little joystick (SparkFun Electronics - Thumb Joystick) to control a bot using XBees. I need to send as wide a range of voltages into an ADC pin on one XBee as possible. Vref will be 3.3V and I'd like to vary the input as much as possible with the full throw of the 10k pot while still keeping battery usage low. The more I can vary the voltage into the ADC the more precise the signal I can send to the bot.

No doubt there's a simple way of doing this, but I'm a software person and need all the help I can get when it comes to basic hardware!

Thanks

Andy

 

[Nigel Goodwin]

Check my PIC joystick tutorial, no ADC required - much more simple than that.

 

[ronp849]

Hi Andy - Most joystick controls that use a pot on each axis suffer from limited travel. Ie Joystick would have approx 90deg of travel whereas a pot would have approx 270deg of travel. The output voltage range would therefore follow the same ratio. From what you say you need the full voltage swing for your Processor A/D.

You will need to amplify the pot voltage via differential amplifier. This can be done with a few resistors and an Op amp or you can select a processor that has Differential inputs and Gain control as part of its on board A/D. The Atmel Tiny26 has this as an example and I am sure there are many others in the Atmel and PIC range of devices that will be suitable. You do not mention the resolution of the A/D but most processors are 10bit or more. You will need to check if the resolution reduces when configured in differential/high gain mode.

 

[andy_rb]

Hi All

Thanks for the quick replies.

I figured there would be some way to do it with a simple amplifier but wasn't sure how. I'll have a look at the op-amp solution.

I want to avoid using a microcontroler in the 'remote control' if possible. I'd like to get away with little more than the XBee and it's internal ADC, the joystick and a few other components. The XBee on the Bot puts out PWM proportional to the ADC input from the joystick which I'll read using the Bot's ATmega chip.

I can't do differential ADC on the XBee but I may be able to get clever with Vref. Will have to think about it a bit more. The ADC on the XBee is 10 bit.

Cheers

Andy