Category: making things

Upon arriving home from work today I found a white box in the mail from Scotland indicating that the new LCD for Ivan’s P3 had arrived. This is the replacement that Colin (the Sequentix guy) offered to people as a replacement for PLEDs which had failed. After eating a bit of dinner I set to installing it.

Because of the spacing of the LCD and function switch board I had to file away a bit of the PCB in order to make it fit nicely. Thankfully Sequentix’s page on the replacement LCDs had mentioned this, so I was expecting to do it.

All in all, it went well. After getting the LCD working I installed the v4 firmware and MemX board, getting the machine wholly up to date.

I’m running into a bit of weirdness with the LCD, though. As can be seen on this page of photos, the display seems to be cutting off some characters during boot, corrupting others, and occasionally causing weirdness. I’ve tried making a new cable and replacing the IC directly connected to the LCD, but that hasn’t been successful. I’m really afraid that the controller on the LCD may be messed up. Hopefully tomorrow I’ll be able to use one of Ivan’s spare LCDs which he was sent (by way of me) by Crystalfontz as replacements for his failed PLEDs.

UPDATE: I just emailed Colin, the Sequentix guy, and asked for suggestions. After talking with a few people I’m starting to feel certain that the problem may simply be that the LCD doesn’t start up fast enough for the P3. It seems that with the HD44780 protocol the LCD talks the user can set up custom characters in the CGRAM (character generator RAM). While I may be way off base, I’m thinking that the P3 sets up the special characters it needs on boot, then tries to display stuff. I think that if the LCD isn’t running stable yet then these characters, along with data written to the display controller itself, could become corrupt or lost, displaying the symptoms like what I’m seeing. Hopefully I’ll find out for sure soon. If this is the problem then a fix would simply require the P3 to wait for another 250ms (or so) at power-on.

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Last night I made quite a bit of progress on Ivan’s P3, getting it up and running, but I did run into a few problems. First, as can be seen above, the PLED which came with the enclosure seems to be failing. It will either display no text, one line of text, or (rarely) both lines, and every time pixels seem small and dim, with the edges of the display fading to nothing. Only a power cycle of the P3 seems to (re-)activate non-working parts of the display. As the P3 still functions even when nothing appears on the display, I believe that it’s actually the display elements of the PLED which is failing.

Here is the PLED in my P3 from 2006, and when it is compared with these two images (1, 2) of the PLED from Ivan’s P3, it seems pretty obvious that something is wrong.

Thankfully there was a spare PLED in the package of parts I received, so tonight I’m going to try that one instead.

Second, I’m not happy with the cables I made for connecting the tempo and data pots to the mainboard, so I’m going to remake them. The tempo pot connection seems to be a bit flaky, so I’m not sure the pins are properly seated in the connector. The cables are also short enough that they are difficult to connect, so I’ll probably redo them with braided 24 gauge hookup wire or something like that.

Finally, the v1.5 mainboard construction notes indicate that when the P3 is being set up for MIDI sync, D2 and D3 should be replaced with 220pF caps in order to add a bit of extra capacitance to the lines to work around false triggers. I didn’t have any 220pF parts, and none came with the kit, so I instead used 330pF parts. I don’t believe this will be a problem, but I made a post to the analogue-sequencer group asking for confirmation.

Beyond those three problems, the build is going quite well. I’m very happy with how both the step board and keypad came out. The IDC ribbon cables, their connection, and power input stuff also worked out great.

I was also able to get the latest bootloader and v3 firmware on the P3, which means that as soon as the other issues are sorted out I can get the MemX and latest v4 beta installed. After that it’ll just be time to install the knobs, test it out, and ship it back to Ivan.

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Today I made a bunch of progress on the Sequentix P3 I’m currently building. Before today I’d only checked out the parts to be sure most of them were there, looked over everything, and did some general setup to be sure assembly could progress. Today I started fitting pieces, and I’m definitely more than half done at this point.

Because this P3 uses a slightly older board set (v1.5) I had to use this set of older DIY Sequentix P3 directions, but this didn’t prove to be too difficult. While I was able to complete the mainboard, I had to make some slight modifications. It seems that the v1.5 P3 board set only supports MIDI sync or DIN sync. One must read carefully through the main board and IO board pages to figure out what extra components to add, which to leave out, and what to do differently. In short, I had to leave out some parts from the mainboard and fit two capacitors where diodes once went and add in an extra pullup resistor on the bottom of the board.

The two capacitors on the top of the board are intended to add a bit of capacitance to the input lines of the PIC which handles MIDI sync. It is suggested that 220 pF parts be used, but as I didn’t have any of them I fitted some spare 330 pF parts. I don’t think this will cause any problems, and hopefully it won’t. The extra resistor on the bottom of the board is to help work around slow rise times on the MIDI output caused by additional capacitance brought about by the inclusion of RFI filters on the IO board.

I’m hoping to be able to power it up for the first time either tomorrow or Tuesday. How late I get home from work will determine how much I’m able to get done each night.

Here’s a few more photos of parts from tonight:

· Completed Mainboard w/o ICs: Top / Bottom
· Completed upper and lower pot boards.
· Pots for the P3, plus spares, with lugs removed and thick 1/4″ washers fitted for spacing.
· Completed IO board, set up for MIDI sync.
· Completed function switch board.
· Twelve resistors.
· Incomplete keypad board with 1N4148 diodes fitted.

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This afternoon I ran by the local FedEx depot at the intersection of Brown Road and Giddings Road in Auburn Hills to pick up a box containing the next P3 I am to build, for another person from the analogue-sequencer Yahoo! Group. It turns out that this facility doesn’t normally receive in-person pickups, as I had to enter through the employee entrance (metal detectors and all), enter the office, and just sit in a waiting area until the person brought out my package.

After a nice bike ride around Dodge Park with Danielle I opened up the package containing the P3 and started sorting through all of the parts, laying them out on the table for easy access. On initial glance everything seems to be there, except for a couple small screws for holding the enclosure together.

This is actually a slightly older enclosure design than I worked with on on my P3, as it doesn’t include niceties like the subpanel to help with the pot assembly, and the clearance around and mounting of the PLED leave a bit to be desired. That said, I imagine assembly will go pretty smoothly.

I’ll get started with the actual assembly tomorrow, although I might take a break for a bike ride if the weather isn’t too threatening.

Oh, and (per usual) there are a few more photos of Ivan’s P3 here in this album in my gallery: Sequentix P3 for Ivan

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