Neuronexus A32 -> Intan/Omnetics adaptor

[Chris Rodgers]

I need to plug in some A32 probes from Neuronexus, which use a 40-pin Samtec MOLC connector, into some 32-channel Intan headstages. I see on this page (https://open-ephys.atlassian.net/wiki/display/OEW/Channel+Map) that someone is using an adaptor that does a sort of similar thing for 64 channels, but it's not clear to me whether this adaptor was purchased from Neuronexus or was made from scratch.

I see that I could buy the adaptor I need for $230 from Neuronexus (http://neuronexus.com/products/accessories/headstage-adaptors) but this is pretty expensive, so I'm thinking about laying out a little PCB adaptor using the mating Samtec connector ($20) and mating Omnetics connector. But before I design that PCB, I thought I'd ask if anyone else has already done this, or knows of a cheap alternative. If not, I'll post whatever I come up with here!

Also, on a barely related note, I see that the I/O Board uses 75 ohm BNC connectors. Isn't 50 ohm more standard? Are we sure the connectors are compatible? I'm getting conflicting info on google about that, for instance, http://www.infoneedle.com/posting/8968 .

[Jakob Voigts]

Hi Chris,

I think that adapter was purchased from neuronexus ( they mention the product number - Adpt-A64-OM32x2 ). Neuronexus seems to make a few variants of this, the image differs from this neuronexus doc: http://neuronexusstaging.info/images/Adaptor_Maps/Adpt-A64-OM32x2-sm.pdf and i used an older one that had the 2 32 ch omnetics connectors aligned in a row.

If you decide to go the diy/pcb route, do you think it might even be possible to make a 64 channel one that can be used for 32 as well? When putting the 2nd 32ch omnetics on the bottom side on the back of the adapter, the pcb would work for intan 64ch headstages (given the correct substrate thickness), and by only populating the front you'd get a cheaper 32 channel variant. Might not be possible due to the channel mapping though- i vaguely remember these neuronexus probes to be a bit complicated with where the gnd/ref pins go etc.

 

Also, on a barely related note, I see that the I/O Board uses 75 ohm BNC connectors. Isn't 50 ohm more standard? Are we sure the connectors are compatible? I'm getting conflicting info on google about that, for instance, http://www.infoneedle.com/posting/8968 .

I was pretty sure we were using 50 all around - at least every board that i've seen/assembled did. They should look pretty obviously different: http://en.wikipedia.org/wiki/BNC_connector#mediaviewer/File:BNC_50_75_Ohm.jpg

Where did you see the 75 ohm variants? Its just a .sch/BOM issue we should just fix it.

 

Jakob

[Chris Rodgers]

Thanks Jakob, if I put together a PCB, I'll post it and get feedback on how we might be able to adapt it for 64 channels. I don't have a 64ch probe or 64ch headstage available to work from, but we can figure it out.

Re 75ohm connectors: I ordered the digikey part linked from the I/O Board wiki. It's 75 ohms. Guess I'll have to replace them with 50 ohm connectors with the same footprint. Which part do you recommend using? 

https://open-ephys.atlassian.net/wiki/pages/viewpage.action?pageId=3211312

I don't see any BOM in the io-board github repository, even though it's discussed in the README.

https://github.com/open-ephys/io-board

[Chris Rodgers]

Ok, I finally got around to making this adapter. I only made a 32ch version because I only have 32ch equipment to test it with.

Here's the info. If anyone wants a PCB, let me know and I can send you one. You will need to buy a $60 Omnetics connector and a $20 Samtec connector to attach to it.

http://www.chris-rodgers.com/neuronexus--omnetics-adapter.html

[Chris Rodgers]

Just an update, I recently also made a 64-channel adapter two connect one A64-style probe to two Omnetics connectors. 

https://oshpark.com/shared_projects/Xw4Z3RGB

This OSH Park website is pretty cool because you can just order one yourself if you want. It's only $8, but you'll need to buy the Samtec and Omnetics connectors too.

I haven't tested this yet. Let me know if you are interested.

[Jakob Voigts]

Hi Chris, this looks great!
Could you add a page titled something like
2x60 ch A64 neuronexus to 2x32ch intan

to this page
https://open-ephys.atlassian.net/wiki/pages/viewpage.action?pageId=491557

just with links to your website, to the OSHpark page and to the parts?
This way we'll keep a somewhat complete list of available adapter boards etc.

[Edgar Bermudez]

Hi Chris,

I am also trying to buy an Adpt-A32-OM32 from neuronexus (http://neuronexus.com/images/Adaptor_Maps/Adpt-A32-OM32_Mar182013.pdf) but they are a bit expensive. I was wondering if I could use your design for a 32-channel adapter and give the DIY a try. I was just wondering how difficult the soldering could be if I order the connectors from digi-key?.

Many thanks!

Edgar

[Rodrigo Pereira]

Hi Chris and Edgar,

I would also be interested in preparing an A32-OM32 adapter using your design for a 32-channel samtec2 Omnetics adapter. Actually, I recently bought 2 samtec connectors and was wondring how to prepare the adapter.

The problem is that I'm in Brazil and it is very hard to get omnetics connectors here. Besides, preparing PC boards in small amounts gets expensive.

best,

Rodrigo

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[Chris Rodgers]

Hi all

I soldered both Samtec and Omnetics connectors to the board. The
Samtec soldering was very easy. The Omnetics soldering is a pain in
the ass, but you can do it.

On my PCB, I made small pads for each leg, and each pad has a tiny
hole in it. That way, you can use either vertical surface mount
Omnetics connector (using the pads), or through-hole (using the
holes). Here are some issues I had:
1. Sometimes the holes are filled by the PCB designer. So you cannot
insert through-hole pins. This is unavoidable for such small holes.
OSH Park sent me three copies, and I think 1 or 2 had filled holes,
but at least one was perfect.
2. Inserting the through hole pins is very difficult, because once you
bend the leg even a little bit, it will be too flimsy to insert the
rest of the way. The best way is to not apply any pressure until every
leg is perfectly in place, and then it will slide through no problem.
3. In contrast, it is easier to place a surface mount connector in
position because you don't have to worry about the holes. But it is
very difficult to solder such fine pitch tiny legs without bridging
conenctions. I tried both a regular iron and a hot air reflow gun.
It's tricky. If you don't have experience with this, I would ask at
your Electrical Engineering department or Electronics shop for some
help.
4. The Omnetics connector will melt and deform in response to a hot
air reflow gun so work quickly! I also built an Open Ephys acquisition
board and attaching that damn Omnetics connector was by far the
hardest part of the entire process.

As far as sourcing parts
1. I contacted Samtec and asked for a free sample of 2 Samtec
connectors and they generously provided them for free.
2. I ordered Omnetics parts directly from Omnetics. The minimum order
is $100, which is 2pcs. (NOT 4pcs as it incorrectly states on their
website).
3. You can also order this stuff from Neuronexus but they raise the
prices by at least 20% over Samtec and Omnetics.

I don't think you can order any of the parts from digi-key. I don't
think digi-key has them for sale.

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