Build Your Own Arcade Controls Forum
Main => Everything Else => Topic started by: SavannahLion on January 23, 2012, 03:44:29 am
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A new idea came to me and I wanted to look into this. Trick is, where am I going to start the research?
Let's take an arbitrary circuit that has an output of -2.5v to +2.5v relative to ground. Call this circuit "A"
Now Circuit "B" operates on 0v to 5v relative to ground. Ground for Circuit "A" and Circuit "B" is fixed and cannot be artificially adjusted.
To keep things simple, let's assume the direction is unidirectional from "A" to "B".
My initial guess was to use an OpAmp and measure the difference in voltage on "A" but I don't understand how I can determine directionality of that difference relative to ground. Or is that even an issue?
Then I started thinking about how the RS232 protocol specifies a -12v/+12v swing and peeked into IC's that deal with RS232 protocols. There I found the MAX232 which translates this -/+ swing to a 0/+ swing. I'm downloading the spec sheet for this now but am I on the right track here? I'm a little put off by MAXIM since I always hear complaints about how MAXIM products have an extremely short production life cycle. I don't really want to build a circuit that centers around a MAX232 and then be left out in the cold a couple of years later if I need to repair/rebuild it. On top of that, the MAX232 doesn't seem to be an analog circuit, so whatever difference comes in, a 0 or a 1 is going to come out. This would be far more interesting if I could get a proper analog difference (hence the OpAmp).
Am I on the right track with this thinking here? This really can't be such a unique situation. After all, every decent oscilloscope I've wished for can measure a negative signal. Any ideas what I should be Googling for?
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So your goal here is to measure a bi-polar signal using a circuit that only has one (positive) rail, or do you just want the output to be from 0-5V but you have any supplies you want available? Does the circuit need to operate all the way down to DC? Are the grounds for the two circuits separate, and, if so, can they be safely tied together at an arbitrary point that isn't ground in both circuits?
FYI, the MAX232 a) isn't going anywhere (it's already like 20 years old and used in everything - several other companies cross it too, and cheaper than Maxim to boot), and b) just has an onboard charge pump to generate a negative rail. Maxim does have some problems sometimes with production capability, but I haven't noted them to EOL stuff without sufficient warning (unlike, say, Cypress). You just may have to meet both their minimum (enough to start a run) and come in within their production capacity within your delivery timeframe (they're fabless, so this varies by how loaded their fabs are).
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Alrighty, hold that thought and let me see if I can find some real world circuits to reference.