| Electronics > Projects, Designs, and Technical Stuff |
| DIY Modular Test Equipment Project |
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| void_error:
--- Quote from: prasimix on June 05, 2016, 03:24:20 pm --- Glad to see that you decided to define multi-modular solution with Mainframe-style possibility. That is ambitious project and hopefully more people will be attracted soon and decide to join you. If I "dream" about something then it's interoperability of what I made with other people designs. I don't have a problem to adopt everything that is already created to share the same "DIY-instrumentation-bus" and works under same software framework and successfully communicate with commercial instruments. Like timofonic I vote for GitHub/Bitbucket openness in one moment because it could make a whole thing more interesting in the long run (and hopefully you are already aware of how looooooong could takes to make something in correct/usable way :)). From my side I'm looking forward to see if your design could become a potential "target" for firmware that we are developing. Not sure for now, but if currently developed code could be ported to PIC that can save literally hundreds of hours for you. --- End quote --- There's still a long way until I start coding. Planning on ordering a few ERC12864-655 displays this month, it'll take another month for them to arrive so that's when work starts. They're about $10 a piece. My general habit is to write modular code and reusing already written code, which I have a lot of, at least for peripherals, so only the display is something I might run into difficulties with. --- Quote from: prasimix on June 05, 2016, 03:24:20 pm ---One more thing because I been there: it's a LCD display or better to say its 128 x 64 (and monochrome) resolution. TFT LCD becomes really dirty cheap and they are not of equally dirty quality! Even if you hate "touch screen" you don't need to rely completely on it: there is no reason why encoders shouldn't be on your front panel together with touch-screen. --- End quote --- LCD description updated. I don't hate touchscreens, I just like knobs and buttons more. I'm not using a touch screen because it would add more complexity to the firmware and it'll take me more time, and I've never worked with touch screens. I did look into using TFT color LCDs but I decided to go the simple way, again, because of the limited amount of time I have for this project, I also have a full-time job. --- Quote from: prasimix on June 05, 2016, 03:24:20 pm ---Finally something that I should mention on the beginning: I'm suggest to not take mechanical aspects too lightly! That can really generate a lots of frustration: because you realized that something is not accessible, cannot be mounted, have EMC or heating issue, etc. Of course today's 3D modeling, thermal modeling, etc. could help you to avoid such mistakes that will push you into another revision, but remember that you are still alone and even with 96 working hours day that will consume all your time (again I'm talking about something that will be usable for you and eventually many others). So, mind the mechanics! Define boundaries within everything will happen first. :-+ --- End quote --- For the User interface at least, I found all the 3D models that weren't already in the DipTrace library, except for the display. Starting next week I'm back to work at my full-time job, had this week off, so don't expect much progress on this project. I may have 3-4 hours of free time every weekday which I could use and a bit more during the weekends. |
| void_error:
Having changed the I/O expanders going to the UI dispay from I2C to SPI I have another decision to make. The MCP23S08 is addressable, up to 4 devices on the same bus using the same chip select. The User Interface uses two which means I have 2 addresses unused, so I can hook up 2 more chips on the same bus. Another board that uses an I/O expander is the Waveform Generator so it could share the CS pin with the ones on the UI if the address is set different from the other two. I'm inclined towards sharing the chip select pin as it frees up an I/O pin on the UI micro. What do you think? |
| void_error:
Made a few more changes to the UI. Replaced the I2C I/O expanders with SPI ones (MCP23S08), both share the Chip Select pin and SPI lines. For the Chip Select that goes to the off-board SPI connector there's a separate pin. I actually used up ALL the pins on the micro except for MCLR/Vpp (input-only and high voltage programming). Pull-downs (33k) are ok with the programming pins, the two XOR gate inputs' capacitances are very unlikely affect programming. With the buzzer being driven by the ICSPDAT pin signal during programming I'm prepared to hear some weird noises. PCB layout is progressing well, about two to three hours a day this week, all except one of the traces are laid out, they only need some tweaking. Before I finish laying out the PCB I thought I'd ask for opinions/advice, just in case I missed something or made a stupid mistake on the schematic below. Feel free to ask any questions. |
| void_error:
The UI board layout is almost compete, some small tweaks and via stitching are still required. Found the 3D models for almost all the parts so here's a sneak peek of the board. It's going to be the front panel for almost everything I build from now on. The dual row connectors on top will either be regular pin headers for connecting to piggy-back boards or shrouded headers for using IDC ribbon cables. The power connectors on the side can be either straight or angled. |
| void_error:
Moved the mounting holes and the 6-pin UART connector on the UI board so I can make the Waveform Generator PCB narrower. Speaking of the Waveform Generator, the schematic is almost complete, I only have to sort a few details out, spent most of the evening looking through datasheets and I still have a few questions unanswered, like the following: If I use MLCCs for decoupling on the AD9835, do I still have to use a 10uF || 100nF pair or can I get away with just one cap? Same question for the LMH6321 output buffer. While looking for MLCC characteristics I ran into this nice selection tool... An unfinished Waveform Generator schematic can be found below. As always, suggestions are welcome. |
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