Board size (and how to reduce it)


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Hi everyone,

I am seeking for a little advice here...

I have an already finished project of a gaming handheld driven by a RP2040. Unfortunately, the RP2040 struggles to deliver the necessary performance.

Now, I think the Teensy is able to deliver that performance. However, since a Sega Genesis emulator is supposed to run, a whole ROM needs to fit into the flash storage. The Teensy 4.1 features enough storage. However, it is too tall to fit into the already existing case. The Teensy 4.0 on the other hand has a perfect size but the storage is just too small and an external flash chip tied via a (single) SPI interface might create a bottleneck.

Now, I was wondering if it was "safely" possible to cut off the lower part of the Teensy 4.1 board, i.e. the part with the SD card reader just beneath the row of holes (beneath hole 27 resp. 38). When I say "safely" I mean "are there any vital traces that are needed for the board to function OR would the cutting - if done properly - only imply to lose the ability to use the SD card reader and the expansion pads for PSRAM/more flash"?

Any advice is highly appreciated. Thanks in advance.
When I say "safely" I mean "are there any vital traces that are needed for the board to function OR would the cutting - if done properly - only imply to lose the ability to use the SD card reader and the expansion pads for PSRAM/more flash"?

I can confirm all the stuff beyond the 5 through-hole pin is non-essential for Teensy 4.1 to run. You'll just lose 18 I/O pins, SD socket, and PSRAM pads.

How to "safely" cut the PCB is a good question. It is a 6 layer PCB, where 2 of the 4 internal layers are GND and 3.3V.
If you can go slightly wider, you might look at the Teensy micromod, which is a Teensy 4.1 with M.2 hookup instead of using through hole pins that Sparcfun sells. Now, at first glance, the carrier boards that they have for micromod seem on the large size. But you can order the DIY attachment kit, and either hand solder to it, or design your own carrier board:

The other way may be to do a DIY Teensy 4.1 getting the MKL02 boot loader chip and buying a IMXRT1062DV*6B or IMXRT1062DV*6A (NXP) processor and W25Q16JV*IM or W25Q64JV*IM (Winbond) flash memory chip. Presumably this is not for the faint-hearted:

The T_4.0 also has USB_HOST pins/ability. If storage space is needed and speed provided can be acceptable, and a SMALL enough USB Flash drive could be connected that would give much larger storage space.

There is a USB_Host thread - off hand the transfer rate isn't known - post here shows it might be 6 to 18 MB/sec :

So USB Host pins and GND and Power to a USB connector to a Flash Drive too big?

Also: Minimal attach is a micro SD card into an adapter with the pins properly soldered for the SD CARD pads on the T_4.0 bottom side.

Both are faster and bigger than using onboard flash for storage.
Thanks very much to all for the input. I will probably go with chopping off the T4.1's bottom.

The problem with external storage is access time (rather than max transfer speed). I am sure one could do some clever caching from, say, and external SD card storage - however, that would add quite some complexity to the project software-wise.
Also, space is quite a big constraint. In case anyone is interested in the original project, you can find all the details in my Github account. resp.

Thanks again very much for the input. I will definitely report back what way I went. Kind regards.
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I once had to cut large 4-layer boards down in size and found that a bandsaw with a fine tooth blade did a good job. Main issue that came up was that the internal power/gnd planes would occasionally short due to slivers of metal bridging them from the sawing motion. A visual inspection and check with a meter were used to catch that.

Teensy is so small that something like a dremel with a fine cut-off wheel would probably work OK. I'd probably cut through the USB Host connector holes since they provide some structural support to the FR-4 layers and would help prevent delamination.
Just wanted you to give a little update: I ended up making thet cut with a CNC milling machine. I was surprised finding the inner layers so close together. After successfully chopping off the lower part, I lay out a little PCB on which I could then mount the Teensy. The PCB also carries a SD card slot tied on via SPI.
It runs Sega Genesis as well as SNES (although this was a little fiddly with "only" 1 MB of RAM - other emulators seem to make use of external PSRAM).
In case anyone is interested in the PCB and/or the details just drop me a line (though the design is a little sloppy).