Narrow-Bandwidth Television Association

Ralph · Posted: Fri Feb 06, 2009 7:03 am Post subject:

Can anyone give me the ratings or a link to the data sheet for the BC348 transistor? For whatever reason, I cannot seem to pull it up on the Internet.

Ralph

Steve Anderson · Posted: Fri Feb 06, 2009 11:55 am Post subject:

AncientBrit · Posted: Fri Feb 06, 2009 5:44 pm Post subject:

Found a link for BC348 pinout here:

http://hamradio.lakki.iki.fi/new/Datasheets/transistor_pinouts/

Cheers,

Graham

AncientBrit · Posted: Fri Feb 06, 2009 5:51 pm Post subject:

...and equivalents to BC348

http://english.electronica-pt.com/db/cross-reference.php?ref=bc348

Graham

gary · Posted: Fri Feb 06, 2009 5:53 pm Post subject:

I can confirm that it is indeed a BC548 (at least on mine)

Klaas Robers · Posted: Fri Feb 06, 2009 6:32 pm Post subject:

Yes sorry, it was a type error. I have corrected it. Thanks.

However I know that this transistorchip has been mounted in different housings and had different numbers. The BC548 is identical to the BC108 in small metal can, the BC148 in triangular plastic encapsulation ("lock fit") and the BC848 (?) SMD transistor. And I have seen more housings. So the first number became more or less a "don't care" for me.

Ralph · Posted: Fri Feb 06, 2009 10:36 pm Post subject:

Thanks to all!

Ralph

AncientBrit · Posted: Fri Feb 06, 2009 11:20 pm Post subject:

> Klaas,

"So the first number became more or less a "don't care" for me. "

That's what I like to hear. In the true spirit of NBTV experimenting!!

Kind regards,

Graham

Ralph · Posted: Sun Feb 08, 2009 4:02 am Post subject:

Just for the record, my MUTR kit arrived early this last week and I finally took the time to assemble it. Perhaps "kit" and "assemble" are excessive terms, given the fact that the whole project went together in about an hour with no soldering or other complex ( Very Happy

) operations. It worked "right out of the box". I will replace the diffuser, but otherwise will keep it "stock" for demonstations. Overall, very well thought out and a nice project at a fair price.

Ralph

Steve Anderson · Posted: Sun Feb 08, 2009 12:04 pm Post subject:

Klaas Robers · Posted: Mon Feb 09, 2009 1:53 am Post subject:

Ralph, I can recommend you to replace the red LED by a orange-amber LED. This is better for the brighness. And a second diffuser might help. I wonder how it would be with a diffuser at both sides of the PCB. I think it will help, but haven't tried it.

I don't like the lens. It gives reflections and hardly any enlargement. I use it without a lens.

I experienced the sync to be with a picture standing too low. Rotating the speed pot changes little and when the setting seems ok the disc might loose sync. I experienced with a resistor in parallel to the motor, but should also do this with a resistor in series with the motor.

But I also got a pdf from MUTR of the sync pattern that is stuck to the back side of the disc. Then I could over glue this with some rotation in order to frame the picture correctly.

Ralph · Posted: Wed Feb 11, 2009 5:09 am Post subject:

Klaas,

I have already installed a better diffuser and will make some other modifications in the next few weeks. I am off that task for the moment and am busy converting the MUTR circuit to a universal televisor pc board. Given how easily the MUTR system fired up, it seemed to be a reliable way to jump start all sorts of televisor projects.

The board is 4 x 4 inches (102 x 102mm) so that nothing is crowded and experimental modifications will be easy. The board uses the IRL530 (or any similar FETs) since, with a suitable heat-sink, that device will run most DC motors. The video portion of the board will accommodate both TO-92 and TO-220 driver transistors, permitting a light sources ranging from a single LED to a large LED array, not to mention an actual neon tube if someone were so inclined. The board is designed so that the LED and sensor for the optical chopper are off the main board, permitting maximum flexibility with respect the the mechanics being used. It will take a week or so to get the board made and I will test it initially using the DE Televisor mechanics. If it works well, and I see no reason why it should not, I will post all the project documentation on my web site.

Ralph

AncientBrit · Posted: Wed Feb 11, 2009 5:27 pm Post subject:

Ralph, that's very interesting.

I've just ordered up an MUTR kit so anything you produce will be of use.

One thing I've noted on the motor control is that the drive is single ended from the FET.

Apart from protecting the FET does the shunt diode provide any form of regenerative braking or does the motor "flywheel" when drive is removed?

If there is little regen. braking I wonder whether a bridge drive to the motor would give a more controlled mechanical response and a tighter servo.

Regards,

Graham

Klaas Robers · Posted: Thu Feb 12, 2009 12:48 am Post subject:

Yes Graham, you are right. The drive of the motor is single ended and the diode is just there to protect the FET fore inductive actions of the motor.

I connected a resistor of 12 ohms accross the motor which gives regenerartive braking and I got the impression that the servo works better. However still the disc might catch in one frame shifted, but sometimes also correct. This can be seen with an oscilloscope across the motor.

Then you also see that the reflective sensor has problems with a wobbling disc. Then the distance disc-sensor is changing, giving a varable phase shift of the picked up pulses. And indeed,the disc is not really flat.

I should also do some experiments with a resistor in series with the motor. Pete Smith says that this helps in certain occasions.

Panrock · Posted: Thu Feb 12, 2009 1:28 am Post subject: