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Forum Index : Microcontroller and PC projects : PicoMite: PicoGAME VGA development
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Mixtel90 Guru  Joined: 05/10/2019 Location: United KingdomPosts: 6818 |
Back on topic: I seem to be getting a bit carried away with Version 1.2 (currently called version 1.X for Xperimental!). I think I've managed to swap the A & B connector functions, made it so you can use the (rather expensive and currently unavailable) adafruit SDcard module as an alternative and given the choice to use the SMPS without trace hacking (well, it's solder blob links). Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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thwill Guru Joined: 16/09/2019 Location: United KingdomPosts: 4047 |
Hi Mick, Did you do this because you thought it was the right thing, or because you thought it was another PCB challenge ? Could you explain what the choice to use a Switched Mode Power Supply means in practice ? Best wishes, Tom Game*Mite, CMM2 Welcome Tape, Creaky old text adventures |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6818 |
Because I was sitting there recovering from covid and it was a PCB challenge. :) Every bit of messing about is a learning experience. lol The SMPS on the PicoMite produces a lot of digital noise. If you are using the audio output, particularly with headphones, it's likely to sound horrible. Disabling it and using a linear regulator is one way of getting quiet audio. Volhout has another way which I'm going to try on one of these boards which should allow use of the SMPS and still get quiet audio. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| al18 Senior Member  Joined: 06/07/2019 Location: United StatesPosts: 205 |
Mick, Are you adding the Adafruit #4682 MicroSD 3V only board to your design? Any other parts changes to the board? |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6818 |
Too awkward to fit the 3v only one - too many pins and the distance from the board edge is a bit too close. I probably *could* do it, but it would mean not being able to use the nice little ebay one. I've not changed anything, only moved things around a bit and added the adafruit board as an option. I'm toying with adding the SMD 3.5mm jack that's used on the CMM2 as an option. Not sure about it yet. EDIT: It'll now accept the SMD jack socket. :) Edited 2022-04-14 06:51 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 4258 |
Mick, Why a board? Why not a SD card connector. The full size noes are not hard to solder. PicomiteVGA PETSCII ROBOTS |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6818 |
Good point. I'll consider that. Originally I thought it would be difficult to get enough space, but my tidying up has helped. I couldn't get that with the larger adafruit as an option as the terminals are almost bang on top of each other. Of course. :) I need to figure out a footprint for the large SDcard holder. I'm not sure that I can find connectors to fit the ones that I have. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| thwill Guru Joined: 16/09/2019 Location: United KingdomPosts: 4047 |
Good afternoon Mick, My parts continue to accumulate, including the controllers. Before I put a couple in the post for you I wanted to check you actually want them?  Note I've had one open and it looks the part - as far as you can tell when all the logic is just a resin blob - but I haven't tested them. Best wishes, Tom Game*Mite, CMM2 Welcome Tape, Creaky old text adventures |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6818 |
I'd love one, thanks Tom. I'm not sure about two? Could I use two of them? Hmmm... They certainly do look the part. :) Don't they have extra buttons? They may be interesting to read. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| thwill Guru Joined: 16/09/2019 Location: United KingdomPosts: 4047 |
I'll stick a pair in the post when I get a chance, they were cheap as chips. The two extra red buttons are the auto/turbo-fire buttons and are connected via an oscillator in the resin blob. They send the same signals as the A or B buttons would if pressed repeatedly. Best wishes, Tom Game*Mite, CMM2 Welcome Tape, Creaky old text adventures |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6818 |
Excellent, thanks. :) EDIT: Option setup for SD written on rear of PCB is wrong. OPTION SDCARD GP13, GP11, GP12, GP10 should be correct. Still need to verify this, but it looks right. :) EDIT EDIT: PCB will now accept full size SDcard socket Hirose DM1AA-SF-PEJ(72) which seems to have good availability. The PCB will no longer accept the adafruit module but it will still accept the original ebay module. PCB will now accept the Switchcraft 35RASMT4BHNTRX 3.5mm jack socket as an alternative to the original. Edited 2022-04-15 03:06 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| al18 Senior Member Joined: 06/07/2019 Location: United StatesPosts: 205 |
Mick, Price seems high for the Switchcraft 35RASMT4BHNTRX. Mouser charges $3.72. By comparison, the eBay module with 10k resistors and 2 capacitors is $2.50 for.1, with quantity discounts greater than 1 Can you still install the thru hole power jack in your new design. |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6818 |
The power jack is the same, not changed that. The Switchcraft 3.5mm jack socket is expensive but easy to get just about anywhere. The board will still accept the original PSG03613 instead though. I found that quite cheaply on ebay, although some of the big suppliers have it too. The Hirose SDcard socket is quite expensive too, but the original ebay microSD module still fits as an alternative. EDIT: Early tests on the first board are ok. Powered via USB at the moment so no PS/2 keyboard, but display is working ok. The SDCARD options given above work too. EDIT EDIT: Constructional hints: Fit the level shifter *before* the PS/2 and VGA sockets - you need room to work. You can either plug it into female headers or fully solder it. I chose the latter. If you are using the pins that come with it note that they are very hard to cut and will damage your best wire snips - use big chunky wire cutters or, and I speak from experience, they will lose the fight with a cutting disk in a Dremel. Alternatively, as there are only 6 connections, you can use bits of component leads, although it's a bit fiddly to do. The pins on the SDcard module do really need to be soldered directly for rigidity. A plug-in connection isn't recommended here. I trimmed the pins down before soldering them - it was far easier than using the Dremel to take the excess off after. I'm a little unhappy with the USB-A 5V output socket. It's very tight along there and the plug is hard up against the power plug. Still, it probably won't get used by many people. I can't juggle much more space as there are PCB mounting pillars in the way under the board. EDIT EDIT EDIT: After a lot of head scratching and wondering where I'd gone wrong - then fixing some dry and unsoldered joints (more than I would normally admit to!) - the keyboard is working. Sound is working and, according to my headphones, L and R are the right way round if you use OPTION AUDIO GP6,GP7. {** OH NO THEY AREN'T! ** - will be fixed on next version} Output to 32R headphones is acceptable (i.e. non-deafening) using the low level output - not tested high level yet. PIN(GP15)=1 switches the LED to green as expected. I'm equipping two boards in different ways. The first one (currently being tested): . All built as circuit diagram. The second one (audio not tested yet, but otherwise at same level as first): . SMPS on the PicoMite is enabled. There is no linear regulator for 3V3 . Video ladder uses 240R/120R instead of all 220R resistors . Audio circuit uses a system described by Volhout, which starts by limiting the 3V3 output from the PicoMite to 0.7V, consequently reducing the noise level. The boards are being tested using the same PicoMite, microSD card and external equipment. On my monitor I'm hardly able to discern any difference in using the white adjust preset, even though it covers the range 180R to 280R. 3mm bi-colour 3-wire LED fits nicely between the DB9 connectors. :) On this early board the D connectors have no pads to solder the fixings to. I was originally going to get some that use a plastic rivet, but these were cheaper. So, on this version, it might be an idea to scrape away some solder resist so that metal clips can be soldered to give extra strength. . Edited 2022-04-16 18:59 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6818 |
Input pins are all working as expected. Fitting the mini joystick (and removing the links to allow the use of potentiometers rather than "paddles") gives a voltage of about 1.64V with the stick centered. It increases in the Up and Right directions. These pins can also be used as digital inputs, of course. I've not tried a 100k "Paddle" pot yet, but I have no reason to suppose that it won't work. On the audio side, I'm not happy with connecting headphones to the PWM outputs via resistors on the version with the SMPS running. It works, but it's simply too noisy. It works ok on the version with the linear regulator (although there is still some noise). Speaking of resistors - I'd now recommend a minimum value of 330R for them. That allows a max volume that protects the PWM output and probably exceeds the maximum recommended decibels by quite a reasonable amount. :) I found that PLAY VOLUME 60,60 was good with 330R. There is a little harshness - probably as there is no PWM capacitor, we are relying on the inductance of the headphones for filtering and it's not very good. I'm going to have a rethink on the audio side, I think. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| thwill Guru Joined: 16/09/2019 Location: United KingdomPosts: 4047 |
Hi Mick, I'm still waiting on bits so I'm hoping you might write a consolidate list of gotchas once you've finished constructing your original boards so as to save me picking through this thread. I'm probably now only going to build one of this version; so I have something to develop against in the short-term. I'll order some Mk (1.)2s once you publish the gerbils. Volhout this means I will definitely have a spare Mk 1 if you want so drop me your post address, otherwise I'll send you a Mk (1.)2 when I've got them. I'm confused. The 9-pin DSUBs have metal rings on the backside of the PCB to solder the clips to. The 15 pin VGA does not, is that what you are alluding to ? When I'm scraping away the solder resist then what am I scraping down to, isn't is just fibre-glass or is there some sort of metal plane - in which case wouldn't that be ground ? Best wishes, Tom Edited 2022-04-17 20:42 by thwill Game*Mite, CMM2 Welcome Tape, Creaky old text adventures |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6818 |
Yep - it's just the 15-pin, sorry. There's copper under that pretty red solder resist. Just scrape a bit away - you don't need to go mad at it. Yes, it's grounded. That's ok. Actually, in spite of my apparently long lists, I've been pleasantly surprised at how well this has gone. Construction just needs a little care (mostly because you need to consider access). It's perfectly usable in it's prototype form. My only niggle is that I'd like the audio to be louder and with less noise while using headphones. Low level output seems to be fine, especially on the unmodified version (the one with the regulator). Low level output will work with my headphones, and gives good quality, but I'd like a little more volume really. I'm playing with the audio side at the moment - you might be able to upgrade that if you feel the need. The next version won't be software compatible because the ports are swapped over and there's been a pin change (GP22 switches port mode rather than GP15). Nothing crazy - it should be easy enough to convert a program between the prototype and final boards. Edited 2022-04-17 22:26 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| thwill Guru Joined: 16/09/2019 Location: United KingdomPosts: 4047 |
Hi Mick, I thought there was something about L & R audio being the wrong way around ? I find the subtleties of the audio even more beyond me than the rest of the hardware discussion. IRL my ears are at best lo-fi and I've never understood the obsession of a certain segment of the slightly older (male) generation with expensive audio equipment/amplifiers. Given the distorted noise that the younger generation listen to directly out of their phone speakers I think it likely that I was at the start of a "downward" slope in-terms of caring about this. Is the intended audio out of the PicoGAME VGA suitable for piping thorugh a VGA=>HDMI converter ? and/or "old" computer multimedia speaker system (such as my trusy HK195) ? what about a modern cheap wired speaker ? Best wishes, Tom Edited 2022-04-17 22:43 by thwill Game*Mite, CMM2 Welcome Tape, Creaky old text adventures |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6818 |
Right - best audio compromise for *my* headphones is to change R7 and R8 to 470R. No other changes needed. It's pretty loud (depending on the material). Other headphones might need these values changing for best results. Left and Right channels are reversed on the audio output. Sorry, I can't do anything about that on the prototype - not without chopping the pcb traces up anyway. If using headphones put them on the other way round. If using speakers swap them round (or stand on your head). :) If you really want to correct things then the best way is probably to cut the two traces to the jack socket on the bottom of the board then cross-connect them to the LB2 centre pins with wire links. It's fiddly. The low level audio output (links set to L) is roughly 1V output. This is a pretty standard level and should feed an external audio input to a VGA-HDMI converter ok. It's also suitable for any *amplified* speakers, such as most PC desktop speakers that are powered by batteries or USB (the speaker in the link should be ok, but it's not really stereo. :) ). The high level setting (links set to H) is the headphone setting, but might be ok with some very sensitive non-amplified speakers. The 470R resistors will easily protect the PicoMite outputs against the virtual short circuit load that these have. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| thwill Guru Joined: 16/09/2019 Location: United KingdomPosts: 4047 |
Thanks Mick, Some more questions since it's a slow Sunday (apologies if the answers are alread above somewhere): 1. The H & L links you talk about above are on LB2. Does this allow you to set the levels of the Left and Right channels independently or am I misinterpreting it ? 2. What are the LB1 jumpers for ? 3. What is U1 for ? Looks like maybe a bigger regulator ? 4. What are th 5V, 3V3 and GND pins on the right of the board intended for ... are they just there because they might be useful ? Thanks, Tom Game*Mite, CMM2 Welcome Tape, Creaky old text adventures |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6818 |
Yep, LB2 will let you set the channel levels independently. LB1 has the middle row of pins connected to the analogue inputs via resistors. It can be used in 3 ways: With no link - the analogue pin is simply connected to the port. An input voltage is provided by a potentiometer between GND and 3V3. This is how JS1 works. With the link in the lower position (UP) - the resistor is connected as a pull-up to 3V3. This can be used with a 100K "paddle" variable resistor to GND or can be used as a digital pull-up if you want a digital input. With the link in the upper position (DN) - the resistor is connected as a pull-down to GND. This is probably of more use with some sort of active high switch input. It was easy to do at the time though. :) U1 won't normally be used. It's intended use is to install a 800mA 78xx-compatible switching regulator to provide the initial 5V supply. This would allow the board to be powered from anywhere between about 9V and 36V in a boat or caravan or somewhere like that. The 5V output comes after U1, so there is still a supply for a HDMI converter. The GND, 3V3 and 5V holes are just somewhere to put a test probe. :) Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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