8 replies to this topic

[GDSever]

The Microchip MCP3202, MCP3204 and MCP3208 can provide 12-bit ADC readings to your Netduino using the SPI communication pins (3), plus a fourth digital output for a chip select line. The attached project file demonstrates the use of these chips to take temperature readings from a couple LM34 temperature sensors on channel 0 and 7 of a MCP3208.

Basic usage of the MCP320X class is as follows:

    // 8 channels. Uses default clock rate & CS pin. Other constructors are provided as well.
    MCP320X myChip = new MCP320X(8);  
    // Read the ADC measurement for channel 0
    ushort myReading = myChip.ReadADC(0);

[edit]The ZIP file was replaced 2010-11-28 to accomodate the MCP3202 chip. The command structure is slightly different, and the example class should handled 3202, 3204 and 3208 chips now.[/edit]

Attached Files

•  MCP3208_bb.png   25.5KB   205 downloads
•  MCP320X.zip   78.97KB   156 downloads

[bill.french]

Thanks for this, I have been playing with an MCP3204 -- i was wondering the "proper" way to combine the two bytes into the reading.. bitwise operators have always been mysterious to me. I got it working but my solution does not look nearly as smart as yours...

I have been having a ton of problems getting decent, stable readings, though. Do you have any sample circuits and pictures you could post?

Here are some premade boards i've been thinking about:
http://www.mikroe.co.../easyadc-board/
http://www.mikroe.co...dc-proto-board/

[GDSever]

Getting stable 12 bit readings is definitely a trick, and I am no signal conditioning expert. I know the MCP320X datasheets have a number of example circuits in them, but I haven't spent alot of time analyzing and trying them out - I would likely go with a commercial solution myself, to be honest. To somewhat compensate for this, you'll notice I have a couple of optional paramters in the ReadADC method, one of them being number of samples. This is an admittedly poor way to somewhat stablize the readings by taking more than 1 and averaging them together. In my day job I deal alot with statistics, so this is how I typically and practically compensate for variation on a daily basis... But I'm sure there are plenty of good hardware methods of doing the same. Best regards!

[GDSever]

I just read the datasheet for the MCP3202. Looks like the bit streams are different than the 3204/8, so I'll have to do a little testing and post a revised class that works for the 3202.

[bill.french]

If you don't mind me asking, what kind of project are you working on?

[GDSever]

If you don't mind me asking, what kind of project are you working on?

My projects typically center around needless technological add-ons to my homebrewing gear (beer). I have tons of pressure and temperature sensors as well as switches, and I'm moving away from my previous embedded development platform to the Netduino, so that means re-developing alot of the libraries I had already in C# (and hopefully VB, once the Netduino supports it).

My current focus is replacing my hard-wired grant with a wireless (Xbee) solution using the Xbee API - something that is very easy to do on the Netduino but would have been near impossible on the previous platform.

Check out my blog if you are interested - link should be in my user profile.

Oh - I also replaced the ZIP file in the first post with a newer version that also supports the MCP3202, if you are interested. Best regards,

[marcelvdk]

Him I've read this post with interest. At this momement i'm testing a 16 bit ADC (ADS8320 from TI). I am trying to figure out your code to adapt it for this ADC. Can you give me some input about what parts to adapt so that i get a good 16 bit readout? I'm new to programming in C#. I've tested it on an arduino and a Mbed and it seems to work oke. The samplerate will be 20Kz in the project i'm doing. Is that a problem for the Netduino? with kind regards, Marcel

[Illishar]

The samplerate will be 20Kz in the project i'm doing. Is that a problem for the Netduino?

20k Hz might be a bit much for netmf. You'd most likely have to implement a native driver at least. (I'm sampling at 25k Hz in native code though.)

[marcelvdk]

20k Hz might be a bit much for netmf. You'd most likely have to implement a native driver at least. (I'm sampling at 25k Hz in native code though.)

Mmmmm , native driver, i guess i'm out of my league here. Can you give me a starting point /direction?

greets,

Marcel