MCP4261 w/realtek ameba RTL8195
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Re: Example Arduino Sketch for MCP4261 Potentiometer Shield?
I just can't seem to get the pins right. Any chance you could help out?
Thanks!!
Adam
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A pdf of the potentiometer shield schematic can be found here
https://bitbucket.org/iorodeo/mcp4261_shield/downloads/mcp4261_shield.pdf
We also have a library for talking the MCP4261 on the shield here in iorodeo_arduino_libs
https://bitbucket.org/iorodeo/iorodeo_arduino_libs/src
In particular see the mcp4261 sub-directory.
There is an example using the Uno shield with the library in the mcp4261/examples/uno_shield sub-directory. The example should work with the library and shield out of the box. The chip selects for the two potentiostat ICs are given in the example and are pins 5 and 6 respectively.
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I haven't used the RTL8195, but the SPI bus seems to have the same pins as the Arduino UNO, i.e., pin 13 = SCK, pin 12 = MISO, and pin 11 = MOSI. Not surprising, as it is made to be compatible. I don't see any reason why the example in mcp4261/Examples/uno_shield/uno_shield.ino wouldn't work. I would guess it is probably just a matter of making sure you have the CS pins set correctly - as in the example.
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I thought so too. I cant seem to make it work though. I tested with an UNO and it worked straight away. I guess I'll keep hacking. Thanks for the response!
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It looks like the RTL8195 has 3.3V IO. The potentiostat shield powers the MCP4261 with 5V. So you are connecting a 3.3V device to a 5V device - I think. I'm not sure if the IO pins on the RTL8195 are 5V tolerant, but you might want to check. Could be related to you issue.
Note, the MCP4261's could be powered off of 3.3V. They have a pretty broad allowed input range 2.7 - 5.5V. This would require cutting one trace - the one going to the 5.5V on the shield - and rerouting this trace to to the 3.3V pin.
The spec sheet for the MCP4261 can be found here. http://ww1.microchip.com/downloads/en/DeviceDoc/22059b.pdf