I must be missing something

J

Jaguarjoe

Senior Member
I was thinking about this while I was laying under my Jeep:

Feed a 0-5v signal into a 10 bit ADC and you get ~1000 bits of resolution, which ain't bad. But-
What would happen if you took that 0-5v signal and subtracted 2.5v from it with an op-amp?
Now you have 0 to +2.5v and 0 to -2.5v.
Take the 0 to +2.5v portion and multiply by 2x with another op-amp to get 0 to +5v and feed that into one ADC input.
Take the 0 to -2.5v portion, invert it and multiply it by 2x to get 0 to +5v and feed that into another ADC input.
Now you have 1000 bits for half of your signal and another 1000 bits for the other half, or 2000 bits for the whole signal.
This doubles your resolution at the cost of a cheap quad op-amp or two and an equally cheap 7660 flying capacitor chip.

Will this work, or is this the electronic version of Washington's voodo economics?
 
erco

erco

Senior Member
Could be made to work with a lot of experimentation, but how much resolution do you need? Is twice the resolution gonna make or break your application? I doubt if the ADC is 100% linear over its whole range, so if you want incredible accuracy, you may need to hand calibrate and make a lookup table.

Me, I'd just go to Harbor Freight and grab a $3 multimeter and build it into my project, or get one of these for $2.39 shipped: http://www.ebay.com/itm/2s-6s-Lipo-Battery-Voltage-Indicator-Checker-Tester-LED-/330587249608?pt=Radio_Control_Parts_Accessories&hash=item4cf8891bc8
 
J

John West

Senior Member
Yep, it can work, if you use the right op-amps (and negative voltage generator) appropriately. I've seen "two-stage" high rez A to D's done in the past in a fairly similar way.

The question is, do you really need another bit of resolution? If so, why not more bits? You might want to just get an A to D with 2 or more additional bits of resolution. They aren't that pricy these days.

For increased resolution over a more limited range, reducing the reference range and or adding op-amp offset and gain will do the trick with just the usual single-ended power supply.
 
J

Jaguarjoe

Senior Member
erco said:
Me, I'd just go to Harbor Freight and grab a $3 multimeter [/url]
Click to expand...
If you visit them now and buy anything, you'll get a coupon for your choice of one of these free gifts- one of those DMM's, or a 4 outlet power strip, or a 40 pc small socket set. They are only available on Labor Day, Sept 5th.
 
J

Jaguarjoe

Senior Member
fritz42_male said:
Should buy Japanese instead
Click to expand...
The Jeep runs well, it's a fine vehicle. Mine has a viscous coupling which automatically splits power fore and aft. That coupling is a wear item, mine is finally going bad. It utilizes Rheopectic fluid, amazing stuff.

Buying foreign cars is problematic for many people in south east Michigan.
 
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P

papaof2

Senior Member
Jaguarjoe said:
Buying foreign cars is problematic for many people in south east Michigan.
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Detroit outlook not withstanding, the odds are, your Jeep is less than 70% US made. The electronics modules (audio, ECU, etc) are most likely imported and possibly the transmission as well.

At one point, Ford made its bigger vehicles (Crown Vic, Mercury Marquis) in Canada or Mexico to improve the CAFE ratings. Not sure how much of that Chrysler Corp is doing.

My Toyota pickup was assembled in California at the same plant that built some models of that year's Pontiac.

Unless it's 60 years old or you build it yourself (and don't use Bosch or NGK plugs), there are no 100% US cars.

John
 
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