T&L Publications

Hello Federico If you are going to test the MAX335 idea, remember that a lightly loaded transformer gives a higher output voltage than that stated. I would try a 9V transformer and use a voltage clamp to limit the input voltage to below +/-15V peak-peak. I have modelled this and you actually get qui...

Hello Federico, No, it is all part of the pixel element. The 100k resistor is the pixel leakage, the capacitor represents the capacitance (main component of the pixel) and the 2R resistor the series resistance of the capacitor. There will also be some inductance, but not worth bothering about. But t...

Hello Federico, The electrical equivalent of the pixel is probably capacitate in nature, may similar to that shown:- http://www.postimage.org/aVO0Df0.jpg The 6818 32-bit shift register feature sourcing output (active pull up at 40mA maximum to 60V maximum) and would be ideal drives for triac's, so w...

Hello dyarker, but we would not be using a trigger pulse. If a pixel is set to on, then the shift register output associated with that pixel will be switched in the on condition permanently. So the triac will retrigger on each cycle. The absolute maximum switch current for the MAX335 is 30mA. The ac...

Hi Guys, I need some time to think this through, and I'm up against it at work at the moment and can't think straight. But regarding triacs (and SSR's as well), if you are switching DC, then you need to reduce the current below the hold-on level for the device to switch off, but we are switching AC,...

With TRIACs you need to find some with very low cut-off current. The typical 1 to 2A TRIAC may cut-off at 10mA, which is less than the pixels use. Hello Dyarker, Of course you are right, didn't think of that one! Back to jolly old drawing board. Federico, I will have to have another think about thi...

Hello Federico, You misunderstand. By discreet, I mean that the switching element is not part of the shift register as it is with the MAX335. You would have a shift register as one device and connect that to 'discreet' switching elements (e.g. triac's). The resulting circuit would operate in the sam...

Hello Federico,

Yes, that device would be ideal, if going for the discreet pixel switching option.

Lots of possibly device similar to this one exist.

Regards
Rob

Hello Federico, A triac is actually an excellent solution, is bi-directional and should not cause any noise problems. You only get these problems when you switch large loads abruptly, especially in the middle of a mains cycle and usually when you switch the triac off. In this application, we can lim...

I think Engineer1138 has it summarised this completely, I can't think of anything to add. If there were NO chance of getting sued within an inch of your life, then this is a reactively simple thing to make (and make safely, as mentioned, the isolation problem is easily solved). But if the lawyers ge...

Hello Federico, If it is RMS, then peak-to peak will be about 21V. So +/-15V swing (Peak-to-peak) will be 10.6V RMS. So this is the MAXIMUM voltage that can be fed to the display if using the MAX335. It may be easier to abandon the MAX335, and use a shift register, driving a output driver. Then ther...

Hello Federico, Here is a quick sketch. http://www.postimage.org/image.php?v=aVtZntA It would need additional decoupling and probably a local data buffer if the number of MAX335 is large. You will note that the transformer is 10VAC to limit the peak voltage to less than 15V, and a bi-directional cla...

Hello Federico, I strongly advise keeping the screen supply separate from the DC supplies. The +/-15V supplies need only supply about an amp maximum (15W+15W) switching supply and the transformer will only be around 20VA and if you use a toroidal, it will be light and have a slim profile. From your ...

Hello Federico, Here is a block diagram of a possible display module and PC-interface. Each module would have an individual select line and a common data and clock line would be fed to all modules. Disadvantage of having 200 pixels on a single module is that in order to write to a single pixel, all ...

Hello Federico,
Here is the best circle I could make up using 28 20x10 blocks. At almost 42 feet across by 33 feet high, it's going to be a monster!

http://www.postimage.org/image.php?v=gxw4Wc0

More to follow.
Regards
Rob