Tuesday, May 24, 2011

Tricaster tally-light interface for EX3s

One of my favorite parts of the job is prototyping and making little interface units so that equipment from different manufacturers can talk to each other.

This gadget allows the Tricaster TXCD850 studio production system to light the tallies on Sony EX3 cameras; although the Tricaster has "wet"-style GPI outputs it can drive the 12V needed for the lights. So, simple buffer circuit with relays to drive the studio tallies;

There are some photos in a Facebook album - click the title link.


Trevor said...


What current you planning through the relay coil when closed?

Don't you want some minimum resistance on the pot you've got on the Base to Earth?


Phil Crawley said...

Well there should be 0.6v between the base and the emitter - that's a silicon junction after all. I can never be bothered to work out the Hfe figure so I stick in a 10k pot!
So, the 12v is split across the relay coil and a resistor - the coil has a very meager 18ohm impedance so the current should be 160mA - that gives the value for the resistor. Since it's quite low I used a 0.2w one.
There is also a diode (not shown) 'backwards' across the coil to suppress back-EMF (Lenz's law and all that).

Phil Watten said...

Hi Phil

Nice work! Are you actually lighting the built-in tallies on the EX3? If so, how are you interfacing to them? Did you take the EX3 apart?



Phil Crawley said...

No - I didn't fancy diving into the EX3s to try and find where you can light the (very little) red light above the view-finder.
Have a look at the last photo on this set;
and you'll see I've stuck it below the prompter monitors. In the little three-camera studio they went into it works well and it means the SM can quickly release the EX3s and use them as road cameras as he needs.