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 Posted - 11/26/2005 : 21:13:50
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Hello,
we are interested to connect an external ADC to our mica2dot,
looking at the schematic we couldn't see any valid pin on the test points for this purpose,
can you suggest us where we could attach this external ADC and which interface could be used (...I2C , SPI ) ??
many Thanks,
Antonio D'Ottavio
PIN DESCRIPTION
TP1 GND
TP2 ADC7
TP3 ADC6
TP4 ADC5
TP5 ADC4
TP6 VCC
TP7 PW1
TP8 PW0
TP9 UART_TXD
TP10 UART_RXD
TP11 RESETN
TP12 SPI_CK
TP13 ADC3
TP14 ADC2
TP15 PWM1B
TP18 GND
TP19 INT1
TP20 INT0
TP21 THERM_PWR
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Ian
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 Posted - 11/26/2005 : 21:20:38
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Here are some suggestions:
- Identify the ADC that is best for your application.
Investigate power-down/sleep power requirements - you do want an ADC that consumes very small power when not converting. The Texas Instruments ADS8344 might be a good choice.
-Determine data rate from ADC
-Determine available interfaces- Data (SPI,I2C etc) and Contol (ChipSelect, Powerdown) of ADC
-Determine HW design
Power and electrical noise issues are very important to consider when designing a sensor board. Study the ADC manufacturer's datasheet and application notes very carefully for suggestions.
MICA2DOT Interfacing
The Mica2DOT has limited I/O because there are only 20 i/o pins available - not 51 as on MICA2.
Some of these are reserved for mote programming and communication (eg TXD0,RXD0,RSTN,SCK) so do not use those unless you understand exactly how they interact.
The 6 lines ADC2-ADC7 are available as general purpose I/O lines if the M2DOT internal ADC is not used. So you have about 12 I/O lines available for your use - which should be more than enough.
These are ADC2-7,PW0,PW1, PWM1B, INT0, INT1, and GPS_ENA.
Review the platform/mica2dot/hardware.h file to see their assignments to ATMega128 ports etc.
ADC Control (ChipSelect etc)
Almost any of the above I/Os can be used. Note the polarity and pullup features of ATMega128 can save you some logic/components on you ADC design.
ADC Data
You will probably need to "bit bang" the data interface (I2C or SPI). There are many examples software to do this in the TOS platform and apps directories. The limitation may be on data rate depending on your application.
When you have the lower level "HPL" drivers designed you can use them to build an equivalent to ADCC module for use by TOS applications.
Hope this helps and good luck,
Ian |
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 Posted - 11/26/2005 : 21:22:16
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Hi,
really thanks for your help, it was really important for us, now I've a starting point, I've seen the datasheet of ADS8344, it is a 16 bit converter so we could use both 2 byte when we transmit he packet and not only 10 bits arranged on 2 byte like with the Atmega128 ADC converter, now I'll study how to connect this ADC to the processor, I'm not sure if to use I2C or SPI, hope to understand soon something more.
We have single ended signal bipolar relative to ground and for this is really interesting the application note "Getting the Full Potential from your ADC (Rev. A).pdf" .
For the software question soon I'll see also this aspect that seems to be the more difficult at the moment.
Many thanks for your help ... |
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External ADC for Mica2Dot
