Yesterday I received two packages in the mail, (a) more T4s to destroy, and (b) samples of FRDM4236's board. So I got to work and assembled two of my slightly modified (stretched) versions of Blackketter's board, and one of FRDM4236's board. The good news is that all three worked immediately with no need for rework, and all have been tested for read and write on all 40 GPIO pins. Fantastic!
After just one evening of working with both these breakouts here are some impressions:
1) They are both useful and neither one is better than the other. they are different and serve different functions. I want to have both in my toolkit.
2) I am now a convert to the use of castellated through holes for attaching to underside pads. In the past I've insisted on installing female headers (on loglow's T3.x breakouts) so that the Teensy could be simply unplugged, thus avoiding a major rebuild if something went wrong (which it too often did). With these new breakouts construction is fast - less than 20 mins - and I have no qualms about committing a T4 permanently to the breakout.
3) Soldering to the castellations is easy and nothing no be afraid of. A tiny bit of non-corrosive flux, a narrow tipped iron, plenty of good-quality soldering braid (I use MG brand - there is a lot of junk out there), and you're good to go. Don' panic if you do get a few solder bridges, that's where the solder braid comes in! Just be quick, and don't let the iron dwell on the pads more than is absolutely necessary. Practice with a cold iron to get the tip angle right to contact the the castellation and the pad.
The Blackketter Board:
a) This might be called a bare-bones breakout because it has no additional components or sockets, and simply exposes the hidden T4 pins in two extra 14 pin columns beside the T4 pins, giving a total of 56 pins. The order of the pins around the board seems somewhat random, (chosen for ease of PC board layout), and you may need to keep a list handy.
b) Because of the adjacent columns of pins this board
cannot be used in a breadboard, and that might be a problem for many users.
c) I've built four of these now. Assembly was easy, with no soldering problems. Only the very first one showed any functional problem, where a single pin is held high, and measures about 6.7 kohm to +3.3v. The rest of that device seems to work fine, and the other 3 units are fully functional on all GPIO pins.
d) Just my personal taste, but I like the form factor of the "squat" 14 pin height for fitting to my prototyping boards, and for now I think I will continue to use these breakouts.
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Aside: I've mentioned previously that for prototyping I use Velleman Eurocards, which are basically FRP 0.1" perf boards with Cu plated horizontal "islands" on the back, and they come with either 1, 2, or 3 holes per island. They are good quality, and I've never had a problem with a pad lifting from heat. The standard Blackketter board only works with one hole islands, whereas I only work with 2 or 3 hole islands. My solution was to use KiCad PCB software to stretch the board in width and include a gap of 0.1" between the two pin columns on one or both edges. The photo above shows the single gap version. However, I found after I built this board (which only works on two hole islands), the the double gap version actually works on both 2 and 3 hole islands, so that's all I be purchasing in the future!. I've had these built successfully in 1.6mm FRP at OSHpark (but not 0.8mm - which was a disaster, as several on this forum found out
).
The FRDM4236 Board:
This is a nicely designed board that creates a breakout in the form factor of a T3.5/T3.6, ie a DIP package with 24 pins/column - totaling 48 pins. The 20 additional pins are allocated for GND, +3.3V, 16 GPIO pins, and two unused pins. The additional GPIO pins (24 - 39) are laid out in order around the board) Across the center of the board are two rows of 5 through holes, one for an I2C OLED display, the other for access to the Teensy pins PRGM, ON/Off, VBAT, GND.
The is a mounting area for a microSD socket. an ON/OFF tactile switch and some SMD components (for the SD card only).
a) This is a very useful general purpose breakout, especially for use with a breadboard, and there is no reason why it cannot be permanently built into a project.
b) The current boards are fabricated as 0.8mm PCBs. Assembly was easy (but read the instructions carefully). FRDM4236 has taken care to make soldering the castellations easier by creating physical barriers between adjacent solder points. No problems once you realize that you have to hold the iron at a steep angle. in the slots. FRDM4236 has been quite clever about the design of the castellations for the 1mm pads. He has made it such that there are small "peninsulars" between the pads to minimize solder flow.
c) The unit worked flawlessly from the initial power-up.
d) There is a problem however. There is no way to switch the power source between VUSB and Vin. As with any T4, Vin is wired to VUSB unless the jumper is cut. On this board there is no provision (or any available pin) to put an SPDT switch or three pin jumper header. (Loglow's boards allow for a switch or header to be soldered on). If you apply voltage to USB while an external source is connected there is a serious risk of damage. I cannot see a clean way to fix it here.
My recommendation for any redesign would be to modify the power connections, use the two empty pins for something useful - my vote would be for VBAT and ON/OFF, and perhaps get rid of the OLED pins and that second row of through-holes.
Will I buy more in the future? Absolutely.
