x0xb0x Sequencer button/LED issue

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heste
 
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x0xb0x Sequencer button/LED issue

Post by heste »

Hi I'm having some issues with my x0xb0x build. I have finished the build and put it altogether. The sound works and the knobs (including the tempo one) works fine. However I'm having a problem with a specific area of buttons sometimes being unresponsive and sometimes giving a less than lighting than others. Typically I can play the synth for a few minutes before these buttons stop lighting the LED when pressed and cause the synth to be entirely unresponsive.

Here's an example of an affected button while the synth is responsive:
Image (https://imgur.com/Vb40RdZ)

When i start the synth there's a second where all LEDs light up. This gives a good overview of the affected area:
Image (https://imgur.com/Vs4LyE8)

I will be forever grateful if anyone can help me debug and diagnose this thing. I have a multimeter and an (uncalibrated) oscilloscope at hand.
The kit from willzyx by the way.

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mmm
 
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Re: x0xb0x Sequencer button/LED issue

Post by mmm »

I'm spitballing here:
LED 7 to 14 are driven by IC7; those are affected.
LED 15 to 17 and 25/26 are driven by IC8; those are affected. But IC8 also drives LED 27, 39, 40 which seem to be not affected.
The LEDs all go to the same ground plane so there should be no differences in ground potential.

Can I see a hi-res picture of the component side? The bottom part with the ICs and resistors is sufficient.

Do the LEDs 2 to 17 (corresponding to numbers 1 to 16 on the front panel) light up the same brightness when using another mode? For example, what happens when you are in Pattern Play mode and just switch through the patterns with the rotary switch? Does the brightness also drop off at some point?

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heste
 
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Re: x0xb0x Sequencer button/LED issue

Post by heste »

That's strange. Could it be some pins of the IC?

Here's some pictures of the board, there a full and two close-ups.

Full:
Image (https://imgur.com/kCNFEd6)

Left side:
Image (https://imgur.com/A0ni3qf)

Right side:
Image (https://imgur.com/uHUNUda)

I tried in pattern mode, it seems to affect exactly the same LEDs. I'm not sure how these modes are supposed to work, so it's difficult for me to tell what's off.
There's also a strange issue with the pattern group selecter, where it rolls over from 8 to 1. I recorded a video to show it properly

https://www.youtube.com/watch?v=61BSzlFoSss

Thanks for taking your time to help!

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mmm
 
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Re: x0xb0x Sequencer button/LED issue

Post by mmm »

heste wrote: There's also a strange issue with the pattern group selecter, where it rolls over from 8 to 1. I recorded a video to show it properly
This is a telltale sign! I'll look into this (and the pictures) in detail tomorrow. Basically the highest bit of the left rotary switch is missing (or permanently pulled low). It would be interesting to learn whether the right rotary switch is also affected: Do the three last modes (keyboard, random and MIDI play) actually work? It probably is sufficient to test the "random" mode for this: if the x0xb0x is putting out a string of random notes it works.

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heste
 
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Re: x0xb0x Sequencer button/LED issue

Post by heste »

That's great!

The keyboard mode will play sounds as i hit the notes and the random mode will immediately start playing notes (and will be affected by the tune, resonance, tempo knobs). I have not tested the MIDI part of the synth yet.

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mmm
 
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Re: x0xb0x Sequencer button/LED issue

Post by mmm »

OK, so that means the right switch is working as it should (both switches use the same lines going to the processor).

The problems are clearly unrelated; let's work on them one at a time and start with the LED brightness. The difference in brightness comes from different current limiting resistors used in the built. It might well be that the "darker" LEDs are actually the correct brightness; this depends on the type of LED and the specified resistors. The original specification called for 10k resistors.
https://www.ladyada.net/make/x0xb0x/fab/seq/index.html gives a list fo the LEDs and the associated resistors. You need to double check each and every one of them again. For example, we've seen that LEDs 2 to 6 and 7 to 15 look different. Let's look at the resistors for LED 6 and LED 7: R244 and R250. R250 looks brown-black-orange to me which would be 10k. R244 however looks orange-orange-brown to me which would be just 330 ohms. This would account for the different brightness.

I don't think the x0xb0x normally uses 330 ohms resistors at all so I have no idea if those are part of a different LED package or if there was some sort of parts mixup.

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heste
 
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Re: x0xb0x Sequencer button/LED issue

Post by heste »

You are correct.

My LED resistor arrived in a bag without any indication of their resistance, so I assumed them to be 10K. The LED resistors were probably all 330 ohm.
I measured a few LED resistors and some are 330 ohms while others are 10K.
It also seems like I have 330 ohms resistors in places where it should be 10K (R206 as an example) in the sequencer. I probably used them exchangably.

I think the LED resistor being 330 ohm is correct, because most of them are at an appropriate luminance while some of them are very dim (they all look a lot brighter on my camera).

I now have a third issue where when i boot it up, it gets stuck at the LEDs lighting. I will leave it turned off until the resistors are replaced - hopefully I havent damaged anything...

Thanks a lot for the help, I will check all my supposed 10K resistors then replace them with correct values - 10K for 10K and 330 ohm for LED resistors. Hopefully that will fix most the issues. I will return with the results.

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mmm
 
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Re: x0xb0x Sequencer button/LED issue

Post by mmm »

heste wrote: It also seems like I have 330 ohms resistors in places where it should be 10K (R206 as an example) in the sequencer. I probably used them exchangably.
Those would be the pulldown resistors for the tactile switches. This could be the reason for the lockup when pressing certain buttons because then there's too much current flowing which in turn could result in a voltage drop on the +5V rail which theoretically could lock up the processor. I'm not sure if this is likely, though.
heste wrote: I think the LED resistor being 330 ohm is correct, because most of them are at an appropriate luminance while some of them are very dim (they all look a lot brighter on my camera).
It depends on the type of LED. If the value is too low it could again result in too much current flowing. There are online calculators that can help find the correct value.
heste wrote: I now have a third issue where when i boot it up, it gets stuck at the LEDs lighting. I will leave it turned off until the resistors are replaced - hopefully I havent damaged anything...
Make sure you're not in "Computer Control" mode - it might appear to be stuck when in that mode.

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