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stalker voltages...

Posted: Tue Dec 28, 2010 7:26 am
by ewarner77
I am working with a Stalker (V1.0 with the 168 MCU) and it appears that the working voltage is 3.3V for this. I understand that this is necessary for the xBee and storage card, however all the shields that have any analog voltage requirements to them seem to have a problem with this. In particular I am working with the LCD keypad shield from DFRobot and it uses a single analog input pin to read 5 different buttons by having each button connect via different resistors which then gives 5 different voltages. This works fine for 5V arduino's but when the reference voltage is 3.3V then half the buttons don't work... I'm wondering if this is something that has been addressed in the V2 stalker with the 328. I tried to look this up on the website, but the 328 version datasheet and manual links just have the 168 information on them. If this hasn't been addressed in the 328 version, is there a reasonable workaround for this??? Any information is greatly appreciated.

Thanks!

Re: stalker voltages...

Posted: Tue Dec 28, 2010 3:03 pm
by SQX
Hi,

Though the stalker v2.0 is a new design, the working voltage of it is 3.3v.

Thanks!

Re: stalker voltages...

Posted: Wed Dec 29, 2010 4:14 am
by ewarner77
SQX -

Thanks for the reply. I had guessed as much, but am trying to confirm things as I go. I'm wondering what would happen if 5V was hooked up to the Aref pin on the MCU (looks like pin 20 in the documentation I can find for the ATMEGA168-20AU)? Would this then make the full range of the analog inputs be 5V rather than the 3.3V that they currently are???

Thanks again!

Re: stalker voltages...

Posted: Wed Dec 29, 2010 9:48 am
by SQX
Hi,

The chip's working voltage (VCC pin4 and pin 6) is 3.3v, and the ADC working voltage (AVcc pin 18) is 3.3V too. So the ADC reference voltage (AREF pin20) can not be higher than ADC working voltage. I have try to connect AREF to 5v, and find that range of the analog is 0~5V, however the AVcc, VCC pins become 5V.

Thanks!

Re: stalker voltages...

Posted: Wed Dec 29, 2010 2:27 pm
by ewarner77
SQX -

Thanks for trying that. I was afraid it might cause a problem with the rest of the board. I guess the question is if pins 4,6, and 20 are all at 5V and then the analog portion of the chip is running it 5V and the digital part is running at 3.3V, does that then drive the XBee and memory card at 5V as well??? If it doesn't, then would that be a viable option to modify the board so that it has 5V on the analog part and 3.3V on the digital parts???

Thanks again!

Re: stalker voltages...

Posted: Wed Dec 29, 2010 2:43 pm
by ewarner77
SQX -

Sorry, I just reread your response and I think you already answered my question when you said that the Vcc is also pulled up to 5V if you put 5V on the Aref pin. I think that would then ripple on down to the XBee and micro SD card holder as well. Anyway, if you have any other ideas I would greatly appreciate it.

Thanks again!