PCB Arrived and Hot out of the Oven

The PCBs arrived last week, unfortunately not in time for the long weekend so I haven’t really had a change to do anything until today and from my initial observations I’m happy with the results.

RFM12B PCB

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2.4GHz MRF24J40MA PCB

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Prototype PCB

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As I mentioned on the Strobit-general Google List and the SPOT-development Google list, they seem to have multiplied from when I placed my order to when I received them, I calculated I would get approx 12 back of each board, in the end I received 32 of each board, go figure…..so if anyone wants a couple of free blank PCB then contact me and I can send you some if you cover the postage costs. Please use the contact form to let me know.

Hot Out of the Oven

Today I assembled the first one! Didn’t take long at all due to the minimal component count. If anything I need to add more solder paste to the RFM12B footprint, but seems to have taken.

RFM12B PCB Assembled

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I’ve partially assembled the board, enough to give me basic functionality so I can do some tests, while the rest of my components I’ve ordered (SMA connectors etc) arrive. Unfortunately my stash of 0603 capacitors were actually 0805 ones in disguise, so I’ve had to use these even though the footprints are for 0603. In the photo you can see some of them installed on their side. Same goes for my bead, I only had some 0805 in my stash but have 0603 on order, just couldn’t wait 🙂

I’ve enabled all the solder jumpers so I don’t need to install the switch and the BAV diode for the time being.

Changes for next board revision:

A couple of things stand out with this board revision, nothing major but niggly enough to warrant changes or at least thinking about them.

Crystal Footprint – One thing so far, I’m kicking myself for not making the crystal footprint a HC-49 SMD, I thought about it before I send the files off for fabrication, instead I opted for the sleek 0503 ceramic smd crystal, problem is they are more expensive and not as easy to come by, so I’ve added this as a change for the next board revision. In future I’ll stick with the stock standard low cost crystal HC-49C footprint.

Switch – Do I really need it? The onboard switch seemed like a good idea at the time, but in reality do I really need it? I’m glad I had the fore thought to add a solder jumper to bypass it. Honestly I will probably more than likely use a switch remotely (i.e. on the side of an enclosure) or on the battery pack itself rather than on the PCB. I may just leave the ability to have a remote switch and remove the onboard footprint all together.

LDO regulator onboard? – I’m still up in the air about this one. Initially I wanted to keep things as low cost as possible (and I still do), and then add additional functionality via the personality boards so keeping the core board to bare minimum components, as I have only intended these to run from battery or from USB, not from a wall wart or A/C plug pack. I have added some reverse protection with the BAV Scotty diode, but this won’t protect the board if someone connects a 9vDC source. Anyway I think I will wait and see how I go with testing and community feed back.

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Author: Stephen Eaton

Geek at heart. Loves to tinker and find out how things work, which inevitably leads to items in pieces and not working for much longer :)

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