Espruino Pico Adaptor PCBs

Hi everyone,

I've been thinking about a set of adaptor PCBs for the Espruino Pico - to make it a bit easier to connect other bits and bobs to it. Hopefully I can get it done as one PCB where you snap off all the different adaptors and then solder pins on them.

Does anyone have any suggestions for adaptors?

Ideas I have so far are:

• Arduino footprint (I'd also set this up so you could adapt the original Espruino board, and would fill spare space with adaptors for some of the stuff below)
  
• General 0.05" to 0.1" adaptor
  
• MAX1551 LiPo battery charger
  
• NRF24L01P wireless
  
• ESP8266 WiFi
  
• CC3000 WiFi (would solder right on apart from GND + power)
  
• WIZnet W5500 Ethernet (would solder right on apart from GND + power)
  
• Generic XBee footprint (will handle SRF via the XRF module)
  
• RFM69HW wireless
  
• HC-05 / HC-06 / HM-10 bluetooth
  
• Audio Jack (see the Audio programming thread)
  
• Model aircraft servos
  
• Micro SD card
  
• Dual H-bridge motor driver (i'm open to ideas for something cheap and easily sourceable)
  
• 20x4 LCD
  
• Wii Nunchuck
  
  

LCDs like the Nokia 5110 should just solder right on, so won't need an adaptor.

Are you planning these for the 0.05" header only, or both? I think for the 0.1" header, many of those things wouldn't need it (like CC3k, RFM, Wiznet, ESP, etc) - just a couple dupont jumpers and you're good.
Then again, I think those'd be perfect things to put onto those 0.05" headers, so connecty boards for that would make great sense.

I really like the idea of being able to stick an LCD right on the board - that's also the sort of thing that makes a long more sense on the pico due to the lower price point and smaller footprint.

I'd say:
AT24 I2C EEPROM, or AT25 SPI EEPROM - I think one or the other would be helpful? I've put EEPROMs onto the prototyping area on 2 of my 3 Espruinos - there are just so many times working with a microcontroller when you want to store just a few bytes in non-volatile memory.
ULN2003/2803 board (put the pads for a 2803, if we want to use a 2003, it could be installed, just not using the last pair of pads), giving us 7/8 higher current outputs on 0.1" header
SOT-23 MOSFET board - as with the ULN2003/2803, only with a buncha mosfets, with pads for a resistor between gnd and each gate for a pulldown.

Is the list of what pins will be on the 0.5" header finalized? This would have some impact on what things might make sense.

What's the footprint of the shield/adapter/coaster* board going to look like? Will it only have one set of 0.05" pin header, or will there be a second set (maybe on the opposite end, rotated 180 degrees) to stack them?

Have you tested that the 0.05" pins form a rigid enough connection? Will we need a little rubber bumper or something under the board to keep it from getting damaged wiggling around?

*"Coaster"? Arduino has "shields" - what would you put your cup of hot javascript on, if not a coaster?

It's be both 0.1 and 0.05 - whatever makes sense really.

While stuff like the CC3000 is trivial to wire up with just 2 extra wires, I think a lot of people would still appreciate an adaptor - it'd only be around 1cm^2 area, so not too pricey.

• AT24/AT25 - do they use the same pinout? Something like that would definitely be handy.
  
• ULN2x03 - good point. I'd thought that the H-bridge might cover that, but actually just having pull-downs is handy sometimes.
  
• MOSFET - yes, again, it'd be a nice one to have.
  
  

The pins are pretty well finalised now. There's 1 I2C, 1.5 USARTs (RX/TX plus one extra RX), GND, 3.3v, 'Bat', and analogs - but no SPI. That's not such a big deal because a lot of the SPI stuff works fine with software SPI though.

I think every adaptor will be different - I'd just focus on trying to keep them small - stackability is probably secondary - but it'd be nice to be able to add extra adaptors onto the Arduino shield (the extra space could contain bluetooth/ESP8266/NRF24/etc pads as well).

I haven't tested the pins yet - but the Bat/3.3v/Gnd are at right-angles to the other pins, so should add some rigidity.

I mentioned on another post, but what do you think about PCB castellations? It's a little late on to add them, but it would be very cool - you could then put your Espruino Pico on your own board (or the Arduino adaptor) without any pins. It could be very low profile then.

Aaah, no SPI? well then, better use an AT24! (AT24 is I2C, AT25 is SPI).

Does the SD card work over software SPI?

ESP8266 - there are a few other board layouts for this making the rounds, at similar prices to the others. Some of these have castellated pads, which might make them a better choice for our purposes.

Re: Castellations - I certainly see the appeal, I think this is a good idea - it would make it just so easy to put the Espruino Pico onto a larger board. I can't see any issues, except maybe a slightly higher risk of accidental shorts. Can this be done without making the board larger?

Does the SD card work over software SPI?

That's the plan - I see no reason why it shouldn't.

ESP8266 layouts

Yes... I think the most popular will probably be the pinned one, which is what I'd do initially I think.

Castellations

I've had a look at this and yes, I think it can be done without increasing the board size. Not it just comes down to whether the PCB manufacturers will do it without charging a load extra.

As you say, shorts might be more of an issue, but it's probably not good practice to leave the board floating around uninsulated anyway...

Intel Edison adapter board with logic level converter for serial communication back and forth from espruino to the edison. :-)

For example: https://www.sparkfun.com/products/13036 (that uses Arduino)

I'm not too convinced by that one I'm afraid... Why would you connect to the edison using GPIO, I2C or Serial when you could just use an existing adaptor board and plug the Pico right into USB?

Besides, I was planning on selling unpopulated boards - and soldering on that crazy fine pitch connector is going to require some good tools and a lot of skill.

@Gordon At the time I wrote the post I forgot about the USB connectivity :-/ I didn't think it would be popular, but I wanted to mention the idea anyways.

From DaveCJ:

• Sx1272/RFM92 868Mhz radio
  
• Screw terminals
  
  

Also from @allObjects:

• Prototyping area
  

@Gordon hi, in regards to using the Lora RF Module from that ebay link you posted which looks like it's from/based on HopeRF.... I read at https://openrf.codeplex.com that they aren't reliable. I'm not sure how much truth is in that statement about HopeRF? Are you creating an area specifically for the HopeRF LoRa module in that ebay listing or LoRa modules using the same dimensions?

Well, DaveCJ (I'm not sure he's on the forum?) said that the RFM69 is a clone of the SX1272, and shares the same footprint - so it should be compatible with other radios.

A MAX31855 thermocouple interface, with spot for screw terminals to connect the thermocouple?

I read at openrf.codeplex.com that they aren't reliable. I'm not sure how much truth is in that statement about HopeRF?

Me neither, and wondering - there's probably some truth to it, but the OpenRF people also seem to be associated with the Whisker LoRa module people, so they'd have a vested interest in spreading FUD on HopeRF.

And:

• Microchip 11ACxxx/11LCxxx 'TT' SOT-23 EEPROMS
  

It would be nice to have a selection of breakout shims for SMT prototyping with I2C chips. Something like:

http://www.adafruit.com/product/1212

Would be cheap and make life easier to experiment with new chips.

Nice idea - thanks!

For a TO-92 packaged 11ACxxx/11LCxxx EEPROM a breakout is not even required: it can go directly into the breadboard. On the other hand, more and more manufacturers drop packages for through hole soldering, and having SMT areas on a shield - next larger pads and some through holes - provide great options for proto typing.

#PCB

AT24 adapter: If it's doublesided, maybe there should be pads on both sides, provided there are traces to cut/bridge to set the address pins - might as well let us cram an AT24 onto each side.

Unless I'm mistaken, the Espruino doesn't support the 11AC/11LC series. They use UNI/O, Microchip's pet single wire serial protocol - as opposed to the DS2xxx series, which uses OneWire, which is Maxim's pet single wire protocol. They seem to be pretty different - UNI/O doesn't support parasite power, and the devices are push-pull, not open drain, and goes at 100 kbps instead of 15.6

@DrAzzy, just had a quick look at UNI/O. Looks like it should be possible to do in a module (at least at 10kHz) with digitalPulse and setWatch. It'd be nice if I added the ability to do digitalPulse to open circuit, but even so I think it should work if the output was connected with a low-ish value resistor.

One more PCB idea - if there's enough space then a small two-pronged soil moisture sensor could be added. Not as useful, but fun to play around with.

Ok, the Pico outline is now available at https://github.com/espruino/EspruinoBoard/tree/master/Pico/Component

I've also started on some 'shims' here, along with a list of what we've come up with so far: https://github.com/espruino/EspruinoBoard/tree/master/Pico/Adaptors

Be warned: absolutely nothing is tested at the moment.

If anyone wanted to help with different shims it'd really be appreciated! At some point I'll come up with a script that will jam them all together into a big gerber file that we can have made.

Great News.
Thank you!

Quick update - I've done quite a few shims already: https://github.com/espruino/EspruinoBoard/tree/master/Pico/Adaptors

However I'm still waiting to get some prototypes back. For some of them (like the bluetooth below) you have to use an SMD Pico because the pins would get in the way.

Does anyone have any thoughts about how best to expose the IO in that case? While we could add another two rows of 0.1" pins down the edges, it would make the board wider and a lot of people making sensors/etc might not want that.

1 Attachment

Regarding having these made - take a look at dirtypcbs. They're a little half-assed, but their prices are low - maybe low enough to make the numbers work out.

https://www.oshpark.com ... Also well priced. I've used them a number of times great quality boards.

oshpark have been really good, especially for small stuff - I used them for the Pico board prototypes. There's free worldwide shipping too, so for small things it's insanely cheap.

@DrAzzy dirtypcbs looks really interesting. I was thinking 'that's not so cheap' and then I realised they make ~10 of them for that! As the volumes go up it gets amazingly good - I'd be very tempted to figure out what the popular boards are and then to get 1000 of each made :)

@Gordon do you think you'd keep the same 0.05" header on any future espruino boards? Not necessarily the same pins, but maybe the same functions. It'd be great to build things knowing that they can be used on newer boards. Also, on this track, maybe an original espruino to nano adapter could be useful.

I use Dfrobot for my pcbs and they've been good and cheap. They've done a couple of snap apart boards for me and they worked well.