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Basic question about driving the reset pin on an RN-42


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#1 Spork

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Posted 16 December 2011 - 12:43 AM

Hi. I have a BlueSMiRF Silver from SparkFun -- it uses the RN-42 Bluetooth module. Pin 5 of the RN-42 is RESET and the RN-42 data sheet describes it as being internally connected to Vcc by a 1K pull up and active low. The RN-42 is a 3.3v device. When I use a jumper to manually and momentarily connect RESET to ground on the Netduino, I get the disconnect/reset behavior I want from the RN-42. I want to drive the same behavior from my C# code. If I permanently connect the RN-42 RESET pin to a Netduino analog output that's initialized to 3.3v, would I be able to momentarily set the analog output to zero and get the same result I got when I manually jumped the RN-42 RESET pin to Netduino's ground? By the way, in the case where I manually jumped RN-42 RESET to Netduino GND, I was kinda expecting 3.3V/1K or 3.3mA of current to flow. But when I jumped it with my multimeter, it read 1.2uA. Am I screwing up the measurement, misunderstanding Ohm's Law, or something else?

#2 Mario Vernari

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Posted 16 December 2011 - 04:43 AM

Hello Spork.

When I use a jumper to manually and momentarily connect RESET to ground on the Netduino, I get the disconnect/reset behavior I want from the RN-42. I want to drive the same behavior from my C# code. If I permanently connect the RN-42 RESET pin to a Netduino analog output that's initialized to 3.3v, would I be able to momentarily set the analog output to zero and get the same result I got when I manually jumped the RN-42 RESET pin to Netduino's ground?


That's right.
You can use any OutputPort to drive low-then-high the reset pin. Quick and dirty.
However, there are no "analog outputs" on the Netduino. An "analog output" is able to give a continuous voltage within a given range, as a duality of the analog port/input.


By the way, in the case where I manually jumped RN-42 RESET to Netduino GND, I was kinda expecting 3.3V/1K or 3.3mA of current to flow. But when I jumped it with my multimeter, it read 1.2uA. Am I screwing up the measurement, misunderstanding Ohm's Law, or something else?


You are right again, but perhaps the multimeter has been set wrongly, or its internal fuse is blown.
Your attempt to measure the current, and applying the Ohm's law is correct!
Cheers
Biggest fault of Netduino? It runs by electricity.

#3 Spork

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Posted 16 December 2011 - 06:03 AM

Thanks, Mario! I didn't want to wire it up without somebody sanity-checking the idea, first. Now that it's hooked up, it seems to work like a charm.




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