SFE Joystick Shield
#1
Posted 20 August 2010 - 12:28 AM
#2
Posted 20 August 2010 - 01:32 PM
I change the jumper for Vref to the 5 V source. This did a find job of centering the signal, but the max values were very unstable. I guess I was over driving the A/D. So I cut the trace from 5 V to the joystick and added a wire from 3.3 to the joystick and Vref. Now every thing works just fine. See the attachment.
Thanks for sharing your findings.
Looks like the fact that Vref is not connected on Netduino causes troubles with some shields, and also is bit confusing for people comming from arduino. Maybe Chris could explain why it was done this way and if there is any technical difficulty to make it connected by default to 3V3 in future revisions.
#3
Posted 20 August 2010 - 03:02 PM
The biggest reason why AREF is not connected to 3.3V internally is because the SAM7X512 chip doesn't support that natively. The AVR chip on the Arduino has an "internal AREF" as an optional integrated feature.Looks like the fact that Vref is not connected on Netduino causes troubles with some shields, and also is bit confusing for people comming from arduino. Maybe Chris could explain why it was done this way and if there is any technical difficulty to make it connected by default to 3V3 in future revisions.
The other reasons we didn't just wire 3.3V to AREF and skip the AREF pin: [a] we wanted people to be aware that the Netduino was a 3.3V device and to be careful not to put 5V into the analog pins when used in analog mode; [b] we wanted to maintain the chip's capability of having an AREF which varies from 2.7V to 3.3V...for our customers who are using Netduinos for commercial engineering prototypes.
That said, I've chatted with engineering about potentially adding an "internal AREF" option in hardware on a future Netduino board revision. It would be a cool feature to have, for sure. For now, connect the AREF pin header to the 3.3V pin header with a jumper wire when using analog inputs.
Chris
#4
Posted 20 August 2010 - 03:15 PM
Personally, I like it the way it is. I was not confused by the AREF at all, my problem was that initially I did not pay attention to the fact that the shield had wired the pots to 5 vdc. Then in my haste to compensate I over drove the A/Ds by attaching AREF to 5V. Through this I learned a lot about the Netduino and its relationship to the Arduino. I won't make the same mistake again and hope that my original post will help others.The biggest reason why AREF is not connected to 3.3V internally is because the SAM7X512 chip doesn't support that natively. The AVR chip on the Arduino has an "internal AREF" as an optional integrated feature.
The other reasons we didn't just wire 3.3V to AREF and skip the AREF pin: [a] we wanted people to be aware that the Netduino was a 3.3V device and to be careful not to put 5V into the analog pins when used in analog mode; [b] we wanted to maintain the chip's capability of having an AREF which varies from 2.7V to 3.3V...for our customers who are using Netduinos for commercial engineering prototypes.
That said, I've chatted with engineering about potentially adding an "internal AREF" option in hardware on a future Netduino board revision. It would be a cool feature to have, for sure. For now, connect the AREF pin header to the 3.3V pin header with a jumper wire when using analog inputs.
Chris
I conform strongly to the concept of modularity, therefore I feel that if the shield uses A/Ds then it is responsible for supplying the AREF. It may not matter much in the case of a connected shield, but having the A/D source supply the AREF is one sure way of insuring that the A/D's are reading accurately.
So my vote would be, If you are going to add "internal AREF" it should be done via a jumper on the Netduino and the jumper should be left off by default.
I plan to make all my projects supply the AREF for accuracy, so don't break my projects please.
#5
Posted 20 August 2010 - 04:59 PM
Personally, I like it the way it is. I was not confused by the AREF at all, my problem was that initially I did not pay attention to the fact that the shield had wired the pots to 5 vdc. Then in my haste to compensate I over drove the A/Ds by attaching AREF to 5V. Through this I learned a lot about the Netduino and its relationship to the Arduino. I won't make the same mistake again and hope that my original post will help others.
I conform strongly to the concept of modularity, therefore I feel that if the shield uses A/Ds then it is responsible for supplying the AREF. It may not matter much in the case of a connected shield, but having the A/D source supply the AREF is one sure way of insuring that the A/D's are reading accurately.
So my vote would be, If you are going to add "internal AREF" it should be done via a jumper on the Netduino and the jumper should be left off by default.
I plan to make all my projects supply the AREF for accuracy, so don't break my projects please.
I literally only just discovered what the hell AREF is even for last night when I tried to work with analog inputs for the first time, but I totally agree. An internal AREF (as long as its controlled by a jumper) would be a nice convenience, but now that I sorta get what I'm doing, I'd rather not give up the bit of flexibility I only just discoverd I have.
#6
Posted 20 August 2010 - 09:50 PM
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