Archive for May, 2012
Yes, that’s right, the wait is over….. my PCBs from Dorkbot PDX have arrived in the post ! Here they are in all their purple loveliness.
Sorry about the photography, this is my electronics blog not my photography blog, so point-n-shoot camera came out and handheld “macro” mode with no flash was the chosen mode.
Man that MPR121 is a *small* package. It’s a QFN20, and a pad pitch of 0.5mm. It makes the pads on the .05” connector look huuuuuge !
When it comes to soldering the QFN20 onto the PCB, the fact that “QFN” stands for Quad Flat No-leads really becomes apparent. You can’t get your normal soldering iron onto anywhere that you could possibly hope to get some solder, the chip, and the pads to meet in that joyous harmony called “properly soldered”. So since I don’t own commercial wave-soldering machine, and I don’t have a toaster oven I could repurpose to be a reflow oven, and I didn’t have a spare frypan around that I could convert/sacrifice to be a soldering skillet, I whipped out the (new*, so far unchristened) Atten 858D+ hot air rework station, whacked a bit of solder paste on the pads, plonked the chip down, fired up the heat, and hey presto, a few minutes later the chip appears soldered to the PCB ! I guess we’ll only see once we get a chance to connect it up to my Fez Hydra and start looking at the driver (although luckily there’s at least one sample out there ). That maybe something for the weekend – bring on the weekend !
* Here’s a great plug for the eBay supplier of my new Atten 858D+. Looking around on eBay, I found lots of eBayers that ship from Hong Kong or China, and the buy-it-now price for this unit was around $59. Then I came across one located in Sydney, and wow, the buy price was only $63. Wow, a $4 “premium” for having someone in AU to buy from. Wow. (Yes, I was impressed). But that’s not where it ends. Clicked buy one afternoon, sometime about 3, and paid with paypal. Before the end of the day, I had an email from Aus Post that a parcel had ben dispatched to me, and it arrived at the PO Box by 8am the next morning. W. O. W. What a great eBay seller. If you’re in AU and want something fast and Carmates has it, my experience says you’d be lucky to find a better dealer.
I needed to make a touch keypad for a project I am doing at home. Looking around, SparkFun have one, here, that I liked the look of – except for my use, I wanted it to be simpler – it had to have up, down, left, right, and OK buttons only.
Errol GMod, the artist formerly known as Errol, over on TinyCLR forums has used the MPR121 to build a touch keypad for the CANxtra, one of the devices that GHI had on run-out sale last year. It seemed pretty easy to understand this design (ha !) so what else was I to do, but design one of my own.
So armed with my knowledge (double ha !) I took some design input from these two sources and threw something together.
My only real requirements were that it needed to have a simple button structure, to fit alongside an LCD display (a standard text-based display with 20×4 characters using an HD44780 controller chip). I decided to use a Gadgeteer standard connector so that I could use it also on a Gadgeteer compatible mainboard if I wanted to.
No fancy 3d renders, no fancy pictures, nothing. Just a set of screen capture images from a preview of the gerber files that I created.
Now the proof will be in the pudding – the gerber files for the boards were submitted to the Dorkbot PDX PCB service, and some time in the future they should arrive back here. Now for the suspenseful part, waiting for the package to arrive, who knows when, and then the joy of trying to solder that miniscule processor onto that board, and test it out ! Here’s hoping it all works !
I’ll update the post when the boards arrive and when I break out the soldering iron !
If anyone thinks they would like the original Eagle files, leave a comment. I’ll get them cleaned up and posted here when I get a chance.