SparkFun Forums

[davethomaspilot]

I've designed a product which uses the Nordic FOB for RF control.

I need more of them, but now it's now a retired product.

Does anyone know where I can get a replacement? I see the case for sale and the Eagle files are still on-line. But, I'm not sure I could build the cards with those tiny parts and fine pitch NRF24L01 parts.

Is there a source anywhere for a replacement FOB? Or, some case that's big enough for a pre-assembled NRF24L01 trancseiver board and buttons?

Thanks,

Dave Thomas

[bennard]

Hey Dave,

Sorry for the late reply. I have often wondered the same thing. I have several of the FOBs, still use them in projects, and want to replace a couple of them. My FOBs get used in a dynamic (dance/party) setting and get soaked with sweat and are corroded. I swapped some of my projects to control with bluetooth and phone app but that can be too bulky and some are just better with the FOB.

It looks like all the components are still available, including the FOB case. You can totally assemble it yourself, with the 0402 sized parts. Use a big magnifying glass or microscope if you need to and hot air/oven.

Id recommend modifying the eagle file a little, to get components out of the FOB 'keep out' area. Ive had a couple components get broken off the board from hitting the FOB rib. Im also wondering if the components can be changed to 0603 to make it a little easier to assemble. There is plenty of space. The FOB case spec sheet says to use 0.031" boards. I use OSH Park and they make 0.063" boards. I put one of my small projects into the FOB and it still clicked closed and the buttons still moved, so I am hoping this wont matter.

My big question is if people are even still using the NRF24L01? If yea, then it would be worth it to hand-make a few more.

ben

[davethomaspilot]

I would definitely buy at least 10 FOBs if they were available. I have orders on hold for systems that need them--instead I'm using a larger hand held unit that too big for wearing on a chain around the neck.

So, I got some boards fabricated from the Eagle design. I also ordered enough parts to build 10 FOBS, but haven't built any yet.

I've done lots of SMT pcbs, but I'm not sure I can do the fine pitch NRF24l01 and 0402 parts. 003 are the smallest I've done and I need a stencil to do fine pitch parts without solder bridges. I'm not sure I can wick away bridges on the NRF24L01.

So, net, I need the FOBs and would much rather buy them than build them myself.

[bennard]

Hi,

I made a few little edits to the SF eagle file and sent it off. It will take a couple weeks to get back, and I will report back after i attempt to put one together. I dont see it being that bad. Reading glasses and hot air go together, and use less paste. I am not offering to build a bunch of these, but am definitely going to speak up if it works out, and be encouraging.

I also have a ridiculous hand made Nordic keypad thing to supplement the FOB. That project lead me to just use bluetooth and my phone (more buttons and less bulk). But the FOB has its place and I really need a couple more.

b

[davethomaspilot]

I'm in a crunch to some more product built by this weekend, but I'll give it a try next week.

I do all my SMT placement work under a big Diopter lens with lots of light. So, that's absolutely a must. But getting paste on the NRF pads is going to be the problem.

There's just no way for me to dispense the tiny amount of solder required without a stencil. For sure I'll get solder bridges. The only question is whether I can wick them away with the pads going under the package.

If I can't, I"ll have to order a stencil from Pololu and try again.

Nearly all the FOBs "die" in a couple of year. The key pad contacts and battery - pad on the pcb get corroded. But, a shot of contact cleaner the pcb (taking care to get the bat - under the battery clip) restores them.

[bennard]

Hi. Well I am reporting back like I said I would.

I made one (actually two) this weekend, and it works. I will soon make some more (for me). It was not really that difficult. Here are some things I noted:

1. The board really does need to be 0.031" thickness per the FOB case specs. Mine is too thick for the case to snap closed correctly. I will have some thinner boards made.
2. While the SFE eagle file seems to show 0402 components, 0603 works fine with their eagle file without modification. Even the FOBs they built and sent us use 0603. I made a board with 0402 components first which worked, but was rough placing parts. And very hard to find them when dropped.
3. Use lots of good runny flux. There are many soldering techniques for QFNs, I guess. I tinned the pcb pads, one big drip of flux, placed the chip, and a few seconds of heat gun. That was it. Almost like they soldered themselves. Bridges didnt happen. Flux is magic.
4. I had to clean both contact parts of the button pads before it would register presses.
5. The absolute biggest time burner was taking one (1) teeny part out of a bag and putting it on the board and then putting that bag away. I think assembly line style construction would be a lot faster.
6. It worked! Should have seen my face. (a) "huh? its loading the code?" and then (b) "what?? it just sent the right signal to the receiver? How did I not screw something up?"
7. As I mentioned previously, mod the eagle file just a little. The SFE guys put the 1.5pf and 3.9nH on the edge of the FOB case KEEP OUT area, which is where there is a rib in the case. One of my originals from them broke because of this.
8. Make sure your mask limit is high enough that your fab fills and paints over the vias. I think this actually matters with this board, with the conductive buttons.

I have a couple mod ideas. Like getting the clear/gray fob cases, and then add a couple leds to the board. One for "tx" and one for "ack". Have them blip on and off, within my debounce time, before it goes back to sleep.

Anyway, GO FOR IT! It was not that bad. Good luck,
-ben

[davethomaspilot]

Thanks for he update!

I still haven't gotten around to building mine.

I already have the cards, so I guess I have the issue with the 1.5pf and 3.9nH interfering with the rib in the case. I guess I'll just use an xacto to cut a notch in the rib for that.

Great catch on the via covering. I'll have to check mine.

Thanks!

Dave Thomas

[davethomaspilot]

So, I finally got around to trying to build a FOB.

I figured I'd try dispensing the solder (Chip-Quik) without a stencil first.

No way can I dispense solder on the Attiny25 or the Nordic pads. I have a yellow "needle" on the syringe. Maybe I'd do better with something smaller, but as I recall when I tried smaller needles I couldn't dispense paste. But maybe I tried too small.

Anyone have experience with a tiny tip using Chip-Quick?

I figured I'd try dispensing the solder anyway, and reflow even though the solder bridged the chip pads.

I didn't have an problems getting the solder on the 0402 pads.

During reflow, on 0402 tombstombed--I was able to push it pack down while still on the hotplate. All the passives turned out great--none of those skewed parts I've seen on just about every FOB I bought from SparkFun.

The chips were a different story. Not surprisingly, there were solder bridges. I didn't think I could "solder wick fix" the bridges on these parts, since a lot of the pads go under the chip. But, using wick on the edges that didn't have adjacent passives that blocked the soldering iron, I was able to clean things up.

I tried removing parts so I could get wick into to fix the bridges on the Nordic pads. Finally, I removed the Nordic and used the wick to clean up the pads. I wasn't careful enough a couple of the pads had very little land area and came off the board when I just cleaning them up to try again.

I'm going to try again, but this time I think I'll do two reflow passes. First time, just the chips, then clean up wick. Then add the passives.

If that doesn't work, I'll try a finer needle to dispense the solder on the pads with no bridges.

Next, I'll order up a stencil.

So, you're a better man than me!

[davethomaspilot]

I just reread your post.

I tinned the pcb pads, one big drip of flux, placed the chip, and a few seconds of heat gun.

Could you elaborate? How did you tin the pads? One big drip of flux? Where, on the board?

So, did you put any paste on the pads at all?

Thanks!