I thought it might be interesting to introduce a Mini variant that did two things: have built in USB for easy interface and did away with Basic Stamp conventions so that all i/o pins are accessible by the breadboard. Designed in the spirit of the BoArduino and RBBB but surface mount with no assembly required (in production), as small as humanly possible, and includes the 2 extra analog pins as a bonus. Oh and it had to be Diecimila compatible with the auto reset and 500mA fuse!
So here is the first working prototype of the Freeduino Mini USB. I have already made some changes to the design as you will see in the schematic and board images largely because of a boneheaded mistake not to bring out the reset pin. So the next prototype will jump from 24pin to 26pin making room for RESET and 3V3 and moves those pins around to make them a little more standardized which it may or may not be. The size will stay the same at 1.75" x .65" (think longer basic stamp). The next version will have larger and hopefully more readable text labels. Also, I brought out an LED from the first IO pin of the FTDI 232 chip so Id like to hear what you think the purpose of that LED should be: power on, tx&rx, ?? (Im leaning towards tx&rx). Otherwise let me know what you think in general.
Once the design has been tested thoroughly (at least 1 more proto run) I will publish the files (based in part on the Freeduino reference) and then if the interest is there we will see about getting some distribution for it. I am also planning a Sans-USB version and maybe a lower part count, USB Key version (think memory stick) whenever time allows.
i like it a lot, i think it needs to have a 'pin 13' led tho so that people can do the 'blink' test. There's already a resistor so why not? (the resistor should come after the pin, i think...since the diecimila does that.)
Yeah I agree too. I tried to cram it in there but it was awfully tight, and ruined the symmetry too! I put the resistor in there because it did fit and a cheap led isnt too hard to hook up for an indicator light. (I still have my NG!) Maybe there is still a way.
i like it a lot, i think it needs to have a 'pin 13' led tho so that people can do the 'blink' test. There's already a resistor so why not? (the resistor should come after the pin, i think...since the diecimila does that.)
Yes, definitely the resistor goes after the pin... I think it caused some problems in one of the NG boards.
i like it a lot, i think it needs to have a 'pin 13' led tho so that people can do the 'blink' test. There's already a resistor so why not? (the resistor should come after the pin, i think...since the diecimila does that.)
As someone who'se designed them both ways, you want after the pin, otherwise you always have to remember that pin13 is "different". While having the LED/resistor and pin in parallel is different too, it's not as much of a consideration.
I whole-heartedly agree with the PIN13 LED. While I understand it might not alway be useful in a Stamp-like role, I think it's come to be an expected part and a key diagnostic bit.
Have you thought of using something smaller like the CP2102, if you're feeling squished.
So Dave Im not sure whether to wait or try to beat you to the punch! ;D
I will see what I can do about the pin13 led. Maybe theres a way.
I stuck with the FTDI 232 because Ive heard the drivers are more stable cross platform than the CP2102. I could have used its smaller package but that would be a pain to prototype so I didnt. And honestly Ive used this chip before so I stuck with what I knew!
Speaking of that chip, Im having a hard time enabling the rx&tx led on that general purpose i/o pin its connected to. Im using MProg to change the 232r eeprom but its not seeming to make a difference. Has anyone done this?
Im hesitant to go with pth mini-b just because thats going to increase the difficulty of assembly. Sparkfun uses the same method of assembly that I do and they will typically use the same part. Something to try out tough.
@ Nathan: D'oh! Thanks so much! I knew there was something and it was staring at me all along. Ok, Ill get on that and fix it up.
Otherwise, Ive managed to get the pin13 LED crammed in there. I flipped the xtal and row of caps/resistor which allowed me to juggle it a bit and get it wired up as suggested. The question here is, is the led too far away from pin13 and/or how should it be labeled?
Past that, Ive tweaked some of the spacing and little minor things but I think its close to another proto run. Any more suggestions?
Is that super necessary? The 232 eeprom can configure that single led to reflect both rx and tx. (I think by default gpio0 is rx and gpio1 is tx but in this case gpio0 will be set to both rx and tx, once i green wire it.) Did you have something else in mind?
Lemor, where'd you go? Im curious about the LED question!
After some creative soldering and green wire work, I got the RX/TX Led working happily. That was a dumb little mistake! Quick little fix in Eagle though and I think Im ready to go. That is unless I have to cram another LED in there....
Im still working on it... Ive added a reverse protection diode and a method for connecting aref to 3.3. Ive got a batch of the second prototypes in front of me but haven't made the time to finish them up.
If there's still enough interest in it after the metaphorical landslide of recent 'duinos, we will make it available before too long.
