BNC to SMA adapter to run TTL trigger through DAQ box digital I/O ports?

[Gabrielle Siemonsmeier]

Hi everyone,

At the risk of revealing my complete ignorance of electronics, I was wondering if it would be possible to use a BNC to SMA adapter to run a TTL trigger through the DAQ's digital I/O ports. I imagine one issue is the difference in voltage (5V vs. 3.3V), so would this require a converter? Open Ephys sells various DAQ accessories including several "Coaxial Cable BNC Plug to SMA Plug", would that do the trick?

I know you can modify the DAQ PCB to solder on a BNC connector (I already have one such modified DAQ which I "inherited"), I was just wondering if there was a way around that. If not, are there instructions on how to do so somewhere?
Cheers,

Gabrielle

[Daniel Aharoni]

Hi Gabrielle,

Great questions. 

Yes you can use a 50ohm (very likely what you have is 50ohm) bnc to sma adaptor. These are all just different types of coax cable connectors and as long as they have the correct impedance of 50ohm you can switch between them without issue. 

As for the voltage levels, the DAQ sold by OEPS is 5V tolerant so you don't need any voltage divider or converter if using their DAQs. If using a DAQ from another vendor or one you built yourself it might or might not be able to handle 5V digital input. We have heard mixed results in this case and it likely depends on the output impedance of the device generating the 5V. A simple voltage divider would work here to drop the voltage to around 3.3V.

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[Gabrielle Siemonsmeier]

Hi Daniel,

Thank you! My DAQs are from Labmaker, I sent them an email to inquire about the voltage tolerance. The TTL trigger comes from our Med Associates conditioning boxes, I'll look into the output impedance.

If using an adapter should work, and since the DAQs have two GPIO SMA ports, is it theoretically possible to have two incoming TTL signals to the same DAQ, e.g. one to trigger recording and another to timestamp specific behavioural events into the recordings? I imagine the J5 connector would have to be reconfigured as alluded to here ? Or is this irrelevant because the software only allows for external triggering but not this kind of TTL input?

[Daniel Aharoni]

Hi,

Unfortunately we have never gotten around to implementing the ability for the DAQ to timestamp incoming digital signals. This is definitely still on our todo list but have no idea when we will actually get around to doing it.

[Gabrielle Siemonsmeier]

Good to know, thank you!

[Hannah Wirtshafter]

Hi Gabrielle,

Did you get this to work? I also have a labmaker box and am having issues triggering using a TTL

Thanks!

[Gabrielle Siemonsmeier]

Hi Hannah,
Unfortunately no; it's the voltage divider I didn't know how to implement (see my more recent post here: https://groups.google.com/g/miniscope/c/J6EiGxYjm18). I did try triggering recordings via TTL on an Open-Ephys DAQ using a BNC to SMA adapter on a digital I/O port and that worked!

[Hannah Wirtshafter]

ug damn!! Was really hoping that wasn't the case...

[Hannah Wirtshafter]

that being said I think something as simple as this should work to convert the signal: https://www.amazon.com/SparkFun-Logic-Level-Converter-Bi-Directional/dp/B01N30ZCW9

[Nate Klett]

Hello, despite reading this (and elsewhere), I am still a bit confused and don't want to ruin any equipment by delivering TTL voltage inputs to ports which are not designed for it. 

Can the DAQ's digital I/O ports be used for TTL triggering,

or do I need to solder in a SMA connector at the empty slot, 

as described here in this 2017 thread? 

I am using a DAQ box from Labmaker ordered in 2020. I am not certain which version it is, but it looks like this:

       

My understanding is that I cannot use the I/O inputs as a TTL input trigger, and that I still need to solder a new connector for the input trigger. Is that correct? Thanks for your input.

post-script: as extra information for future readers, the currently available DAQ boards from Open Ephys are version 3.3, and include the Input Trigger already installed:

[Nat Kinsky]

Hi Nate,

I have the same era Labmaker DAQ box. You are correct, you need to solder a connector to the pads in the red circle in your post. As far as I know, you can't use the existing I/O ports to externally trigger recordings.

I've attached a picture of what I did for your reference. It has been working great. Note that I opted to solder two wires to a BNC connector since all our other systems use BNC ports, not SMA ports.  As a result, I had to move the trigger to the side because a BNC port is too large to fit between the existing SMA connectors. I used a drill press to make the connector hole in the side of the metal box.

Hope this helps,

Nat

[Nate Klett]

Thanks for the confirmation Nat! This is very helpful.