b0rked x0xb0x

March 22, 2006

Setting the power supply to output 5.333 VDC.
(Click for more x0xb0x construction photos…)

Well, last night I finally received my Mouser order with the parts that I was waiting for.

Hmm. Perhaps I should backtrack a bit… After finishing the electrical assembly of my x0xb0x, I found that the LEDs were way too dim. After building the Elenco XP-720K power supply (photo gallery retired), I was able to test out the LEDs with different resistors and find some appropriate ones. It turns out that a 820Ω resistor in conjunction with the LEDs worked out to be exactly what I wanted, bright enough to be seen under a bunch of lighting, but not glaring when in the dark. So, last week I desoldered all 40 resistors which tie to the LEDs, and last night I hooked in the 820Ω resistors, put the x0xb0x back together, cleaned off the flux, then got it all working.

After that installing the new resistors I went through and set everything up with the new Fluke 179 and got it all set up right. The frequency counter in it was especially handy, as it made setting the offset between octives (this synth is 1V/oct). Not long after the synth was all done being tuned, and it sounds great. Then I broke it… More on that later.

Yesterday, as a prerequisite to tuning the synth, I also finished up some work on the Elenco XP-720K (photo gallery retired) by adding heatshrink tubing to the worryingly unprotected IC leads, installing new Bourns 10-turn wirewound pots in place of the original 300° carbon ones, and new knobs from EPD (450-2016). The new knobs were needed as the shafts of the new pots are of a different design, and I also wanted some which allow for a bit finer control. While I like how they look I’m still not sure if they allow for fine enough control. We’ll see…

With the new pots, I am able to easily set the supply voltage to within a few thousandsths of a volt, and with some gentle nudging of the knob I can generally hit the exact voltage I want. Because the pots are wirewound there seems to be a limit to how fine the control I have actually is, but things are still fairly accurate. Adding a second set of wirewound pots (200Ω) as a ‘fine tuning’ control in parallel with the existing ones would help give more control, but it would require drilling more holes and… I don’t know if it is needed. Regardless, I am quite happy with the finished power supply.

So… About how I broke my x0xb0x. Well, to make a long story short, I was playing around with writing my own firmware for it, and after flashing it one of the times, it no longer worked. Details of all what happened can be read here, but the solution ended up being flashing it with alternate firmware, then going back to the original firmware, then wiping the patterns in the EEPROM. I think I had corrupted part of the EEPROM, and as the EEPROM is read as part of setting the tempo as the x0xb0x boots, I think I was making it crash on boot.

Also, I’ve found my firmware with the blinky startup sequence causes my x0xb0x to crash randomly, so that needs work. That’ll come later. Thusly, I’m just using the normal, and originally shipping, v1.04 firmware.

I think I’ll also tag some specific photos of interest here:

· The pile of LED-driving 10KΩ resistors pulled from my x0xb0x.
· Calibrating the x0xb0x’s power supply to 5.333VDC.
· Playing the x0xb0x via MIDI. As a nice surprise, a velocity over ~100 seems to trigger accent.
· The newly heatshrink tube’d IC leads in the Elenco XP-720K.
· Rear view of the Bourns 3504S-1-202 pots in the Elenco XP-720K.
· Two front views of the front of the Elenco XP-720K with the new pots and EPD 450-2016 knobs: 1 · 2