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 Posted: Apr 22, 2012 - 11:03 AM |
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Joined: Feb 16, 2007
Posts: 698
Location: Israel
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I have an application where I need a control voltage (needs to be accurate) from 1.2V to 5.16V. This goes over the capability of the AVR. Note - I don't want to run the AVR on a positive low rail to lift the 5v range up, although this could probably solve the problem but this means all the circuit that communicated with the AVR should also be adjustment and this is without talking about programming and debugging interfaces.
Mu initial idea is to use a summing amplifier and add a constant offset to the AVR output. The problem is that I can use only opamps that have some offset voltage and no adjustment terminals.
Any suggestions?
1.2V to 5.16V |
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Posted: Apr 22, 2012 - 11:23 AM |
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Joined: Oct 30, 2002
Posts: 5720
Location: The Netherlands
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Feed the AVR PWM output to some CMOS 4000 gate that runs at 6V or so and let that gate drive the filter; or simply tie the filter to the AVR output and use an opamp to both amplify and add an offset to the signal (weighted summing amplifier).
I don't see the need for the 1.2V offset, unless you want to use absolutely all PWM bits for the whole range for maximum resolution.
What voltages are available? |
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Posted: Apr 22, 2012 - 11:28 AM |
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Joined: Feb 16, 2007
Posts: 698
Location: Israel
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jayjay1974 wrote:
Feed the AVR PWM output to some CMOS 4000 gate that runs at 6V or so and let that gate drive the filter; or simply tie the filter to the AVR output and use an opamp to both amplify and add an offset to the signal (weighted summing amplifier).
I don't see the need for the 1.2V offset, unless you want to use absolutely all PWM bits for the whole range for maximum resolution.
What voltages are available?
I have 5V and 9V available. 1.2V offset can be added using a non-inverting summing amplifier, however I am a little concerned about the voltage offset added by the TL074. And I need a pretty good resolution, 33mV to be exact. |
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Posted: Apr 22, 2012 - 04:35 PM |
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Joined: Feb 19, 2001
Posts: 25909
Location: Wisconsin USA
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Quote:
This goes over the capability of the AVR.
Umm--not exactly.
Quote:
I have 5V and 9V available.
Make your 5.0V 5.5V, and Bob's your uncle. |
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Posted: Apr 23, 2012 - 04:11 PM |
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Joined: Feb 16, 2007
Posts: 698
Location: Israel
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jayjay1974 wrote:
Feed the AVR PWM output to some CMOS 4000 gate that runs at 6V or so and let that gate drive the filter; or simply tie the filter to the AVR output and use an opamp to both amplify and add an offset to the signal (weighted summing amplifier).
I don't see the need for the 1.2V offset, unless you want to use absolutely all PWM bits for the whole range for maximum resolution.
What voltages are available?
After doing some other adjustment to the circuit, the control voltage range is now 3.84V to 7.8V. I tried bread-boarding a summing amplifier but my supply is 9V and the opamp is not rail to rail (cheap tl071). I will try the CMOS solution... |
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