Ping))) Schematic?
Zoot
Posts: 2,227
It's my understanding that it's good practice to protect a microprocessor pin with a 220ohm (or so) resistor if the pin is connected to any circuit that might generate an output, so that if you screw up your programming, you won't short the pin if it's made an output.
Now, it's also my understanding (correct me if I'm wrong) that open-collector (or open-drain) type bi-directional circuits (say an I2C bus with discrete pull-ups, or a Parallax "AppMod" serial I/O connection where the pull-up is usually internal to the up driving the board -- like the PSC) don't require such protection, because there is a pull-up/pull-down resistor on the line, and the line is driven high or low for state changes, so you can't really get a short circuit.
So, if that's correct, is there either a current limiting resistor or an open/driven setup on the signal pin of a Ping)))? I'm guessing yes, because the documentation always recommends hooking the Ping))) signal right up to a processor pin, and you blow your programming if you triggered the Ping))) then made your processor pin an output.
Any schematics or a description of the Ping))) circuit?
Part of why I ask is that in very noisy environments with a long run of wire to the sensor, it was possible to get false triggers. In one project, I eventually solved my noise problem, but I did a temporary hack where I held the Ping))) line LOW when not in use, which helped prevent noise from causing a false trigger. I protected the up pin with resistor to be safe, but it got me to thinking about the Ping))) setup.
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When the going gets weird, the weird turn pro. -- HST
Now, it's also my understanding (correct me if I'm wrong) that open-collector (or open-drain) type bi-directional circuits (say an I2C bus with discrete pull-ups, or a Parallax "AppMod" serial I/O connection where the pull-up is usually internal to the up driving the board -- like the PSC) don't require such protection, because there is a pull-up/pull-down resistor on the line, and the line is driven high or low for state changes, so you can't really get a short circuit.
So, if that's correct, is there either a current limiting resistor or an open/driven setup on the signal pin of a Ping)))? I'm guessing yes, because the documentation always recommends hooking the Ping))) signal right up to a processor pin, and you blow your programming if you triggered the Ping))) then made your processor pin an output.
Any schematics or a description of the Ping))) circuit?
Part of why I ask is that in very noisy environments with a long run of wire to the sensor, it was possible to get false triggers. In one project, I eventually solved my noise problem, but I did a temporary hack where I held the Ping))) line LOW when not in use, which helped prevent noise from causing a false trigger. I protected the up pin with resistor to be safe, but it got me to thinking about the Ping))) setup.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
When the going gets weird, the weird turn pro. -- HST
Comments
The PING))) has both a 500 ohm Series Resistor internally as well as a 10K pull-down resistor. I hope this helps. Take care.
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Chris Savage
Parallax Tech Support