5 replies to this topic

[Frode]

Hi, in the project I'm working on now I need to connect about 10 analog sensors to my Netduino Plus 2. What are my options for extending the number of analog pins? Is there anything I can do to use the Digital pins? Perhaps add an external multiplexer? Has anyone got some good ideas on how I can hook up all those analog sensors? And another question when it comes to analog inputs. In this thread (http://forums.netdui...s-2/#entry55771) I've read that the N+2 can fry if the analog input voltage is above 3.3V. Is that correct?

[Mario Vernari]

Frode, you can use a couple of 74HC4051, which is a 8-to-1 analog de/multiplexer:

http://www.nxp.com/d...4HC_HCT4051.pdf

Even better, a couple of 74HC4052, which is a double 4-to-1:

http://www.nxp.com/d...4HC_HCT4052.pdf

 

There is also the 4067 which has 16 channels, but you could use 4 analog inputs and the multiplexing is easier.

 

NOTE: the chips must be "HC", not "HCT"!

 

Hope it helps

[Frode]

At Sparkfun I could only find this one -https://www.sparkfun.com/products/299 Is there any reason NOT to use that one vs one of the others you suggested? Its exactly the same just with more pins, right?

[Mario Vernari]

As stated in my previous post, the HC4067 is also suitable.

Sparkfun offers this chip as well, which looks even better than the HC4052:

https://www.sparkfun.../products/10652

 

From my perspective, being both the chips SMD, they would be a nightmare to sold manually: I'd choose a DIP.

Apart this personal consideration, the comparison is between the HC4067 and the TS3A5017. They both act as a "switch" with a small resistance.

 

== HC4067

Pros: a single 24-pins chip offers a 16 channels expansion; good price;

Cons: the resistance of the selected route isn't very low (about 70 Ohms);

 

It needs just one analog and four outputs.

The software would look as follows:

 

for (int i=0; i<16; i++)

{

  a.Write( ... );

  b.Write( ... );

  c.Write( ... );

  d.Write( ... );

  adc.Read();

}

 

 

== TS3A5017

Pros: very low resistance (10 Ohms)

Cons: you need two 16-pins chips; the price is 3x; can't work with voltages greater than 3.3V (that's the same limit of the Netduino, however).

It needs 4 analogs and two outputs.

The software would look as follows:

 

for (int i=0; i<4; i++)

{

  a.Write( ... );

  b.Write( ... );

  adc0.Read();

  adc1.Read();

  adc2.Read();

  adc3.Read();

}

 

 

I think that you should say what's better. I'd like more the second chip, but if you don't have performance yet accuracy problems, the first chip is good as well.

To sum everything up, the HC4067 is an average quality chip, while the TS3A5017 is a good quality one.

Ciao.

[jrlyman3]

You could try a multichannel (16) ADC chip that you can access over I2C like the LTC2498.  It's a 38 pin QFN so that might be a problem for prototyping and hobbyist use, but Digikey does have a $50 eval board.

[Frode]

Thanks, I've ordered both the HC4067, [color=rgb(40,40,40);font-family:helvetica, arial, sans-serif;]TS3A5017[/color] and HC4051. Will try them all and see which one I like best