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| General Electronics Chat This forum is for general chat about electronics, eg: Dont know what a part does? Dont know how to read a circuit? Want to get an opinion? |
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1st May 2003, 02:31 PM
| #1 |
 Bipolar adc...
Hi there..I am not sure about the exact english word (I think it is bipolar) but i am searching for a simple-cheap adc that accepts input in the range of -5V to +5V... I had used adc0804 before but i am not sure if it can convert negative input. In the datasheet there is an interface for -5V to +5V signals but they are using a Beckman Instruments #694-3-R10K resistor array, but i dont understand how it works. I 'd appreciate it if somenone could enlighten me on adc0804's ability of accepting negative input, or maybe suggest me another adc. A complementary dac (bipolar again) i could use in conjuction with the adc, would be fine... Thanx in advance..... | |
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1st May 2003, 03:33 PM
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gatas,, The input stage on that converter is just a 10k-10k resistive voltage divider. I think that any two 10k resistors will work, but I am not sure about why they chose that beckman part.. I believe that company has either changed names or went out of business, so I couldn't check the spec. sheet. Just try to use the most accurate resistors you can get.. Steve | |
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15th October 2005, 07:48 PM
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gatas I think that you should put pin 7(-Vin) to +5V, if you want to read a input from -5V to +5V, but you should need to change the Vref/2 value to +5V. Im not sure about this, but it would work. gil | |
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15th October 2005, 08:59 PM
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It would be unusual for an ADC to cover positive and negative voltages, nor is it required. You simply bias the input of the opamp to +2.5V, a negative voltage will move it down towards zero, and a positive value will move it towards +5V. It's a simple circuit, you need the output of an opamp that can move between -5V and +5V (10V range), when it's input is zero, then the output should be zero as well. Connect the output of the opamp via a resistor to the input of the A2D, and a second resistor from the input of the A2D to 5V, the two resistor should be identical. Notice that the two resistors do two tasks, they shift a negative to positive swing to a zero to positive one, and also divide by two - converting the 10V swing to a 5V one. Your software needs to take care of the rest, it's quite straight forward to do. | |
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