Electronics Help please- DIY Tally setup

[david.elsbury]

Hi all- hopefully one of you more knowledgable electronics types can help me out.

 

I have a Panasonic MX50 vision mixer that I want to modify for tally lights at the cameras.

There is no specific tally outs from this mixer but it does have LED's in each of the buttons on the A & B buss (#101), and an LED to indicate which buss is currently live (#100).

http://i39.tinypic.com/5obcwn.jpg

 

I want a bi-colour LED at the camera end, (or a pair of red/green connected back to back) over just one pair of cable, with red when the camera is currently live, and green when it is previewed (on the non-live buss).

 

I have this circuit diagram, which I intend to use to pull the signal off the existing LEDs- I trust this shouldn't be any problem.

http://i41.tinypic.com/501v2q.gif

 

What I am struggling with is the selection and routing of the indicators from the "live" and "preview" busses. I'd prefer not to do this with relays if possible due to the noise factor (having tons of relays clicking around will become distracting quickly) but here is about where my limits lie- I would have thought that it would probably be required to use a relay to swap the polarity of the pair to the LED at the camera?

 

A bonus would be for the circuit to drive a 10mm LED or similar (something quite bright) on the top of the camera- something that the talent can see.

 

I can live with only having the indicators at the camera being "live" and doing away with the preview if that makes it much easier.

 

Thanks in advance for any help anyone can offer :unsure:

 

Cheers

David

[David Duffy]

I gather you still want to have the LEDs in the Panasonic working? If so, you can't just parallel the opto LED across the existing LED.

 

The opto LED will have a Vf of around 1.2V and while the opto will work, the existing LED (with its Vf of 1.6V - 2.2V) will be cut off.

 

If each existing LED has an associated series resistor, add your opto (with its own series resistor) across the existing LED + resistor combination.

 

|												|
|												|
|----[existing resistor]-----[existing LED] -----|
|												|
-----[  opto resistor  ]-----[  opto LED  ] ------

[david.elsbury]

Aha, right. Yes I was hoping to have both running in parallel. Thanks for that. Will try and dig up a service manual and see how I get on with that side of things.

 

Thanks for the prompt reply, David :)

[boatman]

To drive back-to-back LEDs at the camera you'll need an H-bridge at the CCU end and some simple logic to ensure that only one LED is driven. I'll draw something up for you.

[David Duffy]

You can also do it with 2 resistors (forming a half LED rail), tying one end of the 2 pin (bi-colour) LED to the junction. Then pull the other side of the LED to 0V for one colour, and V+ for the other colour. The 2 resistors will be drawing current from V+ all the time of course and you'd still need some glue logic. Just thought I'd throw the idea out there.

[henny]

Does the mx50 send out anything usefull over rs232.

 

The datavideo se800 tally system works from the 232

[boatman]

Here's a schematic for a two channel version utilising an L298 dual H-Bridge driver, you could always replace that with four transistors. It gives TX priority over PV so that if both are active the red LED is on.

 

http://www.brad.ac.uk/acad/bdrc/images/pdf_icon.jpg

 

I haven't put values for the input resistors as they depend on the voltage available inside the mixer. The forward voltage on a 6N137 is 1.4V and 10mA forward current should be more than enough, so for a 12V indicator supply you'll need approximately 1k.

 

Please note that this only an idea and has not been tested in any way.

[Dmills]

Here is my shot at it.

http://exponent.myzen.co.uk/tally.png

 

It works as follows:

 

If a camera is on bus A and bus A is active then IC1A will output High causing IC2A to drive low and lighting LED 2 (RED), IC2A outputting low will force IC2D output high via D1.

The same thing applies to bus B and a camera selected on B via IC1B.

 

If a camera is selected on A, but bus B is active then IC1C will drive high, eventually causing LED 1 (green) to light as IC2A is driving high.

The same argument applies to selected on B, but bus A is active.

 

There is a third possibility, which has the camera selected on both A & B bus, in which case we need to ensure that LED 2 (red is lit), this is done by R10 and D1, which cause the red mode to always have priority (otherwise both ends of the LED would be high, and the LED would be off).

 

2 Optos, 2 14 pin jelly bean logic packages, one 10mm bi colour LED and a few passives per channel (plus 2 optos for the bus LEDs).

I would suggest that 2 quad optos plus a dual is the actual way to do this for an MX50

 

Anyone got anything better?

 

Regards, Dan.

 

 

 

 

 

 

 

 

A concurrent post has been automatically merged from this point on.

 

Boatman, I am afraid you have me somewhat confused, your circuit has 4 inputs, but really needs at least 5 (or six depending on how the MX50 bus selected lights work), the 50 does not IIRC have a separate preview bus as such, it has two buses and whichever one is not live is used for preview, thus the meaning of a camera being selected on a bus depends on which bus is active to TX at the time).

 

Have I misunderstood something?

 

Also, why the 6N137? If you used generic optocouplers you could save on IC5A and 5B, allowing you to get 4 channels out of that NOR (also generics are way cheaper and you can get them in quad packages).

 

Regards, Dan.

[boatman]

Since the L298 has 2 H-bridges in it, that circuit is designed for 2 cameras. I thought the plan was to hang opto-isolators off the existing LEDs inside the mixer, but have obviously misunderstood. I don't know the MX50 but assumed it would have two internal tally lights for each channel. If it's only got 1 then my circuit won't work.

 

E2A:

 

I happened to have 6N137 optos in my components library, but I agree that a quad opto is the right way to go.

[boatman]

I've just had a good read of the MX50 manual and see that my first attempt at the logic is rubbish and Dan's is much better! I would still advocate the use of the L298 though as it can carry up to 3A per channel which can drive some very bright LEDs.

 

I also notice that the A-Bus & B-Bus LEDs on the MX50 flash as the fader is moved off the end stop. This will mean that the tally lights on a selected channel will flash alternately red and green when the fader is midway, which may not be acceptable. It could be fixed by adding a retriggerable monostable (555) with a period slightly longer than the LED flash period to hold the red LED on. The only minor disadvantage there is that the red LED would stay on for one monostable period after the fader reaches the end stop. Although that may be an advantage.

 

By the time all this logic is in place it would be much simpler to just put in an AVR mega8 or a couple of PIC16F88s. That would be cheaper and the software is fairly trivial.

[Dmills]

By the time all this logic is in place it would be much simpler to just put in an AVR mega8 or a couple of PIC16F88s. That would be cheaper and the software is fairly trivial.

 

If you were going to do a run of the things, maybe, but I get the impression that Davids electronics probably does not run to a in circuit programmer.

 

Actually, while it might save some board real estate, is it cheaper for a one off?

You need the optos either way, so you would only save 8 14 pin jelly bean logic parts which is possibly all of a pounds worth.

 

As to the flashing, it depends on what happens, if they alternate then you will get red/green, if they just flash together then all you will get is flashing red (possibly no bad thing).

 

Regards, Dan.

[Dmills]

I was reading the datasheet on the '298 H bridge driver, and something occurred to me....

 

http://exponent.myzen.co.uk/tally2.png

 

4 complete channels, 3 chips for the logic, 2 drivers, 3 packages of optos, difficult to meaningfully beat that with a micro!

 

I would probably mount the optos on a small board inside the MX50 with the 9 outputs and the common anode brought out to a suitable 10 pin connector, then the rest goes in a suitable box together with its power supply.

 

Including a fuse in the DC rail would be a good idea, shorting one of the outputs will pass quite a lot of current.

The tally indicator at the camera is a bi colour LED and suitable series resistor, you can add a stupid bright red one on top as well (the drivers are good to several AMPS).

 

A trivial refinement would be to make the hex inverter a 74HC14 and use the two unused sections with an RC network between them to remove the flashing on the bus_B signal....

 

Regards, Dan.

[david.elsbury]

Does the mx50 send out anything usefull over rs232.

The datavideo se800 tally system works from the 232

Unsure- hadn't considered the possiblity that the RS232 would output as well as be able to be used for control. Will have to sniff and see what happens.

If you were going to do a run of the things, maybe, but I get the impression that Davids electronics probably does not run to a in circuit programmer.

As to the flashing, it depends on what happens, if they alternate then you will get red/green, if they just flash together then all you will get is flashing red (possibly no bad thing).

No- programmer I don't have and would have to do some hunting to try and track one down.

I'm not sure off the top of my head what the flashing action is, will check that out.

I was reading the datasheet on the '298 H bridge driver, and something occurred to me....

http://exponent.myzen.co.uk/tally2.png

That looks pretty slick, thanks Dan.

 

Anyone else got any suggestions? :) Much appreciated.

 

 

A concurrent post has been automatically merged from this point on.

 

Dan- what equivilant would you suggest if I can't use the PC847? Mouser don't seem to have it available. Also I assume that X1-2, X1-1, etc are the outputs to the camera LED's?

 

Cheers :** laughs out loud **:

[Dmills]

Almost any quad optocoupler will do, or you could even use 4 singles (4N35, CNY17 or something) instead of 1 quad, try things like the Til193, Til199, ILQ1, TLP621-4,ISQ74, but note that I make no warranties with regard to the pinout on these quads being the same as that on the 847 (Which is only on the drawing because it was the first one I found in the CAD system), check the appropriate data sheet.

 

Yea the outputs on the right of the diagram go to the cameras, you will need a series resistor to suit your LED, or more then one if you want to parallel multiple LEDs.

I might suggest putting a 1A quick blow fuse in series with each leg going to the cameras (8 total), it will make a short much less damaging.

 

Note that I have only drawn this thing, not built and tested it.....

 

Regards, Dan.

[boatman]

Dan,

 

That looks good and should work well. Depending on the the capacity of your power supply, it might be better to separate the logic (pin 9) and the LED (pin 4) supplies on the L298. You will lose some volts on a long cable run to the camera and might want to start with a higher voltage for the LEDs.

 

=========

 

David,

 

Here are a couple of quad optos from the Mouser NZ site:

 

782-ILQ621 @ ~4NZD

526-NTE3221 @ ~6NZD

 

but I would go for single channel ones as they are much cheaper and easier to work with if you're building on stripboard. This one would be ideal:

 

757-TLP521-1 @ .501NZD

 

Here's a diagram of how to connect your LEDs. The RED/GREEN one on the left can either be a two wire back-to-back one or two separate LEDS. If you want to add a single bright red LED as on the right then you must have a series diode. This protects the LED as the polarity of the two wires reverses when the green LEDs are lit. Adjust the resistor values to suit the LEDs

 

http://i813.photobucket.com/albums/zz59/styxlawyer/LedConnection.jpg

 

Edited: to add comment about supplies on L298