Hey guys, long time.. haha
I havent been active here for a while but did`` a lot of midiboxing last year, finally built a seq and helped a friend with building one.. needless te say here but still : really nice!!
Anyway, I need to build a few AOUT modules for the 2 seq's and a midibox_cv2 so I decided to have some pcb's made.
I had contact with northernlightx from the forum a few years ago; he was busy with designing a new pcb for the mbhp_AOUT module (max525 version). He had some made but didn't work; he sent them to me so I could help. I found that there were a couple of mistakes on the pcb; had to cut too much traces and the layout wasn't good (confusing, no names/labelling).
Let me say: for me this aout pcb is really something that has to be good quality; ie. clear, efficient, optimized to produce the best signal possible: because it is central in my setup; it provides the connection from midi to modular synthesis AND because it is quite an expensive module (max525ACPP around 35 euros); so that is why i'm quite critical about this pcb.
So I decided to make a new pcb for the AOUT module which I will have made at OSH park soon, but I think if it is a good design it could be put on ucapps as the AOUT_V2 pcb.
So before I have them made, I thought to share it here and see if I forgot something, should do something different etc. If so, let me know so I can make some adjustments/improvements and order some boards. I will then of course build and test them and report back here..
If they work correctly the design can be put on the site as the (long awaited) AOUT_v2 pcb
These are things I had in mind while designing:
-how to adress analog/digital ground stuff
-clear labelling of test points, components, trimmers, in- and outputs
-clear layout, enough room for trimpots that are a bit bigger
-all connectors should be (2x5) IDC connectors
-bipolar option will be possible with extra hardware; more on that later
-power led not included
The design shown below is just to get the idea and to see the stuff I find important. Im actually working on another version with different/better tracing. I'll add the eagle files so you can have a better look.
-how to adress ``analo``g/digital ground stuff
so I used top and bottom ground planes; top ground plane is analog ground, bottom has 2 groundplanes, the biggest on the right side is analog ground, the smaller left plane is digital ground. I have the 6007b placed on top (original was bottom); the area on the bottom around the 6007 has no ground plane to avoid capacitance problems. About tie-ing grounds; he max525 datasheet says connect the 2 grounds together close to the max535 to the best ground trace. JP5 and JP6 connect the grounds together (should I keep this? Have them to be safe because I dont know anything about the math or processes that are involved with proper grounding, I just try to learn& apply the best grounding practice) I have jumpers JP1 and JP2 so you can decide if you get digital power from the power connector (CON2) and send it to your core (with CON1) or if you only get analog power from CON2 and get digital power from the core (CON1).
-clear labelling of test points, components, trimmers, in- and outputs -clear layout, enough room for trimpots that are a bit bigger
-all connectors should be (2x5) IDC connectors
first off, I made some icons with pin names next to all of the IDC connectors. I see that in the image above half of the pin names don't show up but ill fix that.
I didn't make separate test pins for calibrating the outputs because the RX-* resistors are perfect for that. Note the labels inducating the CV out number.
The trimpots are in order; top to bottom is cv out 1 to 8. There is room around the trimmers so they can be a bit bigger.
Also the IDC connector for the outputs (CON3) has the outputs in order. Pin 1 to 8 of connector are CV out 1 to 8.
-bipolar option will be possible with extra hardware;
so I thought A LOT about this since years ago I tried making the bipolar option and had problems. I know for sure that it is possible to make some hardware that will let you switch between an offset of +/- -5V and 0V. (there was some talk about this in the CV-V2 thread and maybe some other forum pages) I would guess it would be possible to make it so you can decide on a patch/preset level wich output should be bipolar; this would be the best ``approach for me. If I want to ``send ``notes ``to a module`` want an unipolar out but if im controlling other stuff a bipolar would sometimes be better. But I would``n't`` know how to program that so i'm just putting the idea out there.
In practice the expansion hardware could be basically an 2 input ``inverted opamp mixer with matched resistors for the so you have a gain of exactly 1 ``on both channels``. ``One mixer input will be the calibrated cv output from the AOUT pcb and`` ``the ``other ``mixer`` input should ``be a signal (provided on the expansion pcb) that you can switch from`` 0v (unipolar) ``to -5V (bipolar).``To make a stable -5V you could use a zener voltage regulator, and then there should be ``some kind of digitally controlled switch`` that can be controlled by a DOUT pin to send either 0V or -5V to the opamp. Haven't designed this yet but should be easy.
The output of the inverting mixer should be inverted again.. Of course you could think; use an non-inverting mixer, but the gain formula of that is not so straightforwrd and I think that was the reason for my problems with using the original bipolar expansion.. But if anyone has a better option; less opamps is always better I guess.
Few questions on this: should we take the calibrated, amplified CV outs or the direct outputs of the max525? I those the first option because then it is a true expansion as in you can use and calibrate the AOUT standalone and just add the expansion if you need it.
To implement the opamp mixer correctly it should have a gain of exactly 1 otherwise the calibrated voltage will be off. Do you think we can do this by using precisely mmatched resistors?
Hmm sorry that was maybe a bit much ``about the possible expansion``.. now ``back to the AOUT
finally some questions I still have about the AOUT_v2 pcb design:
-should the 2 gate outputs be there? I guess so right, doesn't cost a lot and you have some visual aid to see if the module is responding to midi/core
- should there be a connector for chaining th SPI port (dunno if I name it correctly) but like port J2 at the original out module? Is it ever possible to chain more AOUT modules together? I did put it in the design (CON4) but don't know if I did the connections right; maybe someone could check that?
Allright guys lemme know what you think..
cheers, marcel
[AOUT_V2_prot.zip](< base_url >/applications/core/interface/file/attachment.php?id=12737)