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Control surface PCB for 16 encoders/LEDrings Bulk Order


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Dear members, First, I excuse myself to all that I didn't answer individually more early but my life didn't let me lot of time to do so before.   I come back to you to indicate I've finished the de

One thing I would point out is to be careful with shipping.  I think everything came in my order however it was close to not being that way.  The top of the package was ripped open from the boards and

Hi. I inform members of the start of a bulk order concerning a all-in-one PCB integrating DINx4/Doutx4 modules and a control surface with 16 encoders/16 LEDrings. The list ends the November 23t

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Arrived in perfect condition in Denmark yesterday :smile:

Thanks a bunch, they're beautiful <3

 

By the way, what is the recommended brightness in mcd of the leds? Perticularly diffused vs non-diffused?

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I got my boards as well, and the first one is already stuffed!  :smile:

 

lre8x2_old.jpg

 

This evening I will release a new MBNG version which will contain a configuration template for this hardware + some small extensions (e.g. bank switching via the SCS)

 

You might miss following details in the documentation:

 

The LED polarity for newbies: the cathode (short leg) has to show to the center of the LED ring:

lre8x2_led_polarity.jpg

 

The connection to the MBHP_CORE_LPC17 module could be confusing, since the SO pin of J8/9 has to be connected to the SI pin of the LRE2x8 board, and SI to the SO pin (for MBHP_DOUT/DIN we usually have the same names for these signals, this detail has been overlooked).

If you are using "polarized DIL sockets", then just take this picture as orientation:

 

lre8x2_core_connection.jpg

 

Last but not least: the LED brightness topic:

 

By the way, what is the recommended brightness in mcd of the leds? Perticularly diffused vs non-diffused?
 

A very good question, because it seems that this topic is more important than expected.

I used the same "rectangular" LEDs like Jerome, and noticed that the brightness of the LEDs is not acceptable (from my point of view).

 

The LED rings are looking nice on the pictures, but in reality you won't see anything in a bright environment (e.g. if a lamp directly spotlights the board)

 

The reason for this is the time-multiplexed handling.

With a 16x16 LED matrix each LED ring will only be active for 6.25% of the normal time.

This is fact by construction, software can't fixed this (e.g. I tried a higher scan frequency... but for obvious reasons the LED is still only active for 6.25% ;-))

Also the transistor array or lower resistor values won't help for these rectangular LEDs.

 

The results are much better on my initial MB16E construction, and as far as I remember I just used the low-cost red LEDs, which are diffused and have a higher mcd than the standard LEDs.

 

I will order these ones from Reichelt, and should be able to test (and confirm) them this weekend.

 

Best Regards, Thorsten.

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Special notes: the .NGC file configures the ledrings for ULN2803 based Transistor Darlington arrays which will invert the selection lines for the LED rings.

If you've built the PCB without the transistor arrays (which actually don't really improve the brightness), then please change the "DOUT_MATRIX ... inverted=1" definition to "DOUT_MATRIX ... inverted=0", otherwise the LED rings won't work correctly!

I think it was my idea to add the ULN2803 to design :happy:

It does provide a much more substantial current drive to the LED matrix, however it does (I have since discovered) have a minimum output voltage of 0.6 to 1V.  So it is therefore necessary to compensate with lower series current limiting resistor(s). The driver can sink a lot more current than a single HC595 pin, I promise!

 

TK, if you could when you get a moment to do this, solder another resistor across (in parallel with) one of the resistors in the 220R resistor networks. I suggest trying a value of 180R or thereabouts. This should result in the same LED in each LED ring being about twice as bright as the ones next to it?

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I can confirm that the minimum output voltage is around 0.7V.

I already tried lower resistor values - even 47 Ohm - but this doesn't change the brightness of the rectangular LEDs that are stuffed on my board.

This experiment will be repeated once I got the new LEDs with a higher "mcd value" from Reichelt (see also ).

 

Best Regards, Thorsten.

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Is the matrix being driven such that the low side driver (the DOUTs connected to the ULN2803) is driven 1/16 duty cycle?

In other words each ms one low side driver is low and the high side (DOUT connected to resistor network) has a pattern of 16 LEDs for a single LED ring? 

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Damn! if it was the other way round there would be a firmware fix for this!

This suggests the current limit is imposed by the high side driver (and made a problem by the the low duty cycle).

If you wanted to investigate it further: if you where to place a couple of CRO probes across the resistor, set the scope to subtract signals.This way you'd be measuring the instantaneous current (I=V/R) through the R ,LED and driver. Accounting for different values of R measured, you may find the current varies less (than expected) as result of the high side driver output stage being saturated.

It looks as though they are really dim LEDs (low mcd) you have there. Your approach of better LEDs may be the only practical fix.

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No, the current isn't limited.
 

With 220 Ohm I measure a voltage drop of about 2V, which means that the current drain is about 9.1 mA

With 47 Ohm I measure a voltage drop of about 1V, which means that the current drain is about 21 mA

But: the brightness doesn't really differ.

 

As mentioned before, the results are much better on my initial MB16E construction (built 10 years ago) which uses low-cost LEDs with a high mcd value - this will solve the issue for the LRE8x2 board as well.

 

Best Regards, Thorsten.

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No, the current isn't limited.

 

With 220 Ohm I measure a voltage drop of about 2V, which means that the current drain is about 9.1 mA

With 47 Ohm I measure a voltage drop of about 1V, which means that the current drain is about 21 mA

But: the brightness doesn't really differ.

 

As mentioned before, the results are much better on my initial MB16E construction (built 10 years ago) which uses low-cost LEDs with a high mcd value - this will solve the issue for the LRE8x2 board as well.

 

Best Regards, Thorsten.

Ok, good the drivers are working as expected. You will not get 16 x 21mA through the single low side driver pin without the ULN2803. 

 

The crappy LEDs are saturating hence no extra light with more than double the current.

Normally LED should be linear in brighness with respect to current up to, and often over, 20mA.

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The crappy LEDs are saturating hence no extra light with more than double the current.

Normally LED should be linear in brighness with respect to current up to, and often over, 20mA.

 

yes, I've the same impression.  :sad:

 

Best Regards, Thorsten.

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