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Message started by tylerfurtwangler on 03/20/08 at 04:21:47

Title: VREF adjustable?
Post by tylerfurtwangler on 03/20/08 at 04:21:47
Does anyone know of a way to change the reference voltage for the board to something besides 5v?  I would like to use a device that outputs at 2.8v as its digital high, and 0 as its low.  Most chips allow for a vref pin to be used (instead of Vin) when determining its high/low status.

Thanks for the help!

Title: Re: VREF adjustable?
Post by worapoht on 03/20/08 at 11:24:07
change VREF can be done on Analog section only (AREF pin input adjust to AVCC, External, Internal 2.56V. by REFS0/1 in ADMUX register).

but if for logic pin on chip, it refer to CMOS definition, first 1/3 of VCC mean LOW, and 2/3 of VCC to VCC mean HIGH. between of them is undefine may be LOW r HIGH depand on voltage transition.. that depand on VCC.

seem you need something like voltage level detection.
if you need truely 2.8V. level detection , Analog comparator Op-Amp (i.e. LM393) chip may be the right thing to do.. and send to Board later

Title: Re: VREF adjustable?
Post by Vaccumdiode2 on 03/20/08 at 15:14:23
                This would make a Great example.  When you get you circut worked out Please share it with us.  
               If you look on the web you can find all kinds if free circuts.  Basicly I think if you find a simple voltage doubler circut, which may us an OP-amp or a transistor.  
               I take a look around and see if I find anything useful.

Rich AKA Vaccumdiode2

Title: Re: VREF adjustable?
Post by Vaccumdiode2 on 03/20/08 at 17:09:20

Here are few web sites with some ideas on doubling your voltage.



Title: Re: VREF adjustable?
Post by tylerfurtwangler on 03/20/08 at 17:29:18
thanks you all for your responses,

i would like to keep things simple when dealing with external devices and since i would need an opamp per input into the Wiring board, thigns can get complicated.  I have 13 outputs (13 inputs into the Wiring board) which would require 13 opamps.  add in the power /ground lines and any resistor/caps to adjust the output voltage of those opamps and thigns get ugly.

any ideas of how to do this easier?

a little more background:
i got a 9v battery which runs a 5v regulator and an adjustable regulator (set at 2.8v).  the 5v regulator powers an oscillator which is voltage devided down to 2.8 and fed into the clock for a cmos sensor.  the 2.8v reg powers the cmos sensor.  i want to read values coming from the sensor but they are all 2.8v (the voltage in).

thanks again!  i appreciate the help

Title: Re: VREF adjustable?
Post by Vaccumdiode2 on 03/20/08 at 18:07:28

Here one that uses 2 diodes and 2 caps.   It maybe a better option.



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