Can anyone check Multiplexer Schematic?

Dear fellow purveyors of perpetuity,

Could anyone please check my schematic, have been learning easyEDA past few days. Sincere thanks for any help anyone can offer.

It uses a 74HC4067 multiplexer breakout board, similar to the one sold by sparkfun.

TonyAm

Always add a decoupling capacitor on the supply pins.

The photo sensor circuit does not make sense.

Do not run connections thru the I.C. symbol.

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In addition to the suggested capacitors. I believe you want S1 to connected between R13 and R14, then the "other" end of R13 would connect to V+

If you are making a PCB I would suggest you add a capacitor between each pot wiper and ground. Assuming SMD this would take little board real estate and don't have to be populated if you find you don't need them. Else if the pots are remote the capacitor could be very helpful.

Here's an edit. I've added a decoup cap, removed routes from going thru IC.

What I'm trying to do with the photoresistor is have it be read by the analog MUX pin# 4, C3 when switch 1 is closed, and not read anything when SW1 is open. Do I need the R14 1k resistor there?

These will be non-smd parts, but having caps between wiper and gnd would still be good? The pots will be off the board (not soldered to the board), but instead wired to the board at a length of about 4".

Sincere thanks again.
TonyAm

Edit: Added a path to gnd.

2nd Edit: Fixed Gnd & +V routes coming from the decouple cap.

Looks better, pin 19 EN of the mux still runs thru the connector symbol.

A capacitor from the analog Arduino input pin to GND should be good enough.

Yes R1 is needed.

Make sure the decoupling capacitor is close to the Mux power pins.

I changed the position of the power input connector & decouple cap.

What would the value of the caps be for connecting ?

Sincere thanks.

Use 5V and GND symbols, as many as you need, to de-clutter and simplify your schematic. You could add a 5V and GND symbol for each pot, for example.

Good advice when building the circuit or laying out a PCB design, but not relevant to drawing a schematic. A schematic does not need to reflect the actual size, position, orientation or pin positions of components. Only the connections between them are important. Other than that, the arrangement of the schematic should be chosen to make it as easy to read and simple to understand as possible.

Yes, I moved the decoup cap closer to the power pins just to remind me to do so in the board layout. (I forgot about the importance of that).

Thanks.
TonyAm

Agreed, however, my comment was Make sure the decoupling capacitor is close to the Mux power pins. my meaning was "when building the circuit or laying out a PCB design".
:slight_smile:

I know that, but I did not want @tonyame to be confused, so was attempting to clarify how they should interpret your advice.

Physical placement of components like decoupling capacitors is highly important when physically laying out a circuit, but completely unimportant when drawing a schematic. In fact, it would be important not to reflect the physical layout, if placing components on a schematic, to reflect the required physical layout, makes it less easy to read and understand.

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I understand, thank you.

I would suggest you plan for 0.1µF ceramic capacitors. Assuming the pots will be somewhat remote from the multiplexer you would want the capacitors right at the board input for the pots. Here short leads to both the pot input and ground are key to suppressing noise before it enters the board. Once the noise gets onto the board it becomes very difficult to suppress.

Thank you. Is it ok to have routes go under the IC when arranging the pcb?

Yes.


BTW, avoid traces under crystals.

Yes, however for my boards (which are all considered prototypes) I don't connect pins of an IC to other pins of the IC, under the IC.
My logic is I want to be able to cut and jumper those traces in case I need to make a "fix" or some other modification.

I learned this by having to modify an eBay board where an enable pin was connected to ground under the IC. I had to lift the leg (SMD) to make the modification. Not something I enjoy doing.

Regarding schematic component location reflecting the desired board physical location, it do this all the time. For instance I place a regulator required input and output capacitors near the regulator. I don't see how this would adversely effect readability.

I'm also a proponent of notes on the schematic. I like notes in plain language. For instance identifying high current traces or location there two grounds are connected etc.
I will admit others have found my propensity for notes on drawings odd, I think it makes perfect sense. To me it's like commenting code.

Here is an updated version of the analog MUX with pots, a photocell, and caps added to the wipers of each pot. (0.1u ceramic caps connected to each wiper and gnd).

Thanks for the help.
TonyAm