First circuit and PCB

[gcain]

Hi Guys,

I need a small temp and humidity circuit for a sensor that's already been built so decided to use this as a learning exercise.

Could someone please eyeball this and make sure I haven't done anything dumb. Here is the IC being used. The typical application is on page one, the circuit is attached as an image.

The goal is to create a small PCB with temp and humidity interfaced via I2C.



Thanks in advance.


Edit: I just noticed I have pin 1 on the connector as VDD but it looks like it should really be ground?

[gcain]

I think I've made some progress.

Changed the 5pin header to just 5 holes so I can solder leads to them. The order of the pinout seems more sane now. There's a PCB layout too.

[negativ3]

Just an example of creating your own schematic symbols, can make layout much neater and easy to decipher, while keeping pin numbers properly aligned with the footprint.

A very important skill to practice, the more into design/layout you get.

[gcain]

Oh, that is handy!

Thank you for the tip. I'll clean it up now.

[gamalot]

Place a decoupling capacitor near the power supply pin.

[pcprogrammer]

Your second version of the schematic is even worse, and placing text on the copper layer is fine, but don't have it overlap your trace. It is better to put text on the silk screen layer. Does not cost any extra.

To make it a bit more usable, you might want to add a jumper setup to allow address selection of the IC. Can be done with a pullup resistor and a shorting jumper to ground, or a jumper that allows switching between supply and ground. This way you can have two of those modules on the same I2C bus.

I second the decoupling capacitor.

[gcain]

Your second version of the schematic is even worse, and placing text on the copper layer is fine, but don't have it overlap your trace. It is better to put text on the silk screen layer. Does not cost any extra.

I didn't understand what the issue was with the text until you mentioned it being on the wrong layer. Fixed now.

To make it a bit more usable, you might want to add a jumper setup to allow address selection of the IC. Can be done with a pullup resistor and a shorting jumper to ground, or a jumper that allows switching between supply and ground. This way you can have two of those modules on the same I2C bus.

I'll play around and try implement this.

I second the decoupling capacitor.

[gcain]

Place a decoupling capacitor near the power supply pin.

I've used a 100nF from VDD to ground.
Will post an updated image once I work out the IC address jumper.

[xvr]

IC pad should be connected to GND

Take a look at page 36 in datasheet (https://www.ti.com/lit/ds/symlink/hdc2022.pdf) with layout example

[gcain]

Thanks to everyone for the direction so far! It's been a steep learning curve.

How's this one looking now?



If it helps any I am using EasyEDA for this, for no reason other than it's the first application I made some progress in.

I'm not sure how to represent the through holes on the far right yet. Doing it this way appears correct on the 3d render of the PCB.

[xvr]

Add pull down resistor to ADDR pin
Move resistor R3 up so that it is not crossed by the wire.

I'm not sure how to represent the through holes on the far right yet.

I'm not sure how this can be done in EasyEDA, but in KiCAD it can be achieved by placing a "MountingHole" component on the schematic. Perhaps it can be done similarly in EasyEDA.

[gcain]

R5 added to pull ADDR down.
I left it alone initially because in the docs it stated: "Address select pin – connect to VDD, GND or float." Thinking about it a little more, I'd imagine you'd want a definitive declared value for the address selection.

Will look into the mounting hole option.

[gamalot]

If you read the datasheet carefully, you'll notice that pulling the ADDR pin low or leaving it floating ends up doing the same thing. An external pull down resistor is redundant, because the chip already has one inside.

[SCSKITS]

Looking better. I would set up C1 so the ground symbol is facing down like the one on U2 pin 7. Also, why U2, it should be U1 since there are no other ICs on the board. Also try to avoid text overlapping wires. Spread things out a bit if needed. On the IC symbol, I would have the VCC pin on the top (like the ground on the bottom). Move R3 up next to R4. Re-annotate to start with R1. Try to avoid having wires/connections under part symbols.

[xvr]

I left it alone initially because in the docs it stated: "Address select pin – connect to VDD, GND or float."

Yes, it can be left unused if the pin is not connected. However, if you connect a header to it, it may pick up noise. I don't know if the built-in pull-up resistor is sufficient to maintain a stable low level on this pin, so an external pull-up resistor may be desirable (in some cases). Just reserve space for it, but don't install it unless you'll have problems with I2C addressing.

[Doctorandus_P]

For the address selection, I would add another resistor to VDD. That way you can choose later which of the resistors you place on the PCB.

Placing the text of R5 over a wire is not good. Fix that.
For values of capacitors and resistors and such: Be at least consistent. If you don't add "Ohm" to resistors, then also do not add an "F" to capacitors. It's very common to just use the value without the units, thus just "100n" for capacitors.

According to: https://en.wikipedia.org/wiki/RKM_code It's correct to use a capital "K" for resistors in the kilo ohm range, but in practice this is very rare. It creates confusion with K used as units for Kelvin. You are also not consistent here by using a lower case n in "100nF".

[PGPG]

If GND text at arrow (bottom right of schematic) sets the wire net to be GND (I'm not sure as it can be for example only text and not label) then:
GND symbol under IC pin 7 is not needed (but the dot would be needed).
If this GND text is only text than pin2 is not connected to GND (dot would be needed).

[negativ3]

Link pin7 to ground (thermal pad).
Avoid additional resistors as detailed in the datasheet.
Be aware of datasheet recommendations regarding layout/ground planes and polling frequency.
Naming all the nets can be very useful for you when laying out the PCB, plus it's just good practice.
It's quite acceptable to keep decoupling caps off the circuit for neatness but just off to one side, or in an area on the schematic sheet(s) dedicated to decoupling. Keeping track of them is the most important part when you start laying out the PCB.
In my example, the header P1 can be left unpopulated and connect the pads by solder blob, the determining factor for even including the header is how many sensors will share the same bus? If only one sensor, just link ADDR to GND and keep it simple. It's one of the many decisions you make at the outset of designing, in this case I2C bus architecture.

You've already built the sensor circuit? Possible to post up a picture?