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Forum Index : Microcontroller and PC projects : PCB for VGAmite?
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| matherp Guru  Joined: 11/12/2012 Location: United KingdomPosts: 8579 |
Seems to be lots of interest in the humble VGAMite so we certainly need a motherboard PCB. Rather than lots of us doing our own variants it would make sense to have one person create a standard - who wants to volunteer? My thoughts are to start with a specific box as this determines the size of the PCB. This one is both cheap and seems about the correct size but there are lots of different ones out there. Just needs to be something available worldwide and obviously the layout of the various connectors ultimately determine the size. My spec would be as follows: 40-pin edge connector with 1-1 mapping of the Blackpill pins so that the pin numbering works on both VGA connector with RGB selection as per one of the great ideas above SDcard (fullsize to be easy to solder?) battery holder for VBAT PS2 connector USB/UART (Microbridge to keep it through hole?) Through hole USB-B for power/uart On board components are minimal and can all be through hole - pullups to 5V for PS2 signal and data, VGA I/F, 2R2 and 10uF/0.1uF to condition power to SDcard, 100uF tank capacitor across incoming power. Thoughts? Edited 2021-11-29 18:52 by matherp |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 5726 |
Note the need to isolate a PS/2 pullup while programming/updating the firmware. The BOOT1 (PB2) pin has an onboard 10k pulldown so leaving the PS/2 pullup would put it into an indeterminate state. Edited 2021-11-29 19:15 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 8579 |
Good catch  Needs a jumper in the PB2 lineMy recommendation for SD_CS would be PB1 which only loses PWM1C. This leave PA4 for the Flash chip. Edited 2021-11-29 22:03 by matherp |
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| lizby Guru Joined: 17/05/2016 Location: United StatesPosts: 3015 |
Nothing easier to solder or do layout for than this: micro sd card module PicoMite, Armmite F4, SensorKits, MMBasic Hardware, Games, etc. on fruitoftheshed |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 8579 |
Nasty resistors just cause problems and aren't needed |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 5726 |
Looks like a reasonable box - if you don't have to pay the stupid postal charges from the US. Similar box is available from China etc. There's even a UK source if you pay enough! :) 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: 3840 |
Just an idea, Could the PCB and connectors be arranged such that with some surgery (for the connectors) the VGAmite would fit in a standard Raspberry Pi 3/4 case and open up the possibility of putting it in a box with VESA mountings which could then be permanently mounted to the back of a compatible monitor to create and all in 1 (well 2 with the keyboard) unit ? 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: 5726 |
Vesa mounting only needs a strip of aluminium anyway. Personally I'd prefer to have a little extra room in the case than a RPi one, but YMMV. :) Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| flasherror Senior Member  Joined: 07/01/2019 Location: United StatesPosts: 159 |
Does the box dimensions permit an ESP8266 / HC12 / JDY40 RF module connector? |
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| flasherror Senior Member Joined: 07/01/2019 Location: United StatesPosts: 159 |
I like the idea reusing Pi cases, because long term availability of cases probably will not be an issue. Not sure how you would fit a VGA DB15 connector in there! Also, if using Pi cases and the motherboard has space, doing a partial subset (I2C/power) of the GPIO header would allow Pi GPIO modules (RTC, temp sensor, displays etc) to be easily used? Edited 2021-11-30 06:27 by flasherror |
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| flasherror Senior Member Joined: 07/01/2019 Location: United StatesPosts: 159 |
Isn't it easier to short/remove (whichever needed) the resistors rather than solder the SD card socket? |
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Turbo46 Guru Joined: 24/12/2017 Location: AustraliaPosts: 1593 |
I was going to suggest the case as used for the original mono maximite. It would be nice to acknowledge where it all began. But I can only find it on the Altronics web site H0376 though. Bill Keep safe. Live long and prosper. |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2287 |
that would be cool  despite objections, i'd also back using an SD socket pre-assembled on a daughterboard from china, as this allows easy assembly by our (apparently) elderly forum members, no reason to not have it attached by flying wires. peter: is there any (sensible) way to allow for a USB keyboard connected directly? ie, bitbanged at the lowest (1mb/s) USB speed. cheers, rob :-) Edited 2021-11-30 13:22 by robert.rozee |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9061 |
I volunteer, as I have already hinted at that in the other thread.  (that I am planning to do a mainboard for the VGAmite) A full-size SD card socket is quite easy to solder, and everything else as through-hole was how I was planning to do things on my board. I was planning to "Steal" phil99's bit of schematic and buffer the VGA output signal via his NPN emitter-follower idea, and three trimmers to set the individual RGB levels, giving maximum control over what colour you want. I was not and am not planning to expand on that anymore then that - gotta remember the KISS method. I had not considered fitting it to a case, but the same case as used for the CMM1 and CMM2 etc, is cheap, is available worldwide and would probably be what I would go for. Would the members here agree that the BlackPill module should be socketed, or do the members think it would be better to solder it down to the mainboard? I kinda like removable modules, as it is then much easier to plop another module in there if you suspect you have hurt the original module during some testing etc, and you don't then have to unsolder the old one. Thoughts? @ Bill: Re, the original Maximite case, yes, that is a good idea, and I think we'd get everything in there OK. Has my vote.  Edited 2021-11-30 13:39 by Grogster Smoke makes things work. When the smoke gets out, it stops! |
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Cyber Senior Member Joined: 13/01/2019 Location: UkrainePosts: 161 |
Socketed. |
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| Turbo46 Guru Joined: 24/12/2017 Location: AustraliaPosts: 1593 |
Yes socketed please, I guess it could be assembled either way if you omit the sockets. I do have concerns about Phil's circuit because it can stray a long way from the 75ohm input impedance of the monitor. Some monitors may not like it, there may be reflections and it may cause a fuzzy display. Then again I may be talking out of my hat.  Bill Keep safe. Live long and prosper. |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9061 |
OK then, socketed. @ Turbo46: Can you suggest another circuit? I hear what you are saying, but I was simply going to adopt phil99's circuit. @ phil99: Can you comment on the above with respect to your arrangement? Finally, only going to do the PCB if everyone else is happy that I do? Smoke makes things work. When the smoke gets out, it stops! |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 3525 |
For the colors on the VGA: use jumpers to select either green = G only white = R + G + B amber = R + G so in fact you can hardwire green, and then add red and blue as required. -or- (that is quite oldschool) add 3 potmeters. so everybody can select their best rainbow color. Volhout Edited 2021-11-30 17:54 by Volhout PicomiteVGA PETSCII ROBOTS |
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| Calli Regular Member  Joined: 20/10/2021 Location: GermanyPosts: 74 |
We can also wire it to a PWM Pin... :)  |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 8579 |
Can't support the Altronics case as they seem to be the only supplier based on quick Google search and I think a case is a pre-requisite if this is to be a little "computer" so needs to be available worldwide Rob: no idea if USB can be bitbanged and USB in general is something I have studiously tried to avoid - far too complex. Google returns lots of "is it possible" questions but no implementations. Disagree with ESP socket. That sort of connectivity isn't the design brief for this port IMHO Grogster: I'm definitely happy you do it assuming gerbers will be open source. Enjoy getting the pin mapping on the 40-pin edge connector right (remembering CMM2 )Assuming space then I recommend using CR2032 battery holder as the batteries used on the CMM2 seem to be difficult to find in some locations |
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