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I'm trying to make a simple line tracing robot, however I couldn't figure out how to connect AGND and DGND of A/D converter(MCP3208) on a simple perfboard design. I need some guidance how to smooth out the noise for AGND and how to connect these two grounds.

The A/D converter that I'm using(MCP3208)

Thank you!

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  • \$\begingroup\$ What does the data sheet say that confuses you? \$\endgroup\$
    – Andy aka
    Commented Nov 28, 2015 at 11:06
  • \$\begingroup\$ @Andyaka Actually the general connection of ADCs confuses me. Because I hardly managed to provide a stable Vref using zener diode, however, now most of the people says do not connect the AGND and DGND directly. I couldn't find any simplified design that could fit into my simple application. Do I really need to seperate these two GNDs? \$\endgroup\$
    – Burak.
    Commented Nov 28, 2015 at 11:10
  • \$\begingroup\$ So what advice does the DS give you that is confusing? Also note that the DS says AGND and DGND are connected internally on the chip via 5 to 10 ohms. Single ended measurements are always a risk because 0V at one end of your robot aint gonna look the same as the other end. \$\endgroup\$
    – Andy aka
    Commented Nov 28, 2015 at 11:16
  • \$\begingroup\$ Section 6.5 Utilizing the Digital and Analog Ground Pins \$\endgroup\$
    – Passerby
    Commented Nov 28, 2015 at 11:23
  • \$\begingroup\$ @Andyaka Nothing in DS, it's actually the web that confused me Telling me to separate pins. So what connection doyou recommend for this particular chip, I can check that as an answer because It'll provide straightforward explanation to make me understand. I'm using all 8 CHs to IR sensor array, SPI communication with FPGA, I got 4.7V zener diode and 1k Resistor to provide Vref, the only thing left is the grounding, thats what I couldn't figure out, because I'm newbie in electronics, knowing the necessity of separation of these two grounds, I couldn't figure out how to connect those GND pins . \$\endgroup\$
    – Burak.
    Commented Nov 28, 2015 at 11:27

2 Answers 2

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Given your level of experience, I suggest you focus on making a single low impedance ground. Separate analog and digital grounds never benefit digital circuitry. If they are not done correctly, they also do not benefit analog circuitry. So just ground everything together (no separate analog and digital ground). Use boards with continuous solid ground planes. You can also make an artificial GND plane on a single layer board using copper tape.

If you have to run wires from board to board, make half of the wires GND. In other words, for every signal that goes from board to board, there should also be a ground wire. For every power connection that goes from board to board, there should also be a ground wire. Twist each power or signal wire with its dedicated GND. This will save you a lot of trouble.

Each board should have room for a large bulk capacitor of at least 220 uF. This is in addition to the 0.1 uF per power pin and/or whatever is recommended by the chip vendor.

Order a kit of cable ferrites so that you have it ready just in case you have unexpected noise problems. The board-to-board wires can be routed through the ferrites to suppress high frequency noise.

In the schematic, place small resistors in series and small capacitors to ground on the analog inputs coming back from the reflectance array. Basically you want to be able to make an RC low-pass filter at each input. On the layout, place these RC components close to the actual analog input. Make sure you have an array of different resistor and capacitor values on-hand so you can tune the cutoff frequency of the RC filter.

Good luck! Have fun.

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A good place to start on how to connect gnds is the following link:

http://www.analog.com/library/analogDialogue/Anniversary/12.html

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  • \$\begingroup\$ Here, we summarise link contents in the post. It's so that if the link changes, the answer isn't invalidated \$\endgroup\$
    – Alexander M
    Commented Nov 30, 2015 at 3:13

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