First and foremost , is there such thing as a digital resistor , whose resistance can be digitally controlled by a MCP ?
Background info :
Let's say somebody wants to key in exact voltage on a LM317 digitally just by hitting a soft-touch button , would be interested to know how it all pans out :icon_twisted:
Digital pot maybe?
http://www.coolcircuit.com/circuit/programmable_supply/index.html
Your ABCD inputs would connect to an up/down counter which in turn would be controlled by the pushbutton(s).
This gives you 16 precise, somewhat arbitrary, discrete voltages from which to choose.
Quote from: earthtonesaudio on November 28, 2011, 03:03:43 PM
http://www.coolcircuit.com/circuit/programmable_supply/index.html
Your ABCD inputs would connect to an up/down counter which in turn would be controlled by the pushbutton(s).
This gives you 16 precise, somewhat arbitrary, discrete voltages from which to choose.
Not that ! But something like , those programmable power supplies whose voltage(s) goes up when you press the momentary switches .
as stated above
a digital pot at the ref of the LM317 should do the job
Quote from: alparent on November 28, 2011, 02:21:09 PM
Digital pot maybe?
Quote from: xfc on November 28, 2011, 03:33:10 PM
as stated above
a digital pot at the ref of the LM317 should do the job
Quote from: alparent on November 28, 2011, 02:21:09 PM
Digital pot maybe?
Ah yes ! I forgot digital pots are in IC-form , i nearly thought digital pots were still , pots ( mechanical form) :icon_mrgreen:
Another alternative (if your required voltage is less than 5V... some of the more recent PICs have a 32 step DAC inside - you can feed the top of the dac either VCC or a fixed voltage reference derived internally...this allows you a large array of precise voltages you can get the PIC to output - just follow it up with a voltage follower. Keeps it all internal to the PIC...lower parts count blah blag.
Another alternative is a simple dedicated DAC IC (vs a digital pot) ...they have a bufffered output voltage.
Quote from: Gurner on November 28, 2011, 08:28:51 PM
Another alternative (if your required voltage is less than 5V... some of the more recent PICs have a 32 step DAC inside - you can feed the top of the dac either VCC or a fixed voltage reference derived internally...this allows you a large array of precise voltages you can get the PIC to output - just follow it up with a voltage follower. Keeps it all internal to the PIC...lower parts count blah blag.
Another alternative is a simple dedicated DAC IC (vs a digital pot) ...they have a bufffered output voltage.
Hmm , do the AVR's have a similar DAC ? ( i don't really like PIC's :icon_mrgreen: )
Quote from: DavenPaget on November 28, 2011, 09:34:47 PM
Quote from: Gurner on November 28, 2011, 08:28:51 PM
Another alternative (if your required voltage is less than 5V... some of the more recent PICs have a 32 step DAC inside - you can feed the top of the dac either VCC or a fixed voltage reference derived internally...this allows you a large array of precise voltages you can get the PIC to output - just follow it up with a voltage follower. Keeps it all internal to the PIC...lower parts count blah blag.
Another alternative is a simple dedicated DAC IC (vs a digital pot) ...they have a bufffered output voltage.
Hmm , do the AVR's have a similar DAC ? ( i don't really like PIC's :icon_mrgreen: )
No, but you can use one of the square wave PWM outputs with a filter to get 8-bit analogue output, or two with resistors to get a rough 16-bit.
Up to now I've been using a RC lowpass but I'm thinking of switching to one of these:
http://interface.khm.de/index.php/lab/experiments/arduino-dds-sinewave-generator/ (http://interface.khm.de/index.php/lab/experiments/arduino-dds-sinewave-generator/)
I can't find the inductors though; biggest ones I can get are 1mH.
if 1uH is the same as 1mF the Tayda as 4.7uH for 9 cents.
http://www.taydaelectronics.com/servlet/the-484/4.7uH-Inductor/Detail (http://www.taydaelectronics.com/servlet/the-484/4.7uH-Inductor/Detail)
Quote from: alparent on November 29, 2011, 08:27:38 AM
if 1uH is the same as 1mF the Tayda as 4.7uH for 9 cents.
http://www.taydaelectronics.com/servlet/the-484/4.7uH-Inductor/Detail (http://www.taydaelectronics.com/servlet/the-484/4.7uH-Inductor/Detail)
uH = microHenries
mH = milliHenries
It looks like you can get them on eBay but as I don't have a meter that can measure inductance I wouldn't buy from there.
1mH ? no problem . Element14 / Newark / Farnell sells those .
Quote from: DavenPaget on November 29, 2011, 10:12:11 AM
1mH ? no problem . Element14 / Newark / Farnell sells those .
No, no - it needs 4.7mH, I can only get 1mH.
There are pushbutton-controlled digipots:
http://www.maxim-ic.com/app-notes/index.mvp/id/168
Quote from: earthtonesaudio on November 29, 2011, 12:07:55 PM
There are pushbutton-controlled digipots:
http://www.maxim-ic.com/app-notes/index.mvp/id/168
Yes ! Thanks for your help . :icon_mrgreen:
Quote from: nexekho on November 29, 2011, 10:13:52 AM
Quote from: DavenPaget on November 29, 2011, 10:12:11 AM
1mH ? no problem . Element14 / Newark / Farnell sells those .
No, no - it needs 4.7mH, I can only get 1mH.
I did a search , threw up quite a hunk of results .
http://sg.element14.com/jsp/search/browse.jsp?N=2108+203354&Ntk=gensearch&Ntt=4.7mh&Ntx=mode+matchallpartial (http://sg.element14.com/jsp/search/browse.jsp?N=2108+203354&Ntk=gensearch&Ntt=4.7mh&Ntx=mode+matchallpartial)