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Let's_see_Ashley , 09-23-2024, 09:42 AM

Hello everyone!
I'm working on a small project to DIY the SIMCOMM Raspberry Pi hat. I've played along with dimensions, and have elongated.

Can anyone please review the schematics and the PCB layout?

QDrives , 09-23-2024, 12:17 PM

We cannot review a schematic if none is provided.
Which layer is the one with orange traces? You may want to pour copper there to to balance the copper.

Let's_see_Ashley , 09-23-2024, 12:47 PM

sorry My mistake. I forget to attach the schematic. PFA in this messege.

Let's_see_Ashley , 09-23-2024, 12:48 PM

it is In.Cu-2. In-Cu-1 is the green one with a solid ground plane.

QDrives , 09-24-2024, 11:56 AM

"In.Cu2" -- I assume a KiCad name?
Anyhow, you have 3 layers full of copper and one barely. This will make your board bend. Keep copper balanced between the layers (symmetry).

Let's_see_Ashley , 09-24-2024, 02:52 PM

Okay thanks for this feedback will do it.

Let's_see_Ashley , 09-24-2024, 02:53 PM

I want to know if there is any specific guidelines for routing CLK trace. Like any standard impedance control.

QDrives , 09-24-2024, 03:06 PM

Why have a capacitor on them?
And why is the clock resistor 0 ohm and data 22 ohm?

Let's_see_Ashley , 09-25-2024, 10:15 AM

hi, I've used the interface circuit shown on the datasheet of the module. It's shown to have 22ohm resistor for clk signal with 22pf capacitor pulled down.

Let's_see_Ashley , 09-25-2024, 10:18 AM

> The rise/fall time of USIM_CLK should not be more than 40ns.

this is stated for the CLK signal. How can I use this information to calculate the impedance for the trace? and what should be taken care.

QDrives , 09-26-2024, 07:25 PM

That depends more on the output driver. I assume the Raspberry Pi.
If the rise/fall time must be fast, than it is better not to add a capacitor. You also have a TVS diode for protection, so you do not need a capacitor.