Prop Backpack question
sylvie369
Posts: 1,622
I bought one of the Propeller Backpacks when it was the daily deal last week. I'm looking the thing over, and reading the documentation, and I think it might be an ideal way to do something I've been wanting to do, if I'm understanding it correctly.
In my rockets, I have an altimeter that outputs 5V level serial altitude data at 9600 baud. I've been sending those data through level conversion to an XBee to be transmitted to the ground, and that works beautifully. The ARLISS team I've worked with (See the Stamps in Class forum) is sending those data to an onboard Stamp and recording them to a USB drive, also successfully.
I would like to also add some other data to the datastream from the XBee, from analog sensors.
It seems to me that I could connect the altimeter's serial output to the 5V serial three-pin connector on the Backpack, and read them into the Prop that way, without needing any level conversion. I could (once I learn how) also send the analog sensor data in through the two analog inputs to the Prop. Then I could use the Backpack's Propplug connector at 3.3V to send the data out to the XBee for transmission, again without needing any level conversion.
Am I reading things correctly?
In my rockets, I have an altimeter that outputs 5V level serial altitude data at 9600 baud. I've been sending those data through level conversion to an XBee to be transmitted to the ground, and that works beautifully. The ARLISS team I've worked with (See the Stamps in Class forum) is sending those data to an onboard Stamp and recording them to a USB drive, also successfully.
I would like to also add some other data to the datastream from the XBee, from analog sensors.
It seems to me that I could connect the altimeter's serial output to the 5V serial three-pin connector on the Backpack, and read them into the Prop that way, without needing any level conversion. I could (once I learn how) also send the analog sensor data in through the two analog inputs to the Prop. Then I could use the Backpack's Propplug connector at 3.3V to send the data out to the XBee for transmission, again without needing any level conversion.
Am I reading things correctly?
Comments
And yes, you could do what you say.
You could also wire an SD card to A4-A7.
Everything you've said is correct. I would be wary of Cluso's statement about the 150R series resistor, however. That's actually much too low a value. The Prop datasheet specs the maximum forward bias of the input protection diodes at 0.5mA. And (5 - 3.3 - 0.6) / .0005 = 2200 ohms minimum.
-Phil
And similarly, the output from the Backpack through the pins of the Propplug connector can go directly to an (3.3V) XBee pin without anything other than just plain wire, right?
If that's going to work, I think I know how I'm going to spend the off season.
The PropPlug connector can indeed be connected to a 3.3V device like the xBee without any extra protection.