Would you comment on using the following components to level shift from Arduino O/P to SD card I/P?
The diodes would be germanium.
And how about adding D2 to points 1 and 2.
EDIT: Measured the diode drop of an 1N34A @ 5ma it was .3volts
The level shifter is good. The Germanium protects the Silicon. 1mA current : good.
No D2 diode needed.
Uno R3 has LP2895 3.3v regulator, only good for 150mA.
Many (most?) SD cards need more than that.
Bite the bullet and get a more capable regulator and a 4-buffer chip (SCK, MOSI, chip select needed going out at least, I prefer to translate MISO coming back so that 5V devices on SPI don't overdrive the data out line from the SD card).
Adafruit datalogger used to use 74AC125D powered from 3.3V, I used that on my original Bobuino also with a IXF25001MEV33 regulator for current.
Items 15 & 16 here
(altho it looks like I just had the SD DO connected right to MISO, so I hadn't gone to buffering the line then, if no card is inserted while the chip is being bootloaded the card's DO line would not be exposed to higher levels)
http://www.crossroadsfencing.com/BobuinoRev17/
atmega1284_Rev17_itead_dual_uSD.sch (388 KB)
AmbiLobe:
The level shifter is good. The Germanium protects the Silicon. 1mA current : good.
No D2 diode needed.
I'd reduce the resistor to 1k or perhaps less, and keep both diodes, some SDcards need fast edges
to be happy (their inputs are designed for DDR at 50MHz).
SDcards need a lot of supply current when writing, use an external 3.3V regulator, not the weedy 3.3V from the
Arduino or it'll overload.
The diode will pull up on the 3.3 volt power supply. The regulator in the 3.3v supply is made for loads that pull down, not loads that pull up. Negative regulators are appropriate for diode clamps that pull the voltage up. The LM337 is the negative regulator that I use for that reason. My circuit has many diodes pulling upwards in voltage, so I use LM337 for negative voltage regulators running at 6 volts. It is not a negative voltage, but it is more negative than the 9 volt power supply that helps drive the diodes through op amps. So in your case, you can use an LM337 with three terminals :
IN = 0.0v
OUT = 3.3v
ADJUST = resistor network
The load on the 3.3v output of the LM337 includes a resistor to 5v to keep some minimal load current going through the regulator for stability.
Personally, for my SD stuff, I use a naked 328P-PU running @8MHz (internal) and run the 328 and SD breakout at 3.3V.
However, if you must use a 5V Arduino, this is a better interfacing approach to the SD at 3.3V
Link for reference... Chips much cheaper from others.
Thanks for the comments.
I've tons of 74HC245, over kill but they will do the job for standalone projects.
I'll get a Bobuino when it's available.
LarryD:
Thanks for the comments.
I've tons of 74HC245, over kill but they will do the job for standalone projects.
No they won't, they are not level-shifters. The 74LVC245 accepts inputs upto 5.5V when powered
from 3.3V, the 74HC245 definitely does not.
You are absolutely right.
LarryD:
Thanks for the comments.
I've tons of 74HC245, over kill but they will do the job for standalone projects.I'll get a Bobuino when it's available.
Finished updating the design to add the extra 2 pins each at the power & upper digital header, cleaned up a lot of the trace routing (original was my 2nd PCB design, have improved my routing skills a lot since then).
Debating whether to make the board wider (but not longer) to accomodate ICSP header in the usual spot, around where IC1 is now, and push the SD sockets up. Board is 100 x61m now.
Debating whether to make the board wider (but not longer) to accomodate ICSP header in the usual spot
Bob, on my own rendition of a 1284 pcb with DIP40, I did not place the ICSP header in the usual spot. After all, DIP40 is so darn big and the pcb was already somewhat over the UNO form-factor size, plus I was much more interested in having an XBee socket on the pcb, so ICSP got relocated.
Now, of course, I have an Ethernet shield stacked on one of my 1284 boards, and am about to do a 2nd, but cannot plug the shield in properly [so made a h.w. hack].
Since your board basically follows the UNO form-factor, and is designed to appeal to the wider Arduino audience, I'd 110% recommend moving things around to put the ICSP header in the "proper" place.
EDIT: btw, I'd also try to get at least 2 of the mounting holes to line up in the regular positions. 3 of my 4 holes do, and I find that's really crucial for robust stacking of shields. IOW, slide that big puppy back to the left, and add in the ICSP header and holes. You also have room for the usual hole near the D8..D13 header.
CrossRoads:
LarryD:
Thanks for the comments.
I've tons of 74HC245, over kill but they will do the job for standalone projects.I'll get a Bobuino when it's available.
Finished updating the design to add the extra 2 pins each at the power & upper digital header, cleaned up a lot of the trace routing (original was my 2nd PCB design, have improved my routing skills a lot since then).
Debating whether to make the board wider (but not longer) to accomodate ICSP header in the usual spot, around where IC1 is now, and push the SD sockets up. Board is 100 x61m now.
I wouldn't mind wider.
Perhaps some holes next to the female headers so male right angle headers could be added as needed for off board switches or LEDs etc.
For use with Front Panel Bezels 
Thanks for the suggestions.
Re: ICSP placement, this is the layout for my 1284/FTDI board. The ICSP is located next to 1284 pins 2 & 3.
The socketed 1284 sits a scooch high, but the programmer mates ok. The original 1284 will need to be moved a lot.
At the moment, I'm kinda bummed out. Was pricing up 10-lot kit of material for updated Bobuino original, with some parts from DipMicro (easier to locate header type stuff than at Mouser, and also less expensive), 1284P, Rs, Cs, diodes from Mouser, and regulators from Digikey (because Mouser doesn't seem to carry a decent 3.3V regulator).
With estimated stencil/pick & place programming/ass'y cost for CBAS-USA,
shipping from Mouser/DipMicro/Digikey,
shipping to me,
and then shipping out to the world, units costs are too high, $108, big driver is the pick & place/stencil costs. Still need to add regulators and sales tax costs also.
Changing from FT232RL to FT230XS would save a couple of dollars, assuming RTS from it works the same as DTR from FT232RL.
BobuinoRev19draftPL.xlsx (18.6 KB)
Very minimal changes to the layout in reply #9:
- slide C6 down, move C7 to where RTC is.
- slide 1284 left about 1/2".
- slide SD socket 0.1" to the right.
- move ICSP to normal position.
- add 3 holes in standard UNO locations.
- remove all current mounting holes.
- move RTC over to right side, where 1284 vacated.
- move battery to under SD.
- most everything else can stay where it is.
You might even be able to take 0.1" or more off the top of the pcb.
(because Mouser doesn't seem to carry a decent 3.3V regulator).
Also, I'd take DPAKs any day over SOT-223.
The SOT223 is just for the 3.3V. I want to stay away from parts that don't have the tabs grounded so I don't have to carve out a big chunk of ground plane for cooling them. Mouser doesn't seem to carry any like that.
Very minimal - ha ha, I like that 
Nothing is minimal.
I moved stuff around a lot, changed the battery holder size, sort of left if because I want the option of a 2nd card on the bottom, checked the female headers and mounting holes - need to double check ICSP - got it lined up correct even with A5 and D1 - 22.5mm from A5 hole to nearest corner hole (pin 5)?
Letting it autoroute & going to bed, see how bad it is in the morning. Maybe upgrade to eagle 6.5 tomorrow let it try again.
Then clean it up by hand to get the simple connections I placed parts near each other for ...
Thinking maybe I'll add the op-amp, ADC, DAC, REF194, lineout driver that fat17lib has been writing code for too, board cost for 100x100mm same as for 100x65mm, might as well take advantage of this opportunity & use the free space with SPI & serial connections readily av available.
Got the 2nd row headers in too..
CrossRoads:
The SOT223 is just for the 3.3V. I want to stay away from parts that don't have the tabs grounded so I don't have to carve out a big chunk of ground plane for cooling them. Mouser doesn't seem to carry any like that.Very minimal - ha ha, I like that
Nothing is minimal.
I moved stuff around a lot, changed the battery holder size, sort of left if because I want the option of a 2nd card on the bottom, checked the female headers and mounting holes - need to double check ICSP - got it lined up correct even with A5 and D1 - 22.5mm from A5 hole to nearest corner hole (pin 5)?
Letting it autoroute & going to bed, see how bad it is in the morning. Maybe upgrade to eagle 6.5 tomorrow let it try again.
Then clean it up by hand to get the simple connections I placed parts near each other for ...
"- most everything else can stay where it is" <-- that's what minimal means, lol.
Yeah, smt v.reg with grounded tab is a slight problem. I just bit the bullet, and went to all LM317 pin ordering. Tomorrow.
At the moment, I'm kinda bummed out.
I will commit to $25.00 to help out with the development cost.
Larry
I'm more concerned with the final sell cost. $80 was too much for the original 2 years ago, even made it to hackaday where the price was ravished, even tho it combined the functionality of an expanded Uno, RTC, RS232 drive, and SD shield all into 1. And that was me & my wife & my kid assembling them down at Skyjumper's workshop as we didn't have reflow capability yet. Now with the kid off at college and the good eyesight gone with him, I'd like to get automated, reliable assembly in place (the FTDI module is the worst) that raises the labor cost and makes it price prohibitive.
Maybe ditch the discrete FTDI chip and just put in a header like I do on the thru hole board, we can do the other parts fairly easily in a reflow oven.
Offer it as partial kit, PCB with SMD parts only installed, folks can finish all the thru parts themselves.
Maybe ditch the discrete FTDI chip and just put in a header like I do on the thru hole board.
Offer it as partial kit, PCB with SMD parts only installed, folks can finish all the thru parts themselves.
This is reasonable.
I have a FTDI Serial TTL-232 USB Cable : ID 70 : Adafruit Industries, Unique & fun DIY electronics and kits
