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| Logic Analyzer probe resistors? |
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| manlymann:
I need to use a logic analyzer on RS232, modbus etc. Often the bus is more than 5.0VDC. Is there an inexpensive solution to this? Do I just put a resistor in series with my probe? |
| NE666:
First, check the specifications for your particular LA. Many are "5v tolerant", whilst more expensive units often take much more e.g. my MSO 5000 is rated to 40v peak. If either your unit isn't rated for >5v, or you want to be cautious anyway and protect against any accidental overvoltage, then I suggest using a level-shifter board. They are designed for this, inexpensive and quite plentiful on well-known auction sites. https://www.pololu.com/product/2595 |
| egonotto:
--- Quote from: manlymann on August 18, 2024, 11:05:59 pm ---I need to use a logic analyzer on RS232, modbus etc. Often the bus is more than 5.0VDC. Is there an inexpensive solution to this? Do I just put a resistor in series with my probe? --- End quote --- Hello, why do you think you can be helped with so little information? Best regards egonotto |
| artag:
Because he didn't know they differed. If he'd known what NE666 has been able to tell him, he probably wouldn't have needed to ask at all. Learning is not just accumulating new facts, it's understanding what it is necessary to know. |
| Gyro:
You would be better to use a resistive divide rather than just relying on just a series resistor and the LA's input protection. Depending on the transition speed and LA input capacitance, the value of the resistors could probably be quite high to minimise circuit loading. |
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